Saccharomyces uvarum, Geotrichum candidum, Endomycopsis burtonii and Hansemula canadensis have been isolated from deteriorated silages and/or spoiled lactic acid fermented foods. All yeasts could grow in relatively high (100 mmol/l) concentrations of acetate or lactate in Wickerham's assimilation broth but were inhibited by increasing concentrations of these acids. Propionate was much more inhibitory than acetate or lactate. Growth rate, but not final cell yield, was adversely affected by increasing concentrations of these acids. The three acids used in combination were synergistically inhibitory to H. canadensis and G. candidum. Saccharomyces uvarum was inhibited by synergistic mixtures of acetate/propionate. Endomycopsis burtonii and H. canadensis were inhibited by synergistic mixtures of acetate/lactate, acetate/propionate and lactate/propionate. Lactate and propionate had a synergistic inhibitory effect on G. candidum. The mechanism of inhibition of growth of S. uvarum by acetate and propionate was further investigated. Acetate and propionate each caused a reduction in cellular efficiency (Y, μg cells/μmole glucose consumed). Mixtures caused a drastic reduction in growth rate and Y. These results suggest that the cells may expend energy in reducing intracellular concentrations of acetate while propionate probably acts in a different manner.

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Cultures of Streptococcus thermophilis and Lactobacillus bulgaricus produced more acid in mixed than in single strain culture. Growth of S. thermophilus in mixed culture was enhanced during the exponential phase and reached higher numbers in the stationary phase than when grown alone. L. bulgaricus was inhibited in the exponential and stationary phases of growth in mixed culture. L. bulgaricus liberated Seitz-filterable compounds during its growth that stimulated growth and acid production of S. thermophilus. These compounds are believed to be responsible for the commensal response observed in mixed cultures. Because of its rapid growth, S. thermophilus was a better competitor than L. bulgaricus for limiting nutrients in the medium. This resulted in inhibition of the growth of L. bulgaricus. The competitive and commensal response was optimal at 37 C and at a ratio of numbers of lactobacilli to streptococci of 2:1 at inoculation.

Strains of the yeastsCandida curvata andTrichosporon cutaneum were isolated that were able to ferment the lactose of cheese whey and ultrafiltered whey permeate to produce oil. Rapid fermentation rates and lactose utilization were achieved by the Gcurvata strains. The fermentation was more efficient on permeate than whey, because the organisms used whey protein very poorly. Methods of extracting the oil were compared, and the best results were obtained by sequential extraction with methanol and benzene or by ethanol and hexane. The fatty acid composition of the yeasts varied with the growth temperature, fermentation time, and medium. The oil was rich in 18:1, 16:0, and 18:0. The process is a technically feasible means of using whey permeate.

Aerobic deterioration of lucerne, maize and wheat silages was characterized by rapid increases in yeast and mould flora which oxidized lactic and volatile acids resulting in increased temperature and pH. While populations of yeasts and moulds were similar, temperature increases were slightly greater for silages inoculated with Lactobacillus acidophilus and Candida spp. After 48 h the pH of the inoculated silages was higher in general and concentrations of acids were lower than controls. Bacterial growth was slight although continued lactic acid production was probable. In contrast to lucerne and maize silages, the pH of wheat silage remained stable during this period because of high butyric levels, but temperature and yeast populations increased. After 48 h the pH rose above 5 in maize and lucerne, and bacterial growth and metabolic activity resumed resulting in volatile and non-volatile acid production from carbohydrate fermentation and deamination of amino acids. During this phase of aerobic deterioration yeast growth slowed or stopped, but temperatures remained high and pH continued to climb probably because of production of ammonia. The changes in gross composition of the silages did not follow any particular pattern. Losses in dry matter were small (2.5-4.0%) and changes in individual components probably reflect this loss rather than substantial changes. Protein availability in the lucerne silages undoubtedly decreased, as protein losses were high. It is concluded that the aerobic deterioration of silage is enhanced by the addition of L. acidophilus and Candida spp. at ensiling.