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IMPORTANCE OF MATURITY INDICES

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IMPORTANCE OF MATURITY INDICES Powered By Docstoc
					                                          Horticulture

                                    Post Harvest Technology

                   Harvesting, Handling and Storage of Horticultural Crops

                                A.S. Dhatt and B.V.C. Mahajan
                       Punjab Horticultural Postharvest Technology Centre
                            Punjab Agricultural University Campus,
                                            Ludhiana

                                           (16-07-2007)


CONTENTS

Introduction
Harvesting
       Types of indices and their components
       Harvesting tools, containers and methods
Handling
       Packing house operations
       Precooling of horticulture produce
       Packaging of horticulture produce
       Post harvest treatments
Storage
       Controlled atmosphere storage
       Hypobaric storage or low-pressure system
Ripening of fruits

Keywords
Harvesting, Handling, Storage, Horticultural crop




                                                    1
1. Introduction

The horticultural produce includes fruits, vegetables, flowers and other ornamental plants,
plantation crops, aromatic and medicinal plants and spices. However, in this chapter, information on
fruits and vegetables is only included. According to Oxford English Dictionary, fruit can be defined
as „the edible product of a plant or tree, consisting of seed and its envelope, especially the latter
when it is juicy or pulpy‟. The consumer definition of fruit would be „plant products with aromatic
flavours, which are either naturally sweet or normally sweetened before eating. The classification of
fruits and vegetables is arbitrary and according to usage. Botanically many crops, defined as
vegetables, are fruits (tomato, capcicum, melons etc.). Morphologically and physiologically the
fruits and vegetables are highly variable, may come from a root, stem, leaf, immature or fully
mature and ripe fruits. They have variable shelf life and require different suitable conditions during
marketing. All fresh horticultural crops are high in water content and are subjected to desiccation
(wilting, shriveling) and to mechanical injury. Various authorities have estimated that 20-30 percent
of fresh horticultural produce is lost after harvest and these losses can assume considerable
economic and social importance. That is why, these perishable commodities need very careful
handling at every stage so that deterioration of produce is restricted as much as possible during the
period between harvest and consumption.

2. Harvesting

Fruits harvested too early may lack flavour and may not ripen properly, while produce harvested too
late may be fibrous or have very limited market life. Similarly, vegetables are harvested over a wide
range of physiological stages, depending upon which part of the plant is used as food. For example,
small or immature vegetables possess better texture and quality than mature or over-mature
vegetables. Therefore harvesting of fruits and vegetables at proper stage of maturity is of paramount
importance for attaining desirable quality. The level of maturity actually helps in selection of
storage methods, estimation of shelf life, selection of processing operations for value addition etc.
The maturity has been divided into two categories i.e. physiological maturity and horticultural
maturity.

      Physiological maturity: It is the stage when a fruit is capable of further development or
       ripening when it is harvested i.e. ready for eating or processing.

      Horticultural maturity: It refers to the stage of development when plant and plant part
       possesses the pre-requisites for use by consumers for a particular purpose i.e. ready for
       harvest.

Importance of maturity indices:
    Ensure sensory quality (flavour, colour, aroma, texture) and nutritional quality.
    Ensure an adequate postharvest shelf life.
    Facilitate scheduling of harvest and packing operations.
    Facilitate marketing over the phone or through internet.

Definitions related to maturity and ripening:
i) Mature: It is derived from Latin word ‘Maturus’ which means ripen. It is that stage of fruit
development, which ensures attainment of maximum edible quality at the completion of ripening
process.

                                                  2
ii) Maturation: It is the developmental process by which the fruit attains maturity. It is the transient
phase of development from near completion of physical growth to attainment of physiological
maturity. There are different stages of maturation e.g. immature, mature, optimally mature, over
mature.
iii) Ripe: It is derived from Saxon word „Ripi’, which means gather or reap. This is the condition of
maximum edible quality attained by the fruit following harvest. Only fruit which becomes mature
before harvest can become ripe.
iv) Ripening: Ripening involves a series of changes occurring during early stages of senescence of
fruits in which structure and composition of unripe fruit is so altered that it becomes acceptable to
eat. Ripening is a complex physiological process resulting in softening, colouring, sweetening and
increase in aroma compounds so that ripening fruits are ready to eat or process. The associated
physiological or biochemical changes are increased rate of respiration and ethylene production, loss
of chlorophyll and continued expansion of cells and conversion of complex metabolities into simple
molecules.
v) Senescence: Senescence can be defined as the final phase in the ontogeny of the plant organ
during which a series of essentially irreversible events occur which ultimately leads to cellular
breakdown and death.

A. Types of indices and their components
i) Visual
a) Size and shape: Maturity of fruits can be assessed by their final shape and size at the time of
harvest. Fruit shape may be used in some instances to decide maturity. For example, the fullness of
cheeks adjacent to pedicel may be used as a guide to maturity of mango and some stone fruits
(Figure 1).
              Fig 1 : Judging mango harvest maturity by shape of shoulder




                 Immature
                Immature                Half mature
                                        HalfMature                    Mature
                                                                       Mature


Figure 1. Judging mango harvest maturity by shape of shoulder
                       (Source : Wardlaw and Leonard, 1936)

Some cultivars of banana become less angular in cross section as development and maturation
progress (Figure 2). Size is generally of limited value as a maturity index in fruit, though it is
widely used for many vegetables, especially those marketed early in their development. With these
produce, size is often specified as a quality standard, with large size generally indicating
commercial over-maturity and under-sized produce indicating an immature state. The assumption,
however, is not always a reliable guide for all-purpose.




                                                    3
                     Three -quarters        Light full three - quarters




                     Full three -quarters                Full


Figure 2 : Cross section of the middle banana fingers showing the chanages in
           angularity as they mature on the plant (Source : Von Loesecke, 1949)

The visual appearance of fruit and vegetable is the most important quality factor, which decides its
price in the market. The consumer (wholesaler or retailer) observes the quality of fresh fruits and
vegetables with their visual or external appearance. The produce should attain proper shape and
size. Medium size produce is always preferred by the consumers, because they tend to view large
fruits as more mature. The appearance of the product is the most critical factor in the initial
purchase, while subsequent purchase may be more related to texture and flavour.

Therefore, subjective evaluation of size and shape of the produce should be conducted to meet the
desired quality characteristics.

b) Colour: The loss of green colour of many fruits is a valuable guide to maturity as shown in Plate
1. There is initially a gradual loss in intensity of colour from deep green to lighter green and with
many commodities, a complete loss of green colour with the development of yellow, red or purple
pigments. Ground colour as measured by colour charts, is useful index of maturity for apple, pear
and stone fruits, but is not entirely reliable as it is influenced by factors other than maturity. For
some fruits, as they mature on the tree, development of blush colour, that is additional colour
superimposed on the ground colour, can be a good indicator of maturity. Examples are red or red-
streaked apple cultivars and red blush on some cultivars of peach.

Objective measurement of colour is possible using a variety of reflectance or light transmitance
spectrophotometer. Colour perception depends on the type and intensity of light, chemical and
physical characteristics of the commodity, and person‟s ability to characterize colour. Although
human eye is used to evaluate colour but results can vary considerably due to human differences in
colour perception. Therefore, an instrument (objective method) is used to provide a specific colour
value based on the amount of light reflected off the commodity surface or light transmitted through
the commodity. This instrument can measure small differences in colour accurately and can be
automated in the packing line. This instrument is popularly known as Colour Difference Meter. This
instrument use colorimetric method for colour measurement.


