Eb. Somers et al., Biofilm formation and contamination of cheese by nonstarter lactic acid bacteria in the dairy environment, J DAIRY SCI, 84(9), 2001, pp. 1926-1936
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.