Some factors involved in milk lipase activation by agitation

SummarySeveral factors which influence the shape of activation curves relating the degree of agitation-induced lipolysis in raw milk to the temperature of agitation were investigated. Curves of the type previously reported (Fitz-Gerald, 1974) containing a maximum at 12–15 °C resulted from low speed agitation with incorporation of air, with fresh (< 12-h old) milk, with milk of fat content ≥ 3·0 % approx. and by low temperature incubation of activated milks. Activation curves containing no distinct maximum at 12–15 °C were obtained from high speed agitation and homogenization, with milks of low fat contents and with aged (≥ 24-h old) milk. Agitation at low temperatures resulted in a maximum degree of activation in fresh milk after 2–4 h cold storage.During agitation of raw milk redistribution of lipase activity between the cream and skim-milk phases occurred. The extent of redistribution depended on the time and temperature of agitation. Cream prepared from milk agitated at low temperatures contained lipase activity several times greater than cream from unactivated milk. The practical significance of this effect is discussed.