                                                    4
       Plate 1: judging maturity of mango and tomato by colours

ii) Physical indices
a) Firmness: As fruit mature and ripen they soften by dissolution of the middle lamella of the cell
walls. The degree of firmness can be estimated subjectively by finger or thumb pressure, but more
precise objective measurement is possible with pressure tester or penetrometer (Plate 2). In many
fruits such as apple, pear, peach, plum, guava, kinnow etc. firmness can be used to determine
harvest maturity. Penetrometer measures the pressure necessary to force a plunger of specified size
into the pulp of the fruit. Such pressure is measured in pounds and kilograms force.




                              Plate 2 : Penetrometer




                                                5
b) Specific gravity: As fruit mature, their specific gravity increases. This parameter is rarely used in
practice to determine when to harvest a crop but it could be where it is possible to develop a suitable
sampling technique. It is used, however, to grade crops into different maturities. To do this the fruit
or vegetable is placed in a tank of water; those that float will be less mature that those that sink. To
give greater flexibility to the test and make it more precise, a salt or sugar solution can be used in
place of water. This changes the density of the liquid, resulting in fruits or vegetables that would
have sunk in water floating in the salt or sugar solution.

iii) Chemical Measurement
Measurement of chemical characteristics of produce is an obvious approach to the problem of
maturity determination. The conversion of starch to sugars during maturation is a simple test for the
maturity of some apple cultivars. It is based on the reaction between starch and iodine to produce a
blue or purple colour. The intensity of the colour indicates the amount of starch remaining in the
fruit. The total soluble solids of the fruit can be measured with refractometer, which indicate the
harvest maturity of fruits. Acidity is readily determined on a sample of extracted juice by titration
with 0.1 N NaOH. The sugar acid or TSS acid ratio is often better related to palatability of fruit
than either sugar or acid level alone.
a) Soluble Solids Content (SSC): Soluble solid content (SSC) also called total soluble solids (TSS),
can be determined in a small sample of fruit juice using hand refractometer (Plate 3). The
spectrometer measures the refractive index, which indicates how much a light beam will be slowed
down when it passes through the fruit juice. The refractometer has different scales (0-32OB), (28-
62OB) and (56-92OB) which can be read directly. For large size fruits, these should be cut from stem
to blossom end and to the centre of the fruit to account for variability in SSC from top to bottom
and inside to outside of the fruit. The fruit tissues should be mescerated thoroughly in pastle motor
and then from the mescerated pulp the juice is extracted by passing through muslin cloth. A drop of
juice is then put on the prism of the refractometer and TSS content can be read directly on the scale.
However, in case of small fruits like grapes, the juice content can be extracted by simply pressing
the whole fruit.




                                    Plate 3 : Refractrometer




                                                   6
  The temperature of the juice is a critical factor for accuracy, because all materials expand when
  heated and becomes less dense. Good quality refractometers have a inbuilt temperature
  compensation capability. Always clean the refractometer before each reading and to standardize it
  with distilled water.

  b) Titratable acidity: Titratable acidity (TA) can be determined by titrating a know volume of juice
  with 0.1N NaOH to end point of pink colour as indicated by phenolphethalin indicator. The
  milliliters of NaOH needed are used to calculate the TA. The TA expressed as per cent malic, citric
  or tartaric acid can be calculated as follows:

          TA =           ml NaOH x N (NaOH) x acid meq. Factor* x 100
                                       Juice titrated
      * the following acid meq. factor may be used for different fruits


         Acid                       Acid meq. factor            Commodities
         Citric                     0.0064                      Berries, citrus fruits, pineapple
         Malic                      0.0067                      Apple, pear, peach, tomato
         Tartaric                   0.0075                      Grape

  iv) Calculated indices:
   a) Calendar Date : For perennial fruit crops grown in seasonal climate which are more or less
  uniform from year to year, calendar date for harvest is a reliable guide to commercial maturity.
  Time of flowering is largely dependent as temperature and the variation in number of days from
  flowering to harvest can be calculated for some commodities by use of degree-day concept. Such
  harvesting criteria can be developed by the growers based on their experiences.

  b) Heat Units An objective measure of the time required for the development of the fruit to maturity
  after flowering can be made by measuring the degree days or heat units in a particular environment.
  It has been found that a characteristics number of heat unit or degree-days is required to mature a
  crop under usually warm conditions, maturity will be advanced and under cooler conditions,
  maturity is delayed. The number of degree days to maturity is determined over a period of several
  years by obtaining the algebraic sum from the differences, plus or minus, between the daily mean
  temperatures and a fixed base temperature (commonly the minimum temperature at which growth
  occurs). The average or characteristic number of degree-days is then used to forecast the probable
  date of maturity for the current year and as maturity approaches, it can be checked by other means.

  Maturity Indices for selected fruits and vegetables

Fruits/ Vegetables        Maturity indices or characteristics

Almonds                   splitting of hull, separation of hull from shell, development of abscission zone
Apple
  „Golden Delicious‟      12% SSC, 18 lb firmness
  „Red Delicious‟         11% SSC, 18 lb firmness
 Asian Pears              skin colour change from green to yellowish green
 Pathar Nakh              145 days after fruit set
 Baggugosha               135 days after fruit set

                                                    7
Banana                      disappearance of angularity in a cross section of the finger
Ber                         colour break stage (when light yellow colour appear)
Cherry                      TSS = 14-15%, light red colour
Grapes (table)              minimum SSC % of 14 to 17.5, depending on cultivars, SSC/TA of 20 or
                            higher.
Guava                       colour break stage ( when skin colour changes from dark green to light green)
Lemon                       30% or more juice by volume
Lychee/litchi               TSS: total acid ratio of 30-40, bright red in colour
Kinnow                      TSS/acid ratio 12:1 to 14:1
Kiwi fruit                  TSS – 6.5%, Firmness = 14 lbs
Mango                       changes in shape (increase fullness of cheeks or bulge of shoulder), flesh
                            colour yellow to yellowish-orange
Papaya                      skin shows yellowing
Peaches                     ground colour change from green to yellow (varied for different cultivars)
Plums                       skin colour changes
Pomegranate                 minimum 1.85% TA and red juice colour
Strawberries                2/3 of berry surface showing pink or red colour
Beans                       Pods are filled, seeds immature.
Brinjal                     Immature, glossy skin, 40days from flowering.
Broccoli                    Adequate diameter, compact, all florets should be closed.
Cabbage                     Firm head
Cantaloup                   ¾ to full slip under slight pressure, abscission from vine.
Carrot                      Immature, roots reached adequate size.
Cauliflower                 Mature and atleast 6” in diameter, compact
Cucumber                    Immature and glossy skin
Garlic                      Well filled bulbs, tops dry down
Ginger                      8-9 months after planting
Melon                       Ground colour change to white with greenish tint, slightly waxy peel.
Mushroom                    Caps well rounded, partial veil completely intact.
Okra                        Pod 2-4” long, not fibrous, tips of pods pliable.
Onion (dry bulbs)           When 10-20% of tops fall over
Peas                        Pods well filled but not faded in colour.
Pepper                      Fruit size and colour (depends on colour and intended market)
Potatoes                    Harvest before vines die completely, cure to heal surface wounds.
Radish (spring)             20 to 30 days after planting.
Radish (winter)             45 to 70 days after planting.
Tomatoes                    Seeds fully developed, gel formation advanced in atleast one locule.
Watermelon                  Flesh colour 75% red, TSS = 10%
   Source : Lisa Kitinoja and James Gorny, 1998


  B. Harvesting tools, Containers and Methods

  Majority of fruits and vegetables are harvested by hands using scateurs, clippers or diggers (Figure
  3). Mechanical harvest in currently used for fresh market crops that are roots, tubers, rhizomes and
  nut crops. A number of commodities destined for processing such as wine grapes, prunes, peaches
  etc. are harvested with machines because harvest damage does not significantly affect the quality of
  processed product as the commodities are processed quickly. Harvesting practices should cause as

                                                   8
little mechanical damage to produce as possible. The following points should be kept in mind while
harvesting the crop.:
1.      Gentle picking and harvesting will help reduce crop losses.
2.      Wearing cotton gloves, trimming finger nails, and removing jewellary such as rings and
        bracelets can help reduce mechanical damage during harvest.
3.      Produce should be harvested during coolest part of the day not wet from dew or rain.
4.      Empty picking containers with care.
5.      Keep produce cool after harvest (provide shade).




