葡萄糖氧化酶用于改善啤酒风味稳定性存在的缺陷及改进措施

啤酒的风味稳定性已成为影响啤酒质量的一个限制性因素。因为啤酒的风味稳定性与啤酒的含氧量有密切的关系，因此，除去啤酒中的氧，可明显改善啤酒的风味稳定性。葡萄糖氧化酶可用于脱除啤酒中的氧，但在改善啤酒风味稳定性方面还存在一定的缺陷。介绍了葡萄糖氧化酶用于啤酒脱氧的缺陷及改进措施。     

SOME REACTION PRODUCTS FROM NONENZYMATIC BROWNING OF GLUCOSE AND METHIONINE

Column and thin-layer chromatographic analysis revealed that acetone, butanal, ethanal, methanal, methional, furfural and 2-propenal were in the monocarbonyl fraction from heat induced glucose and methionine nonenzymatic browning reaction mixtures. Methional was found to be responsible for the characteristic boiled potato-like aroma of the reaction mixture. 2-Propenal was identified as the 3-carbon aldehyde degradation product of methionine.     

EFFECT OF SUGARS AND MAILLARD REACTION PRODUCTS ON POLYPHENOL OXIDASE AND PEROXIDASE ACTIVITY IN FOOD

The effect of glucose, fructose and sucrose aqueous solutions on polyphenol oxidase (PPO) and peroxidase (POD) activity was studied. Solutions with high concentrations of sugars showed a slight inhibiting effect on PPO while an activation was observed for POD. Glucose solutions, tested after sufficient heat treatments, showed an inhibiting action only on PPO activity. Maillard reaction products, obtained by heating a glucose/glycine solution, caused an unexpectedly strong inhibiting effect on both enzymes. The inhibition became more evident with increasing heating times of the glucose/glycine solution, reducing the activity of PPO and POD nearly to zero. Thus, the Maillard reaction products, already known for their antioxidant properties, were also shown to have a strong inhibiting effect on enzymatic browning.     

MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE

Lambic and Gueuze are special Belgian beers obtained by spontaneous fermentation. Micro-organisms involved in this fermentation were counted and differentiated using several selective growth media. Micro-organisms were also isolated from samples of Lambic of different age and originating from different casks and brews and identified by classical tests. The following general pattern of microbial development was observed. After 3 to 7 days the fermentation started with the development of wort Enterobacteriaceae and strains of Kloeckera apiculata. These organisms were overgrown after 3 to 4 weeks by strains of Saccharomyces cerevisiae and S. bayanus. These were responsible for the main fermentation, lasting for 3 to 4 months. This was followed by a strong bacterial activity. This period was dominated by the growth of strains of Pediococcus cerevisiae. These reached their maximal numbers during the summer months and were responsible for a fivefold increase in lactic acid concentration. In some casks they caused ropiness. After the main fermentation period Lambic is very sensitive to spoilage by acetic acid bacteria of the genus Acetomonas. The presence of air may be the determining factor for their development. After 8 months a new increase in yeast cells was noted. These belonged now mainly to the genus Brettano-myces bruxellensis and Br. lambicus. They caused a further slow decrease in residual extract and the appearance of special flavours. Oxidative yeasts of the genera Candida, Cryptococcus, Torulopsis and Pichia were also detected and may be responsible for the formation of a flim on the beer surface after the main fermentation.     

A TWO‐STEP CONTROLLED LACTIC FERMENTATION OF CABBAGE FOR IMPROVED CHEMICAL AND MICROBIOLOGICAL QUALITIES*

ABSTRACT

Traditionally, lactic fermentation of vegetables is spontaneous and uncontrolled leading to unstable and inconsistent product. The present work used Leuconostoc mesenteroides and Lactobacillus plantarum in a two‐step controlled fermentation to ensure shelf stable, fermented cabbage with 0.5% added salt concentration. The pH, titratable acidity, lactic bacterial counts, sugar utilization and amino acid profile of the final product were periodically monitored. The pH in controlled cabbage fermentation dropped to less than 4.5, within 60 h of fermentation and glucose was completely utilized in 15 days while about 15–18% of glucose remained in spontaneously fermented cabbage. The spontaneously fermented cabbage samples had a significantly lower content of amino acids such as tyrosine, histidine, threonine, alanine, valine, phenylalanine, isoleucine, leucine, methionine and developed off‐flavors at the end of 90 days of refrigerated storage. In contrast, controlled lactic fermentation stabilized the product in the first 15 days of fermentation and was organoleptically acceptable up to 3 months.

