Effect of ethanol and low pH on citrulline and ornithine excretion and arc gene expression by strains of Lactobacillus brevis and Pediococcus pentosaceus

The accumulation of citrulline and ornithine in wine or beer as a result of the arginine catabolism of some lactic acid bacteria (LAB) species increases the risk of ethyl carbamate and putrescine formation, respectively. Several LAB species, which are found as spoilage bacteria in alcoholic beverages, have been reported to be arginine degrading. This study evaluates the effect of ethanol content and low pH on the excretion of citrulline and ornithine by two strains belonging to the potential contaminant species Lactobacillus brevis and Pediococcus pentosaceus. In the conditions that most affected cell viability, arginine consumption per cell increased noticeably, indicating that arginine utilization may be a stress responsive mechanism. L. brevis showed a higher accumulation of ornithine in the media than P. pentosaceus. In the presence of ethanol, a higher expression of the arcC gene was found in P. pentosaceus, which resulted in a lower excretion of citrulline and ornithine than in L. brevis. This suggests that L. brevis is more likely to produce these amino acids, which are precursors of ethyl carbamate and putrescine.     

Nitrogen regulation involved in the accumulation of urea in Saccharomyces cerevisiae

Rice wine is a popular traditional alcoholic drink with a long history in China. However, the presence of the potential carcinogen ethyl carbamate (EC) raises a series of food safety concerns. Although the metabolic pathway of urea (the major precusor of EC) has been characterized in Saccharomyces cerevisiae, the regulation of urea accumulation remains unclear, making the efficient elimination of urea difficult. To demonstrate the regulatory mechanisms governing urea accumulation, three key nitrogen sources that can inhibit urea utilization for a commercial S. cerevisiae strain were identified. In addition, regulators of nitrogen catabolite repression (NCR) and target of rapamycin (TOR) pathways were identified as being involved in urea accumulation by real‐time quantitative PCR. Based on these results, preferred nitrogen sources were found to repress urea utilization by converting them to glutamine or glutamate. Moreover, the results indicated that the manner of urea metabolism regulation was different for two positive regulators involved in NCR; Gln3p can be retained in the cytoplasm by glutamine, while Gat1p can be retained by glutamine and glutamate. Furthermore, this was confirmed by fluorescence location detection. These new findings provide new targets for eliminating EC and other harmful nitrogen‐containing compounds in fermented foods. Copyright © 2013 John Wiley & Sons, Ltd.     

气相色谱法测定蜂蜜中10种拟除虫菊酯类农药残留

目的为了结合《蜂蜜卫生标准》的修订要求中补充农药残留等相关指标和检验方法的需要,建立气相色谱法同时测定蜂蜜中10种拟除虫菊酯类农药残留的方法。方法通过对毛细管柱的类型、溶剂的种类、固相萃取小柱种类的选择实验,确定应用二氯甲烷为提取溶剂,经弗罗里硅土固相萃取柱净化,DB-17(0.25 mm×0.25μm×20 m)的毛细管柱作为分离柱,以GC-ECD测定,峰面积定量。结果 10种农药加标回收率为77.3%～103.0%,相对标准偏差2.5%～7.5%,检出限为0.000 5～0.005 mg/kg(当称样量为5.00 g时)。结论该方法适合蜂蜜中多种拟除虫菊酯类农药残留的同时检测。     

发酵食品中氨基甲酸乙酯的研究进展

目的 对发酵食品中氨基甲酸乙酯的研究进展进行综述。方法 查阅有关氨基甲酸乙酯致癌机理、形成机理、含量降低方法以及检测方法的文献, 进行总结。结果 氨基甲酸乙酯具有遗传毒性和致癌性, 在发酵食品中较为常见, 氨基甲酸乙酯的形成受多种因素的影响, 其检测方法主要有红外光谱法、色谱法、色谱/质谱联用法。 结论 应建立对各种发酵食品氨基甲酸乙酯含量的标准检测方法及限量标准, 为我国发酵食品中氨基甲酸乙酯限量标准的制定和确保我国发酵食品的安全性提供科学依据。     

复合固定化酸性脲酶酶膜的制备及应用

用复合固定化方法将酸性脲酶固定在壳聚糖-明胶膜上,探讨了固定化的条件和性质、稳定剂对固定化酶膜的作用、固定化酶膜反应器在黄酒中的应用。结果表明:采用质量浓度为1.0%的壳聚糖和0.75%的明胶混合制备含0.579U/cm2酸性脲酶的酶膜,储存半衰期可达81d;在固定化酶膜中加入10%的甘油,在不影响成膜状态和强度的前提下,固定化酶活回收率由66.4%提高到82.25%,储存半衰期可达100d;将16cm2的酶膜采用间歇振荡法分批处理30mL黄酒12h,在尿素去除率仍达50%以上的前提下,可连续处理8批黄酒,较未加稳定剂的提高2个使用批次,酶膜的使用半衰期有明显提高;将约为500cm2的酶膜以卷式膜形式做成酶膜反应器,以0.5mL/min的流速连续处理2L黄酒时,70h后,尿素去除率仍可达50%,且基本未改变黄酒的风味,并最终达到降低氨基甲酸乙酯(EC)的目的。     