   Fig 3 : Different tools used during harvesting (Source : Lisa Kitinoja and James Gorny, 1998)

                                                9
Clean harvesting tools and containers should be used to protect the produce quality. Disinfect tools
with one part chlorine bleach: one part clean water solution before use. The use of containers that
can be easily filled and carried by workers minimizes damage to produce. The containers that are
smooth on the inside, or provide clean, disposable liners made from paper or cardboard should be
used.

i) Picking bag: Cloth bag with openings on both ends can be easily worn over the shoulders with an
adjustable harnesses (Figure 4). In case metallic buckets are to be used for harvesting, fitting cloth
over the opened bottom can reduce damage to crop. Fitting canvas bags with adjustable harnesses,
or by simply adding some carrying straps to baskets also helps to reduce handling losses.




      Fig.4: Picking Bags (Source : Friend manufacturing Co. , 1993)


ii) Picking poles and catching sacks: These tools can be easily made by hand. A long pole attached
to a collection bag, allow the harvester to cut catch produce growing on a tree without climbing on
tree. The collection bags can be hand woven from strong cord or sewn from canvas. The hoop used
as the collection bag rim and sharp cutting edges can be made from sheet metal, steel tubing or
recycled scrap metal.

iii) Clippers and Knives: Some fruits such as citrus, grapes and mangoes, need to be clipped or cut
from the plant (Figure 3). Clippers or knives should be kept well sharpened and clean. Peduncles,
woody stems or spurs should be trimmed as close as possible to prevent fruit from damaging
neighboring fruits during transport. Care should be taken to harvest pears so that the spurs are not
damaged. Pruning shears can be used for harvesting fruits and some vegetables.

iv) Tripod ladders: A ladder with three legs is very convenient and more stable than a common
ladder (Figure 3). A ladder help harvesting crops such as mango, kinnow, pears, peaches, plums
without damaging tree branches.




                                                 10
v) Harvesting containers: Plastic crates are relatively expensive to purchase, but are reusable and
easy to clean. These have required features like stacking strength, ventilation holes and long life.
These can be used for harvest, storage, cooling, transport and even for display in retail markets.
Various brands and styles are manufactured, but all can be stacked securely if they are not over-
filled. Picking baskets, bags and buckets can easily be carried and filled by workers. Harvesting
containers can be made by fitting fabric over opened bottom of ready-made baskets, fitting ready
made canvas bags. All of these will reduce mechanical damage to produce.

Harvesting: Once the quality crop is produced, it should be harvested with great care for marketing
as shown in Plate 4. The goals of harvesting systems are:
        a)     To gather the commodity from the field at proper stage of maturity.
        b)     With a minimum amount of damage and losses.
        c)     In a cost effective way.
Method of Harvesting: Harvesting of crops can be done manually or mechanically.
 i) Hand Harvesting: Usually done for fruits destined for fresh markets.
Primary Advantages
        Harvesting of fruit or vegetable can be done at appropriate maturity.
        The produce will suffer minimum damage.
Disadvantages
        It is a time consuming process.
        More labour is required during harvesting season.




                              Plate 4 : Harvesting Techniques
                                                 11
ii) Mechanical Harvesting
Primary Advantages
        The produce can be harvested at a faster rate.
        Less manpower is required as compared to hand harvesting .
Disadvantages
        Damage can occur to crops.
        Not suitable for marketing of fresh commodities.

The fruits required for processing may be harvested mechanically, but it is important to process
them soon, otherwise deterioration can take place.

Field packing: Selection, sorting, trimming and picking the produce in the field at the time of
harvest is refered to as field packing and has great potential to reduce mechanical damage by
reducing the number of handling steps between field and consumer.

3. Handling

A) Packing house operations: The packing house operations include the following steps:-

        -       Dumping / collection
        -       Pre-sorting
        -       Washing / Cleaning
        -       Sizing / Grading
        -       Bunching / Wrapping
        -       Postharvest Treatments
        -       Packing
        -       Cooling
It is important to minimize mechanical damage by avoiding drops, rough handling and bruising
during the different steps of pack house operations. Secondly the pack house operations should be
carried out in shaded area. Shade can be created using locally available materials like, shade cloth,
woven mats, plastic tarps or a canvas sheet hung from temporary poles. Shade alone can reduce air
temperatures surrounding the produce by 8-17°C.

i) Dumping: The first step of handling is known as dumping. It should be done gently either using
water or dry dumping. Wet dumping can be done by immersing the produce in water. It reduces
mechanical injury, bruising, abrasions on the fruits, since water is more gentle on produce. The dry
dumping is done by soft brushes fitted on the sloped ramp or moving conveyor belts. It will help in
removing dust and dirt on the fruits.

ii) Pre-sorting: It is done to remove injured, decayed, mis-shapen fruits. It will save energy and
money because culls will not be handled, cooled, packed or transported. Removing decaying fruits
are especially important, because these will limit the spread of infection to other healthy fruits
during handling.

iii) Washing and Cleaning: Washing with chlorine solution (100-150 ppm) can also be used to
control innoculum build up during pack house operations. For best results, the pH of wash solution
should be between 6.5-7.5

                                                 12
 -     Mangoes, bananas should be washed to remove latex.
 -     Kiwifruit should be dry cleaned or brushed after curing or storage.

iv) Sizing / Grading: Grading can be done manually or by automatic grading lines. Size grading can
be done subjectively (visually) with the use of standard size gauges. Round produce units can be
easily graded by using sizing rings.




                                80 mm           75 mm        70 mm

Several types of mechanical sizes are available for small scale operations. One type is composed of
a long slanted tray with a series of opening which coverage (largest at the top, smallest at the
bottom). This type of sizes works best with round commodities.

The grading of fruits plays an important role in domestic and export marketing of fruits. Different
fruits have different grades on the basis of their size and weight.

