麦汁关键氨基酸对Lager酵母发酵性能的影响

为探究麦汁中氨基酸在啤酒酿造中的作用,研究了麦汁中4种关键氨基酸(谷氨酸、脯氨酸、缬氨酸和赖氨酸)对酵母发酵性能的影响。以工业Lager酵母(Saccharomyces pastorianus TT-1)为研究对象,通过关键氨基酸添加的发酵实验,在合成培养基中对关键氨基酸在酵母增殖及风味物质代谢中的作用进行了分析,并进一步在工业生产麦汁中对其作用进行了验证。结果表明,谷氨酸和脯氨酸抑制酵母增殖;赖氨酸会促进酵母的增殖;缬氨酸会促进高级醇的生成。     

利用代谢组学方法分析不同糖化条件对酿酒酵母代谢途径以及啤酒中风味物质形成的分析

在啤酒发酵过程中，麦汁的好坏会直接影响啤酒的品质。为了探究不同的糖化工艺对发酵后酒品质的影响，运用代谢组学的方法，分析了不同糖化条件对麦汁成分造成的差异，从代谢水平上解释了啤酒发酵过程中不同糖化工艺产生的麦汁对酿酒酵母代谢途径的影响。通过对质谱检测后所得的数据经过进行主成分分析和偏最小二乘判别分析，确定了不同糖化工艺产生的麦汁会影响酿酒酵母的氨基酸代谢、有机酸代谢以及脂质和脂肪酸代谢等代谢途径；主要涉及精氨酸的生物合成，苯丙氨酸、酪氨酸和色氨酸生物合成，缬氨酸、亮氨酸和异亮氨酸生物合成，甘氨酸、丝氨酸和苏氨酸代谢，D-氨基酸的代谢，赖氨酸降解，以及脂肪酸生物合成等途径，这些途径对啤酒风味有较大影响，研究结果为啤酒中风味物质的调控提供了一定的理论指导。     

如何降低啤酒的双乙酰含量

双乙酰是啤酒发酵的副产物,超过阈值,就会产生不愉快的馊饭味。所以在啤酒生产中,把双乙酰做为衡量啤酒成熟的一个重要指标。一、影响双乙酰生成的主要因素1.麦汁中氨基酸的含量及种类,缬氨酸     

使用亚硫酸和硫酸盐以提高麦芽质量的研究

众所周知,双乙酰会给啤酒带来馊饭味,一般要求其含量在0.2毫克/升以下,越少越好。缬氨酸能通过抑制α—乙酰乳酸的生成,反馈抑制双乙酰的生成。因此,增加麦汁中α—氨基态氮(FAN)含量,是减少啤酒中双乙酰含量的一个重要途径。要使麦汁中有足够的α—氨基态氮(FAN),最根本的办法是从提高麦芽质量着     

α-氨基氮对啤酒发酵过程中杂醇油生成的影响

探讨了α-氨基氮总量及缬氨酸、亮氨酸含量对啤酒发酵过程中杂醇油生成的影响。试验表明，当麦汁中α-氨基氮总量为180～200mg/L时，杂醇油的生成量最低。在α-氨基氮总量为l90mg／L的麦汁中，分别添加50mg／L的缬氨酸和亮氨酸，结果表明，添加缬氨酸的啤酒发酵液杂醇油生成量增加了24mg／L，而添加亮氨酸的啤酒发酵液杂醇油增加了51mg／L，此结果说明由亮氨酸形成异戊醇的途径是影响啤酒中杂醇油的主要因素之一。     

缩短露天罐发酵周期的探讨

啤酒企业要在不增加设备的投资情况下提高啤酒产量 ,创造最佳的经济效益 ,缩短发酵周期则是有效的途径。而控制双乙酰生成 ,加速双乙酰还原 ,是缩短发酵周期必须首先解决好的问题。可以从以下几个方面入手。１ 麦汁质量麦汁是酵母发酵的营养基液 ,是酵母所需氮源、碳源的提供体。麦汁组成是否合理 ,关系到酵母性能与发酵 ,代谢与啤酒最终质量。１ １麦汁中必须含有足够的α -氨基氮 ,以保证酵母生长对缬氨酸的需要及有效反馈抑制α -乙酰乳酸的过量生成。每升每度麦汁中α氨基氮的含量≥１５ｍｇ／Ｌ ,如１２°Ｐ麦汁≥１８０ｍｇ／Ｌ,１０…     

