Harvest Discrimination of Pomegranate Fruit: Postharvest Quality Changes and Relationships between Instrumental and Sensory Attributes during Shelf Life

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					Harvest Discrimination of Pomegranate Fruit:
Postharvest Quality Changes and Relationships
between Instrumental and Sensory Attributes
during Shelf Life
Olaniyi Amos Fawole and Umezuruike Linus Opara

    Abstract:     Harvest maturity discrimination was carried out for “Ruby” pomegranate cultivar in simulated handling
    conditions for long distant supply chains. Fruit were harvested at 3 different maturities along days after full bloom
    (DAFB); Harvest 1 (H1) at 133 DAFB, H2 at 143 DAFB, and H3 at 157 DAFB. The effects of harvest maturity and
    storage duration on fruit quality attributes during a 6-wk period of cold storage (5◦ C, 95% RH) and subsequent 5 d
    of shelf life (20◦ C, 75% RH) were investigated. Instrumental evaluation of aril color, juice content, juice absorbance
    (520 nm), total soluble solids (TSS), pH, titratable acids (TA), and phytochemical components including total phenolics,
    flavonoids, and anthocyanins were carried out. Textural properties of arils which included hardness, toughness, bioyield
    point, and Young’s modulus were also investigated. During the shelf life period, arils from individual fruit were rated by
    a trained sensory panel based on appearance, taste, and texture. Relationships between the instrumental and descriptive
    sensory data were explored and fruit harvest maturities were discriminated using discriminant analysis. Among the
    attributes evaluated, TSS : TA, sweet taste, and the CIE hue angle (h◦ ) were the most decisive attributes distinguishing
    the harvest maturities. The optimum time for harvesting was at 143 DAFB (H2) when fruit TSS : TA ratio was > 55,
    which coincided with significantly higher rating for sweet taste in fruit at H2 than at H1 and H3 during shelf life. The
    harvest index proposed in the current study could be used as a guide to establish a reliable harvest maturity index to assist
    in assuring fruit quality in consideration of long supply chains for the investigated cultivar.

    Keywords: discriminant analysis, harvest index, pomegranate, sensory attributes, storage

    Practical Application:  The harvest index proposed in the current study could be used as a guide to establish a reliable
    harvest maturity index to assist in assuring fruit quality in consideration of long supply chains for the investigated cultivar.

                                                                                                                                                            S: Sensory & Food
    In addition, the current study provides a basis for future studies towards the development of science-based tools for
    determining optimum fruit maturity and postharvest handling protocols for pomegranate cultivars grown globally.

Introduction                                                                          to increase exports, allowing producers to fill the counter-season
   Pomegranate (Punica granatum L.) belongs to the Punicaceae                         window during spring and early summer months in Northern
family. The fruit has long been valued for its flavourful and juicy                    Hemisphere (Brodie 2009). Pomegranate fruit is non-climacteric
edible part (aril), and more lately for commercial juice produc-                      and thus cannot continue the ripening process after detachment
tion (Wetzstein and others 2011). Rising consumer interest and                        from the parent plant (Kader 2006). Fruit maturity indices are
awareness on pomegranate as a medicinal food has spurred global                       usually based on a wide range of physico-chemical characteris-
increase in production and marketing of pomegranate fruit and its                     tics that are judged either objectively or subjectively. Although
products. Commercial orchards of different pomegranate cultivars                      quality parameters such as fruit size, shape and peel colour are
are grown in different countries (Al-Said and others 2009; Holland                    important external attributes for grading and marketing, fruit peel
and others 2009; Opara and others 2009; Bchir and others 2010),                       colour does not indicate the extent of ripening or readiness of
with 90% of the world pomegranate production occurring in the                         the arils for consumption (Kader 2006; Holland and others 2009;
Northern Hemisphere (Holland and others 2009). South Africa                           Fawole and Opara 2013a); hence, additional maturity indices such
is one of the recognized producers in the Southern Hemisphere,                        as aril colour, total soluble solids and acidity are commonly used
competing with countries such as Chile, Australia, Peru and Ar-                       in fruit quality assessment to meet market requirements (Ben-Arie
gentina (Fawole and Opara 2013c). Consequently, the export op-                        and others 1984; Kader 2006; Martinez and others 2006). Chace
portunity has, in recent years, encouraged large scale production                     and others (1981) established a maturity standard for ‘Wonderful’
                                                                                      pomegranate cultivar grown in California based on their finding
                                                                                      that 1.8% titratable acidity level and total soluble solids content
MS 20130389 Submitted 3/18/2013, Accepted 5/6/2013. Authors are with
Postharvest Technology Research Lab., South African Research Chair in Postharvest
                                                                                      above 17% was the most satisfactory maturity standard. Other
Technology, Faculty of AgriSciences, Stellenbosch Univ., Private Bag X1, Stellenbosch authors proposed that the minimum harvest maturity indices
7602, South Africa. Direct inquires to author Opara (E-mail:        for Califonia-grown ‘Wonderful’ pomegranates were red juice
                                                                                      colour equal to or darker than Munsel colour chart 5R-5/12 and

C 2013 Institute of Food Technologists R
doi: 10.1111/1750-3841.12176                                                                    Vol. 00, Nr. 0, 2013 r Journal of Food Science S1
Further reproduction without permission is prohibited
                    Discrimination of pomegranate fruit harvests . . .

