啤酒酿造中双乙酰的微生物代谢工程调控

双乙酰是啤酒中的重要风味物质，也是影响啤酒成熟和质量的关键因素之一。以酵母细胞内双乙酰的代谢途径和微生物代谢工程为基础，通过分析细胞内双乙酰的代谢网络，设计合理的重组DNA——增加ILV5和ILV3基因拷贝数，提高缬氨酸生产通量；改变ILV2基因，降低双乙酰的前驱物质α-乙酰乳酸的生成；构建含α-乙酰乳酸脱羧酶（ALDC）基因的工程菌；在啤酒发酵过程中外加α-乙酰乳酸脱羧酶制剂——以此来降低或阻断双乙酰的生成，从而缩短啤酒的发酵周期。本文综述了啤酒酿造中双乙酰的微生物代谢工程调控的研究进展。     

啤酒酿造中的双乙酰及其酶法控制研究进展

啤酒成熟的一个重要方面是啤酒风味物质的成熟,双乙酰是主要指标之一.双乙酰含量是成熟期的时间限制因子,双乙酰在啤酒罐装后的回升问题也不容忽视.啤酒酿造中控制双乙酰的一个主要方法是以α-乙酰乳酸脱羧酶来改变代谢支路,将双乙酰的前体物质α-乙酰乳酸直接快速地转化为乙偶姻,从而降低α-乙酰乳酸转变为双乙酰的量,缩短啤酒成熟时间,减少成品啤酒中双乙酰的回升,提高啤酒风味稳定性.本文主要介绍双乙酰的代谢途径、α-乙酰乳酸脱羧酶在啤酒酿造中降低双乙酰的作用机理以及国内外有关α-乙酰乳酸脱羧酶的研究进展情况.     

生物技术在控制啤酒中双乙酰含量方面的应用

双乙酰是啤酒中的重要风味物质，其含量是控制啤酒质量的一个重要指标。近年来许多生物技术广泛应用于啤酒生产，发酵过程中加入α-乙酰乳酸脱羧酶，可降低双乙酰的峰值和在酒液中的含量，缩短发酵时间。最适pH为6，最适温度为35～40℃。磁性固定化ALDC的应用可简单方便地与酒液分离，不影响啤酒风味，从而实现生产的连续化、自动化，缩短生产周期，大大降低生产成本。LLS催代酶的应用可促进双乙酰的还原、减少α-乙酰乳酸含量，防止双乙酰反弹。构建酵母工程菌株和选育低双乙酰产生的酵母菌，可构建低乙酰乳酸合成酶，催化丙酮酸和活性乙醛在胞内过量合成双乙酰的前体物质乙酰乳酸．从而降低双乙酰含量。(孙悟)     

啤酒中的双乙酰

双乙酰是啤酒中的风味物质，主要由前体物质α－乙酰乳酸在酵母细胞外经非酶氧化脱羧作用形成，然后在细胞内由酵母还原酶作用而消除。控制双乙酰含量的途径：减少α－乙酰乳酸的生成；加速α－乙酰乳酸的分解和双乙酰的还原。具体鬼话为：强化酵母质量管理；保证麦汁组成合理；保证发酵前期的发酵速度；保证后发酵的发酵速度；双乙酰还原阶段提高罐压；增强啤酒还原性。     

国产α—乙酰乳酸脱羟酶在啤酒生产中的应用

双乙酰的前驱物质是α-乙酰乳酸,在生产过程中添加α-乙酰乳酸脱羧酶可迅速降解α-乙酰乳酸,从而降低双乙酰含量,缩短发酵周期。通过两年来对进口和国产α-乙酰乳酸脱羧酶的试用比较,认为国产α-乙酰乳酸脱羧酶的使用效果完全可靠,能够替代进口同类酶制剂。     

