Factors causing spoilage - fats- rancidity ,oxidative.pptx

Factors causing spoilage - fats- rancidity ,oxidative.pptx

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  SPOILAGE- FATS- RANCIDITY, OXIDATIVECHANGES AND ENZYMES
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  • The shelflife of a product refers to the length of time a product may be stored without becoming unsuitable for use or consumption. • After the shelf life of a product has reached, the food undergoes processes which results in food spoilage (rancidity). • Lipid oxidation is one of the major reasons that foods deteriorate and is caused by the reaction of fats and oils with molecular oxygen leading to off-flavours that are generally called rancidity. • Foods that are high in lipids and might become rancid include potato chips, peanut butter, crackers INTRODUCTIO N
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  Rancidity/ Rancidification Physico-chemical change inthe natural properties of the fat leading to the development of unpleasant odor or taste or abnormal color particularly on aging after exposure to atmospheric oxygen, light, moisture, bacterial or fungal contamination and/or heat. When a fatty substance is exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours. Saturated fats resist rancidity more than unsaturated fats that have double bonds. Oil becomes rancid (rancid oil) because of the decomposition of fats it has, or sometimes milk becomes rancid because of not heating it in the humid atmosphere, etc. Butter becomes rancid by the foregoing process and by hydrolysis, which liberates volatile and malodorous acids, particularly butyric acid. Saturated fats such as beef tallow are resistant to oxidation and seldom become rancid at ordinary temperatures.
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  Rancid food
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  Types of Rancidity Hydrolyti c rancidity Oxidative rancidity Ketonic rancidity Microbial rancidity This Photoby Unknown author is licensed under CC BY-NC-ND.
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  Hydrolytic rancidity Results fromslight hydrolysis of the fat by lipase from bacterial contamination leading to the liberation of free fatty acids and glycerol at high temperature and moisture. These free fatty acids can then undergo further auto-oxidation leads to oxidative rancidity. Fatty acids are organic compounds containing carbon, hydrogen, and oxygen that combine with glycerol to make a lipid. Glycerol is the storage form of fat in animals Volatile short-chain fatty acids have unpleasant odor. Example : - Long time storage at unrefrigerated temperatures, butter contamination with microbes producing lipases can accelerate hydrolytic Rancidity (Off flavour in butter)
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  Oxidative rancidity Oxidative rancidityinvolves oxidation of fatty acid Oxidative rancidity occurs when oxygen is added across the carbon to carbon in unsaturated fatty acid The process can be catalyzed by light (photo-oxidation) and enzyme Oil fish (such as herring and mackerel) contain a high proportion of unsaturated fatty acid and are prone to oxidative rancidity Exposure to air, cooking, and some chemical contaminants can accelerate oxidation To reduce the oxidation, antioxidants are added to the oils.
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  Three Phase Process InitiationPhase Molecular oxygen combines with unsaturated fatty acids to produce hydroperoxides and free radicals ◦ Requires an oxidative initiator (e.g. heat, light, metals, enzymes Propagation Phase (autoxidation phase) The reactive products of the initiation phase react with additional lipid molecules to form other reactive chemical species Termination Phase Relatively unreactive compounds are formed including hydrocarbons, aldehydes, and ketones (volatile odors) Three Phase Process
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  Three distinct classes ofsubstance occurring in oxidized fat have been shown to be toxic: Peroxidised fatty acids (peroxidised fatty acids destroy both vitamin A and E in foods). Oxidized sterols (thought to be involved in the causation of atherosclerotic disease). Polymeric material (under normal food processing conditions these appear in small enough quantities to be insignificant).
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  Ketonic Rancidity It isdue to the contamination with certain fungi such as Asperigillus Niger, Pencillium glaucum on coconut or other oilseeds. Ketones, fatty aldehydes, short chain fatty acids and fatty alcohols are formed. The tallowy odor developed may be due to aldehydes and ketones formed by the action of the enzymes present in the fungi on oils. Moisture accelerates ketonic rancidity.
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  MICROBIAL RANCIDITY In microbialrancidity, micro-organisms such as bacteria, mold and yeasts use their enzymes to break down the chemical structures in oil producing off odour and flavour. Water is needed for growth of micro-organisms. It can be prevented by elimination of micro-organisms i.e., sterilization.