                    titratable acidity below 1.85% (Elyatem and Kader 1984; Kader and        fruits per box) were stacked on a pallet and stored at 5◦ C with 95%
                    others 1984). These characteristic quality attributes are acquired       relative humidity (RH) based on current industry practice. Cold
                    during fruit maturation and ripening and are cultivar dependent          storage was terminated after 6 weeks followed by the shelf life
                    (Ben-Arie and others 1984; Gil and others 1996). As a result,            period of five days at 20◦ C and 75% RH to simulate a reasonable
                    the choice of a reliable harvest index should reflect the quality         retail sale period (Artes and others 2000). Temperature (◦ C) and
                    requirements of harvested fruit and also enable postharvest deliv-       relative humidity, RH (%) inside the cold room were recorded on
                    ery of fruit to consumers based on desired nutritional and sensory       hourly basis using three Tiny Tag TV-4500 data loggers (Gemini
                    attributes (Kader 2006).                                                 Data Logger, Sussex, UK) with functional ranges of −40◦ C to
                       Sensory quality attributes and nutritive value of fruit play an       +85◦ C and 0% to 100% RH, respectively.
                    important role in consumer satisfaction and repeat purchase. Juice
                    taste, aroma, aril texture and appearance are generally considered       Fruit quality evaluation
                    important sensory attributes (Gadˇ e and others 2011). However              Fifteen fruit per harvest were evaluated at 2-week intervals dur-
                    like other fruits, pomegranate also undergoes postharvest quality        ing cold storage and during the shelf storage for key quality indices
                    losses during handling and storage. Apart from common exter-             (total soluble solids, pH and titratable acidity). Other quality pa-
                    nal postharvest quality defects such as bruises, decay and water         rameters such as textural and phytochemical attributes were eval-
                    loss, leading to browning symptoms in both peel and arils (Kader         uated before cold storage and during shelf life period. Descriptive
                    2006; Mirdehghan and others 2006), internal quality losses also          sensory evaluation was conducted only during shelf-life, when
                    occur. These include loss of colour as a result of degradation of        the fruit was assumed to be available to consumers. Instrumental
                    anthocyanin (Turfan and others 2011), and decrease in vitamin C          and sensory measurements were carried out using eight individual
                    concentration, total soluble solids and titratable acidity, which are    fruit at shelf life for the purpose of correlation and discriminant
                    accompanied by a reduction of acceptability in terms of freshness,       analyses.
                    juiciness and taste (Gil and others 1996; Artes and others 2000;
                    Labb´ and others 2010; Turfan and others 2011). Internal break-
                          e                                                                  Instrumental analyses
                    down is another physiological disorder in pomegranates, resulting           Colour analysis. Aril colour was assessed in CIELAB coordi-
                    to light streaky appearance and a ‘flat’ taste of the arils (Pantastico   nates (L∗ , a∗ , b∗ ) using a Minolta Chroma Meter CR-400 (Minolta
                    ??).                                                                     Corp, Osaka, Japan). Duplicate colour measurements were made
                       To ensure postharvest delivery of good quality fruit to con-          on arils (per fruit) placed in a colourless glass Petri dish. The
                    sumers, particularly for long supply chains, it is necessary to de-      colour parameters chroma (C∗ = (a∗2 + b∗2 )1/2 ) and hue angle
                    fine picking maturity standards (Brown and Walker 1990). This             (h˚ = arctan (b∗ /a∗ )) were calculated (Al-Said and others 2009).
                    will ensure an appropriate balance between harvest maturity and          Pomegranate juice (PJ) colour absorbance was measured at 520
                    postharvest quality. The objective of this study was to determine        nm using a Helios Omega UV-vis spectrophotometer (Thermo
                    decisive harvest maturity indicators for optimum postharvest per-        Scientific technologies, Madison, USA). The data on colour at-
                    formance of pomegranate fruit (cv. “Ruby”) based on a combi-             tributes are presented only for fruit before storage and after shelf
                    nation of sensory and instrumental quality attributes.                   life, as the changes during 6 weeks of cold storage were negligible.
S: Sensory & Food

                                                                                                Measurement of pH, titratable acidity and total soluble
                    Materials and Methods

                                                                                             solids. Juice extraction (without crushing the kernels) was done
                                                                                             on the remaining arils using a blender (Mellerware, South Africa).
                    Fruit                                                                    Juice pH value was determined at room temperature using a pH
                       Pomegranate (cv. “Ruby”) grown on a commercial                        meter (Crison, Barcelona, Spain). Titratable acidity (TA) was de-
                    pomegranate orchard in Porterville (Western Cape, South Africa)          termined by titration (to a pH 8.2) using a Metrohm 862 compact
                    were investigated. In other to ensure comparable crop load and           titrosampler (Herisau, Switzerland), and the results were expressed
                    fruit size, flower and fruit thinning was carried out on randomly         as percentage tartaric acid equivalents. Total soluble solids (TSS)
                    tagged trees (4 year-old) at the beginning of the season. Fruit were     were measured using a digital refractometer (Atago, Tokyo, Japan).
                    harvested at three harvest maturities (H1 – H3) between March            TSS/TA ratio and BrimA index, a criterion for acceptance of fruit
                    and April in 2012 during the usual harvest season. The first harvest      juice expressed as BrimA = TSS – k ∗ TA, were calculated, where
                    (H1) occurred at 133 days after full bloom (DAFB) on 16th March,         k is the tongue’s sensitivity index normally ranging between 2 –
                    the second harvest (H2) on 26th March (143 DAFB) and the third           10 (Jordan and others 2001). In this study k = 2 was used (Fawole
                    harvest (H3) on 9th April (157 DAFB). During each harvest, a             and Opara 2013a; 2013b; 2013c). All measurements were made
                    sample of 150 fruit was harvested, taking care to avoid fruit with       on individual fruit samples.
                    sunburn, blemish and cracks. Harvested fruit were transported in            Determination of total phenolic concentration. Total
                    an air-conditioned vehicle to the Postharvest Technology Labo-           phenolic concentration (TPC) was determined in triplicates by
                    ratory at Stellenbosch University where they were further sorted         the Folin-Ciocalteu colourimetric method (Makkar and others
                    for colour and size uniformity before cooling overnight at room          2000) and results were expressed as gallic acid equivalents (GAE)
                    temperature. The same experimental and handling procedure was            per 100 mL PJ.
                    conducted in the same manner at the three separate harvests.                Total flavonoids concentration. The total flavonoids con-
                                                                                             centration (TFC) was determined using the method described by
                    Fruit storage                                                            (Yang and others 2009) and results were expressed as catechin
                       The study took into account a storage period that simulated the       equivalents (CAE) per 100 mL PJ.
                    time that elapses from harvest to consumption in the commercial             Total anthocyanin concentration. Total anthocyanin con-
                    export chains. Fruit were packed in single layers in 4.5 kg open         centration (TAC) was quantified using the pH differential method
                    top boxes with no lids according to industry practice. Fruit did         (Wrolstad 1993). In triplicates, PJ extracts (1 mL) were mixed
                    not receive any postharvest chemical treatments. Packed boxes (15        with 9 mL of pH 1.0 and pH 4.5 buffers, separately. Absorbance

