Comparative characterization of baking lipase substrate specificities using emulsions and the p-nitrophenyl assay

For use in cakes, lipases with suitable substrate specificity are needed to minimize the release of short-chain fatty acids that cause undesirable off-flavors. We analyzed the substrate specificities of 17 lipases using the p-nitrophenyl (PNP)-assay. These results were compared to the reactions of the lipases with the baking fats rapeseed oil, margarine and butter in a new model emulsion. The free fatty acids (FFA) released from this model emulsion were quantitated by gas chromatography. The broad spectrum of lipase specificities seen in the PNP-assay was not apparent in the patterns of FFA released from the model emulsions. There, all lipases released similar percentages of FFA depending on the fat and emulsifier used. The prediction of lipase reactions via the PNP-assay should therefore be critically reevaluated for real food systems such as cakes.