COMPOSITION AND PHYSICOCHEMICAL CHARACTERISTICS OF GOAT MILKS CONTAINING THE A-ALPHA(S1) OR O-ALPHA(S1) CASEIN VARIANTS

The composition of goat milks originating from three animals homozygou s for alpha(sl) casein, variant A, and from three others, homozygous O , was compared monthly over a lactation. Mean fat value was higher by 4.7 g kg(-1) in A milk, the difference between A and O reaching 9.8 g kg(-1) in the early lactation. Total nitrogen matter was higher by 6.8 g kg(-1) in A milk on the whole lactation. Total casein levels in A a nd O milks were respectively 21.2 and 17.8 g kg(-1). Caseins (CN) othe r than cc,, were at similar levels in the two groups of milks, alpha(s l)CN was similar to 5.2 g kg(-1) in A milk and similar to 0.0 g kg(-1) in O milk. Mineral contents showed a high individual variability. Ren net coagulation tests led to higher firming rates and higher firmness in A milks, while coagulation time was not different between A and O m ilks. Total fatty acid proportions in milks were different: more short and medium length saturated fatty acids in A milk, balanced by a lowe r C16 level. Lipolysis was by far lower in A milk and the relative pro portion of fatty acids in the free fatty acid fraction was different i n A and O milks, meaning a difference in lipase level and/or in lipase specificity due to the enzyme itself or to its environment. In contra st, proteolysis of the plasmin type was higher in A milks. (C) Inra/El sevier, Paris.