ABSTRACT
The growth of psychrotrophic bacteria during cold storage of raw milk is frequently accompanied by production of heat-stable extracellular proteinases and lipases. This chapter discusses general features of assays that have been applied in buffer systems to lipases of psychrotrophic bacteria. Methods involving measurement of the rate of release of free fatty acid (FFA) from triglycerides have been widely applied to the assay of lipases of psychrotrophic bacteria. As an alternative to titrimetric determination of FFA, colorimetric methods involving their conversion into copper soaps can be used. The determination of radioactive fatty acids released by lipolysis of triolein labeled with C- or H-oleic acid has been used in the assay of the lipases of Escherichia coli, and of Staphylococcus aureus but not apparently to lipases of psychrotrophic bacteria. In diffusion assays generally, the optimal concentration of lecithin is a compromise; high concentrations give distinct zones but low sensitivity, whereas low concentrations give high sensitivity but less distinct zones.