Grade designation and quality of fruits: Minimum requirements are :
Fruits should be
a) clean, round, free from any visible foreign matter
b) fresh in appearance, free of pests
c) free from damage caused by pests or diseases
d) free of any foreign smell and/or taste

The grades of different fruits and vegetables suggested by Directorate of Marketing and Inspection
(DMI) are as under:

Kinnow

                Size code             Fruit Size        No. of fruits in 10
                                   (diameter) mm             kg pack

                    A                   60-64                   84
                    B                   65-69                   72
                    C                   70-72                   60
                    D                   72-74                   54
                    E                   75-79                   51
                    F                   80-85                   45




                                                13
Mangoes

               Grade         Fruit weight (g)         Max. permissible
                                                  difference between fruits
                                                    within packages (gm)

                  A              100-200                      50
                  B              201-350                      75
                  C              351-550                     100
                  D              551-800                     125

Grapes
          Grade             Large berries bunch      Small berries
                                weight (g)         bunch weight (g)

          Extra class               200                  150
          Class I                   150                  100
          Class II                  100                   75

Guava
              Size code        Weight (gm)          Diameter (mm)

                  A                >350                  >95
                  B              251-350                86-95
                  C              201-250                76-85
                  D              151-200                66-75
                  E              101-150                54-65
                  F               61-100                43-53

Litchi
              Grade          Fruit Diameter
                                  (mm)

              Extra class          33
              Class I              28
              Class II             23

Pomegranate
               Grade        Fruit weight (g)      Diameter
                                                   (mm)
                  A               400                90
                  B               350                80
                  C               300                70
                  D               250                60
                  E               200                50


                                           14
        Cabbage

                  Size Code        Weight in gms.

                      A              201-600
                      B             601-1200
                      C          1201 and above

Tomato

                  Size Code                  Diameter (in mm.)

                                      Minimum                    Maxiumum
                      1               From 30             to        34
                      2               From 35             to        39
                      3               From 40             to        46
                      4               From 47             to        56
                      5               From 57             to        66
                      6               From 67             to        81
                      7               From 82             to       101

                      8                  From 102 and
                                         above

Onion

          Size code       Diameter (in      Difference between the diameter
                             mm.)           of the smallest and largest onion
                                             in the same package (in mm.)

               A              10-20                         5
               B              21-40                        15
               C              41-70                        20
               D          71 and above                     30

B) Precooling of Horticulture Produce

Pre-cooling of the produce soon after their harvest is one of the important components of the cool
chain, which ultimately affect the shelf life of the produce. The main purpose of precooling is to
immediately remove the field heat from the produce.

Method of pre-cooling :
      -       Room cooling
      -       Forced air cooling
      -       Hydrocooling
      -       Vacuum cooling
      -       Package icing


                                                    15
i) Room cooling : It is low cost and slow method of cooling. In this method, produce is simply
loaded into a cool room and cool air is allowed to circulate among the cartons, sacks, bins or bulk
load.
Advantages:
-      Produce can be cooled and stored at the same room thus saves on handling costs.
-      No extra cost for pre-cooling equipment.
-      Suits for crops, which are marketed soon after harvest.
Disadvantages:
-      It is too slow method of cooling
-      Space requirements for room cooling are more as compared to storage, thus loss of storage
       capacity.
-      Unsuitable for packed produce.
-      Excessive water is lost from the produce due to slow cooling.
Horticulture crops suitable for rooms cooling are: Potato, onion, apple and citrus

ii) Forced-air cooling: Forced air-cooling is mostly used for wide range of horticultural produce.
This is the fastest method of pre-cooling. Forced air-cooling pulls or pushes air through the
vents/holes in storage containers. In this method uniform cooling of the produce can be achieved if
the stacks of pallet bins are properly aligned. Cooling time depends on (i) the airflow, (ii) the
temperature difference between the produce and the cold air and (iii) produce diameter.
Advantages:
     Fast method of pre cooling
     Suitable for wide range of highly perishable commodities.
     Uniform cooling, if palletized containers or bins are properly aligned.
     Cooling times can be controlled for different types of produce by controlling the air flow
        rate.
Horticultural produce suitable for forced air cooling are: Grapes, Berries, Pears, Peach, Oranges,
Strawberries tomato, and other tropical and subtropical fruits.

iii) Hydrocooling : The use of cold water is an old and effective cooling method used for quickly
cooling a wide range of fruits and vegetables before packaging. For the packed commodities it is
less used because of difficulty in the movement of water through the containers and because of high
cost involved in water tolerant containers. This method of cooling not only avoids water loss but
may even add water to the commodity. The hydrocooler normally used are of two types :
a) Shower type : In this type of hydrocooler, cold water is pumped to an overhead perfortated pan
which produces a shower over the produce which may be in bins or boxes or loose on a conveyer
belt passing beneath. The water leaving the produce may be filtered to remove debris, then passed
over refrigeration coil where it is recooled.
b) Immersion type: In this type of hydrocooler, the produce is brought in contact with cold water by
using a conveyor (flume type) or by lowering bins / boxes in tank of water which is continuously
cooled by mechanical refrigeration system. Poor cooling would result if the product simple moved
with the water. Flume hydrocoolers convey the product either against (counter flow) or across
(cross flow) the flow.

Efficient cooling depends upon adequate water flow over the product surface. Immersion type
hydrocoolers usually take longer time to cool produce than shower type cooler. Generally the small
quantity chlorine or other chemicals are added in the water to sanitize it.


                                                16
Advantages :
    Less energy is used as compared to forced air cooling.
    Hydrocooler can be easily integrated into an packing operations and become a step within a
      simple packing line.
    Moisture loss does not take place.
Disadvantages :
    Most of the packages don‟t tolerate wetting.
    Wax layer of some fruits like pear, plum, apple are removed by using spray type of
      hydrocooler :

Horticultural produce suitable for hydrocooling are: Mango, peach, cherry, sparagus etc.

iv) Vacuum cooling:Vacuum cooling take place by water evaporation from the product at very low
air pressure. In this method, air is pumped out from a larger steel chamber in which the produce is
loaded for pre-cooling. Removal of air results in the reduction of pressure of the atmosphere around
the produce, which further lowers, the boiling temperature of its water. As the pressure falls, the
water boils quickly removing the heat from the produce. Vacuum cooling cause about 1 per cent
produce weight loss (mostly water) for each 6 0 C of cooling.
Advantages :
     Packed produce can be cooled if the pack allows moisture transfer.
     Fast and uniform cooling takes place.
     Most energy efficient method.
Disadvantages :
     High capital cost
     Produce losses more moisture

To overcome the more loss of water from the produce, another method of water spray vacuum is
used, (modification of vacuum cooling), called hydro-vac cooling.

v) Package-icing :In some commodities, crushed or flaked ice is packed along with produce for fast
cooling. However, as the ice comes in contact with the produce, it melts, and the cooling rate slows
considerably. The ice keeps a high relative humidity around the product. Package ice may be finely
crushed ice, flake ice or slurry of ice. Liquid icing distributes the ice throughout the container,
achieving better contact with the product. Packaged icing can be used only with water tolerant, non-
chilling sensitive products and with water tolerant packages (waxed fiberboard, plastic or wood).

C. Packaging of Horticulture Produce

What is Packing? According to UK institute of packaging

    A coordinated system of preparing goods for transport, distribution, storage, retailing and
     end use.
    A means of ensuring safe delivery to the ultimate consumer in sound conditions at minimum
     cost.

Objective of Packaging:
   1. It helps in safe transportation, storages, marketing and distribution of produce.
   2. It protects the produce from pilferage, microorganisms and adverse weather condition.

                                                17
   3. It is also used to advertise the product.

Requirements of a Good Package:
    Should be environment friendly.
    Should have sufficient strength in compression and against impact and vibrations
    Should be stable during the entire distribution chain.
    Should be compatible with the automatic packing/filling, handling machines (mechanical
       filling systems)
    Should facilitate special treatments like pre-cooling.
    Should have consumer appeal.
    Should be easily printable.
    Should be cost effective.

