Enzymatic Browning Experiment

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Determination of different inhibitors that inhibit the rate of Enzymatic Browning in different fruits and vegetable.

➢ Citric Acid (1% solution)
➢ Acetic Acid (1% solution)
➢ Ascorbic Acid (1% solution)
➢ Sugar (1%.Solution)
➢ Sodium chloride (1% solution)
➢ Sulfite salt (1% solution)
➢ Samples (Potato, Banana, Apple)

Enzymatic Browning:

Enzymatic browning (oxidative) is a reaction between oxygen and a phenolic substrate catalyzed by polyphenol oxidase result in orthoquinone, which in turn rapidly polymerized to form brown pigments or melanin. This is the common browning that occur in cut fruits and vegetables


Phenolase enzymes that have been isolated from food sources are oligomers and contain one copper prosthetic group per subunits. Thus, if damage to plant tissue is sufficient and oxygen and copper are present, browning occurs. Such operation as cutting, peeling and bruising are sufficient to cause enzymatic browning. Phenolase is active at mild Acidic pH (5-7).

Enzymatic browning does not occur in intact plant cells since phenolic compounds in cell vacuoles are separated from the polyphenol oxidase, which is present in the cytoplasm. Once tissue is damaged by slicing, cutting or pulping, however, the formation of brown pigments occurs. Both the organoleptic and biochemical characteristics of fruits and vegetables are altered by pigment formation. The rate of enzymatic browning in fruit and vegetables is governed by the active polyphenol oxidase content of the tissues, the phenolic content of the tissue, pH, and temperature and oxygen availability within the tissues.

This includes:
• Reducing agents;
• Acidulants
• Chelating agents
• Complexing agents
• Enzyme inhibitors
• Enzyme treatments.

Methods to Inhibit Enzymatic Browning:

➢ The elimination of oxygen from the cut surface of fruits or vegetables greatly retards the browning reaction. Browning however occurs rapidly upon exposure to oxygen. Exclusion of oxygen is possible by immersion in water, syrup, brine, or by vacuum treatment. ➢ This copper prosthetic group of polyphenol oxidases must be present for the enzymatic browning reaction to occur. Chelating agents are effective in removing copper. ➢ Inactivation of the polyphenol oxidases by heat treatments such as steam blanching is effectively applied for the control of browning in fruits and vegetables to be canned or frozen. Heat treatments are not however practically applicable in the storage of fresh produce. ➢ Polyphenol oxidase catalyses the oxidation of phenolic substrates such as caffeic acid, protocatechuic acid, chlorogenic acid, and tyrosine. Chemical modification of these substrates can however prevent oxidation. ➢ Certain chemical compounds react with the products of polyphenol oxidase activity and inhibit the formation of the colored compounds produced in the secondary, non-enzymatic reaction steps, which lead to the formation of melanin. ➢ Citric, malic and phosphoric acid can also serve as chelaters for copper. ➢ Many techniques are applied in the prevention of enzymatic browning. Relatively new techniques, such as the use of killer enzymes, naturally occurring enzyme inhibitors and ionizing radiation, have been explored and exploited as alternatives to heat treatment and the health risks associated with certain chemical treatments. Processing technologies applied in the control of enzymatic browning in fruits and vegetables are now reviewed.


Initial Observation:

(Pictures are taken at Food Enzymology Labs, F.S.T Department, University Of Karachi.)

Final Observation:

After 10mins of interval:
After 20mins of Interval:
After 30mins of Interval:

After 40mins of Interval:

(Pictures are taken at Food Enzymology Labs, F.S.T Department, University Of Karachi.)

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