732阳离子交换树脂对屎肠球菌谷氨酸脱羧酶活性的促进作用

通过对732阳离子交换树脂对屎肠球菌谷氨酸脱羧酶（glutamate decarboxylase,GAD,EC4.1.1.15）活性的影响进行探讨,构建了732阳离子交换树脂-细胞GAD复合转化体系。结果表明：经含0.2?mol/L?L-谷氨酸（L-glutamic acid,L-Glu）的0.2?mol/L乙酸-乙酸钠缓冲液（pH?4.2）平衡的732阳离子交换树脂可显著提高屎肠球菌细胞GAD的转化活性,γ-氨基丁酸（γ-aminobutyric acid,GABA）产量较对照组增加了32.30%;L-Glu/谷氨酸一钠（monosodium glutamate,MSG）（2∶1）固体混合物能有效调节反应体系的pH值和维持反应液的底物浓度,显著增加GABA产量,当添加量为30?g/L时,GABA产量较不添加L-Glu/MSG（2∶1）固体混合物的对照组提高了52.40%;732阳离子交换树脂与L-Glu/MSG（2∶1）固体混合物对细胞GAD的转化活性具有协同促进作用,适宜的732阳离子交换树脂-细胞GAD复合转化体系组成为732阳离子交换树脂10?g、0.3?mol/L?MSG溶液（溶于0.2?mol/L乙酸-乙酸钠缓冲液,pH?4.2）10?mL、100?mg/mL屎肠球菌细胞悬液10?mL和L-Glu/MSG（2∶1）混合物30?g/L。在该反应体系下,80?r/min、40?℃水浴振荡器反应24?h,GABA产量为（4.57±0.11）mmol,较对照组GABA产量（（2.29±0.08）mmol）提高了99.56%。     

响应面法分析微量元素对ALDC酶活力的影响

考察了微量元素对乙酰乳酸脱羧酶活的影响，通过单因子实验确定微量元素的最佳产酶浓度，进一步通过回归方法计算出微量元素的理论最佳产酶浓度，并用响应面分析法确定微量元素的最佳配比：微量元素配比为Mg^2 0．022g/L，Mn^2 0．00076g/L，Zn^2 0．00296g/L，酶活提高了3倍。     

The ability of biogenic amines and ammonia production by single bacterial cultures

The amino acid decarboxylating activity and production of biogenic amines, trimethylamine and ammonia by Morganella morganii (two strains), Klebsiella pneumoniae (three strains), Hafnia alvei (two strains), Enterococcus faecalis, Photobacterium phosphoreum, Micrococcus sp., Psychrobacter immobilis, Corynebacterium sp., Vibrio fischeri, Vibrio harveyi and Pseudomonas putida were investigated using a rapid HPLC method. In a laboratory medium containing amino acid (histidine, ornithine, lysine, tyrosine and arginine), not all bacterial strains produced the biogenic amines but most of them produced histamine, putrescine, cadaverine and ammonia. Cadaverine production by Klebsiella pneumoniae (8152), Klebsiella pneumoniae (673), Klebsiella pneumoniae (2122), Hafnia alvei (6578), Hafnia alvei (11999), Vibrio fischeri (25) Vibrio harveyi (42) and Pseudomonas putida (10936) was 531, 422, 532, 485, 472, 343, 547 and 343 mg/l, respectively in lysine decarboxylase broth. Tyramine was produced in highest concentration (526 mg/l) by Enterococcus faecalis (775). Agmatine was not produced apart from Psychrobacter immobilis (100) in an arginine decarboxylase broth.     

麦胚富集γ-氨基丁酸的培养条件优化

采用水浴保温的方法对麦胚中γ-氨基丁酸（GABA）进行富集,研究了培养温度、时间、液料比和培养液pH对麦胚中GABA含量和谷氨酸脱羧酶（GAD）活性的影响,采用响应面法对麦胚富集GABA的培养条件进行了优化。结果表明,在一定范围内培养温度、时间、液料比和培养液pH可有效提高麦胚中GAD活性,促进GABA积累。Box-Behnken实验结果显示,麦胚富集GABA的最优培养条件为培养温度46℃,时间1.5h,液料比6∶1（mL/g）,培养液pH4.6。在此培养条件下,麦胚中GABA最大富集量为36.78mg/g,是麦胚原料的5.51倍。方差分析表明,所建的回归模型能够很好的预测麦胚中GABA富集量的变化。      