Materials for Packaging:
    Wood – boxes, bins, trays, barrels, pallets
    Jute/canvas – sacks
    Paper and card board – liners, boxes, trays
    Plastic – Rigid - crates, pallets, trays
                      Flexible – films (single & multi layered)
                      Polystyrene boxes / trays
    Combined materials – CFB and plastic
CFB has almost replaced wood and jute and is considered as most important package material to be
used in combination with other materials.

Some materials used for fresh horticultural produce include:
    Wooden box having CFB liners.
    CFB box with plastic film wraps
    CFB trays with wooden corner supports
    CFB laminated or waxed containers.
    CFB box with plastic retailer packs (strawberry boxes)
    CFB or polystyrene trays/boxes with plastic film wraps.

Packaging Type: There are many types of packing containers available for horticultural produce,
and they come in a huge range of sizes.
   i) Bags and Sacks: Paper, polyethylene film, woven polypropylene. These give little protection
   to the crop from handling and transport damage, potato, onion, canots etc.
   ii) Woven Baskets: These are traditional containers in which crops are placed after harvest. The
   produce is damaged in these baskets when they are stacked one above the other during transport
   and distribution.
   iii) Wooden field box: These are made from thin pieces of wood, widely spread so they are
   light in weight and cheep to make. These can be used for all types of fruits and vegetables.
   iv) Plastic field boxes: They are strong and durable. They are made from moulded polyvinyl
   chloride, poly propylene or polyethylene. They have smooth surface, which does not damage
   the produce. Initially, they are expensive to buy, but can be used repeatedly.
   v) Pallet boxes: They are most commonly base on the standard size for a European pallet of 1 x
   1.2 m and about 0.5 m high. These have capacity of about 500 kg. They are usually made from
   wood but plastic ones are also available. They are used for whole range of crops, which are
   commonly loaded into them in the field and transported directly to the store.


                                                  18
   vi) Fiberboard boxes: They are made from either laminated or more commonly corrugated
   fiberboard. They may be used for directly field packing of produce and transported to pack
   house or destination market.
   vii) Polystyrene boxes : Popularly called thermocol boxes, provides enough protection to
   produce, are light in weight, hygrimic and keeps the produce for longer periods at pack
   temperature.

The three containers styles illustrated here are constructed from corrugated fiberboard. The regular
slotted containers is fully collapsible and the most economical. Collapsible containers can be
flattened and stacked during marketing and transport easily and less expensive, and take much less
space to store while empty in the packinghouse.




                                   Source: Fibre Box Association

Half of full-telescopic containers have the highest stacking strength and protect against bulging but
are more costly. The choice of package style will depend on what commodity is to be pack and how
to use the container throughout the post harvest system (during cooling, for long-term storage, as a
display).




                                                 19
The container known as a Bliss box has very strong corners, but is not collapsible. Bliss boxes for
fresh fruits and vegetables most commonly have either flaps that meet in the middle of the top or
that form an open topped tray, which is covered with a separate lid.




                                     Bliss Box

A simple wooden tray with raised corners is stackable and allow plenty of ventilation for fragile
crops such as ripe tomatoes.



                  Stackable cartons reinforced
                  with wooden corners supports




Smaller consumer sized containers can be packed into large container.

                                         Individual
                                         consumer
                                          packages




           Cartons designed to hold six small containers per layer


                                                 20
Adding a fiberboard divider to a carton will increase stacking strength. Wooden inserts, or
fiberboard folded into tight triangles and placed in all four corners can be especially useful when a
carton needs strengthening.

Using a polyethylene liner in a fiberboard carton can help protect produce and reduce water loss in
commodities such as peach, plums, pears, citrus, cherries, kiwi fruits etc. Water vapor given off by
the product is contained within the liner, increasing the RH around the product and decreasing the
rate of water loss. The liner can also reduce abrasion damage that results from fruit rubbing against
the inside of the box. It is important to keep produce cool to prevent causing damage in cartons
lined with polyethylene due to gas composition changes related to increased respiration rates.

When a locally made containers have sharp edges or rough inner surfaces, a simple, inexpensive
liner can be used to protect produce from damage during handling.

General Dos’ and Don'ts for Packaging High Quality Produce
   The packages should be sturdy and capable of standing up to handling, cooling and storage
    conditions.
   Rough packages such as baskets and wooden crates should be lined with cardboard inserts.
   Packages used for heavy produce should be reinforced with corner supports or folded dividers.
   Avoid using very large packages since the produce suffers more damage during handling of
    large packages.
    For delicate produce such as berries, grapes, summer squash and ripe stone fruits use shallow
    packages having single layer or double layers.
   Avoid overfilling or under filling packages.
   For adequate ventilation of packages about 5% of the surface area per side should be vented.
   For immobilizing the produce in a package, use packaging materials such as trays, cups, wraps,
    liners and pads.
   To decrease the rate of water loss from produce like cherries perforated plastic film liners
    should be used.
   Take care while using fillers and liners in packages so that the ventilation holes are not blocked.
   Labeling containers with your logo or farm name help in creating a brand name for quality
    produce.
   Consumer packages that can be used to display produce during marketing should be considered.
   Use large packages to pack 'consumer packages' such as gift packs or display trays for
    providing better protection to the containers during stacking, transport and marketing.
   For reducing produce damage, packages with handles to carry should be considered.

D. Post harvest Treatments

Fresh fruits are living tissues subject to continuous change after harvest. Some changes are desirable
from consumer point of view but most are not. Post-harvest changes in fresh fruit cannot be
stopped, but these can be slowed down within certain limits to enhance the shelf life of fruits. The
                                                   21
post-harvest treatments play an important role in extending the storage and marketable life of
horticultural perishables.
i) Washing with chlorine solution: Chlorine treatment (100-150 ppm available chlorine) can be used
in wash water to help control inoculums build up during packing operations. Maintain pH of wash
water between 6.5 and 7.5 for best results.
ii) Ethylene inhibitors/Growth regulator/ fungicide treatments: 1-MCP (1-methyl cyclopropene),
AVG (Amenoethoxyvinyl gycine), siver nitrate, silver thiosulfate, cycloheximide, benzothiadiazole
etc. are some of the chemicals which inhibit ethylene production and / or action during ripening and
storage of fruits.The growth regulators or fungicidal application such as GA3 or cytokinius, bavistin,
procloraj, imazalil etc. can be effectively used to extend/ enhance the shelf life of fruits.
iii) Calcium application: The post-harvest application of CaCl2 or Ca (NO3)2 play an important role
in enhancing the storage and marketable life of fruits by maintaining their firmness and quality.
Calcium application delays aging or ripening, reduces postharvest decay, controls the development
of many physiological disorders and increases the calcium content, thus improving their nutritional
value. The post-harvest application of CaCl2 (2-4%) or Ca (NO3)2 for 5-10 minutes dip extend the
storage life of pear upto 2 months, plum upto 4 weeks and apple upto 6 months at 0-2OC with
excellent colour and quality. Calcium infiltration reduces chilling injury and increase disease
resistance in stored fruit.
iv) Thermal treatments :
a) Hot water treatment: Fruits may be dipped in hot water before marketing or storage to control
various post-harvest diseases and improving peel colour of the fruit (Table 2). In mangoes, the hot
water treatment is recommended at 50-52OC for 5 minutes to reduce the fungal infection during
ripening or storage. This treatment help in attaining uniform ripening within 5-7 days. Fruit should
not be handled immediately after heat treatment. Cooling of fruit with water showers or forced air
should be provided to help return the fruit to their optimum temperature as soon as possible after
completion of the treatment.

