Lipase activity in Swedish raw milk

Abstract: Bovine milk contains several enzymes which can affect the quality of milk. One of these enzymes are lipases which hydrolyse the triacylglycerides in milk. In this process off-flavours, odour and product defects are generated. By controlling the enzymes activity, milk quality can be increased and therefore milk and dairy products can be stored for a longer time. This is desirable since the world demand for long shelf-life milk and milk products is increasing. To monitor the quality of raw milk and control the enzyme activity, a well-functioning method to detect lipase activity is desired. Thus, the aim of this thesis was to investigate and improve an existing method to determine lipolytic activity which is based on a fluorescent approach. With this method, a sensitive fluorescent measurement of the lipase activity directly in the natural milk environment is possible. Once the method was evolved, raw milk samples from different regions in Sweden and from different origins, i.e. farm and dairy, were investigated and evaluated for possible differences in lipase activity. No significant difference was found between samples from farm and dairy origins. Between the different regions a significant difference was discovered. The lowest lipase activity in milk was found in milk from the south (Skånemejerier) followed by milk from the mid region of Sweden (Arla) and the highest lipase activity was seen in milk from the north (Norrmejerier). The lipase activity was also correlated to other previously measured properties of the milk. A significant negative correlation to some long chain fatty acids could be seen. This indicates that long chain fatty acids inhibit lipase activity in the milk which has previously been observed in the adipose tissue of rats and in goats milk. The long chain fatty acid content in milk can be influenced by the feed. Thus, the results of this thesis indicate that the raw milk quality could be improved by increasing the amount of long chain fatty acids in the milk through the feed and thereby reduce lipase activity.