                    S2 Journal of Food Science r Vol. 00, Nr. 0, 2013
Discrimination of pomegranate fruit harvests . . .

was measured at 510 and 700 nm in pH 1.0 and 4.5 buffers and Chambers (2010). During the final training sessions, the panel
result was expressed as cyanidin-3-glucoside equivalents using the practised intensity rating of the individual attributes on the line
following equations:                                                  scales and panel performance assessment was carried out.
                                                                         Sensory evaluation. All sensory assessments were conducted
              A = (A510 −A700 )pH1.0 − (A510 −A700 )pH4.0         (1) on the same time for the harvest maturities at ambient room
                                                                      temperature (20◦ C) in the Sensory Laboratory, Food Science De-
                                                                      partment, Stellenbosch University, South Africa. Individual test-
              Total anthocyanin concentration (mg/mL)                 ing booths equipped with serving windows and controlled light-
                 = (A × MW × DF) ÷ (ε×L)                          (2) ing were used. Pomegranate arils (∼10 g) of the three harvest
                                                                      times were randomized and coded with three-digit random num-
where A = Absorbance, ε = Cyd-3-glucoside molar absorbance bers in clean Petri dishes. Sensory ratings were recorded using
(26,900), MW = anthocyanin molecular weight (449.2), DF = the Compusense five sensory data acquisition program (Guelph,

dilution factor, L = cell pathlength (1 cm). Final results are ex- Ontario, Canada).
pressed as cyanidin-3-glucoside equivalents per 100 mL PJ (mg
C3 gE/100 mL PJ).                                                     Statistical analysis
   Texture dynamics of pomegranate aril. Compression tests               Mean values of all the studied variables are presented. Anal-
were performed using a texture profile analyzer (TA.XT Plus, Sta- ysis of variance (ANOVA) was carried out using Statistica soft-
ble Microsystems, England) with a 35 mm compression probe. A ware (Statistical 11.0, StatSoft Inc., Tulsa, OK, USA) according
total of 10 arils extracted from each fruit were used, and a test to Duncan’s multiple range test. Mean values for different harvests
was run per aril aligned horizontally on the compression plat- with storage duration were separated, and where appropriate, 2-
form. The operating conditions of the instrument were: pre-test way ANOVA was carried out. Graphical data presentations were
speed 1.5 mm/s, 0.5 mm/s test speed, 10.0 mm/s post-test speed, performed using GraphPad Prism software version 4.03 (Graph-
and 0.20 N trigger force (Al-Said and others 2009). The force- Pad Software, Inc. San Diego, USA). Sensory data were pre-
deformation curves generated were analysed for bioyield point processed for application in multivariate analyses. Panel perfor-
(N) that is defined as the point on the force-deformation curve mance was monitored using Panel Check Software (Version 1.3.2,
at which the juice content in compressed aril just oozed without www. In the event of significant non-normality
the tearing of the aril sac. When loading is continued beyond the (p < 0.05) outliers were identified and removed (Koch and others
bioyield point, a rupture occurs (Mohsenin 1986). Young’s modu- 2012). Discriminant analysis (DA) was performed (using XLStat,
lus or elasticity (N/mm2 ) was calculated as the slope from the start version 7.5.2, Addinsoft, New York, USA) on the three harvest
of the compression to that of the bioyield point. Rupture force times to establish if the harvest times were indeed distinctly dissim-
or hardness (N) was calculated as the maximum force required for ilar with both instrumental and sensory attributes investigated and
complete breakage of the test sample while the rupture energy or to explain the harvest times using the attributes that contributed
toughness ( was determined from the area under the curve significantly to the harvest times.
(Al-Said and others 2009).

