Butter, peroxide value

Butter, peroxide value, 658, 660, 665 t-Butyl alcohol, tetroxide formation, 740 t-Butyl cumyl peroxide air pollutant, 622 determination, 707 hydroperoxide determination, 685 t-Butyl hydroperoxide (TBHP)... 

This specification is for butter oil, which is butter with the water removed. The free fatty acid limit is to detect lipolytic rancidity while peroxide value specification is to limit oxidative rancidity. The copper limit arises because copper catalyses the oxidation of fats. The absence of neutralising substances is to prevent a high titration for free fatty acids being covered up by the addition of alkali. 

Butter should be stored at 4.4°C or lower or at less than — 17.8°C, if it is to be held for more than 30 days (62). The International Dairy Federation (IDF) has produced specifications for milkfat (64), which include reference to the feedstock. (These specifications relate to the time of manufacture but are often used as purchase standards.) The highest grade, anhydrous milkfat (AMF), must be produced from fresh milk, cream, or butter, to which no neutralizing substances have been added. It should have a clean, bland flavor when tasted at 20-25°C and a peroxide value (PV) of less than 0.2 meq oxygen/1 kg fat. Anhydrous butter oil may be produced from butter or cream of different ages and has no pronounced, unclean, or other objectionable taste or flavor. The term butter oil should be used where there is no pronounced unclean or other objectionable taste or odor. The FAOAVHO Codex standard for milkfat is shown in Table 15 (65). 

The quality assurance program for manufacture of butter oil, or anhydrous milkfat (AMF), also focuses on the quality of the raw materials. Naturally, many of the same considerations apply to handling raw cream for AMF manufacmre that apply to butter, except that vacreation is not used. As it is stored under ambient conditions, care against oxidation is essential. Oxidation is perhaps the most important mechanism by which milkfat deteriorates in quality. As the oxidation reaction is autocatalytic (i.e., the products of the reaction act as catalysts to promote further reaction), the normal quality-control tests, peroxide value and free fat acidity, could give misleading results when applied to stored butter. Methods of deaeration have been developed that could reduce potential oxidation (74). 

Flavor defects in milk and cream are collectively referred to as the oxidized flavor , in butter as metallic or tallowy . Oxidized flavors are noticeable in stored milk at very low levels of oxidation, usually at a peroxide value less than 1, because the low molecular weight off-flavor compounds are more readily volatilized in the predominantly aqueous matrix of milk. The development of oxidized flavor is most evident in fluid milk, cream and butter, because they have mild and more delicate flavors. 

Feeding menhaden (fish) oil at 2% of the dry matter intake of the diet also lowered milk fat concentrations. The level of CL A was increased by approximately 3.6 fold, but there was also a concurrent 4-5 fold rise in the level of vaccenic acid. Increasing the oil intake to 3% had no additional effects. The level of n-3 fatty acids in the milk was increased, mainly due to increased levels of eicosapentaenoic acid (EPA 20 5n-3), as was the level of total trans monoenes. The effects of pasteurization and oxidation on the raw milk were examined but no significant changes were observed and the CLA isomer profile was unchanged. There were no significant flavour differences found between the milk (and butter made from the milk) of cows fed 2% menhaden oil and control samples. The higher polyunsaturated fat content of the butter meant that it was softer at 4°C and 20°C, but the acid value and peroxide value of the butter were similar to those of control samples even after 3 months. A consumer evaluation of milk from cows fed a fish oil diet found no difference in acceptability compared with the control milk (Ramaswamy et al, 2001). 

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