Determination of free fatty acids and lipase activity in milk: quality and storage markers.

The free fatty acid (FFA) content together with the lipase activity control can be considered as useful indexes of good quality and correct storage of food, especially for milk. The quantitative analysis of FFA in different kinds of milk has been performed by a potentiometric method, using a new extractive methodology outlined herein. The lipase activity has been controlled by a sensitive calorimetric method, previously validated by us, based on the direct measure of the heat quantity involved in the enzymatic reaction. In order to verify the milk quality after the healing treatments and/or during the shelf life, the behaviours of FFA content and of lipase activity have been outlined in function of storage time and pH variations on different typologies of milk. The FFA content in sample of fresh pasteurised milk was found to be quite high after the 5th/6th day of storage at +4 degrees C, meanwhile the pH values were always constant and only after the 9th day begun to decrease. At the same time the lipase activity, directly measured, was found to be appreciable after the 6th day of storage, giving an exothermic answer at the calorimeter, similar to that of a milk sample where only three international units of standard lipase were added.