Dairy Chemistry And Biochemistry

110 DAIRY CHEMISTRY AND BIOCHEMISTRY

population. Suggested causes of spontaneous rancidity include:

0 a second lipase located in the membrane rather than on the casein
micelles;
0 a weak membrane which does not adequately protect the fat from the
normal LPL; and
0 a high level of lipoprotein co-factor which facilitates attachment of the
LPL to the fat surface; this appears to be the most probable cause.

Mixing of normal milk with susceptible milk in a ratio of 4: 1 prevents
spontaneous rancidity and therefore the problem is not serious except in
small or abnormal herds. The incidence of spontaneous rancidity increases
with advancing lactation and with dry feeding.

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/ Who‘e mi’k

( b)

Figure 3.21 Flow of cream and skim milk in the space between a pair of discs in a centrifugal
separator (a); a stack of discs (b); and a separator disc showing holes for the channelling of
milk and spacers (caulks) (c). (From Towler, 1994.)