EFFECTS OF AERATION DURING THE CULTIVATION OF PITCHING YEAST ON ITS CHARACTERISTICS DURING THE SUBSEQUENT FERMENTATION OF WORT

The characteristics of cultivated yeast were studied after continuous aeration, aeration for the first hour and without aeration. The fatty acid content increased under aerobic conditions, while the level of storage sugars increased under anaerobic conditions. In a fermentation test, total number of cells and their viability and also the intracellular level of storage sugars and fatty acids were higher in yeast cultivated under aerobic conditions than in yeast cultivated under anaerobic conditions. Since there were no significant differences between the performance of yeast cultivated under continuous aeration and those with aeration for the first hour, the latter offer the best economic choice.     

THE EFFECT OF YEAST TREHALOSE CONTENT AT PITCHING ON FERMENTATION PERFORMANCE DURING BREWING FERMENTATIONS

The effect of yeast trehalose content at pitching on the fermentation performance during brewing fermentations was studied using a commercial strain of lager yeast, Saccharomyces cerevisiae (AJL 2155). Pitching yeasts with different trehalose contents were obtained by collecting cells in suspension after 96 h and 144 h of fermentation in EBC tubes in 10.8°P brewers wort at 14°C. The trehalose content of the pitching yeast had no effect on growth, specific gravity and ethanol production during the subsequent fermentation. A high trehalose content of the pitching yeast, however, sustained cell viability during the initial stage of fermentation, increased the carbohydrate utilisation rate and increased the production of isoamyl alcohol and isobutanol. For these aspects of fermentation performance, the trehalose content of the pitching yeast may prove useful in evaluating the vitality of pitching yeasts within the brewery .     

醋酸、盐酸酸化对碘法滴定测定保险粉含量的影响

保险粉是一种重要的化工产品,大量用于印染行业,其含量的高低可反映质量的优劣。采用碘法滴定测量其含量,并探讨了醋酸酸化和盐酸酸化对测定的影响。结果表明用盐酸酸比用醋酸酸化测含量受时间和温度变化的影响小,测定结果更接近真实值。     

EFFECT OF STORAGE ON THE NUCLEIC ACID COMPOSITION OF BAKER'S YEAST*

General changes are described in the nucleic acid content of yeast stored for 20 days under extreme conditions (35 °C). The total amount of nucleic acid increased in the first phase of 6–8 days storage. In the second phase, during which the yeast started to autolyse, the nucleic acid content diminished, first slowly and then more quickly. The quantity of acid-soluble nucleotides increased with storage. The amount of dead yeast cells is low during the first period, but starts to increase quickly during the second period. Changes in the rRNA, 5S RNA, tRNA, mRNA and DNA, fractionated on MAK columns, were investigated over a 20-day storage period. The contents of the RNA fractions increased initially during storage. The amount of rRNA attained its maximum value after 5 days, followed by DNA (7 days), then tRNA (10–12 days) and lastly 5S RNA; thereafter they all decreased. The mRNA fraction diminished rapidly: after only two days' storage the incorporation of labelled uracil into mRNA had declined by about 90%, showing that the ability to synthesize mRNA was soon lost. The short half-life of mRNA ensures its absence in yeast stored for longer periods.     

EFFECT OF INCORPORATING ADDITIONAL OLEIC ACID INTO THE PLASMA MEMBRANE OF BAKER'S YEAST ON THE PERMEATION OF PYRUVIC ACID

Addition of Tween 80 to the growth medium of baker's yeast (Saccharomyces cerevisiae) under anaerobic conditions resulted in an increased content of 9-cis-octadecenoic acid (oleic acid) in a membrane preparation consisting mainly of plasma membrane. There was no significant effect on the pyruvate decarboxylation capacity of disintegrated cells, but that of intact cells was significantly enhanced, presumably because of an oleate-induced increase in the permeability of the plasma membrane to pyruvate.     

多菌种混合乳酸菌发酵酸豆奶工艺研制

本文研究了市售酸牛奶和自制酸泡菜中分离筛选菌种，确定菌种间的比例。通过对生产过程中的条件进行初步摸索，以鲜豆奶为主要原料，采用多菌种混合液态发酵，可生产出色、香、味俱佳，不舍任何防腐剂的纯天然酸豆奶新产品，从而为工业化生产乳酸菌发酵酸豆奶提供技术依据。     

THE FREE FATTY ACID CONTENT OF FISH OIL: THE EFFECT OF LIME ADDITION ON THE REDUCTION OF THE FREE FATTY ACID CONTENT OF FISH OIL DURING THE FISH MEAL AND OIL PRODUCTION PROCESS

Addition of small amounts of calcium hydroxide (slaked lime) to fish, press liquor or polishing water in the fish meal and oil production process leads to a considerable reduction in the free fatty acid content of the resulting fish oil.