Detection of lipase in skim and whole milk powders using triheptanoin as a substrate

As lipase catalysed hydrolysis of milk fat decreases the sensory quality of most dairy products, we developed an assay to measure lipase activity in skim and whole milk powders. Milk powder was incubated with triheptanoin at pH 6.0 for 7 days at 37 °C and the release of heptanoic acid was measured using headspace solid phase microextraction and gas chromatography mass spectrometry. The assay was applied to model samples containing milk powders spiked with commercial lipase preparations, and variables such as substrate amount and pH were optimised. Triheptanoin as a substrate was compared with both tributyrin and trioctanoin. Triheptanoin behaved in a manner similar to that of trioctanoin, but gave the analytical advantage of minimal interference from background levels of free fatty acids (FFAs). The response of the assay was linear over time and with enzyme concentration. The detection limit of the assay was calculated to be 0.05 nmol FFAs released min−1 g−1 powder.