CHAPTER 2.0 REVIEW OF RELATED LITERATURE
2.1 Fruit Juices A fruit juice is a non-alcoholic beverage that is a clear unfermented liquid which is developed from the removal of the sweet water sap generally from ripe fruits (Gatchalian & de Leon, 1992). Juice is prepared by mechanically squeezing or macerating fresh fruits or vegetables without the application of heat or solvents. Popular juices include but are not limited to apple, orange, grapefruit, pineapple, tomato, mango, carrot, grape, cranberry and pomegranate (www.wikipedia.com, 2008). According to Paul (1975), the large market for fruit juices is due to their relatively low cost and a high nutritional value coupled with modern diet appeal. In the Philippines, consumption of fruit juices has increased considerably from P3 billion (at current prices) in 1993 to about P7.2 billion in 2000, a hefty increase of 137% (Monteclavo et. al., 2005).
2.2 Nutritional Composition of Fruit Juices Table 1-2. Food Composition of Fruit Juice (Orange) Nutritional Component EP % Water (g) Energy (kcal) Protein (g) Fat (g) Carbohydrate (g) Crude Dietary Fiber (g) Ash (g) Calcium (mg) Phosphorus (mg) Iron (mg) Retinol (µg) 5
Amount 100 % 39.6 244 Traces 0.7 59.5 0.3 0.2 34.0 2.0 0.3 0.0
β-carotene (µg) Total Vitamin A (µg) Thiamin (mg) Riboflavin (mg) Niacin (mg) Ascorbic Acid (mg) Source: Food Composition Table, FNRI 2.3 Problems Associated with Fruit Juices
10.0 2.0 Traces 0.02 0.0 0.0
For fruit juices, the common undesirable problems that fruit processing manufacturers are encountering are fermentation spoilage for canned fruit juices, foodborne illnesses outbreaks, cloudy sedimentation, poor flavor, and browning. Among these problems, browning is regarded as one of the most important problems related to color deterioration in processed fruits. Browning is the process of becoming brown, especially referring to food. Browning foods may be desirable, as in caramelization, or undesirable, as in an apple turning brown after being cut. Foods turn brown through an enzymatic or a nonenzymatic process (www.wikipedia.com, 2008).
2.4 Enzymatic Browning Enzymic browning is a chemical process involving polyphenol oxidase or other enzymes that create melanins, resulting in a brown color (www.wikipedia.com, 2008). Enzymatic browning can be observed in fruits (apricots, pears, bananas, grapes), vegetables (potatoes, mushrooms, lettuce) and also in seafood (shrimps, spiny lobsters and crabs). Enzymatic browning of fruits and vegetables creates heavy economic losses for growers (FAO, 2008).
2.5 Prevention of Enzymatic Browning The control of browning is one of the most important issues in thefood industry, as colour is a significant attribute of food which influences consumer decision and brown foods (especially fruits) are seen as spoiled. Several methods can be applied to avoid enzymatic browning, based on inactivating the enzyme (heat) or by removing essential components (most often oxygen) from the product (FAO, 2008). 2.5.1 Blanching. Blanching is a short heat treatment which destroys or
inactivates enzymes before freezing of products. Blanching brightens the colour, softens the texture, but has little effect on nutrient content or flavour as it is a relatively short process (FAO, 2008). 2.5.2 Refrigeration. Refrigeration and chilling are used to prevent spoilage of
vegetables and fruits during distribution and retailing. Chilling is applied often for broccoli, berries, spinach, peas, bananas, mangoes, avocados, tomatoes. At temperatures below 7 °C the polyphenoloxidase enzyme activity is inhibited, but the enzyme is not inactivated. Therefore the temperature should be well controlled (FAO, 2008). 2.5.3 Freezing. Like refrigeration, freezing inhibits, but not inactivates the
enzyme. After thawing, the enzyme activity will resume (FAO, 2008). 2.5.4 Change in pH. The enzyme activity is pH dependent. Lowering of the pH
to 4.0 by the addition of citric, ascorbic or other acids inhibits the enzyme activity. During home-preparation of vegetables or fruits lemon juice or vinegar is often sprinkled on the fruit to prevent browning (FAO, 2008).
Dehydration. Dehydration is caused by the removing water molecules
from the product. The PPO enzyme needs sufficient water to be active. By drying the enzyme is inhibited, but not destroyed (FAO, 2008). 2.5.6 Irradiation. Irradiation, or as it is sometimes called "cold pasteurization",
is a process in which food is submitted to ionized radiation in order to kill bacteria and reduce the enzyme activity. Irradiation is often applied in meats, seafood, fruits, vegetables, and cereal grains for long-term preservation (FAO, 2008). 2.5.7 High Pressure Treatment. High pressure treatment also called High
Pressure Processing (HPP) is a technique of food processing where food is subjected to elevated pressures (500-700 atmosphere) to achieve microbial and enzyme inactivation (FAO, 2008). 2.5.8 Addition of Inhibitors. The added inhibitors can act in three ways:
inactivation towards the enzymes, inactivation towards substrate, and inactivation towards the product. Some common inhibitors used in foods are sulphiting agents, ascorbic acids and analogs, cysteine, phosphates, EDTA, organic acids, citric acid, phosphoric acid, peptides, and glutathione (FAO, 2008).
2.6 Glutathione Glutathione is a biologically active sulfur amino acid tripeptide compound consisting of L-cysteine, L-glutamic acid, and glycine. It is commonly known as GSH. Wu et. al. (2004) defined as the most abundant low molecular weight thiol. Glutathione is not an essential nutrient since it can be synthesized from the amino acids L-cysteine, L-
glutamate and glycine (www.wikipedia.com, 2008). The chemical structure is shown in Figure 2-1.
Figure 2-1. Chemical Structure of Glutathione
2.7 Biological and Health Functions Glutathione is a very powerful anti-oxidant that protects the body by targeting and destroying reactive oxygen molecules and free radicals. It is found in high concentration in the liver, where it binds to heavy metals such as mercury and lead, chemical pollutants, and carcinogens and transforms them into form that can easily flushed out of the body via enzymatic pathway (United Shelter Health Products, 2008). Wu et. al. (2004) stressed that glutathione deficiency contributes to oxidative stress, which plays a key role I aging and the pathogenesis of many diseases (including kwashiorkor, seizure, Alzheimer’s disease, liver disease, HIV, AIDS, etcetera). Furthermore, it involves in the synthesis and repair of DNA, helps recycle Vitamin C and Vitamin E, blocks radical damage, facilitates the transport of amino acids, and enhances the antioxidant activity of Vitamin C.
2.8 Biological and Health Risks According to the United Shelter Health Product (2008), glutathione is generally considered to be free of side effects. There are no untoward side effects nor interactions 9
with oral administration reported even in prolonged use. Moreover, no toxicities have been reported or suspected as being associated with glutathione. However, recent study suggests excessive use can be harmful for the heart. Glutathione produces cholesterol in the veins and arteries leading to possible heart attack. Hence, it is recommended that proper dosage must be observed. When use as antioxidant and as anti-aging, the maintaining dose should be 10 mg per kg bodyweight per day. But when use as skin whitener, 20 to 40 mg per kg bodyweight per day in 2 to 3 divided doses is recommended (United Shelter Health Products, 2008).
2.9 Application to Fruit Juices