酶制剂及辅料比对高粱麦汁功能特性的影响

为考察酶制剂及高粱用量对麦汁功能特性的影响,以未发芽高粱为辅料进行糖化,在糖化过程中采用不同的原辅料比例,并添加不同的酶制剂及其组合,对所得麦汁的功能特性进行分析.结果表明,高粱用量的增加会使麦汁的浸出率,TSN、FAN、氨基酸、还原糖含量及过滤速度、粘度、色度降低,且pH值升高;α-耐高温淀粉酶能够明显降低糊化醪的粘度,提高麦汁浸出率;中性蛋白酶能够提高麦汁中TSN、FAN及氨基酸的含量;真菌α-淀粉酶在提高麦汁还原糖含量的同时,也能提高麦汁的过滤速度,且对过滤速度的影响和β-葡聚糖酶相似.     

糖化过程质量控制

本文阐述了糖化过程操作对质量的影响,着重阐述了麦汁过滤阶段高浊度麦汁的危害,和麦汁过滤操作要点。1麦芽粉碎麦芽粉碎对麦汁组成分、麦汁过滤速度以及提高原料利用率都非常重要。如为了追求麦汁得率将麦芽对辊间距调得很小,粉碎过细,会造成麦皮中有害物质过多浸出,同时会因糟层过紧出现过滤困难,这些都会对麦汁质量造成伤害。     

啤酒酵母代谢形成SO_2影响因素的研究

对酵母代谢形成SO2的影响因素从麦汁组成、糖化工艺以及发酵工艺3个方面进行了研究。通过对麦汁组成方面的研究表明,增加麦汁中蛋氨酸的含量可以减少酵母代谢产生的SO2,增加麦汁中的苏氨酸的含量可以促进酵母代谢形成SO2,麦汁中硫酸根含量的增加可以使酵母代谢形成SO2的量增加;通过对糖化工艺方面的研究可知,使用辅料会减少发酵时产生的SO2,在麦汁中添加Zn2+会增加发酵时产生的SO2;通过对发工艺方面的研究可知,提高麦汁的充氧量会减少SO2的产生,低的酵母接种量有利于SO2的生成,高浓发酵会使发酵后SO2的含量显著增加。     

平衡罐对麦汁过滤的影响及操作要点

采用平衡罐和变频泵送系统代替鹅颈阀和麦汁受皿器的过滤槽,能提高麦汁清亮度,缩短麦汁过滤时间。但在实际运行中,如平衡罐设计不合理,麦汁过滤操作不当反而会使过滤麦汁质量下降,过滤速度慢。本文就采用平衡罐和变频泵送系统过滤槽对麦汁过滤的影响进行简要分析。1 平衡罐工作原理麦汁过滤时,由泵抽送的滤出麦汁量和能通过麦糟层滤出的麦汁量要保持一致,若超过麦糟层滤出的滤出量,就会产生强烈的吸力而使悬浮于麦糟     

L-缬氨酸高产菌XQ-8补料分批发酵的研究

在分批发酵优化条件基础上,通过对补料分批发酵方式发酵过程的各种参数,包括产酸率、转化率和发酵周期等进行了研究,确定了L-缬氨酸高产菌XQ-8补料分批发酵的最优条件。在最优补料分批发酵条件下发酵72h左右,L-缬氨酸产量达72g/L,糖酸转化率达38%以上,其结果明显优于分批培养。     

The effect of vitamins A and E on the amino acid composition of proteins in different segments of the brain in aged animals]

The amino acids protein composition was studied in different segments of the brain in young (1.5 month old) and old (23-months) rats. The research covered also a short-lived action of vitamins A and E on the amino acids protein composition in the brain of 23-months old rats. The levels of the glutamic, aspartic acids, lysine, serine, of the sum of valine+methionine was found to be down, whereas the content of other amino acids proved invariable. After vitamins A and E loads the glutamic and aspartic acids in the brain segments under investigation was found to be up. In individual segments the content of lysine, thyrosine, valine+methionine experienced a certain normalization.     

