Aroma volatiles, acid production and proteolytic activity in the fermented milk of five lactobacillus cheese adjuncts were studied The lactobacillus strains were previously characterized as desirable or undesirable adjuncts in cheese. The five lactobacilli varied widely in volatile production, acid production and proteolytic activity. The presence gf a lactococcus did not enhance volatile production or proteolytic activity (P < 0.05). Methyl ketones, 2-heptanone and 2-nonanane, were produced in large quantities by the desirable cheese adjuncts (P < 0.05). Proteolytic activity was also higher in the two desirable cheese adjuncts (P < 0.05). Proteolytic activity was also higher in the two desirable cheese adjuncts (P < 0.05). Methanethiol was produced by one desirable and one undesirable adjunct. It was not possible to cluster the lactobacilli using principal components analysis of volatile production and proteolytic activity as desirable or undesirable cheese adjuncts. (C) 1999 Academic Press.