Adaption of a commercial lipase kit to measure bile salt-stimulated lipase in human milk

A highly sensitive, fluorometric method for measuring activities of two major lipases in milk, lipoprotein lipase (LPL) and bile salt-stimulated lipase (BSSL) is described. Human milk LPL showed linear activity from 65 to 347 U/L (U = 1 mu mol/min) and the quantification limit was theoretically about 65 U/L. For human milk BSSL, the linear range was from 10 to 267 U/L and the quantification limit was 18 U/L. The mean LPL and BSSL activities were 409 +/- 13 U/L and 5263 +/- 132 U/L, respectively. This corresponded well to the values reported in literature. The residual LPL and BSSL activities were reduced dramatically to 21%, and 2%, respectively, when the milk was heated to 55 degrees C; heating to 50 degrees C caused only nominal reductions of LPL and BSSL (activities remaining similar to 82% and 87%, respectively). No BSSL activity was detected in cow, camel, goat milk or in infant formula.

Automated summary

This study presents a highly sensitive fluorometric method for measuring lipase activities in milk. The linear range for human milk lipoprotein lipase (LPL) was found to be 65-347 U/L, while for bile salt-stimulated lipase (BSSL), it was 10-267 U/L. Heating the milk to 55 degrees Celsius dramatically reduced the residual activities of LPL and BSSL, whereas heating to 50 degrees Celsius caused only nominal reductions. No BSSL activity was detected in cow, camel, goat milk or in infant formula.