Sorghum fermented kisra bread. I--Nutritive value of kisra

Kisra is a fermented sorghum bread which constitutes the staple diet of the Sudanese population. Kisra fermentation for three popular sorghum varieties was investigated. The objective was to determine the nutrient content as well as the amino acid pattern during this fermentation. The results indicated that there was a slight increase in protein content as a result of Kisra fermentation and an appreciable drop in starch. Total and non-reducing sugars decreased markedly at the commencement of the fermentation process; while crude fibre content increased. Threonine and lysine remained practically unchanged during Kisra fermentation. Tyrosine and methionine were enriched as a result of fermentation for all three sorghum varieties. Dabar and Fetirita Kisras were enriched in threonine and valine while in Mayo Kisra these amino acids decreased compared to the grain. Tyrosine content of Dabar Kisra improved but diminished in Fetirita Kisra.     

纸层析法测定缬氨酸含量的改良

改进了缬氨酸含量的测定方法。探讨了茚三酮与缬氨酸完全反应的质量分数范围;将传统的静置洗脱更改为匀速摇床洗脱,使洗脱更完全;在此基础上,详细研究了操作过程中的相关参数,使结果更精确。结果表明,该方法有很高的准确度和精密度,操作简便,成本低,可以广泛应用于茚三酮反应测定氨基酸。     

荔枝酒酿造过程中氨基酸的变化

利用高效液相色谱法(HPLC)对不同发酵温度的荔枝酒酿造过程中氨基酸含量的动态变化进行了分析研究。结果表明,荔枝汁和荔枝酒中均含有丙氨酸、苏氨酸、缬氨酸、谷氨酸、丝氨酸等14种氨基酸,其中,丙氨酸是荔枝汁和荔枝酒中的主体氨基酸,含量分别达1 139.682 mg/L、341.049～412.161 mg/L。不同发酵温度的荔枝酒酿造动态过程中,其游离氨基酸的种类和含量变化较大,且变化趋势各异。不同贮藏方式对荔枝酒中氨基酸含量和种类影响也不同。通过比较,发酵温度12℃优于15℃,发酵温度为15℃的荔枝酒中氨基酸含量在贮藏过程中变化幅度较大,不稳定,且影响风味的氨基酸较多。     

Nutritional studies on agadagidi

The analysis showed a gradual fall of the sugar content as fermentation period increased. Ascorbic acid content decreased while nitrogen and crude protein increased during fermentation. The predominant amino acids are leucine, lysine, valine, asparagine and glutamic acid, methionine, phenylalanine.     

山西老陈醋压醅后熟过程中微生物和风味物质的动态变化规律

该研究对山西老陈醋压醅后熟过程中醋醅的理化指标及微生物数量的动态变化规律进行研究。结果表明,在压醅后熟过程中,醋醅中总酸、不挥发性酸、氨基酸态氮和可溶性固形物含量呈上升趋势,还原糖、水分和总酯含量呈先上升后下降的趋势;细菌总数呈先上升后下降的趋势,酵母菌呈先下降后上升再下降的趋势,霉菌未检出;有机酸总量呈先增长后下降的趋势,压醅第3天含量达到最高值为（9.30±0.13） g/100 g,乙酸和乳酸为主体有机酸;共检测出80种挥发性风味物质,其中大部分风味物质含量呈下降趋势;与之相反,氨基酸含量则呈现上升趋势,与压醅第0天相比,压醅第5、6天氨基酸总量显著上升,最终氨基酸总量提高33.82%,其中,丙氨酸、谷氨酸、亮氨酸、缬氨酸为压醅过程中的主体氨基酸。     

Use of bacterial extracts to enhance amino acid breakdown in dry fermented sausages