                                                                                                                                                 S: Sensory & Food
                                                                       Result and Discussion
Instrumental and sensory measurements during shelf life

period                                                                 Initial measurements of major maturity indices at fruit
   Sample preparation. Each fruit was manually peeled in a             harvest times
sterile condition and arils were placed into clean labeled beakers.       Pomegranate fruit harvested at different maturity times showed
After peeling, the extracted aril from each fruit was weighed and      degrees of heterogeneity in some of the key quality attributes.
divided unequally into the 2:1 ratio, the larger portion (75%) for     Among the CIE aril colour parameters, only the colour redness
sensory evaluation and the other (25%) for instrumental analysis.      (a∗ ) statistically distinguished the harvest maturities investigated,
   Instrumental analysis. The same experimental protocols              showing significant (p < 0.05) increase with increasing harvest
were followed as previously described for all instrumental mea-        times (Table 1). This suggests that the desirable red colouration in
surements.                                                             pomegranate aril increased with delayed fruit harvest, probably due
   Panel training. The training of the panel was conducted ac-         to the continued accumulation of anthocyanins with advancing
cording to the consensus method (Koch and others 2012). The            maturity as previously reported for the cultivar (Fawole and Opara
panel was comprised of 9 members (7 women and 2 men) with              2013a). In addition, juice contents and absorbance increased also
previous formal sensory evaluation and descriptive analysis expe-      increased with prolonged harvest times, with fruit juice at H1
rience. The panelists were provided with a range of fruit arils at     having significantly (p < 0.05) lower values than later harvested
various maturity levels, followed by the development of descrip-       fruit (Table 1).
tors and scores. The panelists were required to test the attributes       Titratable acidity (TA) decreased with prolonged harvest times
in the order of appearance, flavour and texture. A score sheet was      and was significantly higher in H1 fruit (Fig. 1). Drastic decline
then developed which was used by the panel to scale the intensity      in juice acidity levels in H1 compared to H2 and H3 is an indica-
of each of the descriptors on a 100 mm unstructured line scale         tion that fruit was properly still actively undergoing the maturity
ranging from low intensity (0 mm) corresponding to the word            process. The observed decline in fruit acidity may be attributed
anchor “none” to high intensity (100 mm) corresponding to the          to the cumulative effects of increasing fruit juice content and the
word anchor “prominent”. Descriptors that were not suitable (for       use of organic acids as respiratory substrates that occur during fruit
instance, aroma) for the product were eliminated. Retention of         maturation (Diakou and others 2000).
a descriptor in the initial list was on the basis that the attribute      Changes in total soluble solids (TSS) showed that fruit maturity
should be relevant to the product and be easily perceived by each      indices follow different patterns. Contrary to juice acidity pat-
panel member. Sensory attributes were adopted from Koppel and          tern, total soluble solids (TSS) increased significantly (p < 0.05)

                                                                                             Vol. 00, Nr. 0, 2013 r Journal of Food Science S3
                    Discrimination of pomegranate fruit harvests . . .

                    Table 1–Effect of harvest maturity on changes in color properties, phenolic concentrations, and mechanical properties of
                    pomegranate arils (cv. “Ruby”) at harvest dates and during simulated shelf life of 5 d at 20◦ C.

                                                                           Harvest                                              Shelf life                                  Significance levelA
                    Attribute                               H1                H2                H3               H1                H2                H3                 A                 B             A∗ B
                    L∗                                    22.07b            20.21b            20.10b            26.95a           20.62b            20.31b            0.006           <0.0001           0.004
                    C∗                                    23.94ab           24.72ab           27.86a            21.34b           22.91ab           23.07ab           0.021            0.212            0.624
                    h◦                                    30.19b            24.82d            24.28d            34.98a           29.27c            29.20cd          <0.0001          <0.0001           0.249
                    aA                                    21.93c            23.73b            26.52a            17.79e           20.35d            20.59d           <0.0001          <0.0001           0.020
                    Juiciness (mL/100 g aril)             61.18b            66.56a            67.90a            61.12b           65.08ab           67.20a           <0.0001          <0.0001           0.005
                    Juice abs.                             1.99c             3.10a             3.00a             1.79c            2.74b             2.91a           <0.0001          <0.0001           0.031
                    TAC (mg/100 mL)                       21.08c            31.58a            30.47ab           18.99c           27.95b            29.58ab           0.015           <0.0001           0.425
                    TPC (mg/100 mL)                      489.32a           293.27b           233.38b           440.83a          259.53b           226.58b            0.105           <0.0001           0.632
                    TFC (mg/100 mL)                      385.19a           251.96b           206.44b           347.02a          222.97b           200.43b            0.104           <0.0001           0.002
                    Hardness (N)                          90.80a            92.11a            90.83a            81.80b           85.05b            85.27b           <0.0001           0.403            0.062
                    Toughness (N.mm2)                     88.82a            93.71a            90.18a            80.02b           88.24a            87.55a            0.003            0.016            0.386
                    Bioyield point (N)                     7.45ab            7.54ab            7.86a             5.81c            6.67bc            6.81b           <0.0001           0.088            0.481
                    Young modulus (N/mm)                   4.90a             5.06a             4.94a             4.41a            4.48a             4.50a            0.022            0.912            0.967
                    Mean values with different letter(s) across harvest and shelf life period indicate statistically significant differences (P < 0.05) according to Duncan’s multiple range test. H 1, H2, and
                    H3 = Harvest times 1, 2, and 3. TAC = total anthocyanin concentration; TPC = total phenolic concentration; TFC = total flavonoid concentration.
                      Factor A = harvest times; Factor B = Storage period.

