Biosynthesis of milk constituents

The book does not cover the technology of the various dairy products, although brief manufacturing protocols for some products are included to facilitate discussion however, a number of textbooks on various aspects of dairy technology are referenced. Neither are the chemical analyses, microbiology and nutritional aspects of dairy products covered, except in a very incidental manner. The effects of dairy husbandry on the composition and properties of milk are discussed briefly, as is the biosynthesis of milk constituents in both cases, some major textbooks are referenced. 

Injection of radioactively labelled substrates, e.g. glucose, into the bloodstream permits assessment of the milk constituents into which that substrate is incorporated. It may also be possible to study the intermediates through which biosynthesis proceeds. 

Thiazole IV (Table 5.22) can occur in milk when it is heated, and is responsible for a stale off-fiavor. Thiazole V (Table 5.22) is a constituent of tomato aroma. The aroma of tomato products is usually enhanced by the addition of 20-50 ppb of thiazole V (for the biosynthesis of the compound, see Section 5.3.2.5). 

Other Acylglycerols. If some of the DGs in freshly drawn milk are involved in biosynthesis, it is possible that they are enantiomeric and are probably the sn-1,2 isomer. If so, the constituent fatty acids are long chain. Their configuration can be determined by stereospecific or other analyses, but it is difficult to accumulate enough material for analysis. Nevertheless, Lok (1979) isolated the DGs from freshly extracted cream as the trityl derivatives. Trityl chloride reacts selectively with primary hydroxyls. The stereochemical configuration of the DGs was identified as sn-1,2 therefore, these residual DGs were most likely intermediates of biosynthesis. If the DGs were products of lipol-ysis, they would be a mixture of 1,2/2,3 isomers in a ratio of about 1 2, since milk lipoprotein lipase preferentially attacks the sn-1 position of TGs (Jensen et al. 1983). 

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