      Table 2: Hot water treatments for different fruits.
       Commodity       Pathogens                      Temp. (°C)     Time (min)
       Apple           Gloeosporium sp.               45             10
                       Penicillium expansum
       Grapefruit      Phytophthora citrophthora 48                  3
       Lemon           Penicillium digitatum          52             5-10
                       Phytophthora sp.
       Mango           Collectotrichum                52             5
                       gloeosporioides
       Orange          Diplodia sp.                   53             5
                       Phomopsis sp.
                       Phytophthora sp.
       Papaya          Fungi                          48             20
       Peach           Monolinia fructicola           52             2.5
                       Rhizopus stolonifer
      Source : Lisa Kitinoja and James Gorny, 1998

b) Vapour heat treatment (VHT): This treatment proved very effective in controlling infection of
fruit flies in fruits after harvest. The boxes are stacked in a room, which are heated and humidified
by injection of steam. The temperature and exposure time are adjusted to kill all stages of insects
(egg, larva, pupa and adult), but fruit should not be damaged. A recommended treatment for citrus,

                                                 22
mangoes, papaya and pineapple is 43OC in saturated air for 8 hours and then holding the
temperature for further 6 hours. VHT is mandatory for export of mangoes.
v) Fumigation: The fumigation of SO2 is successfully used for controlling post-harvest diseases of
grapes. This is achieved by placing the boxes of fruit in a gas tight room and introducing the gas
from a cylinder to the appropriate concentration. However, special sodium metabisulphite pads are
also available which can be packed into individual boxes of a fruit to give a slow release of SO 2.
The primary function of treatment is to control the Botrytis Cinerea. The SO2 fumigation is also
used to prevent discolouration of skin of litchis.

Fumigation with 1.2% sulphur dioxide for 10 minutes was shown to be effective in reducing skin
discolouration in fresh litchis, especially if it is combined with a 2 minute dip in IN HCl acid
directly afterwards. Immediately after sulphur dioxide treatment litchi fruit may appear a uniform
yellow colour and then turn red again after 1 or 2 days. Some people are allergic to sulphur,
particularly those who have chronic respiratory complaints, and it may be necessary to label fruit or
boxes of fruit to indicate that these have been fumigated with sulphur. Paper pads or wraps
impregnated with biphenyl fungicides are commonly applied to citrus fruits. The chemical
vaporizes slowly, protecting the fruit from fungal infection.
vi) Irradiation: Ionizing radiation can be applied to fresh fruits and vegetables to control micro-
organisms and inhibit or prevent cell reproduction and some chemical changes. It can be applied by
exposing the crop to radiations from radioisotopes (normally in the form of gamma-rays measured
in Grays (Gy), where 1 Gray = 100 rads.

A combination of hot water treatment (55°C for 5 minutes) followed by 30 Gy irradiation was
found to be the best treatment for shelf life extension and quality maintenance of mangoes. After
this treatment mangoes had a storage life of 38 days (at 15°C), 28% rotting and no irradiation
injury. Irradiation can also be used to control postharvest diseases of other fresh fruit and
vegetables.
vii) Waxing: Waxing of fruits or vegetables is a common post-harvest practice. Food grade waxes
are used to replace some of the natural waxes removed during harvesting and sorting operations and
can help reduce water loss during handling and marketing. It also helps in sealing tiny injuries and
scratches on surface of fruits and vegetables. It improves cosmetic appearance and prolongs the
storage life of fruits and vegetables. The wax coating must be allowed to dry thoroughly before
packing.

The commercial available waxes are citrashine, Staryfresh, Sta-fresh 451, Semper Fresh, Carnauba
wax etc. Coatings may be applied by either by dipping, brushing or spraying on the fruits &
vegetables. Different countries have their own rules and regulations for the use of coatings on
horticultural produce. As of now, only coating with beeswax and carnauba is allowed in India.

4. Storage

The management of temperature and relative humidity are the most important factors determining
storage life of horticultural produce. The natural means like ice, cold water, night temperature have
been used for long time for protecting food materials from spoilage and these are still common.
However, with the development of innovative technologies, it is possible to achieve optimal
environments in the insulated stores.
Objective of storage:
 Regulate the market in an orderly manner.
 Avoid glut and distress sale in the market, thus prolonging the market period.
                                                 23
 In long-term storage, making the food available in off-season.

Lowering the temperature to the lowest safe handling temperature is of paramount importance for
enhancing the shelf life, reducing the losses and maintaining higher quality during marketing.
Always, handle produce gently and never store produce unless, it is of the best quality. Damaged
produce will lose water faster and have higher decay rates in storage when compared to undamaged
produce.

Tips for storage of high quality horticultural produce
    Store only high quality produce, free of damage, decay and of proper maturity (not over-ripe
       or under-mature).
    Know the requirements for the commodities you want to put into storage, and follow
       recommendations for proper temperature, relative humidity and ventilation.;
    Avoid lower than recommended temperatures in storage, because many commodities are
       susceptible to damage from freezing or chilling.
    Do not over load storage rooms or stack containers closely
    Provide adequate ventilation in the storage room.
    Keep storage rooms clean.
    Storage facilities should be protected from rodents by keeping the immediate outdoor area
       clean, and free from trash and weeds.
    Containers must be well ventilated and strong enough to with stand stacking. Do not stack
       containers beyond their stacking strength.
    Monitor temperature in the storage room by placing thermometers at different locations.
    Don‟t store onion or garlic in high humidity environments.
    Avoid storing ethylene sensitive commodities with those that produce ethylene.
    Avoid storing produce known for emitting strong odors (apples, garlic, onions, turnips,
       cabbages, and potatoes) with odor-absorbing commodities.
    Inspect stored produce regularly for signs of injury, water loss, damage and disease.
    Remove damaged or diseased produce to prevent the spread of problems.

Storage of compatible groups of fruits and vegetables: Some fruits or vegetables can be stored
together due to their common temperature and relative humidity conditions and some can not be
stored together. The table3 gives an over view of storage of compatible groups of fruits and
vegetables

   Table 3: Compatibility groups of fruits and vegetables

  Group          Temperature              Crops                      Status of commodities
 Group 1      0-2oC and 90-95% RH      Apple, Apricot, Asian Produce ethylene.
                                       Pear, Grapes, Litchis,
                                       Plum,               Prunes,
                                       Pomegranate, Mushroom
                                       Turnip Peach.
 Group 2      0-2oC and 90-95%RH       Asparagus, Leafygreens, Sensitive to ethylene.
                                       Broccoli, Peas, Spinach,
                                       Cabbage,            Carrot,
                                       Cauliflower, Cherries.
 Group 3      0-2oC and 65-70% RH      Garlic, Onions dry.         Moisture will damage these

                                                24
                                                                    crops.
 Group 4      4-6oC and 90-95% RH       Cantaloupes, Guava,
                                        Mandarin, Tangerines.
 Group 5        8-10oC, 85-90% RH       Beans, Potatoes (with
                                        CIPC treatment),
                                        Cucumber, Brinjal, Okra
                                        Pepper.
 Group 6       13-15oC, 85-90% RH Mangoes, Banana, Tomato
                                        ripe, Grapefruit
              Source : Lisa Kitinoja and James Gorny, 1998
Undesirable effect of ethylene:
 Accelerated senescence
 Accelerated ripening
 Loss of green colour
 Abscission of florets
 Toughening
 Poor flavor
The symptoms of chilling injury are as follows: If fruits and vegetables are stored at a temperature
below their optimum temperature will subject to chilling injury (Table 4). Therefore for maintaining
proper quality the produce should be stored at the recommended temperature and relative humidity
conditions (Table 5).

