Potential spoilage of extended shelf-life (ESL) milk by Bacillus subtilis and Bacillus velezensis

Abstract

We aim to quantify and compare biofilm-induced proteolysis and lipolysis of Bacillus subtilis and Bacillus velezensis with that of the planktonic cells. Planktonic and biofilm cells were enumerated in a flow cytometer after incubation. The concentrations of proteolytic and lipolytic enzymes produced by the submerged biofilm and planktonic cells of the isolates were quantified. There were significant differences (P < 0.05) in the log counts of cells within the biofilms as well as concentrations of enzymes within biofilms and planktonic cells in UHT milk. The enumerated cells ranged from 5.6 log CFU/cm 2 for B168 to 7.4 log CFU/cm 2 for B48, respectively while the highest means of proteolysis and lipolysis were observed in B48 (1034 ρL/CFU) and B50 (34.5ρL/CFU± 0.44) respectively. The result of this study indicated that the spoilage potential for both biofilms and planktonic culture are strain-dependent. The implication to the industry is that weak biofilm formers have better spoilage potential than the strong biofilm formers in spore forming bacilli.