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The antimicrobial mode of action of the phenolic antioxidant butylated hydroxyanisole (BHA) against Staphylococcus aureus Wood 46 was examined. The compound was taken up very rapidly by the cells and adsorption was completed within 15 min. Exposure of a growing suspension to 50 μg of BHA/ml was bactericidal, but this concentration had no significant effect on the viability of a non-growing suspension. However, concentrations over 100 μg/ml were lethal to the latter and this bactericidal activity was related to leakage of nucleotides. Protoplasts produced by lysostaphin treatment undergo lysis when exposed to concentrations as low as 25 μg/ml. A mutant resistant to 50 μg of BHA/ml adsorbed the same amount of BHA but protoplasts from this strain were less susceptible to lysis. It was concluded that BHA is a member-active agent.

Saccharomyces uvarum var. carlsbergensis is heat sensitive and when dried by usual procedures exhibits very poor survival. Our results demonstrate that these cells are capable of accumulating trehalose when submitted to an osmotic treatment using 20% solutions of either sorbitol or dextrin endowing them with the capacity of surviving posterior dehydration.

Five yeast extracts (YE) were fractionated by ultrafiltration (UF) with 1, 3, and 10 kDa molecular weight cutoff membranes, concentrated by freeze-drying, and the resulting powders of yeast extract filtrates (YEF) were evaluated for their growth-promoting properties on nine cultures of lactic acid bacteria (LAB). There was an increase in alpha-amino nitrogen content of the YEF powders as the pore size of the UF membranes used to filter the YE solutions decreased. The source of YE had a much greater effect than UF on the growth of LAB. This was also the case for the YEF contents in total and alpha-amino nitrogen. Growth curves of the LAB showed that maximum growth rate (mumax) data were on average 30% higher with bakers' YE than with brewers' YE, while maximum optical density (ODmax) values were on average 16% higher with bakers' YE. This could be related to the higher nitrogen content of the bakers' YE used in this study. Modification by UF of the YE had no significant influence on the growth of 4 of the 9 LAB strains. The three strains of Lactobacillus casei were negatively influenced by UF, as they did not grow as well in the media containing the YEF obtained after filtering with 1 and 3 kDa membranes. On a total solids basis, the 2.5 x retentates from the 10 kDa membrane gave, on average, 4% lower mumax and 5% lower ODmax values as compared to cultures where the corresponding YEF was used as medium supplement. This could also be partially related to the different nitrogen contents of the filtrates and retentates.

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