PRACTICAL APPLICATIONS

Use of defined single or mixed starters and precise control of the cabbage fermentation process go a long way in ensuring a consistent product without the need of any chemical preservatives or harsh processing conditions. The present work made use of the benefits of heterofermentative pathway to create a product similar to naturally fermented cabbage in terms of flavor and used the homofermentative pathway to stabilize the product and showed that it is possible to obtain a satisfactory and stable product by the two‐step controlled fermentation as far as commercializing and mechanizing the product is concerned. The amino acid contents are also shown to be more in controlled than spontaneously fermented cabbage.     

STUDIES ON CONJUGATE EFFECTS OF SUBSTRATE (GLUCOSE) AND PRODUCT (ETHANOL) ON CELL GROWTH KINETICS DURING FERMENTATION OF DIFFERENT YEAST STRAINS

The conjugate effect of substrate (glucose) and product (ethanol) has been studied on yeast growth during the course of fermentation. The study was made on five yeast strains Kloeckera apiculata, Saccharomyces uvarum, Saccharomyces bayanus, Saccharomyces cerevisiae UG5, and Saccharomyces cerevisiae sake. The results attest a different action of added alcohol as compared with produced alcohol for all strains. It is also verified that kinetic behaviour, namely ethanol inhibition, varies with initial substrate concentration, and so a new parameter, the added alcohol concentration at which biomass productivity declines to one-half its value with no added ethanol, is proposed to quantify ethanol inhibition     

ON THE DIFFERING RATES OF FRUCTOSE AND GLUCOSE UTILISATION IN SACCHAROMYCES CEREVISIAE

Fructose is utilised slower than glucose when the two sugars are fermented separately. This phenomenon occurs in a growth promoting medium as well as in brewers wort when using the brewing yeast Saccharomyces cerevisiae. The use of a fructose adjunct in wort at concentrations of 2% w/v and above, may result in residual concentrations of fructose to remain at the end of fermentation and consequently taint the beer with a sweet off-flavour. Glucose and fructose have no effect on maltose utilisation. Thus they do not exert catabolite repression on the maltose membrane transport system in the particular brewing strain of S. cerevisiae under investigation, when fermented in brewers wort.     

酱油的国家卫生微生物标准探析与建议

对酱油的国家卫生微生物现行标准进行分析探讨,重点分析大肠菌群、致病菌和霉菌作为酱油卫生标准的检验意义.建议酱油的卫生微生物学标准体系：将大肠菌群修改为耐热大肠菌群,致病菌修订为金黄色葡萄球菌,增设霉菌和酵母菌计数.     

THE STRUCTURAL AND STORAGE CARBOHYDRATES OF SACCHAROMYCES CEREVISIAE: CHANGES DURING FERMENTATION OF WORT AND A ROLE FOR GLYCOGEN CATABOLISM IN LIPID BIOSYNTHESIS

Detailed analysis of the structural and storage carbohydrates of Saccharomyces cerevisiae (NCYC 240) during wort fermentation showed that there were no significant changes in the amounts of trehalose or alkali-soluble glycogen. However, glucan and mannan individually increased from ca4% of the yeast dry weight at pitching to ca6% during the first 3–17 h of fermentation, butthen declined to the former level. In the first 2 h of fermentation, prior to yeast multiplication, acid-soluble glycogen was rapidly dissimilated from ca 40% to ca 6% of the yeast dry weight. During this period of oxygen uptake, wort sugars were not removed by the yeast. Glycogen, therefore, was the sole source of metabolic energy for lipid resynthesis and hexose transport appeared to require the formation of a component membrane. During the latter phase of fermentation when the yeast was not growing but expending energy for maintenance of cellular functions, glycogen reserves were slowly depleted; after a period of prolonged anaerobic storage, the content of glycogen fell well below that which was initially present in the pitching yeast.     

