OBJECT Essays - Food And Drink, Chemistry, Fruit Juice, Biochemistry

OBJECT Essays - Food And Drink, Chemistry, Fruit Juice, Biochemistry OBJECT Inhibition of Polyphenol Oxidase activity in Apple by using some natural and synthetic anti browning agents . REQUIREMENTS Acidic fruit juices (pineapple, orange, lime, lemon ) 1% Salt solution 1% HCL solution 1% NAOH solution Tap water Apple slice s THEORY E nzymatic browning is one of the most important reactions that occur in fruits and vegetables, usually resulting in negative effects on color, taste, flavor, and nutritional value. The reaction is a consequence of phenolic compounds' oxidation by polyphenol oxidase (PPO), which triggers the generation of dark pigments. This is particularly relevant for apples, which are rich in polyphenols and highly su sceptible to enzymatic browning. In plant cells, phenolic compounds are located in the vacuoles, whereas polyphenol oxidase ( PPO) is located in plastids. Damaged areas in cells allow the contact between PPO and phenolic compounds, triggering the reaction known as enzymatic browning. Examples of beneficial enzymatic browning: Developing color and flavor in Coffee, Cocoa beans, and tea. Developing color and flavor in dried fruit such as figs and raisins. Examples of non-beneficial enzymatic browning: A non-desirable enzymatic browning reaction is involved in the formation of brown spots on the peel of bananas ,avocados,apples and potatoes Polyphenols - main components in enzymatic browning Polyphenols , also called phenolic compounds, are group of chemical substances present in plants (fruits, vegetables) which play an important role during enzymatic browning, because they are substrates for the browning-enzymes. Phenolic compoun ds are responsible for the colo r of many plants, such as apples, they are part of the taste and flavo r of beverages (apple juice, tea), and are important anti-oxidants in plants. Polyphenols are normally complex organic substances, which contain more than one phenol group (carbolic acid): Polyphenol oxidase (PPO ) Polyphenoloxidases are a class of enzymes that were first discovered in mushrooms and are widely distributed in nature. They appear to reside in the plastids and chloroplasts of plants, although freely existing in the cytoplasm of senesci ng or ripening plants. Polypheno loxidase is thought to play an important role in the resistance of plants to microbial and viral infections and to adverse climatic conditions. Polyphenoloxidase also occurs in animals and is thought to increase disease resistance in insects and crustaceans. In the presence of oxygen from air, the enzyme catalyzes the first steps in thebiochemicalconversion of phenolics to produce quinones, which undergo further polymerization to yield dark, insoluble polymers referred to as melanins . These melanin form barriers and have antimicrobial properties which prevent the spread of infection or bruis ing in plant tissues. Example of a general reaction of polyphenols by Polyphenol Oxidases that catalyzes enzymatic browning. The production of Quinones undergoes more reactions which eventually form brown pigments on the surface of fruits and vegetable. PREVENTION OF ENZYMATIC BROWNING The control of the enzymatic browning is of great importance to the horticulture industry, because this reaction occurs in many fruits and vegetables, often negatively affecting the attributes of color, taste, flavor, and nutritional value. It is estimated that more than 50% of fruit market losses ar e a result of enzymatic browning . Researchers are especially interested in studying the control (inhibition) of browning by different methods that can be employed to maximize this inhibition and ultimately pr olong the shelf l ife of commodity.Several methods can be applied to avoid enzymatic browning, based on inactivating the enzyme (heat) or by removing essential components (m ost often oxygen) from the product Blanching is a short heat treatment to destroy or inactivate enzymes before freezing of prod ucts (mainly vegetables). The enzyme activity is pH dependent. Lowering of the pH to 4.0 by the addition of citric,ascorbicor otheracidsinhibits the enzyme activity. Addition of chemical inhibitors like acidulants ,chelating agents, reducing agents may also directly react with enzyme and substrate or change the product composition . METHOD Cut one apple into small thin slices in such way that its pulp portion is exposed to our reagent . Separately place an apple slice in petri dishes and labeled them . With natural anti browning agent, in four samples out of all, squeeze some suitable amount of fresh fruit juices on apple slice. With the synthetic browning agent, firstly prepare solutions