                    between H1 and H3 in the cultivar (Fig. 1). TSS values increased                              Change in pH, titratable acidity (TA) and total soluble
                    from 15.29◦ Brix (H1) to 17.24◦ Brix (H3). All the harvest times                              solids (TSS) during storage
                    differed significantly (p < 0.05). Ripening of pomegranates is                                    Juice pH was significantly (p < 0.0001) influenced by the in-
                    closely associated with increase in TSS (Fawole and Opara 2013a).                             teraction between harvest time and storage duration (Fig. 1). For
                    The observed overall increase in TSS with prolonged harvest times                             H1 and H2, significant (p < 0.05) increases in juice pH were
                    could possibly be due to the continued hydrolysis of starch to sug-                           observed throughout fruit cold storage, followed by slight decline
                    ars with increased ripening time (Kulkarni and Aradhya 2005). As                              during shelf life period (Fig. 1). For H3 however, juice pH re-
                    a result of changes in TSS and TA, the fruit TSS:TA ratios and                                mained relatively stable throughout cold storage and at shelf life
                    BrimA also increased significantly (p < 0.05) with prolonged har-                              (Fig. 1). This resulted to lower pH value in H3 than in H2 and
                    vest (Fig. 1). Previous studies have shown the effects of different                           H3 after 6 weeks and during shelf life (Fig. 1). Fruit pH value is
                    harvest times on pomegranate fruit chemical attributes (Shwartz                               dependent on the dissociation and release of ionic hydrogen from
                    and others 2009; Borochov-Neori and others 2011). For example,                                the carboxyl group of organic acids in the fruit (Ding and Ong
                    in two accessions of ‘Wonderful’ cultivar grown in Israel, Shwartz                            2010). The observed changes in fruit pH values during storage of
                    and others (2009) reported significant difference in titratable acid-                          H1 and H2 could be an indication of the content of and dynamics
S: Sensory & Food

                    ity, pH and total soluble solids contents of mature fruit harvested                           in fruit organic acids. The observed stability in juice pH in H3
                    at weekly intervals.

                                                                                                                  fruit is in agreement with the study by Elyatem and Kader (1984),
                                                                                                                  who reported no significant difference in fruit pH values in fruit
                    Change in aril colour properties during storage                                               (cv. ‘Wonderful’) stored for 8 weeks at 5◦ C.
                       Differences in aril colour property measured as CIE L∗ , a∗ , C∗ ,                            A decreasing trend in TA level with prolonged storage was ob-
                    and h◦ during cold storage at 5◦ C for 6 weeks did not change                                 served in H1, whereas in H2 and H3, TA levels first increased
                    significantly (p < 0.05) among the harvest times (data not shown).                             significantly (p < 0.05) between the initial harvest period and 4
                    A similar observation was reported by Gil and others (1996), who                              weeks and declined afterwards until to shelf life period (Fig. 1).
                    found no significant differences in aril colour of pomegranate                                 This shows that irrespective of harvest times, fruit acidity would
                    fruit harvested at different maturities after storage at 5◦ C for 1.5                         decline during shipping period as demonstrated in this study. The
                    months. However, increase in h◦ and decrease in a∗ suggest that                               observed decline in TA could probably be due to the ongoing
                    the overall aril colour depreciated between the initial harvest and                           metabolism in the fruit during storage (Kader and others 1984).
                    shelf life periods (Table 1). It appeared that aril colour depreciation                       Our findings agree with Artes and others (2000), who reported
                    was significantly (p < 0.05) influenced by the combined effects                                 significant decreases in pomegranate fruit (cv. ‘Molla de Elche’)
                    of fruit harvest times and storage period on the CIE h◦ while the                             stored at 5◦ C for 90 days and six additional days at 20◦ C. The in-
                    interaction between the main factors was significantly (p = 0.020)                             teraction effect between harvest times and storage duration played
                    evident on the CIE a∗ (Table 1).                                                              a significant (p < 0.001) role on fruit TA levels during the simu-
                       Although it was not statistically significant, the declining trend                          lated storage 6-week storage at 5◦ C plus subsequent shelf life of 5
                    in juice absorbance values corroborated the decrease in the ob-                               days at 20◦ C (Fig. 1).
                    served aril colour properties (Table 1). Absorbance values measured                              In general, H3 had higher total soluble solids (TSS) contents
                    at 520 nm declined between initial measurements at harvest and                                than in earlier harvests and the difference were maintained dur-
                    shelf period. Anthocyanins are light-absorbing plant-based pig-                               ing storage and shelf life period (Fig. 1). TSS contents decreased
                    ments and are responsible for the red colour of pomegranate juice                             significantly (p < 0.05) in all the harvests from 2 weeks of stor-
                    (Shulman and others 1984). Our findings indicated that fruit har-                              age through to shelf life period. There were significant differ-
                    vested at later times had higher red colouration which was better                             ences among fruit harvests after shelf life, H3 offering signif-
                    maintained during postharvest handling than in early harvested                                icantly (p < 0.05) higher TSS contents at the end of market
                    fruit.                                                                                        life.

                    S4 Journal of Food Science r Vol. 00, Nr. 0, 2013
Discrimination of pomegranate fruit harvests . . .

