Upregulation of protease and lipase via rsmE deletion accelerates spoilage of UHT milk by Pseudomonas fluorescens.

Heat-resistant enzymes produced by Pseudomonas fluorescens are major factors to dairy spoilage. This study found that knockout of the rsmE in the Gac/Rsm system simultaneously enhanced the protease and lipase activities, motility (swimming and swarming), and flagellar number of the strain. The mutant exhibited higher potential for early spoilage in UHT milk, as indicated by an increased Turbiscan Stability Index (TSI), larger particle size, and decreased absolute zeta potential. The milk inoculated with the mutant could also be clearly distinguished from the wild-type by electronic tongue/nose analysis. These results indicated that rsmE affects the spoilage-related phenotypes of P. fluorescens by regulating protease and lipase systems, providing molecular insight into its spoilage mechanism.