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 μmol/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 °C; heating to 50 °C caused only nominal reductions of LPL and BSSL (activities remaining ∼82% and 87%, respectively). No BSSL activity was detected in cow, camel, goat milk or in infant formula.