Dynamics of γ-aminobutyric acid in wheat flour bread making

The dynamics of the health-improving non-protein amino acid γ-aminobutyric acid (GABA) during bread making were studied. Wheat flour contains trace levels of GABA (<15 ppm) and ca. 160–175 ppm of its precursor, glutamic acid (GA). During dough mixing, the levels of both GA and GABA largely increased. While wheat flour endogenous glutamic acid decarboxylase (GAD) performs some minor conversion of GA into GABA, yeast is the main contributor to GABA formation. Comparison of amino acid levels of dough samples, without or with yeast, indicated that yeast favours both GA and GABA formation already during mixing. Fermentation decreased both GA and GABA contents, due to amino acid consumption by the yeast, which used more GA than GABA. Proofing and baking resulted in large GABA losses, the latter probably in Maillard browning reactions during baking. Thermal loss of GA was less pronounced than that of GABA. Breads contained only trace levels of GABA and ca. 90–130 ppm of its precursor. Exogenous supplementation of recombinantly produced GAD of Yersinia intermedia decreased GA levels in mixed and fermented dough and increased GABA levels. The highest GAD dosage used resulted in fermented doughs with ca. 300 ppm of GABA, i.e. three times higher than the level present in the reference sample (no GAD added). After baking, a significant GABA level was left in the bread samples (ca. 115 ppm) and GABA-enriched breads were obtained. Addition of sodium glutamate (100–380 ppm) to a bread recipe containing no added GAD clearly indicated that its precursor was not the limiting factor for GABA conversion during bread making since the resulting breads contained no GABA, or only trace levels (ca. 20 ppm).     

In situ production of γ-aminobutyric acid in breakfast cereals

Breakfast cereals are an important part of an equilibrated diet in the Western world, making them extremely suited for carrying health benefits. Intake of γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter of the nervous system, has been related to blood pressure lowering in hypertensive individuals. In vivo, GABA is formed from glutamic acid (GA) by glutamic acid decarboxylase (GAD), a widely distributed enzyme in prokaryotic and eukaryotic species. We here enriched breakfast cereals with GABA by recipe and process optimisation. The dynamics of GA and GABA were monitored throughout the production process. Addition of exogenous recombinantly produced GAD of Yersinia intermedia increased GABA levels by 2- to 5-fold. As only trace levels of GABA (<15 ppm) and relatively low levels of its precursor (GA, <100 ppm) are present in the wheat and rice flour used, a well-thought ingredient choice (inclusion of quinoa flour (ca. 90 ppm GABA and 700 ppm GA) or bran enrichment (ca. 66 ppm GABA and 500 ppm GA)) also significantly increases the GABA content in the final flakes. Finally, a strict control of the heating steps during the production process reduces GA and GABA losses. Consumption of one portion (30 g) of the here produced enriched breakfast cereals can even meet up to 55% of the daily intake earlier reported to lower blood pressure (ca. 10 mg).     

草酸脱羧酶的性质及应用研究进展

草酸脱羧酶（oxalate decarboxylase,Oxdc）属Cupin蛋白超家族,是一种包含Mn2+的均一聚合酶,能够在没有辅因子的条件下催化草酸转化为甲酸和CO2,是植物、微生物中促使草酸代谢降解的主要酶之一。该酶已在农业、食品、工业生产、医疗和生物监测等领域得到了广泛的应用。本文综述近年来在Oxdc来源、结构、作用以及实际应用方面的研究,着重讨论其在泌尿系统草酸盐结石病症方面的作用,为有效预防治疗泌尿系统结石症的研究提供理论参考。     

Development of a real-time PCR assay with an internal amplification control for detection of Gram-negative histamine-producing bacteria in fish

Prompt detection of bacteria that contribute to scombrotoxin (histamine) fish poisoning can aid in the detection of potentially toxic fish products and prevent the occurrence of illness. We report development of the first real-time PCR method for rapid detection of Gram-negative histamine-producing bacteria (HPB) in fish. The real-time PCR assay was 100% inclusive for detecting high-histamine producing isolates and did not detect any of the low- or non-histamine producing isolates. The efficiency of the assay with/without internal amplification control ranged from 96-104% and in the presence of background flora and inhibitory matrices was 92/100% and 73-96%, respectively. This assay was used to detect HPB from naturally contaminated yellowfin tuna, bluefish, and false albacore samples. Photobacterium damselae (8), Plesiomonas shigelloides (2), Shewanella sp. (1), and Morganella morganii (1) were subsequently isolated from the real-time PCR positive fish samples. These results indicate that the real-time PCR assay developed in this study is a rapid and sensitive method for detecting high-HPB. The assay may be adapted for quantification of HPB, either directly or with an MPN-PCR method.     

THE BIOCHEMISTRY OF MATURATION

Negative and positive aspects of maturation are respectively related to aroma and taste modifications. Vicinal diketones, hydrogen sulphide, acetyldehyde being primarily responsible for ‘green’ beer flavours an important feature of maturation is the adjustment of their concentration during the lagering period. The role of secondary fermentation in the removal of these undesirable by-products and the importance of sulphury compounds in determining the typical character of lager beer are reviewed. Particular emphasis is placed upon new enzymatic and genetic approaches to overcome vicinal diketone problems in accelerated fermentation systems using free and immobilized cells. The presence in beer of amino acids, peptides, nucleotides and organic as well as inorganic phosphates is, in part, due to the secretion of these materials by the yeast during lagering. Most of these compounds are contained in internal pools and their actual participation in flavour maturation depends upon intracellular breakdown and accumulation, changes in cell permeability and subsequent exchange possibilities between the yeast cell and the surrounding beer. Participation and practical implications of medium chain length fatty acids in the development of autolytic and yeasty flavours are discussed.