  Table 4: Chilling injury symptoms of different fruits
Commodity                 Lowest safe temperature oC      Chilling injury symptoms
Apple                                2-3                  Soft scald, brown core
Bananas                             12-13                 Dull colour when ripened
Guavas                               4-5                  Pulp injury, decay
Lemon                               11-13                 Pitting, membrane staining
Mango                               10-13                 Uneven ripening, grayish skin
Ber                                  7.5                  Surface pitting, appearance of brown
                                                          streaks on the peel


     Table 5:Recommended Temperature and RH conditions

Name of commodity                   Temp (oC)             RH (%)      Approximate Shelf-Life
Apple                                  -1-4                90-95      1-12 months
Apricot                                 0-1                90-95      1-3 weeks
Asian pear                              0-1                90-95      2 months
Banana                                13-15                90-95      1-4 weeks
Ber                                     7.5                90-95      2 weeks
Grape                                 -0.5-0               90-95      2-8 weeks
Guava                                   6-8                90-95      2-3 weeks
Kiwi ; Chinese gooseberry                0                 90-95      3-5 months
Lemon                                 10-13                85-90      1-6 months

                                                 25
Loquat                                        0             90        3 weeks
Lychee, Litchi                               1-2           90-95      3-5 weeks
Mandarin (Kinnow)                            4-5           90-95      2 months
Mango                                        13            85-90      2-4 weeks
Mushrooms                                     0             90        7-14 days
Nectarine                                  -0.5-0          90-95      2-4 weeks
Papaya                                      7-13           90-95      1-3 weeks
Peach                                        0-1           90-95      2-4 weeks
Pear                                      -1.5-0.5         90-95      2-7 months
Pineapple                                   7-13           85-90      2-4 weeks
Plum and prunes                              0-1           90-95      2-5 weeks
Pomegrante                                    5            90-95      2-3 months
Strawberry                                    0            90-95      7-10 weeks
Sweet cherries                             -1-0.5          90-95      2-3 weeks
Asparagus, green                             1-2          95-100      2-3 weeks
Beans                                        4-7           90-95      7-10 days
Bitter gourd                               10-12           85-90      2-3 weeks
Broccoli                                      0           95-100      10-14 days
Cabbage                                       0            90-95      3-6 weeks
Carrots                                       0            90-95      6-8 months
Cauliflower                                   0            90-95      3-4 weeks
Eggplant                                   10-12           90-95      1-2 weeks
Garlic                                        0            65-70      6-7 months
Ginger                                       13            65-70      6 months
Lettuces                                      0            90-95      2-3 weeks
Okra                                        7-10           90-95      7-10 days
Onion                                         0            65-70      1-8 months
Peas                                          0            90-95      1-2 weeks
Bell Pepper                                 7-10           90-95      2-3 weeks
Radish                                        0            90-95      1-2 months
Tomato                                     10-13           90-95      1-3 weeks
Turnip                                        0            90-95      4-5 months
Watermelon                                 10-15           90-95      2-3 weeks
    Source : Lisa Kitinoja and James Gorny, 1998

Controlled atmosphere (CA) storage

The term imply, the addition or removal of gases resulting in an atmospheric composition different
from that of normal air. Thus the levels of carbon dioxide, oxygen, nitrogen, ethylene, and
metabolic volatiles in the atmosphere may be manipulated. Controlled atmosphere storage generally
refers to keeping produce at decreased oxygen and increased carbon dioxide concentrations and at
suitable range of temperature and RH. Systems where atmospheric control is accurately controlled
are generally called CA storage and where degree of control “less accurately” monitored are called
MA (modified atmosphere) storage. In MAP (modified atmospheric packaging) produce is enclosed
in polymeric films and is allowed to generate its own atmsophere (passive MAP) or air of known
composition is flushed into the bag (active MAP) and depending upon gas / vapour transmission
characteristics of the film on appropriate atmosphere develops in the package to prolong shelf life.
MAP is ideally combined with temperature control for maximum benefit
                                                     26
Benefits of CA storage
       -      Slow down respiration and ethylene production rates, softening and retard senesence
              of horticultural produce.
       -      Reduce fruit sensitivity to ethylene action
       -      Alleviate certain physiological disorders such as chilling injury of various
              commodities, russet spotting in lettuce, and some storage disorders including, scald
              of apples.

Harmful effects of CA storage
      -       Initiation or aggravation of certain physiological disorders can occur, such as
              blackheart in potatoes, brown stain on lettuce, and brown heart in apples and pears.
      -       Irregular ripening of fruits, such as banana, mango, pear and tomato, can result from
              exposure to O2 levels below 2% or CO2 levels above 5% for more than 2 to 4 weeks.
      -       Off- flavors and off-odours at very low O2 or very high CO2 concentration may
              develop as a result of anaerobic respiration and fermentative metabolism.

      Table 6: Recommended CA or MA conditions for selected fruits and vegetables

      Commodity                 Temperature (°C)             % O2               % CO2
      Apple                               0-5                 1-2                  0-3
      Banana*                           12-16                 2-5                  2-5
      Cherry, sweet                       0-5                3-10                10-15
      Mango*                            10-15                 3-7                  5-8
      Peach, clingstone                   0-5                 1-2                  3-5
      Pear, European                      0-5                 1-3                  0-3
      Asparagus                           1-5                 Air                10-14
      Beans, green                       5-10                 2-3                  4-7
      Broccoli                            0-5                 1-2                 5-10
      Brussels sprouts                    0-5                 1-2                  5-7
      Cabbage                             0-5                 2-3                  3-6
      Cantaloupes                         2-7                 3-5                10-20
      Cauliflower                         0-5                 2-3                  3-4
      Okra                               7-12                 Air                 4-10
      Onions (bulb)                       0-5                 1-2                 0-10
      Pepper (bell)                      5-12                 2-5                  2-5
      Radish (topped)                     0-5                 1-2                  2-3
      Tomatoes (green)                  12-20                 3-5                  3-5
      ripe                              10-15                 3-5                  3-5
       * CA is especially beneficial during transit
       (Source : Adel A. Kader, 2002 )

Hypobaric storage or Low-pressure system

Hypobaric storage is a form of controlled atmosphere storage in which the produce is stored in a
partial vacuum. The vacuum chamber is vented continuously with water saturated air to maintain
oxygen levels and to minimize water loss. Ripening of fruit is retarded by hypobaric storage, due to
the reduction in the partial pressure of oxygen and for some fruits also to the reduction in the

                                                 27
ethylene levels. A reduction in pressure of air to 10 kilopascals (0.1 atmosphere) is equivalent to
reducing the oxygen concentration to about 2 per cent at normal atmospheric pressure. Hypobaric
stores are expensive to construct because of the low internal pressures required, and this high cost of
application appears to limit hypobaric storage to high value produce such as cut flowers. Secondly
control of gases during the storage cannot be manipulated.

5. Ripening of Fruits

Ripening is a dramatic event in the life of a fruit during which structure and composition of unripe
fruit is so altered that it becomes acceptable to eat. Ripening marks the completion of development
of a fruit and the commencement of senescence and it is normally an irrevesible event.

Categories of fruits : On the basis of ability to ripen after harvest, sharp rise in respiration rate
during onset of ripening and production and/or response to ethylene , the fruits are divided into 2
categories. First group produce very small quantity of ethylene and do not respond to ethylene
treatment (except in terms of degreening), and these fruits should be picked when fully ripe to
ensure good flavour and quality. For example Citrus, cherry, litchi, pineapple, pomegranate, berries
etc.