基于PCR方法敲除黄酒酵母精氨酸酶基因的工程菌构建

用一种高效快速的免克隆方法-长侧翼同源PCR(LFH-PCR),构建基因敲除组件,然后通过化学转化方法把敲除组件转入黄酒酵母细胞中,利用同源重组机制精确敲除精氨酸酶基因(CAR1),构建了黄酒酵母工程菌株。结果表明,敲除CAR1基因的工程菌与出发菌株相比,酒液中尿素的含量降低了72%,氨基甲酸乙酯含量降低了38%,并且该菌株的遗传稳定性好,发酵性能与出发菌株基本一致。     

Ethyl carbamate kinetics in double distillation of sugar cane spirit. Part 2: influence of type of pot still

This study aimed to assess the influence of the pot still configuration on the reduction of ethyl carbamate content in double‐distilled sugar cane spirit, as well as to describe the effects of double distillation on this reduction. Ethyl carbamate is a potentially carcinogenic compound that may be present in high concentrations in sugar cane spirit, and therefore could become a public health problem, as well as a factor hindering Brazilian exports of this beverage. In sugar cane spirit production in Brazil, neither pot still configuration nor distillate reflux and cooling/condensation systems are standardized. In this study, ethanol, copper and ethyl carbamate contents were assessed (GC‐MS) in sugar cane spirits that were double‐distilled in pot stills with different reflux and cooling systems. Double distillation removed 94–98.5% of ethyl carbamate from sugar cane spirit. Pot stills with high reflux rates (equipped with dephlegmator or rectifying system) were more effective in reducing the ethyl carbamate content in double‐distilled sugar cane spirit. Copyright © 2013 The Institute of Brewing & Distilling     

Human health risk of dietary intake of organochlorine pesticide residues in bovine meat and tissues from Veracruz, México

Tissue distribution patterns of organochlorine pesticides in bovine carcasses varied significantly among seasons, geographic locations and tissues. The highest concentrations of Σ-DDT during the dry season were detected in lungs from Paso de Ovejas (2,834.90μg/kg lipid) and, during the rainy season, Lindane and Σ-HCH in muscle and lung samples from Paso de Ovejas (995.80 and 1,690.10μg/kg lipid). Estimated daily intakes of γ-HCH and Σ-DDT (3.35 and 1.22μg/kg bw/day) through consumption of muscle tissues from Paso de Ovejas and Puente Nacional during the rainy season showed the highest contribution. During the rainy season the highest non-cancer Hazard Ratios estimated corresponded to γ-HCH (3.97) and Σ-DDT (4.39) detected in muscle samples from Puente Nacional. The highest Hazard Ratios of cancer risk to the 95th centile daily consumption through meat corresponded to p,p'-DDT from Alvarado (7.76E+06) and from Paso de Ovejas for γ-HCH (1.50E+05) during rainy season. The results indicate potential non- and carcinogenic risks to consumer health through meat consumption.     

酿酒酵母对黄酒酿造中氨基甲酸乙酯代谢及黄酒品质的影响

氨基甲酸乙酯(Ethyl carbamate, EC)是存在于黄酒中的一种潜在致癌物质。本文通过研究酿酒酵母代替酒药发酵对黄酒品质的影响,为应用实验室菌株探究黄酒发酵体系中氨基甲酸乙酯形成的代谢基础提供依据。利用本实验室分离的野生型酿酒酵母(Saccharomyces cerevisiae,SC)和纯酿酒酵母(BY4741)替代酒药,并且按照工业化黄酒酿造工艺进行发酵实验。经高效液相色谱分析,BY4741和SC发酵组发酵液中尿素浓度和氨基甲酸乙酯浓度与酒药发酵组差异不大;酿造后期添加硫酸铵作为补充氮源,能在一定水平上减少氨基甲酸乙酯的浓度;发酵结束并煎酒后的成品经检测分析,酒精度、风味物质组成及氨基酸组成差异不大,说明应用BY4741和SC替代酒药进行酿造以及酿造过程中添加硫酸铵不影响产品的质量。本研究结果表明,酿酒酵母替代酒药进行发酵对黄酒品质影响较小,可应用于模拟体系中探索氨基甲酸乙酯形成的调控因子。     

固相萃取-气相色谱-质谱法测定腐乳中氨基甲酸乙酯

目的建立一种固相萃取-气相色谱-质谱法(solid phase extraction-gas chromatography-mass spectrometry,SPE-GC-MS)检测腐乳中氨基甲酸乙酯的方法。方法利用D5-氨基甲酸乙酯同位素做内标物,样品用20%乙醇水溶液提取后,利用碱性硅藻土固相萃取柱净化,洗脱液经浓缩后用气相色谱-质谱法测定样品中氨基甲酸乙酯。结果该方法的加标回收率在88.8%~104.1%之间,相对标准偏差(relative standard deviation,RSD)小于10%,定量限为2.0μg/kg(S/N=10)。结论该方法提取效果好,可以有效去除干扰物质,检测灵敏度、准确度均满足检测工作要求。