The goal of the present investigation was to study the influence of various brewing parameters on the total lipid content as well as the fatty acid composition of the yeast. The effects of fermentation temperature, aerobic vs. anaerobic growth, yeast strain, and adjunct level were explored. The results revealed that yeast contained more lipids and more unsaturated fatty acids when grown at lower temperatures. Aerobic growth conditions increased the amount of unsaturated acids and sterols. The fatty acid composition of three yeast strains displayed some differences when grown under identical conditions and the total lipid content rose markedly when increasing portions of corn syrup were used for wort production. In an effort to determine the site of these lipid changes, yeast cells were homogenized and subjected to a differential centrifugation. Three different subcellular particles were obtained and analyzed for lipids. An attempt was made to correlate some of these findings with the accumulation of ethyl acetate in the resultant beer.
The addition of amylogiucosidase to fermenting wort produced changes in the spectrum of carbohydrates. Some oligosaccharides were broken down to a larger extent than others, and maltotriose and maltose were depleted at a higher rate than under normal conditions. It was also noted that the glucose concentrations increased in fermentations to which amyloglucosidase had been added. In order to determine whether the reduction in maltotriose and maltose was caused by the enzyme alone or by assimilation as well as enzymic degradation, maltotriose depletion rates were compared in fermentations with Sacch. cerevisiae and with Sacch. uvarum. The results indicated assimilation as well as degradation.Further evidence of maltotriose fermentation was obtained when glucose was continuously pumped into a fermentor at a rate approximating to the glucose formation by the enzyme. Also, under these experimental conditions, it was found that glucose levels increased, while maltose and maltotriose concentrations decreased. However, the observed increase in glucose during the fermentation was lower than would be expected from the mechanical addition, indicating a simul taneous uptake of glucose, maltose and maltotriose.
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