The effect of the intracellular cell-free extracts (ICFEs) of two bacterial strains (Lactobacillus sakei GO and Bacillus pumilus) on the amino acid catabolism and the sensory properties of dry fermented sausages, was investigated. Extracts were added to sausages alone or in combination with a protease, papain. Amino acid breakdown was monitored by the changes in free amino acids, ammonia and amine content during the ripening process. A 15% decrease in the content of free amino acids was observed in sausages added with the ICFE from L. sakei GO. Furthermore, the extract of L. sakei GO significantly reduced (54-68%) the content of the amino acids considered as precursors of the typical ripened flavour, i.e., valine, leucine and isoleucine. Chemical changes were not reflected in a significant improvement of the sensory quality of sausages added with the ICFEs. The potential use of the bacterial ICFEs studied in the present work for the manufacture of dry fermented sausages, and its comparison with the use of fungal extracts, are discussed.     

Monitoring the ripening process of Cheddar cheese based on hydrophilic component profiling using gas chromatography-mass spectrometry

We proposed an application methodology that combines metabolic profiling with multiple appropriate multivariate analyses and verified it on the industrial scale of the ripening process of Cheddar cheese to make practical use of hydrophilic low-molecular-weight compound profiling using gas chromatography-mass spectrometry to design optimal conditions and quality monitoring of the cheese ripening process. Principal components analysis provided an overview of the effect of sodium chloride content and kind of lactic acid bacteria starter on the metabolic profile in the ripening process of Cheddar cheese and orthogonal partial least squares-discriminant analysis unveiled the difference in characteristic metabolites. When the sodium chloride contents were different (1.6 and 0.2%) but the same lactic acid bacteria starter was used, the 2 cheeses were classified by orthogonal partial least squares-discriminant analysis from their metabolic profiles, but were not given perfect discrimination. Not much difference existed in the metabolic profile between the 2 cheeses. Compounds including lactose, galactose, lactic acid, 4-aminobutyric acid, and phosphate were identified as contents that differed between the 2 cheeses. On the other hand, in the case of the same salt content of 1.6%, but different kinds of lactic acid bacteria starter, an excellent distinctive discrimination model was obtained, which showed that the difference of lactic acid bacteria starter caused an obvious difference in metabolic profiles. Compounds including lactic acid, lactose, urea, 4-aminobutyric acid, galactose, phosphate, proline, isoleucine, glycine, alanine, lysine, leucine, valine, and pyroglutamic acid were identified as contents that differed between the 2 cheeses. Then, a good sensory prediction model for “rich flavor,” which was defined as “thick and rich, including umami taste and soy sauce-like flavor,” was constructed based on the metabolic profile during ripening using partial least squares regression analysis. The amino acids proline, leucine, valine, isoleucine, pyroglutamic acid, alanine, glutamic acid, glycine, lysine, tyrosine, serine, phenylalanine, methionine, aspartic acid, and ornithine were extracted as ripening process markers. The present study is not limited to Cheddar cheese and can be applied to various maturation-type natural cheeses. This study provides the technical platform for designing optimal conditions and quality monitoring of the cheese ripening process.     

CHEMICAL COMPOSITION AND AMINO ACID CONTENTS OF BRAZILIAN BEANS (Phaseolus vulgaris)

SUMMARY— The chemical composition of 12 varieties of beans (Phaseolus vulgaris) was determined. Varieties most commonly found on Brazilian markets were chosen for this work. The average moisture content was 11%, ash 3.5%, fat 1%, protein 25%, starch 40%, crude fiber 4% and pentonsans 7%. The content of minerals in mg/100g sample was: phosphate 1000, iron 3.2, calcium 40 and magnesium 210. The content of essential amino acids in mg/g protein, calculated on a dry basis, was: lysine 72–106, threonine 46-61, valine 29–54, methionine 3–18, isoleucine 28-49, phenylalanine 33–118 and tryptophane 103-138. The product was rich in lysine and threonine as compared to the FAO table for essential amino acids require in the human diet. It was poor in methionine, isoleucine, valine, tryptophane and leucine.