Biofilm formation and contamination of cheese by nonstarter lactic acid bacteria in the dairy environment

Defects in cheese, such as undesirable flavors, gas formation, or white sur face haze from calcium lactate crystals, can result from growth of nonstart er lactic acid bacteria (NSLAB). The potential for biofilm formation by NSL AB during cheese manufacturing, the effect of cleaning and sanitizing on th e biofilm, and bacterial growth and formation of defects during ripening of the contaminated cheese were studied. Stirred-curd Cheddar cheese was made in the presence of stainless steel chips containing biofilms of either of two strains of erythromycin-resistant NSLAB (Lactobacillus curvatus strain JBL2126 or Lactobacillus fermentum strain AWL4001). During ripening, the ch eese was assayed for total lactic acid bacteria, numbers of NSLAB, and perc entage of lactic acid isomers. Biofilms of L. curvatus formed during cheese making survived the cleaning process and persisted in a subsequent batch o f cheese. The starter culture also survived the cleaning process. Additiona lly, L. curvatus biofilms present in the vat dislodged, grew to high number s, and caused a calcium lactate white haze defect in cheese during ripening . On the other hand, biofilms of L. fermentum sloughed off during cheese ma king but could not compete with other NSLAB present in cheese during ripeni ng. Pulsed-field gel electrophoresis results verified the presence of the two b iofilm strains during cheese making and in the ripening cheese. Probable co ntamination sites in the plant for other NSLAB isolated in the cheese were identified, thus supporting the hypothesis that resident NSLAB biofilms are a viable source of contamination in the dairy environment.