                                                                                        Harve st 1                                Harve st 2                                Harve st 3
                                                                     4                               a                                                        ab
                                                                                   def      cd            abcd              de       cd        abc   abcd            abcd     abcd       bcd    bcd
                                                                           ef                                       f



     Total soluble solids ( Brix) Titratable acidity (% tartaric)

                                                                    0.4    a       ab                                                ab
                                                                                            bc       cd                    bcd                                       cde
                                                                                                            e       e                                         de               cde
                                                                                                                                                f                                         f      f


                                                                                                                    b                                         a       ab
                                                                          defg     cdef      fg                             cde     defg       eg      g                       bc        bcd
                                                                    15                               h     h



                                                                    70                                                                         ab      a                                  a      a
                                                                                                                    bcd                                      abc
                                                                                                                                                                      def      cd
                                                                    50                                      f               ef
                                                                                   f         f                                        f

                                                                           f                         f
                                                                                                                    b                                         a       ab
                                                                                   d                                       cd                                                  bc        bc
                                                                    15     d                d                                        d         d      d                                         d
                                                                                                     e     e

                                                                                                                                                                                                          S: Sensory & Food



                                                                          0        2        4        6    Shelf     0       2        4         6     Shelf    0       2        4         6     Shelf

                                                                                 Storage time (week)                      Storage time (week)                      Storage time (week)

                                                                                                                       Significance level
    Parameter                                                                                                   Harvest (A)            Storage duration (B)                          A*B
    pH                                                                                                          <0.0001                0.0057                                        <0.0001
    Titratable acidity (TA)                                                                                     <0.0001                <0.0001                                       <0.0001
    Total soluble solids (TSS)                                                                                  <0.0001                <0.0001                                       0.079
    TSS/TA                                                                                                      <0.0001                <0.0001                                       <0.0001
    BrimA                                                                                                       <0.0001                <0.0001                                       0.0383
Figure 1–Chemical changes in “Ruby” pomegranate as influenced by harvest maturity during simulated 6-wk storage at 5◦ C and subsequent shelf life
of 5 d at 20◦ C. Different letters on bars across harvest times mean statistically significant differences (P < 0.05) according to Duncan’s multiple range

                                                                                                                                                      Vol. 00, Nr. 0, 2013 r Journal of Food Science S5
                    Discrimination of pomegranate fruit harvests . . .

                       In comparison to a similar study on ‘Mollar’ pomegranate cul-       concentrations (with the exception of TFC; p = 0.002) (Table 1).
                    tivar, after 6 weeks of storage at 5◦ C, decreases in TSS contents     The TPC and TFC in fruit harvested early in the season were
                    in harvested at two maturity stages were not significant (Gil and       significantly (p < 0.05) higher than in H2 and H3 and the dif-
                    others 1996). Both harvest time and storage duration significantly      ferences were maintained during shelf life (Table 1). The highest
                    (p < 0.0001) influenced TSS content (Fig. 1).                           anthocyanin concentration was found in H2 and the concentra-
                       The changes in TA and TSS values were reflected in the TSS/TA        tion decreased significant during shelf life period (Table 1). There
                    ratio, which increased with storage period among fruit harvests.       are very few studies on changes in pomegranate phenolic concen-
                    It is noteworthy that in H2 and H3 the TSS/TA ratio remained                                              e
                                                                                           tration during fruit storage. Labb´ and others (2010) studied the
                    steady during storage (Fig. 1), probably suggesting that the TSS       behavior of two Chilean pomegranate varieties stored at 5◦ C over
                    and TA contents declined in equal proportions during postharvest       12 weeks. The authors reported the decrease in aril colour (degra-
                    storage. According to Ben-Arie and others (1984), TSS/TA ratio         dation of anthocyanins) and fruit quality as well as a decrease in
                    is a more reliable indicator than TSS to differentiate quality and     the antioxidant capacity of the investigated cultivar. The sharp de-
                    characterize flavour of different harvest times of pomegranate fruit.   crease in polyphenols including anthocyanins in pomegranate dur-
                    The observed sharp decline in TA level, with a rather gradual          ing shelf life period could be attributed to the change of enzyme
                    decrease in TSS resulted to significant (p < 0.05) fluctuations in       activities resulting to phenolic degradation. According to Oren-
                    TSS/TA ratio in fruit. The TSS/TA ratio in later harvests (H2          Shamir (2009), the degradation process begins with intracellular
                    and H3) first declined significantly (p < 0.05) between the initial      decompartmentation and cell layer damage in fruit during storage,
                    harvest times and then increased afterwards (Fig. 1). During shelf     hence exposing the pigments to micro-environmental conditions
                    life period, the values of TSS/TA in early harvested fruit (H1)        that differ from those in on-tree fruit, including enzymes that are
                    were significantly lower than in later harvests (Fig. 1), suggesting    not located in the vacuoles when the fruit cells are intact.
                    reduced flavour quality. The interaction effect between harvest
                    time and storage duration played a significant (p < 0.001) on the
                                                                                   Change in aril texture after storage
                    changes in TSS/TA ratio. Postharvest storage duration and harvest
                    times had significant (p < 0.05) influences on BrimA values (Fig.  Textural property of arils is an important quality attribute in
                    1), resulting to significant decreases in BrimA between harvest the pomegranate industry. The mechanical properties related to
                    times and shelf life period. The changes in BrimA value were a texture that were evaluated included hardness, rupture energy or
                                                                                   toughness, bioyield and Young’s modulus of elasticity. Aril tough-
                    reflection of the levels of TSS and TA in fruit during storage, with
                    early harvested fruit (H1) having the lowest BrimA index.      ness showed no significant (p < 0.05) changes among harvest and
                                                                                   during storage period, with the exception of H1 during shelf life
                                                                                   (Table 1). Aril hardness did not differ significantly (p < 0.05) as
                    Changes in phenolic concentration after storage                a result of harvest times but rather declined significantly in all
                       In general, there were no significant (p > 0.05) interaction the harvests during shelf period. The Young modulus remained
                    effects between harvest times and storage duration on phenolic unaltered among harvests during storage and the subsequent shelf
S: Sensory & Food

                                                                                                               Figure 2–Radar plot showing averaged sensory

                                                                                                               scores (scale = 0 – 100; n = 72) of pomegranate
                                                                                                               fruit at 3 different harvest times analyzed after
                                                                                                               storage for “Ruby” cultivar. ∗ Indicates significant
                                                                                                               difference (P < 0.05) between harvest times.
                                                                                                               Fruits were stored at 5◦ C for 6 wk and a 5-d shelf
                                                                                                               life period at 20◦ C before sensory evaluation. H1,
                                                                                                               H2, and H3 = Harvest times 1, 2, and 3.

