Enzymatic browning in foods

Introduction Occurrence of enzymatic browning Advantages Disadvantages Prevention of enzymatic browning Commercial aspects References

Contents

is a chemical process which occurs in fruits and vegetables by the enzyme polyphenoloxidase, which results in brown pigments

Polyphenol oxidase acts as a catalyst to speed up the process which can occur rapidly at warm temperatures when the pH is between 5.0 and 7.0. Polyphenol oxidase is a copper-containing enzyme that catalyzes or causes the oxidation of phenol compounds contained in plant tissues

Enzymatic browning

Molecular weight (128,00) Enzymatic browning occurs when plant

tissue is exposed to air resulting in a brown colored pigment, melanin, being produced as a result of a series of biochemical reactions.

Phenolases which are enzymes found outside the cell wall come in contact with colorless phenols which are found inside the cell causing the brown color to appear.

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Melanin is any of a group of brown or black pigments

occurring in plants and animals. Melanin provides the color in the skin of humans

Diseases caused due to difiecncy of melanin are

Yellow oculocutaneous albinism (These people have white hair and white skin at birth but may develop normal pigmentation as they reach infancy and childhood)

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Deafness Neurodegenerative (lack of

neuromelanin in the brain areas) Oculocutaneous albinism (absence of

melanin in the hair, skin and eyes) It is generally accepted that two kinds of

PPO enzyme exist in nature catechol oxidase laccase

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Catechol oxidase which oxidizes o–diphenols to quinones

(catecholase activity) and also hydroxylates monophenols to o–diphenols

Laccase capable of oxidizing both o–and p–

diphenols. Other than these PPO enzymes

Polyphenols is a main component in enzymatic browning

It is also called phenolic compounds,are group of chemical substances

They are substrate for the browning enzymes Phenolic compounds are responsible for the

colour, taste and flavour Polyphenols can be divided into Anthocyanins (colours in fruits) Flavonoids (catechins, tanins in tea and wine)

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Fruits (Apples, pears, peaches, apricots, and bananas)

Vegetables (Potatoes, lettuce, brinjal) Cereals (wheat flour, rice) Sea foods (shrimps, spiny lobsters and

crabs)

Enzymatic browning common in

When fruits and vegetables tissues are exposed to oxygen then its colour become brown

Such oxygen exposure occurs when the pealing, cutting and bruising of fruits and vegetables

Additionally, using copper or iron pans, length of exposure to air, and humidity increase this process

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The main cause of enzymatic browning by which the oxidation of phenolic substrate occurs during

Handling Ripening Storage and processing of fruits and vegetables

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It is known that the final product melanin has antimicrobial properties, which prevents any infection and inflammation to the plant or fruits

Melanin also has antibacterial, antioxidant, and anticancer properties

Enzymatic browning in some food it is beneficial because it increase colour and flavour like in cocoa, tea, coffee, raisins, and prunes.

Advantages

Nutritional qualities Sensory qualities like bad odour, taste and

flavour Unappealing to consumer Decrease shelf life

Disadvantages

Blanching (temp between 70 c° and 100 c°)

It has two types Blanching in steam Control enzymatic browning in canned

and frozen fruits and vegetables Microwave blanching Microwave energy can be used for

blanching because it causes an inactivation of enzymatic systems in foods

Prevention of enzymatic browning

Refrigeration Prevent spoilage of fruits and vegetables Temp should be below 7 c Freezing Freezing is a technique often used to stop

browning reactions in fruit. Indeed, freezing causes a decrease in available water for enzymatic reactions

Change pH By lowering the pH to 4.0 by addition of citric

and ascorbic acid

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In homes lemon juice or vinegar should sprinkled can inhibit enzymatic browning

Dehydration Common methods for dehydration is Freezing drying By removing the moisture by sublimation

(change from solid to gas) under vacum Lowering water activity

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By adding water binding chemicals like salts (Nacl), sucrose, honey and syrups

Irradiation This process is used for killing bacteria and

inhibit enzymes activity Several types are X-rays and gamma rays High pressure treatment Food is subjected to elevated pressures

(500-700) atmosphere

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Reducing agents such as sulphiting agentsascorbic acid and analogs, cysteine, glutathione

Chelating agents such as phosphates, EDTA,organic acids

Acidulants such as citric acid and phosphoric acid

Addition of inhibitors

Treatment with supercritical carbon dioxide (SC-CO2)

Supercritical carbon dioxide (fluid carbon dioxide at high pressure) treatment is mostly applied to destroying micro-organisms but can also be applied for enzyme inactivation, especially for inactivation of PPO in shrimps, lobsters and potatoes

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Removal of reactive textile dyes

Removal of phenolic contaminants from waste water, effluents and contaminated soil

Commercial aspects

Guo, Y., Z. Zhou, Y. Yuan and T. Yue. 2013. Survey of patulin in apple juice concentrates in Shaanxi (China) and its dietary intake. Food Control., 34(2): 570-573.

Es-Safi, N.-E., et al. 2003. "Implication of phenolic reactions in food organoleptic properties." J.Food Composition and Analysis 16(5): 535-553.

Houška, M., et al. 2006. "High pressure and foods—fruit/vegetable juices." J.Food Eng., 77(3): 386-398.

Refrences

Lacroix, M. and B. Ouattara. 2000. "Combined industrial processes with irradiation to assure innocuity and preservation of food products—a review." Food research inter., 33(9): 719-724.

Mcevily, A.J., R. Iyengar and W.S. Otwell. 1992. Inhibition of enzymatic browning in foods and beverages. Critical reviews. Food Sci. and Nutr., 32(3): 253-273.

Zhang, L., et al. 2006. "Effect of γ irradiation on quality-maintaining of fresh-cut lettuce." Food Cont., 17(3): 225-228.

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