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Influence of processing temperature and seasonal change in diet on lipase activity and lipolysis during the mechanical separation of bovine milk

Published online by Cambridge University Press:  01 June 2009

Eric C. Needs ,
Malcolm Anderson ,
Stuart J. Payne  and
Elizabeth A. Ridout
Eric C. Needs
Affiliation:
*National Institute for Research in Dairying (University of Reading), Shinfield, Reading RG2 9 AT, UK
Malcolm Anderson
Affiliation:
*National Institute for Research in Dairying (University of Reading), Shinfield, Reading RG2 9 AT, UK
Stuart J. Payne
Affiliation:
*National Institute for Research in Dairying (University of Reading), Shinfield, Reading RG2 9 AT, UK
Elizabeth A. Ridout
Affiliation:
*National Institute for Research in Dairying (University of Reading), Shinfield, Reading RG2 9 AT, UK
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Summary

The effect of separating conditions on lipase activity and free fatty acid levels in preheated milk, cream and skim milk was measured on nine occasions during a 12-week period covering the seasonal change from winter feeding to summertime grazing. This change consisted of four periods each representing a different type of forage intake, namely: silage, kale, daytime grazing and 24 h grazing. Milk was separated at 30, 40, 50 and 60°C with preheating times of 10, 25 and 55 s. Results were expressed both as absolute values and in terms of changes relative to the original unheated milk. Lipase activity and free fatty acid concentration were significantly reduced as separation temperature increased but were not influenced by holding time. The loss of activity in cream was progressive so that at 60°C only 40% of the original activity remained. Up to 50°C little change occurred in preheated milk or skim milk activity, while at 60°C 83 and 76% respectively of the original activity remained. The amount of activity calculated to be associated with the fat fraction of the cream also decreased with temperature. Activity varied significantly with date; maximum values were observed during the first 3 weeks of summertime grazing. Relative activity values indicated that the susceptibility of milk lipase to heat inactivation also varied with date. Lipolysis was also significantly affected by date. Cream free fatty acid levels were lower during the period of daytime grazing and were significantly higher than those in preheated milk. The correlation between lipase activity and free fatty acid levels was generally poor, accounting for between 0 and 34% of the variance. Possible reasons for the effect of separating temperature on lipolysis in cream are discussed.

Type
Original Articles
Information
Journal of Dairy Research , Volume 52 , Issue 2 , May 1985 , pp. 255 - 266
Copyright
Copyright © Proprietors of Journal of Dairy Research 1985

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References

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