温度对Zymomonas mobilis糖代谢关键酶活力和代谢流量的影响

以运动发酵单胞菌(Zynwmonas mobilis)ATCC31821为模式菌株,研究不同温度条件对其葡萄糖代谢关键酶活力的影响.采用全自动发酵罐,在整个发酵过程中通过充入氮气调节发酵液的溶氧量(DO)=0%,添加0.5mol/LNaOH溶液控制pH=5.5,发酵温度分别控制为25、30、35、40℃,发酵24h,测定其糖代谢网络中ED、HMP、TCA等途径的关键酶活力和代谢物成分.结果表明,在发酵温度为30～35℃时,乙醇脱氢酶(ADH)、葡萄糖-6-磷酸脱氢酶(G-6-PDH)、丙酮酸脱羧酶(PDC)、葡萄糖激酶(GK)、丙酮酸激酶(PK)和甘油醛-3-磷酸脱氢酶(GD-3-PDH)的活力较高,菌体的ED途径代谢活跃,碳素流量增加,乙醇生产量和糖转化率较高,而TCA途径的苹果酸脱氢酶(MDH)和异柠檬酸脱氢酶(ICDH)等活力较低,进入TCA途径的碳素流量明显减少;发酵温度为25、40℃时,TCA途径的酶活力升高,ED途径的酶活力减弱,生成乙醇的代谢流量减少,因此温度是z.mobilis发酵过程中调控菌体细胞生长和糖代谢的一个重要因素. 、葡萄糖-6-磷酸脱氢酶(G-6-PDH)、丙酮酸脱羧酶(PDC) 葡萄糖激酶(GK)、丙酮酸激酶(PK)和甘油醛-3-磷酸脱氢酶(GD-3-PDH)的活力较高,菌体的ED途径代谢活跃,碳素流量增加,乙醇生产量和糖转化率较高,而TCA途径的苹果酸脱氢酶(MDH)和异柠檬酸脱氢酶(ICDH)等活力较低,进入TCA途径的碳素流量明显减少;发酵温度为25、40℃时,TCA途径的酶活力升高,ED途径的酶活力减弱,生成乙醇的代谢流量减少,因此温度是z.mobilis发酵过程中调控菌体细胞生长和糖代谢的一个重要因素.葡萄糖-6-磷酸脱氢酶(G-6-PDH)、丙酮酸脱羧酶(PDC) 葡萄糖激酶(GK)、     

α-乙酰乳酸脱羧酶和α-氨基氮影响啤酒发酵中双乙酰产生的试验研究

通过对α-乙酰乳酸脱羧酶的加入与否，以及麦汁中α-氨基氮含量不同时对双乙酰产生情况的研究，结果表明：在发酵第2～12d的过程中，双乙酰变化呈现一定的规律性，在4d时达到峰值，同时α-乙酰乳酸脱羧酶的加入和高α-氨基氮含量的麦汁会减少双乙酰的产生量。     

酶共催化降低啤酒中双乙酰含量的研究设想

对啤酒生产工业中双乙酰的危害、生成机制和目前除去双乙酰的方法做了简要介绍。从实际角度出发，建设性提出了α－乙酰乳酸脱氢酶和葡萄糖氧化本 催化除去双乙酰的构想，并结合酶制剂本身性质和啤酒发酵工艺过程提出了这一构想的实现可能性。     

在不影响啤酒质量的情况下加速啤酒成熟

去除双乙酰是加速啤酒成熟的关键步骤，双乙酰是α—乙酰乳酸经非酶氧化脱羧而来。啤酒成熟的阶段就是酵母还原酶将双乙酰还原成乙偶姻的过程。往接种麦汁中加入α—乙酰乳酸脱羧酶是一个既简单又有效的限制双乙酰生成、加速啤酒成熟的方法。α—乙酰乳酸脱羧酶将α—乙酰乳酸直接转变成乙偶姻，并且没有生成双乙酰这个中间产物。最近食品和药物管理局(简称FDA)允许美国的酿造业使用α-乙酰乳酸脱羧酶。通过实验可以了解Maturex L的性质和实际使用效果。     

浅淡控制和预测双乙酰反弹

双乙酰是酵母发酵过程中的代谢产物之一 ,其含量已成为判断啤酒成熟的依据。目前 ,双乙酰的形成机理普遍认为是酵母合成缬氨酸的中间产物 ,α—乙酰乳酸的分解产物。各啤酒厂家根据各自经验、实际情况 ,选用适合酵母品种 ,调整麦汁组成和合理的发酵工艺 ,也有添加α—乙酰乳酸脱羧酶的 ,生产各自风格的啤酒 ,双乙酰还原已不成问题 ,但啤酒生产中双乙酰反弹却是不少厂家遇到的课题之一。双乙酰反弹指在贮酒期间或过滤灌装过程中双乙酰值回升 ,贮酒期间双乙酰反弹一般是污染引起的或二罐法生产啤酒 ,倒酒过程吸入氧 ,我公司现采用一罐法生产系…     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

