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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