EFFECT OF PHYSICAL FACTORS ON ACETIC ACID PRODUCTION IN BRETTANOMYCES STRAINS

Four species of Brettanomyces (intermedius, bruxellensis, custersianus, clausenii) were examined to ascertain their acetic acid production capacity. The results showed that B. bruxellensis was the strain with the best volumetric productivity and specific production rate (P = 0.065 gL^?1 h^?1; V_p = 0.43 gg^?1h^?1). The best kinetic parameters were reached (P = 0.133 gL^?1 h^?1; Y_p/s = 0.23; P_max = 11.64 gL^?1) at an airflow of 288 Lh^?1 (0.6 vvm, OTR = 124 mgO₂L^?1 h^?1), and substrate inhibition was not observed. The influence of temperature and agitation on acetic acid production by B. bruxellensis in a glucose medium was investigated at different levels, 26, 30, 34C and 250, 350, 450 rpm, respectively. Temperature and agitation were shown to be deci‐sive factors (P < 0.05) in acetic acid production at 288 Lh^?1(0.6 vvm, OTR = 124 mgO₂L^?1 h). The optimal conditions for a high volumetric productivity were 30C and 250 rpm, respectively.     

EFFECT OF ETHANOL VAPOR ON GROWTH AND TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM IN A HIGH MOISTURE BAKERY PRODUCT

To determine the effect of ethanol vapor on toxin production by Clostridium botulinum, studies were done in English style crumpets (a_w 0.990, pH 6.5) challenged with 500 spores/g C. botulinum types A and proteolytic B and packaged in high gas barrier bags [ethanol transmission rate (ETR) 0.21 g/m²/day @ 25 C]. Crumpets were packaged in air with either commercially available ethanol vapor generators (Ethicap® 2, 4 or 6G) or cotton wool pads saturated with 2, 4 or 6 g of 95% food grade ethanol and stored at 25C. Toxin was detected in all inoculated control crumpets (0% ethanol) after 5 days at ambient temperature (25C). Ethicap® 2G delayed toxicity for 10 days while complete inhibition (>21 days) was observed in all crumpets packaged with 4 or 6G Ethicap® or with 2, 4 or 6 g of ethanol per pad. However, all crumpets were overtly spoiled by this time. Both headspace ethanol and absorption of ethanol by crumpets increased as a function of Ethicap® size/weight of ethanol. Based on these preliminary studies, ethanol vapor would appear to be an effective additional barrier to control the growth and toxin production by C. botulinum in high moisture bakery products and ensure the safety of these products at ambient temperature.     

EFFECT OF THEOBROMINE ON GROWTH AND AFLATOXIN PRODUCTION BY ASPERGILLUS PARASITICUS

Theobromine (0, 2, 4, and 8 mg/ml) had little effect on growth and aflatoxin production by Aspergillus parasiticus NRRL 2999 in a glucose-mineral salts-yeast extract medium, indicating that the anti-aflatoxigenic activity of cocoa beans is not due to the presence of this methylxanthine.     

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 ACETIC ACID AND CMC ON RHEOLOGICAL AND BAKING PROPERTIES OF FLOUR

The effects of addition of acetic acid (0.05, 0.1, 0.2 and 0.4%) and carboxymethyl cellulose (0.25, 0.5, 1.0, 2.0%) on rheological, gas release and bread making properties of flour were examined. Water absorption, dough stability, dough development time, loaf volume and overall acceptability scores decreased, while degree of softening and bread firmness increased with an increase in acetic acid concentration. Addition of CMC showed similar effects on dough stability, dough development time and degree of softening. Maximum dough height (H_m), maximum height of CO₂ production (H,_m), gas formation and retention decreased with the increase in acetic acid and CMC levels. Addition of 0.05% of acetic acid in combination with 0.25% CMC was most effective in improving dough characteristics, and overall acceptability scores.     

THE EFFECT OF OSMOTIC PRESSURE ON THE PRODUCTION AND EXCRETION OF ETHANOL AND GLYCEROL BY A BREWING YEAST STRAIN*

When the cells of a lager brewing yeast Saccharomyces uvarum (carlsbergensis) were grown in minimal media containing sucrose and a non-metabolized sugar sorbitol, significant levels of intracellular ethanol were obtained. Intracellular ethanol concentration decreased as the osmotic pressure of the medium was lowered and the proportion of extracellular ethanol increased. A reduction in cell viability occurred when there were high levels of intracellular ethanol. The total amount of glycerol produced increased with increased osmotic pressure, but glycerol diffused out of the cells faster than ethanol.     

混合培养在酒精发酵中的研究进展

综述了近年来混合培养在酒精发酵研究中的进展情况。混合培养具有纯种培养所不具备的诸多优点 ,因而具有较大的发展潜力 ,开始被人们所重视。在酒精发酵中 ,混合培养的研究主要有两个方面 :一为淀粉和纤维素等多糖原料的直接酒精发酵 ;二为混合单糖主要是葡萄糖和木糖共发酵生产酒精     

麦麸发酵生产混合酶制剂的培养基条件优化

采用SAS软件中的Plackett-Burman及响应曲面中心点组合实验设计对发酵生产阿拉伯木聚糖酶和阿魏酸酯酶混合酶制剂的培养基条件进行优化。使用Plackett-Burman设计评价了8个培养基因素对混合酶制剂产量的影响,得到主要影响因素;以此为基础,采用响应曲面中心点组合设计确定了麦麸发酵生产混合酶制剂的最佳培养基条件:麦麸10%、NH4NO30.28%、KH2PO40.2%、MgSO·47H2O0.08%、NaNO30.31%、pH5.5。