Occurrence of bisphenol-F-diglycidyl ether (BFDGE) in fish canned in oil

The levels of bisphenol-F-diglycidyl ether (BFDGE) were quantified as part of a European survey on the migration of residues of epoxy resins into oil from canned fish. The contents of BFDGE in cans, lids and fish collected from all 15 Member States of the European Union and Switzerland were analysed in 382 samples. Cans and lids were separately extracted with acetonitrile. The extraction from fish was carried out with hexane followed by re-extraction with acetonitrile. The analysis was performed by reverse phase HPL C with fluorescence detection. BFDGE could be detected in 12% of the fish, 24% of the cans and 18% of the lids. Only 3% of the fish contained BFDGE in concentrations considerably above 1mg/kg. In addition to the presented data, a comparison was made with the levels of BADGE (bisphenol-A-diglycidyl ether)analysed in the same products in the context of a previous study.     

Contribution of European research to risk analysis

The European Commission's, Quality of Life Research Programme, Key Action 1—Health, Food & Nutrition is mission-oriented and aims, amongst other things, at providing a healthy, safe and high-quality food supply leading to reinforced consumer confidence in the safety of European food. Its objectives also include the enhancing of the competitiveness of the European food supply. Key Action 1 is currently supporting a number of different types of European collaborative projects in the area of risk analysis. The objectives of these projects range from the development and validation of prevention strategies including the reduction of consumers risks; development and validation of new modelling approaches; harmonization of risk assessment principles, methodologies, and terminology; standardization of methods and systems used for the safety evaluation of transgenic food; providing of tools for the evaluation of human viral contamination of shellfish and quality control; new methodologies for assessing the potential of unintended effects of genetically modified (genetically modified) foods; development of a risk assessment model for Cryptosporidium parvum related to the food and water industries; to the development of a communication platform for genetically modified organism, producers, retailers, regulatory authorities and consumer groups to improve safety assessment procedures, risk management strategies and risk communication; development and validation of new methods for safety testing of transgenic food; evaluation of the safety and efficacy of iron supplementation in pregnant women; evaluation of the potential cancer-preventing activity of pro- and pre-biotic ('synbiotic') combinations in human volunteers. An overview of these projects is presented here.     

低温带皮菜籽粕微粉的不同粒级部分的功能特性

为研究低温带皮菜籽粕微粉的不同粒级部分的功能特性,以经低温脱脂的带皮菜籽粕为原料,经微粉碎后筛分成212~425μm、150~212μm和106~150μm的3个不同粒级的微粉样品,检测这些样品的吸水性、吸油性、乳化性和乳化稳定性、蛋白质体外消化率。结果表明:1 3个不同粒级的微粉样品之间的粗纤维含量存在显著差异,表明三者的结构组成成分有一定差异。23个微粉样品的乳化活性和乳化稳定性随粒度级别的减小而显著增加(P0.01)。33个微粉样品的蛋白质体外消化率随粒度级别的减小而显著增加(P0.01)。4不同粒级带皮菜籽粕微粉样品的吸水性与吸油性受其结构组成物质不同和粒度的双重影响,与粒度的相关性不明显。     

Microbiology of food taints

Fresh and processed foods are often spoilt by the presence of undesirable flavours and odours caused by microbial action. The aim of this paper is to review the current knowledge of microbiologically induced taints that occur in a wide range of foodstuffs, including meats, poultry, fish, crustaceans, milk, dairy products, fruits, vegetables, cereals and cereal products. Examples have been chosen where the compounds responsible for the taint have been identified and sufficient data obtained to demonstrate the involvement of microorganisms. However, in some cases the full identity of the causative organism may not have been elucidated. The types of microorganisms covered by this review include bacteria, fungi, yeasts, actinomycetes and cyanobacteria. Although cyanobacteria do not in general infect foods, their presence in aqueous systems and water supplies can lead to off-flavours in aquatic organisms and processed foodstuffs. Several examples of each of these processes are discussed. Wherever possible, the likely biosynthetic pathway used by the microorganism to produce the offending compound in a foodstuff is indicated.     