                    S6 Journal of Food Science r Vol. 00, Nr. 0, 2013
Discrimination of pomegranate fruit harvests . . .

Table 2–Pearson correlation coefficients among instrumental Table 4–Summary of variable selection table showing attributes
and sensory attributes of “Ruby” pomegranate fruits at shelf that contribute most to the harvest groups using a stepwise (for-
lifeA .                                                      ward) analysisA .

Sensory                                               Instrumental                       Cultivar Variable IN/OUT Status Partial R2 F statistic                 Pr > F
attributes                             r                attributes                r
                                                                                     “Ruby”              TSS:TA           IN           0.654          19.838     < 0.0001
Overall         Aril color     0.803 TSS                      TA              −0.531                   Sweet taste       IN            0.474           9.024       0.002
  appearance    Overall flavor 0.547                           TSS:TA           0.757                         h◦          IN            0.431           7.188       0.005
Sweet taste     Sour taste    −0.643                          BrimA            0.998
                                                                               0.571 Partial R = determination coefficient; F statistic = F ratio test; Pr > F = P-value at
                                                                                     A         2
Juiciness       Crunchiness    0.778                          Juice content
                                                                                     significance level of 0.05.
                Crispness      0.807                          Anthocyanin      0.601
Crispness       Crunchiness    0.785                          T. phenolic     −0.629
                                     TA                       TSS:TA          −0.945
Sensory against. instrumental                                 BrimA           −0.584    The overall decreases in aril textural property after shelf life for
                                                                                         the cultivar suggest the softening of arils during the simulated shelf
Overall flavour    C∗                0.548                Anthocyanin          −0.605
Sour taste        L∗               −0.517                T. phenolic           0.689     period. This could be attributed to cell membrane deterioration
Grittiness        TA                0.510 TSS:TA         BrimA                 0.796     due to higher temperature under shelf life condition (Bchir and
Grittiness        h◦                0.579                Anthocyanin           0.702                                                              e
                                                                                         others 2011). Similar results were reported by Labb´ and others
Hardness          h◦                0.569                T. phenolic          −0.754     (2010) who showed the loss of firmness in arils during fruit storage
                  C∗               −0.502 BrimA          Juice content         0.566
                                                                                         at 5◦ C for 8 weeks.
                                                         T. phenolic          −0.648
                                                         Anthocyanin           0.601
                                             Anthocyanin T. phenolic          −0.765     Sensory characteristics during shelf-life
                                                         h◦                   −0.537        This study showed that long term storage and shelf life con-
                                             T. phenolic h◦                    0.537
                                             C∗          h◦                   −0.552
                                                                                         dition of pomegranate arils inevitably led to reduction in visual
                                                         a∗                    0.974     appearance and flavour. Differences in sensory attributes of arils
                                             h◦          Hardness             −0.728     at different fruit harvests after 5 days of shelf life are shown in
 Relationships with correlation coefficients >0.5 are presented. Values highlighted in
                                                                                         Fig. 2. Significant differences were observed in some of the sen-
bold represent strong (>0.75) correlations.                                              sory attributes evaluated. Fruit sensory attributes such as overall
                                                                                         flavour, sweet taste, sour taste and grittiness clearly distinguished
                                                                                         the different harvests (Fig. 2). Grittiness intensity was significantly
Table 3–Variables and factors (F1 and F2) correlations of dis-                           (p < 0.05) higher in early harvested (H1) fruits than the other
criminant analysis for the sensory and instrumental data.
                                                                                         harvests (Fig. 2). In addition, overall flavour and sweet taste were
Variables                                           F1                             F2    significantly (p < 0.05) higher in H2 than in H1 and H3 (Fig. 2).
Sensory rating
                                                                                         The most significant difference found among fruit harvests was the
Aril color                                        0.447                          0.060   overall flavour attribute. The intensity of the attribute increased
Overall appearance                                0.465                          0.131   (on a scale of 0 – 100) from 63.5 in H1 to 67 in H2 and then de-

                                                                                                                                                                             S: Sensory & Food
Overall flavor                                     0.500                          0.204   creased to 64.9 in H3. The observed differences in shelf life flavour
Sweet taste                                       0.376                          0.909   intensities of fruit from different harvests might be attributed to the

