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。     

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。     

酿酒酵母的基因育种及其应用

分析了双乙酰、高级醇低生成量酿酒酵母的基因育种及其应用 ,有助于今后工程菌种的科研开发和啤酒发酵工艺水平的提高     

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)     

浅论如何控制啤酒中的双乙酰

1　双乙酰在啤酒发酵过程中代谢机理双乙酰是连二酮类化合物的生物合成途径 ,一个分支点 ,如何有效地控制双乙酰及其相关物质的形成与清除 ,解决促进加速啤酒成熟 ,缩短发酵周期是极其关键重要环节。因为α -乙酰乳酸脱羧生成双乙酰的反应是一个非酶的氧化分解反应 ,此反应并不严格要求氧的存在 ,一些金属离子如铁铜等参与反应在无氧供给时其它电子供给体亦能促进氧化作用的进行。依靠活性酵母使双乙酰还原为口味界限值高的 2 ,3 -丁二醇。酵母代谢过程中会形成一定数量的α -乙酰乳酸 ,但在酵母细胞内的α -乙酰乳酸不会转化为双乙酰 ,而分…     

酿酒酵母苏氨酸合成酶缺失对高级醇生成量的影响

通过构建酿酒酵母苏氨酸合成酶基因(THR4)缺失的工程菌株,研究该基因对酿酒酵母高级醇生成量的影响。以质粒pUC-19为载体,KanMX抗性基因为筛选标记,构建了重组质粒pUC-TABK,经PCR扩增得到YAKanMX-YB重组盒,并以酿酒酵母AY15单倍体α5为出发菌株,通过醋酸锂转化和G418抗性筛选,获得THR4基因缺失的突变株α5-T7。将转化子和亲本菌株分别进行模拟酒精发酵及酒精浓醪发酵,发酵结束后进行发酵性能和高级醇生成量的测定。结果显示,与亲本菌株相比,突变株正丙醇生成量分别提高了1.61倍和2.6倍,异戊醇生成量分别提高了0.27倍和0.24倍,而异丁醇生成量没有明显差异,表明THR4基因缺失会使酿酒酵母高级醇特别是正丙醇生成量提高。     

酿酒酵母与球拟酵母混合发酵对白酒风味物质的影响

为研究球拟酵母在白酒发酵过程中对风味物质生成量的影响,将工业酿酒酵母AY15、高产酯酿酒酵母MY15分别以不同接种体积比、不同接种顺序与球拟酵母WY2进行混合发酵,以3种酵母单独接种发酵作为对照,检测其发酵过程中发酵性能、乙酸酯及高级醇生成量的变化。在不同接种体积比试验中,高产酯酿酒酵母和球拟酵母接种体积比为1∶2时,乙酸乙酯生成量达到351.65 mg/L,比MY15菌株纯种发酵提高27.78%,且发酵周期缩短至4 d。在不同顺序接种试验中,先接种酿酒酵母AY15和MY15,再接种球拟酵母,对应的乙酸乙酯生成量分别提高了24.55%和12.78%,而异戊醇生成量分别降低了10.58%和24.24%。结果表明,酿酒酵母与球拟酵母混合发酵时,球拟酵母对酿酒酵母的产酯能力具有强化作用,且不影响酿酒酵母的产酒精能力。     

纤维素酶及其在酒精工业中的应用

纤维素酶应用于发酵酒精工业可提高燃料酒精和白酒的出酒率、原料的利用率、缩短发酵时间.对纤维质原料制酒精的研究主要有酿酒酵母的合理运用和性能改良、发酵过程优化、提高利用率,降低成本等.克隆或原生质体融合技术可改良发酵菌株的纤维素酶基因,构建工程发酵酵母,提高纤维素的利用率,对产酒精具有广阔的发展前景.     

啤酒生产过程中双乙酰的控制

在发酵过程中，筛选分离提高双乙酰的酵母变异菌株，提高其对双乙酰的还原速率；提高发酵温度，增加通风搅拌，降低麦汁的pH值，以加速α－乙酰乳酸的分解速度；在主酵中添加α－乙酰乳酸脱羧酶、利用CO2洗涤、添加抗坏血酸（Vc)等控制双乙酰。（庞晓）     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Chlorohydrins of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) in canned foods and ready-to-drink coffees from the Japanese market

BADGE.2HCl and BFDGE.2HCl were determined in 28 samples of ready-to-drink canned coffee and 18 samples of canned vegetables (10 corn, 5 tomatoes and 3 others), all from the Japanese market. HPLC was used as the principal analytical method and GCMS for confirmation of relevant LC fractions. BADGE.2HCl was found to be present in one canned coffee and five samples of corn, BFDGE.2HCl in four samples of canned tomatoes and in one canned corn. No sample was found which exceeded the 1mg/kg limit of the EU for the BADGE chlorohydrins. However the highest concentration was found for the sum of BFDGE.2HCl and BFDGE.HCl.H₂O at a level of 1.5mg/kg. A Beilstein test confirmed that all cans containing foods contaminated with BADGE.2HCl or BFDGE.2HCl had at lest one part coated with a PVC organosol.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

European priorities for research to support legislation in the area of food contact materials and articles

A strong science base is required to underpin the planning and decision-making process involved in determining future European community legislation on materials and articles in contact with food. Significant progress has been made in the past 5 years in European funded work in this area, with many developments contributing to a much better understanding of the migration process, and better and simpler approaches to food control. In this paper this progress is reviewed against previously identified work-areas (identified in 1994) and conclusions are reached about future requirements for R&D to support legislation on food contact materials and articles over the next 5 or so years.     

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.     

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

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

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.