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  Factors causing Fatrancidity TEMPERATURE AND PH These are the important factor which influences the food items rich in fat and oils become rancid. Suitable temperature and alkaline pH are required for the hydrolytic action of microbial lipase. Temperature and pH indirectly influence the auto- oxidation and hydrolysis. rate of reaction of oxygen with fats roughly doubles for every lOoC increase in temperature HEAT AND LIGHT Presence of heat and light accelerate the rate of reaction of fats with oxygen, i.e., heat accelerates auto-oxidation. Heat and light act as the energy source for the production of free radical in rancidity and reversion of oils and fats. Light has a promoting influence on oil oxidation through photo- oxidation
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  Factors causing Fatrancidity PRESENCE OF MICROORGANISMS – MICROBIAL LIPASE Certain microorganisms can produce the hydrolytic enzyme called lipase, which directly interferes the hydrolysis of triglycerides and produce glycerol's and fatty acid. These fatty acids undergo auto- oxidation to form rancid. The microbial lipase requires suitable pH and other conditions for its activity upon fats and oil. POLYUNSATURATION The more polyunsaturated a fat is, the faster it will go rancid. Vegetable oils have to become several times more rancid than animal fats. Presence of polyunsaturation in oils and fats makes them more susceptible to rancidity than monosaturated and other types of saturated fatty acids.
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  Factors causing Fatrancidity PRO-OXIDANTS Metals act as pro-oxidants by electron transfer whereby they liberate radicals from fatty acids or hydroperoxides Two of the more active metals to induce oxidation are copper and iron of which copper is the most pro-oxidative The presence of metals is due to possible contamination with machinery and equipment during processing or could have been present in the seed from the start. OXYGEN AVAILABILITY The availability of oxygen is an important rate-determining factor as oxidation cannot take place without oxygen samples with a high surface area in contact with air oxidise more rapidly Oxygen can be replaced by utilising a protective gas practice such as nitrogen blanketing that will protect oil in storage tanks, during bulk transport and when packaged against oxidation
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  Enzymes Extracellular enzymes causingspoilage in thermally treated foods are proteases, lipases, phospholipases and amylases. It initiates the oxidative rancidity of plant lipids containing high proportion of unsaturated fatty acids and causing off- flavors. This Photo by Unknown author is licensed under CC BY-SA.
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  Enzymes involved inlipid degradation LIPOXYGENA SE Lipoxygenases are a family of (non heme) iron containing enzymes most of which catalyses the deoxygenation of polyunsaturated FA in lipids. Most common in plants where they may be involved in a plant physiology including growth and development, pest resistance, and responses to wounding. Catalyses fatty acid hydroperoxide formation in a manner similar to nonenzymic systems. LIPASE An enzyme that catalyzes the hydrolysis of fats(lipids). Lipases are a subclass of the esterase. Lipases perform essential roles in digestion, transport and processing of dietary lipids (e.g. triglyc erides,fats,etc )
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  Effects of rancidityon the food use of fats and oils Flavour deterioration Deterioration of colour and texture attributes Off odours such as beany, grassy, painty, fishy, tallowy or plain rancidity Loss of nutritional value Formation of possible toxic oxidation products
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  Hazards of RancidFats The products of rancidity are toxic, i.e., causes food poisoning and cancer. Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E). Rancidity destroys the polyunsaturated essential fatty acids. Rancidity causes economical loss because rancid fat is inedible.
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  Prevention of rancidity Avoidanceof the causes (exposure to light, oxygen, moisture, high temperature and bacteria or fungal contamination). By keeping fats or oils in wellclosed containers in cold, dark and dry place (i.e., good storage conditions). Adding nitrogen to the bag to replace the oxygen Removal of catalysts such as lead and copper that catalyze rancidity. Addition of anti- oxidants to prevent peroxidation in fat. They include phenols, naphthols, tannins and hydroquinones. The most common natural antioxidant is vitamin E
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  Measuring Rancidity Rancidity ismost commonly detected by taste or smell, but chemical tests can also check for rancidity. There are many tests used to determine the quality of an oil; some tests are predictive and others are indicative. Measuring oxidation involves testing for the primary and secondary breakdown products. o peroxide value (PV). o anisidine value (AV) o Totox value - are used to show the whole oxidation story. (AV+ 2PV) o acid value (free fatty acid FFA) o Iodine value (IV).
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