Second group produce much larger quantities of ethylene during ripening and exposure to ethylene
treatment will result in faster and uniform ripening. For example apple, pear,stone fruits, mango,
papaya guava etc

A) Ripening facilities
i) Ripening room : Fruit are ripened in specially built rooms that must be gas tight, have systems for
controlling humidity and concentrations of carbon dioxide and ethylene, and have equipment to
control product temperature. Ripening rooms are usually insulated but they typically operate at
temperature 15-210 C. The ripening process is always done at relative humidity above 85%.
ii) Temperature : Ripening is controlled on the basis of fruit pulp temperature. It should be
measured during each cycle with a calibrated pulp thermometer. Simultaneously, room air
temperature must also be regularly monitored with calibrated thermometer.
iii) Relative humidity : The refrigeration system must be designed to contain 85-95% RH. Humidity
below this range causes excessive product weight loss . Humidifiers are needed to add moisture to
the air in rooms. Air humidity should be periodically monitored with a wet and dry bulb
psychrometer.
iv) Air flow : Air flow is needed to distribute ethylene gas to the product and to add or remove heat
from the product during ripening cycle. Boxes must be stacked with space between them to allow
good air flow around each box. Boxes or pallet bins should be vented to allow air flow. If packaging
materials are placed in the boxes they should not block vents. Poor venting will cause high fruit
temperatures and non-uniform ripening.

After product has reached ripening temperature ethylene gas is added. The gas can be added with
three systems. 1) A patented ethylene generator produces ethylene from ethyl alcohol. It produces a
relatively constant flow of gas for atleast 24 hours. 2) pure ethylene can be purchased in small
pressurized cylinders holding three cubic feet of gas. The cylinder is opened in the room providing a
rapid release of gas, which will provide an adequate level during the process, if the room is fairly
gas tight. 3) For larger operations use ethylene gas available in larger cylinders and use flow meters
to measure a prescribed amount into the room.


                                                  28
  B) Ripening Techniques
  i) Ripening with ethephon / Ethrel : Ethephon (2-choloroethyl-phosphonic acid) is commercially
  available and is registered for pre-harvest use on a variety of crops for controlling developmental
  processes or inducing ripening. This chemical is approved for post-harvest use on fruits crops for
  enhancing ripening. For post-harvest treatments, the known quantity of ethephon is diluted in water
  and fruits are dipped in the solution for a specified period. This substance ensures that there is
  uniform ripening of fruits. This technique provides a safe and effective method of ripening of fruits
  compared to the conventional technique of using calcium carbide.
  ii) Ripening with Ethylene gas: In this technique, the fruits are exposed to low level of ethylene gas
  (10-100ppm) in an air-tight ripening chamber for 24 to 72 hours so as to induce ripening. The most
  important thing in this technique is temperature and relative humidity control inside the ripening
  chamber, which should range between 15-250C and 90-95% relative humidity, depending upon the
  fruit type. Several methods are used to provide proper ethylene concentration in the ripening room.
  a) Gas Cylinders: Ethylene is available in large steel cylinders where it is stored under pressure. As
  it is highly flammable, the use of pure gas is discouraged. Therefore, it is usually used diluted with
  nitrogen or other inert gases. Typical mixtures are 95 per cent nitrogen and 5 per cent ethylene or
  95.5 per cent nitrogen and 4.5 per cent ethylene. The measured quantities of ethylene are introduced
  in ripening room at regular intervals or continuously and the flow is regulated through metering
  devise or flow meter. Any piping leading into the ripening room should be grounded to prevent
  possible electrostatic ignition of ethylene gas.
  b) Shot system: On small scale, commodities can be treated using shot method with ethylene
  liberated from ethephon. A calculated amount of ethephon in stainless steel bowl is placed around
  the room. The fruits are stacked in the room and sodium hydroxide is added to ethephon and all
  ventilation to the room is then blocked. When sodium hydroxide reacts with ethephon, ethylene gas
  is released that ripens the fruits, Precaution should be taken while handling sodium hydroxide and
  ethephon as these are corrosive. Safety glasses and rubber gloves should be used while their
  handling.
  c) Ethylene generator: This is a device that is portable and placed inside the ripening room. A liquid
  (ethyl alcohol) is filled into the tank fitted with ethylene generator and it is connected to an electric
  power source. The ethyle alcohol gets heated in a controlled manner in the presence of a catalyst
  that produces ethylene gas. Gas is maintained inside the ripening room until colour break occurs in
  the fruits.

    Table 7 : Ripening conditions for some fruits

Commodity                   Ethylene               Ethylene           Ripening         Predicted storage after
                       concentration (ppm)       exposure time        temperature      treatment
Apple(Grany Smith)     10 ppm                    6 days               25°C             Less than 4 months at 0°C
Banana                 100-150 ppm               24-48 hours          14-18°C          Less than 7 days at 14°C
Mango                  100 ppm                   12-24 hours          15.5-25°C        Less than 7 days at 10-
                                                                                       13°C
Tomato (mature green   100 ppm                   3-3.5 days to        18°-20°C (65°-   7 days after reaching the
stage)                                           reach      breaker   68°F) with 90-   red stage
                                                 stage and 5-16       95% RH
                                                 days, depending
                                                 on temperature, to
                                                 reach full red
                                                 stage
                                 (Source : Adel A. Kader, 2002 )



                                                      29
iii) Calcium carbide : In India and many other developing economies, the banana and mango are are
ripened with the use of calcium carbide, which releases acetylene and ethylene on interaction with
moisture coming from fruits. This chemical is harmfull to human health and its use for ripening of
fruits is band in India under section 44-AA of PFA rules 1954.

References
1.    Dhatt, A.S., Mahajan, B.V.C., Sandhu, K.S., Garg, A and Sharma, S.R. (2007) Handbook on
      Post harvest Handling of Fruits and Vegetables. 3rd edition, PHPTC, PAU, Ludhiana
2.    Friend Manufacturing Corporation, Prospect Street, P.O. Box 385, Gasport, New York
      14067, USA.
3.    Kader Adel A (2002). Post harvest Technology of Horticultural Crops. 3rd Edition,
      University of California, Agricultural and Natural Resources.
4.    Kader Adel A and Merita Cantwell (2006). Produce Quality Rating Scales and Color Charts.
      Postharvest Horticulture Series No 23. Post harvest Technology Research & Information
      Center University of California, Davis
5.    Kitinoja, L and Gorny, J. (1998) Post-harvest technology for fruits and vegetables Produce
      marketers: Economic opportunities. Quality and Food Safety by, Department of Pomology,
      University of California, Davis. A joint publication of UC Post harvest Outreach Program
      and Punjab Horticultural Post harvest technology Centre, USAID/ACE
6.    Thompson A.K. (1996) Post harvest Technology of Fruits and Vegetables. 1st Edition,
      Blackwell Science, Inc. USA.
7.    Wardlaw, C.W. and Leonard, E.R. (1936). The storage of West Indian Mangoes, Low
      Temperature Research Station Memoir 3, 47 pp.
8.    Wills, R; McGlasson, B; Graham, D and Joyce, D (1998) Post harvest: An Introduction to
      the Physiology and Handling of Fruit, Vegetables and Ornamentals. 4th Edition, CAB
      International,UK.
9.    Von Loesecke, H.W. (1949). Bananas. Wiley Inter-sciences, London.




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