Butter, oxidative stability

Also on the positive side, severe heat treatment of cream improves the oxidative stability of butter produced therefrom due to the exposure of antioxidant sulphydryl groups. As discussed in section 9.2.2, lactones formed from hydroxyacids are major contributors to the desirable cooking quality of milk fats but contribute to off-flavours in other heated products, e.g. milk powders. 

The effect of storage temperature on the oxidative stability of milk and milk products is unclear. Storage, in air, at 2°C inhibited the development of oxidized flavor in dry whole milk when compared with control samples held at 38°C (Pyenson and Tracy, 1946). Oxidative deterioration of UHT cream occurred two to three times more rapidly at 18°C than at 10°C, while little or no oxidation occurred at 4°C (Downey, 1969). The oxidation-reduction potential of butter and the rate of flavor deterioration have been reported to increase as the storage temperature increased (Weihrauch, 1988). 

The deodorization of cocoa butter is necessary to reduce free fatty acid content and to give a product that satisfies the present day requirement of a neutral bland flavor. Deodorization is a suitable method for partially eliminating chlorinated insecticides from cocoa butter. The normal deodorization temperatures are in the range 160-180°C. The oxidative stability of various cocoa butters listed in Table 4 shows extremely high values, and these are unaffected during the deodorization process. Stability against oxidation depends on natural antioxidants present in cocoa butters. The tocopherol composition in Table 5 shows a predominance of... 

Vegetable oils go to a number of end uses, edible and industrial. Some of the edible uses of vegetable oils are shortening, margarine, salad oils, frying oils, hard butters, and surfactants. Further processing such as hydrogenation is used to produce hard fats or to enhance oxidative stability [107—114],... 

The iodine value is a measure of the relative degree of unsaturation in oils as determined by the uptake of appropriate halogen compounds. Because melting point and oxidative stability are related to the degree of unsaturation, iodine value provides an estimation of these quality factors. The greater the iodine value, the more the unsaturation and the higher the susceptibility to oxidation. Peanut oil (IV 82-107) is more saturated than com (IV103-128), cottonseed (IV 99-113) or linseed (IV 155-205) oils however, it is considerably less saturated than coconut (IV 7.7-10.5), palm (IV 44-54), or butter (IV 25 12) oils. 

The cocoa bean (Theobroma cacao) is the source of two important ingredients of chocolate cocoa powder and a solid fat called cocoa butter.To evaluate the oxidative behavior of cocoa butter, the autoxidation of refined and unrefined butter samples is accelerated (oxidized at day light at room temperature and at 90 C). The quantity of certain aldehydes formed during the oxidation of cocoa butter is examined by gas chromatography. The oxidation stability of butter is evaluated over a 12 week period. ... 

Soft butters have been produced by feeding encapsulated polyunsaturated oils in order to overcome the problem of biohydrogenation (Barbano and Sher-bon, 1980 Kuksis and McKarthy, 1964 Scott et al., 1972a,b Storry et al., 1974, 1980). Using encapsulation techniques the 18 2 content of butterfat can be increased from 2-3% to 35% but problems of oxidative stability arise (Edmunson etal., 1974). The effect of feeding protected lipids on the composition of the milk fat globule membrane has been reported (Smith etal., 1977) (Table 3.159). 

An accelerated test procedure was developed to evaluate the oxidative stability of food lipids with viuying degrees of saturation. The procedure is based on ESR spectroscopy and the spin trap N-t-butyl-a-phenylnitrone (3). Four different food lipids were analyzed lipid fraction from mayonnaise enriched with fish oil, rapeseed oil, dairy spread made from rapeseed oil and cream, and butter. A good correlation was found between degree of saturation and the delay in radical formation, induction period, under accelerated conditions. The order of stability of lipid was as anticipated mayonnaise < rapeseed oil < dairy spread < butter. 

Today palm oil is widely used in food applicahons and preferred for frying and baking applications because of its good oxidative stability and high solid fat content. Palm oil contains about 50% saturated (42 8% palmitic and 4-5% stearic acids) and 50% unsaturated fatty acids (37-41% linoleic and 9-11% linolenic acids). The fatty acid composition of palm kernel oil resembles that of the coconut oil rather than that of palm oil. Palm kernel oil is rich in lauric (about 48%), myristic (16%) and oleic (15%) acids. Both palm oil and pahn kernel oil are commercially separated into stearin (solid) and olein (liquid) fractions for special applications. The stearin fraction obtained from palm kernel can be used as a cocoa butter substitute. The olein fraction is used in baked goods and soap manufacturing. Imitation palm-oil-based cheese, hand and body lotion, fatty acid methyl esters for use as fuel or solvent, and epoxidized pahn oil to produce plasticizers and stabilizers for conventional polyvinyl chloride plastics are some of the other products that are produced from palm oil (Basiron, 2005). 

Nielsen et al. (1996b) reported significant accumulation of OS in dairy spreads compared to butter. The concentration of OS was 4 times higher in dairy spreads than in butter after storage at 4°C for 13 weeks, and 7-keto was the dominant oxidation product, at 1.3 and 5.7 pg/g lipid in the stored butter and dairy spread, respectively. This difference in stability is undoubtedly related to the high content of PUFA in dairy spreads. 

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. 

Although in fluid milk the phospholipid fraction is more susceptible to oxidation than the triacylglycerol fraction, in dry milk products, the triacylglycerol fraction is more susceptible to oxidation and the phospholipids act as antioxidants. Thus, solvent-extracted milkfat containing phosphohpids is much more stable to oxidation than milkfat free of phospholipids, obtained by melting churned butter (also called butter oil). The susceptibility of milk phospholipids to oxidation appears to be dependent on whether they are suspended in water or fat. This difference of oxidahve stability influences the development of different flavor defects in various dairy products. With butter, which is a water-in-oil emulsion system containing an aqueous phase of phospholipids dispersed in fat, the phosphohpids oxidize more readily than the triacylglycerol components. 

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