FoxFro2.5forWindows中结构化查询语言的特色及应用

Fox Pro 2 .5 for Windows实现的结构化查询语言 (SQL )中的 SEL ECT语句与 ANSI标准 SQL SELECT的功能相比作了较大的扩充 .查询结果的输出实现了多样化 ,如输出到显示器、打印机、文件、标准数据库、光标数据库或数组中等 .并通过实例分析讨论了 SEL ECT语句的灵活应用技术 .     

化纤含醇含油污水厌氧失效及其恢复

从厌氧处理的机理出发 ,对化纤含醇含油污水厌氧处理失效的现象、原因进行了全面阐述和分析 ,并提出了对厌氧失效进行及时处理和有效恢复的具体措施     

METHIONINE AND SULPHATE AS COMPETING AND COMPLEMENTARY SOURCES OF SULPHUR FOR YEAST DURING FERMENTATION

Study of the uptake of sulphate and methionine by an ale yeast from a range of media showed that utilisation of sulphate was fairly strictly controlled but assimilation of methionine was not. Cells never took up more than about 0.3 mMol sulphate per litre whilst methionine, up to an initial concentration of 10 mMol per litre, was completely absorbed. Sulphate-grown cells had low intracellular pools of amino acids and methinonine was never detected. Methionine-grown cells contained methionine in both cytosol and vacuole and the concentration of several other amino acids also increased in such a way to suggest that methionine catabolism was occurring. With mixed sulphur sources methionine prevented uptake of sulphate when the concentration of sulphate was high but not when it was low suggesting the presence of two sulphate transporters with different control properties. Sulphate did not influence uptake of methionine. Addition of other amino acids to the medium did reduce the rate and extent of methionine uptake but not the intracellular pool sizes. Pilot plant studies suggested that SO₂ production in a brewery is more likely to be a reflection of the overall nutritive status of the wort rather than be connected to the initial methionine concentration .     

WORT COMPOSITION AND BEER FLAVOUR. II. THE INFLUENCE OF DIFFERENT CARBOHYDRATES ON THE FORMATION OF SOME FLAVOUR COMPONENTS DURING FERMENTATION

Wort, to which was added various amounts of solutions of glucose, fructose, sucrose or maltose, was fermented, and in the resulting beers the concentrations of the following flavour components were determined by gas chromatography: ethyl acetate, isobutyl acetate, iso-amyl acetate, 2-phenyl ethyl acetate, ethyl caproate, ethyl caprylate, n-propanol, isobutanol, amyl alcohols, 2-phenyl ethanol, caprylic acid and capric acid. The concentrations of these compounds were affected in different ways by the various amounts of sugar added, and some differences were observed etween the different carbohydrates.     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

ASPECTS OF ADJUNCT FERMENTATION: II. COST CALCULATIONS FOR LAGER BREWERIES

The application of the adjunct fermentation method (see previous paper) to the fermentation of lager beer leads to potential savings in capital cost. These are calculated in detail for the case of a new brewery construction and for the case when, in an existing brewery, its capacity is to be increased by using adjunct fermentation. The results show that the procedure would be more profitable than conventional fermentation when applied to the new construction, and extremely so when used to increase production from an existing brewery.     

金刚石制品在信息产业中的应用及市场展望

信息产业是近年来增长最快的产业之一。其中信息材料的生产及加工对信息产业发展起着极为重要的作用。同时，它也给超硬材料产业提供了一个新的应用领域。本文概要介绍了金刚石制品在加工信息材料中的应用及市场前景。     

双酶协同法糖化玉米及L-乳酸发酵工艺的研究

通过均匀试验对双酶协同作用进行了玉米糖化条件、发酵条件的研究,得出最佳糖化条件为：糖化温度64℃、α-淀粉酶添加量0.0435g/20g玉米粉、糖化酶添加量0.0742g/20 g玉米粉、pH 5.7、糖化时间6h,还原糖含量可达119.96g/L;最佳发酵条件为：发酵温度37℃、接种量10%、发酵时间48 h,添加麸皮量为30g/100g玉米粉,乳酸得率136.92g/L.