Sour taste                                       -0.225                        −0.694
Astringency                                      -0.100                         -0.365   variability in fruit chemical attributes such as total soluble solids,
Crispness                                        -0.138                         -0.113   acidity and phenolics (Ben-Arie and others 1984; Kader 2006).
Crunchiness                                      -0.104                         -0.144      In general, sensory attributes such as sour taste, astringency, bit-
Juiciness                                        -0.002                         -0.084   terness and alcohol taste were rated extremely low in the harvests,
Grittiness                                      −0.678                           0.083
Sensory hardness                                −0.503                           0.174
                                                                                         followed by the ratings assigned to kernel hardness and grittiness.
Instrumental measurement                                                                 Furthermore, the same score was recorded for crunchiness and
pH                                               -0.034                         -0.267   crispness of fruit harvests (Fig. 2).
TSS                                               0.707                         -0.263
TA                                              −0.816                           0.086
TSS:TA                                            0.870
                                                                                     Pearson’s correlation between instrumental and sensory
BrimA                                             0.739                              measurements during shelf life
Juice content                                     0.429                         -0.378  Significant relationships that exist among attributes measured
Anthocyanin                                       0.696                         -0.295
                                                                                     are presented in Table 2. There were strong positive correlations
Phenolics                                       −0.696                           0.295
L∗                                              −0.537
                                                                                     between overall appearance and aril colour (r = 0.803), crisp-
C∗                                                0.283                              ness and crunchiness (r = 0.785), while juiciness strongly related
h◦                                              −0.677                               with crunchiness (r = 0.778) and crispness (r = 0.807). The rela-
a∗                                                0.422                         -0.312
                                                                                     tionships juiciness shared with crunchiness and crispness is note-
Hardness                                          0.242                         -0.024
                                                                                     worthy and suggests that juiciness could be an integrated repre-
Toughness                                         0.424                          0.143
                                                                                     sentation of the textural properties of the pomegranate aril. A
Correlations was at P < 0.05. Values highlighted in bold indicate strong to moderate similar observation was highlighted by Harker and others (2002),
correlations between variables and their corresponding factors.
                                                                                     who referred to juiciness as a textural attribute that defines many
                                                                                     fruits. Furthermore, there was a significant but negative corre-
                                                                                     lation between sweet taste and sour taste. This is well in agree-
period (Table 1). The influence of harvest time and storage dura- ment with Koppel and Chambers (2010) who reported significant
tion on aril toughness was significantly (p < 0.05) evident, whereas negative correlation between sweet and sour taste of thirty-three
aril hardness and bioyield were significantly (p < 0.05) influenced pomegranate juices. Strong relationships found amongst instru-
only by harvest time (Table 1).                                                      mental measurements included positive correlations amongst TSS,

                                                                                                               Vol. 00, Nr. 0, 2013 r Journal of Food Science S7
                    Discrimination of pomegranate fruit harvests . . .

                    BrimA and TSS:TA as well as between C∗ and a∗ (r = 0.974)               of the investigated pomegranate fruit clearly depends on complex
                    and strong negative correlations between TA and TSS:TA (r =             interactions of different parameters, of which only the interactions
                    −0.945), TSS:TA and phenolic (r = −0.754) and anthocyanin and           amongst the instrumental parameters seem promising and practi-
                    phenolic (r = −0.765). Moderate correlations were found be-             cable. This raises the question on the reliability of prediction of
                    tween some sensory and instrumental attributes but none of the          pomegranate sensory attribute by instrumental measurements. It
                    relationship seems to be applicable in practice. For instance, a mod-   has been showed in other pomegranate cultivars grown in western
                    erate positive correlation (r = 0.548) was found between overall        Herzegovina that analytical measurements cannot be substituted
                    flavour and chroma (C∗ ). In practice, no relevant prediction of                                       z
                                                                                            for sensory evaluation (Gadˇ e and others 2011).
                    pomegranate juice flavour could possibly be made using aril colour
                    intensity since colour measurement technique apply only to colour       Discriminant analysis (DA)
                    of aril tissues. Other relationships found were moderate correlation       Thirteen quality attributes showed correlation values > 0.5 (Ta-
                    between sour taste and lightness (L∗ ), grittiness and TA, and those    ble 3), with the stepwise model indicating that three of the at-
                    of sensory hardness with h◦ and C∗ (Table 3). The overall quality       tributes (TSS:TA, sweet taste and h◦ ) contributed significantly to

                                                                                                                Figure 3–Variables and observations charts of
                                                                                                                discriminant analysis (DA) for “Ruby” cultivar
                                                                                                                using instrumental (italicized) and sensory (bold)
                                                                                                                attributes. H1, H2, and H3 = Harvest times 1, 2,
                                                                                                                and 3.
S: Sensory & Food

                    S8 Journal of Food Science r Vol. 00, Nr. 0, 2013
Discrimination of pomegranate fruit harvests . . .

Table 5–Confusion matrixes showing the number of correct and Ben-Arie R, Segal N, Guelfat-Reich S. 1984. The maturation and ripening of the ‘Wonderful’
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                                                                                                     Climate effects on anthocyanin accumulation and composition in the pomegranate (Punica
From\To          Harvest 1        Harvest 2        Harvest 3         Total      % Correct            granatum L.) fruit arils. J Agric Food Chem 59:5325–34.
                                                                                                  Brodie L. 2009. Pomegranate production in South Africa. SA Fruit J 8:30–5.
Harvest 1             8                 0                0              8          100.00         Brown GS, Walker TD. 1990. Indicators of maturity in apricots using biplot multivariate analysis.
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Harvest 2             0                 8                0              8          100.00         Chace EM, Church GG, Poore HH. 1981. The Wonderful variety of pomegranate. USDA Circ.
Harvest 3             0                 1                7              8           87.50            98:15.
Total                 8                 9                7             24          95.83                                                           e
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   This study is based upon research supported by the South                                                                                           e          ı
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African Research Chairs Initiative of the Dept. of Science and                                       cold storage of pomegranate. J Agric Food Chem 54:8495–500.
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Stellenbosch Univ. for contributions to the statistical analysis. The                                tent, and antimicrobial properties of pomegranate fruit (Punica granatum L.). Food Bioprocess
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                                                                                                                             Vol. 00, Nr. 0, 2013 r Journal of Food Science S9

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