Analysis for organic residues from aids to polymerization used to make plastics intended for food contact

Polymers intended for food contact use have been analysed for organic residues which could be attributed to a range of substances employed as polymerization aids (e.g. initiators and catalysts). A wide range of polymers was extracted with solvents and the extracts analysed by gas chromatography-mass spectrometry (GC-MS). The overwhelming majority of substances identified were not derived from aids to polymerization but were oligomers, additives and adventitious contaminants. However, a small number of substances were identified as initiator residues. These included tetramethylsuccinonitrile (TMSN) which was observed in two polymers and it derived from recombination of two azobisisobutyronitrile (AIBN) initiator radicals. Methyl benzoate, benzoic acid, biphenyl and phenyl benzoate were detected in one poly(methyl methacrylate) sample and in two polyvinylchlorides and they are thought to be derived from benzoyl peroxide initiator. TMSN was subsequently targeted for analysis of poly-(methyl methacrylate) plastics using proton nuclear magnetic resonance spectrometry (¹     

Tests of potential functional barriers for laminated multilayer food packages. Part II: Medium molecular weight permeants

Experiments were performed to characterize the kinetics of the permeation of different medium molecular weight model permeants: bisphenol A, warfarin and anthracene, from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick orientated polypropylene--OPP) into the food simulants olive oil and 3% (w/v) acetic acid. The characterization of permeation kinetics generally observed the permeation models previously reported to explain the experimental permeation results obtained for a low molecular weight group of model permeants. In general, the model permeants exhibited behaviour consistent with their relative molecular weights with respect to (a) the time taken to attain steady-state permeation into the food simulant in which they were more soluble, (b) their subsequent steady-state permeation rates, and (c) their partition between liquid paraffin and the OPP membrane.     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. I: Interlaboratory studies of methods of analysis

This paper describes the first part of a project undertaken to develop mussel reference materials for Paralytic Shellfish Poisoning (PSP) toxins. Two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin (STX) and decarbamoyl-saxitoxin (dc-STX) in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the second part of the project: the certification exercise. In the first study, 18 laboratories were asked to measure STX and dc-STX in rehydrated lyophilized mussel material and to identify as many other PSP toxins as possible with a method of their choice. In the second interlaboratory study, 15 laboratories were additionally asked to determine quantitatively STX and dc-STX in rehydrated lyophilized mussel and in a saxitoxin-enriched mussel material. The first study revealed that three out of four postcolumn derivatization methods and one pre-column derivatization method sufficed in principle to determine STX and dc-STX. Most participants (13 of 18) obtained acceptable calibration curves and recoveries. Saxitoxin was hardly detected in the rehydrated lyophilized mussels and results obtained for dc-STX yielded a CV of 58% at a mass fraction of 1.86 mg/kg. Most participants (14 out of 18) identified gonyautoxin-5 (GTX-5) in a hydrolysed extract provided. The first study led to provisional criteria for linearity, recovery and separation. The second study revealed that 6 out of 15 laboratories were able to meet these criteria. Results obtained for dc-STX yielded a CV of 19% at a mass fraction of 3.49mg/kg. Results obtained for STX in the saxitoxin-enriched material yielded a CV of 19% at a mass fraction of 0.34mg/kg. Saxitoxin could not be detected in the PSP-positive material. Hydrolysis was useful to confirm the identity of GTX5 and provided indicative information about C1 and C2 toxins in the PSP-positive material. The methods used in the second interlaboratory study showed sufficiently consistent analysis results to undertake a certification exercise to assign certified values for STX and dc-STX in lyophilized mussel.     

The Ministry of Environmental Protection Issued "Feasible Technology Guidelines for Pollution Prevention and Control in Wood Pulping Process of the Paper Industry (Trial)" and Two Other Guiding Technical Documents

On December 27t＂, 2013, the Ministry of Environmenta Protection announced that, in order to implement ＂The Environmental Protection Law of the People＇ s Republic of China＂, improve the working system in environmenta protection technologies, and promote technologica advancement in pollution prevention, the Ministry of Environmental Protection sponsored the formulation of three guiding technical documents including ＂Feasible Technology Guidelines for Pollution Prevention and Contro n Wood Pulping Process of the Paper Industry （Trial）＂     

1~(st) Intelli-Tissue~ EcoEc Tissue Machine Supplied by PMP Group Successfully Put into Operation in China

正On April 29th,2014,Intelli-Tissue EcoEc tissue machine supplied by PMP Group successfully put into operation at Hebei Xuesong Paper Co.,Ltd.,this is the first such kind of paper machine of PMP Group in China.