Rancidity hydrolytic oxidative

Lipids are hydrolyzed by moisture and heat into free fatty acids, though hydrolytic enzymes may be deactivated by extrusion. Also, unsaturated fatty acids may imdergo oxidative rancidity (Camire et al., 1990). 

In addition to positive aspects, numerous flavor and textural defects may be associated with the fat phase of ice cream. Such flavor defects are usually related to either autoxidation of the fat, resulting in oxidized flavors (cardboardy, painty, metallic) or, especially in the case of milk-fat, lipolysis of free fatty acids from triglycerides by the action of lipases (referred to as hydrolytic rancidity). A significant content of free butyric acid gives rise to very undesirable rancid flavors. These defects tend to be present in the raw ingredients used in ice cream manufacture, rather than promoted by the ice cream manufacturing process itself. However, processing... 

Lipids strongly influence, for good or evil, the flavour and texture of foods, especially high-fat products such as butter. The influence of various colloidal features of milk fat on the properties of milk and cream is considered in Chapter 4, while the crystallization of milk fat and how this may be controlled, modified and measured are reviewed in Chapter 5. Unfortunately, lipids are subject to chemical and enzymatic alterations which can cause flavour defects referred to as oxidative and hydrolytic rancidity, respectively. The storage stability of high-fat foods, especially mildly flavoured foods like milk, cream and butter, is strongly influenced by these changes which have been reviewed in Chapters 6 and 7. 

Lipase activity results in hydrolytic rancidity. There is little or no change in flavor of the bran with an increase in FFA (5). Lipoxygenase activity, however, increases with the presence of FFA resulting in oxidative rancidity (36). It is oxidative deterioration that is responsible for the flavor and odor of rancid rice bran. 

Development of disagreeable odour and taste in fat or oil upon storage is called rancidity. Rancidity reactions may be due to hydrolysis of ester bonds (hydrolytic rancidity) or due to oxidation of uhsaturated fatty acids (oxidative rancidity). 

Homogenization markedly reduces the propensity to oxidative rancidity, perhaps due to redistribution of the susceptible lipids and pro-oxidants of the MFGM (however, the propensity to hydrolytic rancidity and sunlight oxidized flavour (due to the production of methional from methionine in protein) is increased). 

The presence or activity of water in foods may also enhance the rate at which deteriorative chemical reactions occur. Some products may become rancid through free radical oxidation even at low humidities and thus become unacceptable. Labile nutrients such as vitamins and natural color compounds are oxidized more rapidly when stored at low moisture levels. Enzyme-mediated hydrolytic reactions may reduce the quality of the food product. Other reactions such as the Maillard type of nonenzymatic browning may be enhanced by the presence of higher levels of water. On the other hand, water content is crucial for the textural characteristics and the sensory perception of foods. A food may be found unacceptable by consumers simply because it does not satisfy their textural (sensory) anticipation. 

Oxidation of milk lipids is an important cause of flavor deterioration of dairy products that is often referred to as oxidative rancidity, to distinguish it from hydrolytic rancidity resulting from lipolysis. Milk products have complex compositions, physico-chemical properties, and contain natural prooxidants... 

Lipases in stored butter gradually release fatty acids from tri-acylglycerols, and their presence can be detected as a rancid and soapy flavour when they reach 30-40% of their threshold concentrations, which is a result of their synergism. The reaction is called hydrolytic rancidity. Responsibe for the rancid flavour is mainly butyric acid, followed by caproic acid. Caprylic acid has a rancid soap-like flavour, capric and lauric acids only have soapy flavours. Odour (and taste) threshold concentrations in butter made from sweet cream are 50 (60) mg/kg for butyric acid, 85 (105) mg/kg for caproic acid, 200 (120) mg/kg for caprylic acid, >400 (90) mg/kgfor caprinic (capric) acid and >400 (130) mg/kg for lauric acid, respectively. In long term stored butter, active oxidative rancidity products are (E)-non-2-enal, (Z)-non-2-enal in particular, while less active products are (Z)-hept-4-enal, oct-l-en-3-one and others. The rancid and soapy odour in butter can also be caused by contamination with anion active detergents, such as natriumdodecyl sulfate. 

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