保加利亚乳杆菌浓缩培养的研究

对培养保加利亚乳杆菌的基础培养基进行筛选,确定为MRS培养基。然后优化培养条件:发酵时间为12h,起始pH值为5.80,发酵温度为40℃。最佳培养基:MRS培养基 7.5%番茄汁 12%麦芽汁 0.009mol/LCaCl2 2%乳清。通过中和试验,保加利亚乳杆菌菌体浓度可达到9.55×109mL-1。     

保加利亚乳杆菌冻干菌种的研究

对酸奶发酵菌种之一--保加利亚乳杆菌的增菌培养基进行了筛选,得到了高活菌数的保加利亚乳杆菌增菌培养基,并进行冷冻升华干燥得到保加利亚乳杆菌的冻干菌种。结果表明:在添加有10%麦芽汁、10%番茄汁、0.05%CaCO3、1.0%乳糖的MRS基础培养基中培养保加利亚乳杆菌18h后活菌数可达到3.96×1011cfu/g。其冻干菌种的活菌数为2.53×1011cfu/g。     

冻干保加利亚乳杆菌增菌培养基的筛选

本文采用正交实验对冻干保加利亚乳杆菌的增菌培养基进行了筛选,研究了保加利亚乳杆菌在增菌培养基中的活菌数及菌活力,以寻找冻干保加利亚乳杆菌发酵的最适收获期。结果表明:冻干保加利亚乳杆菌的增菌培养基为:MRS基础培养基、麦芽汁体积分数为10%、番茄汁体积分数10%、CaCO3的质量分数为0.05%、乳糖的质量分数为1.0%。保加利亚乳杆菌的最适收获期为发酵18h,此时为对数生长期后期,活菌数为3.96×1011cfu/g,OD值为0.922,菌活力为500T、pH4.46。增菌培养基增菌效果明显,经增菌培养基培养所得活菌数是基础培养基的202倍,且菌活力也较基础培养基强,OD值和滴定酸度分别是基础培养基的5.6倍和1.3倍。     

保加利亚乳杆菌菊芋复合汁增菌培养基的优化筛选

以菊芋为主要原料,以自行分离选育的高活力保加利亚乳杆菌(Lactobacillus bulgaricus)L.b-DR为试验菌株,研究了在菊芋汁培养基中添加单一营养因子对保加利亚乳杆菌L.b-DR细胞生长量的影响;利用正交试验优化筛选出保加利亚乳杆菌L.b-DR的菊芋复合汁增菌培养基。试验结果表明:在菊芋汁基础培养基中添加番茄汁、乳糖、蛋白胨、碳酸钙,可显著促进试验菌株的细胞生长(P<0.01);利用L934正交试验筛选出菊芋复合汁增菌培养基的最佳配比是:在菊芋汁培养基中添加7.5%番茄汁,1.5%乳糖,1%蛋白胨,0.3%碳酸钙。保加利亚乳杆菌L.b-DR经过复原脱脂乳培养基和液体MRS培养基活化后,以1%(约1×106cfu/mL)接入菊芋汁复合增菌培养基中,37℃培养16h,活菌数可达1.50×109cfu/mL,较对照菊芋汁培养基的活菌数提高23.96倍,与实验室常用的MRS培养基的活菌数相当,而其成本较实验室常用的液体MRS培养基的成本降低了2400元/t。     

不同菌种发酵绿茶对其茶多酚及咖啡碱含量影响的研究

分别以保加利亚乳杆菌、嗜热链球菌、嗜酸乳杆菌三种菌种为生产菌株,以脱脂乳为培养基,茶汁添加量分别为20%、30%、40%.在37℃恒温条件下经6、12、18、24、36、48h发酵后,以紫外分光光度法测定其中茶多酚以及咖啡碱的含量.当茶汁添加量为30%,以保加利亚乳杆菌发酵12～18h时,培养基中茶多酚含量的增加速率最快.当茶汁添加量为30%,以嗜酸乳杆菌发酵12～18h时,咖啡碱含量达最大值.     

提高保加利亚乳杆菌抗冷冻性的研究

保加利亚乳杆菌(Lactobacillus bulgaricus)L.b-DR经脱脂乳培养基和MRS培养基活化、菊芋汁复合培养基培养、离心收获菌体,以12%脱脂乳作为冷冻保护剂,进行了冷冻试验。研究了在培养基中添加活性成分、培养基的起始pH值、培养温度、细胞收获的菌龄、保护剂的pH值对细胞冷冻存活率的影响。结果表明:在菊芋汁复合培养基中添加0.1%甘油或0.5%VE、培养基的起始pH值为6.0、37℃培养、对数末期或稳定初期收获菌体、保护剂pH值调至6.0,可显著提高保加利亚乳杆菌L.b-DR的冷冻存活率(P<0.05)。     

乳酸菌培养基-菠萝皮汁与MRS的对比试验

以植物乳杆菌为发酵菌种,对菠萝皮汁和MRS两种培养基进行了对比试验,结果表明:植物乳杆菌在两种培养基中的生长速度、产酸能力和最大活茵数在方面均无显著性差异,菠萝皮汁替代MRS培养基作为乳酸菌发酵培养基具有可行性.     

酸奶中保加利亚乳杆菌的分离和鉴定

利用MRS琼脂培养基对保加利亚乳杆菌进行分离，分别挑取可疑茵落进行革兰氏染色，对镜检结果为革兰氏阳性菌，且细菌形状为杆状的菌种进行糖发酵试验生物化学鉴定。结论：在MRS琼脂培养基上，菌落较大、透明、灰白色，镜检细菌形状为杆状，麦芽糖和七叶苷发酵试验均为阴性，乳糖发酵阳性的菌种，即为保加利亚乳杆菌。     

酸乳中混合乳酸菌的分离及鉴定

利用MRS琼脂培养基和Elliker琼脂培养基分别对保加利亚乳杆菌和嗜热链球茵进行分离.然后,分别挑取疑似茵落进行革兰氏染色,对镜检结果为革兰氏阳性茵,且细茵形状为杆状和球状的菌种进行生物化学鉴定.采用糖发酵试验进行生化鉴定.对保加利亚乳杆茵进行麦芽糖、七叶苷、乳糖、蔗糖和葡萄糖5种糖的发酵试验,而对于嗜热链球菌进行葡萄糖、麦芽糖和蔗糖的发酵试验.而后,对葡萄糖、蔗糖发酵阳性,麦芽糖发酵阴性的菌种进行45℃培养.结论表明:在MRS琼脂培养基上,茵落较大、透明、灰白色,镜检细菌形状为杆状,麦芽糖和七叶苷发酵试验均为阴性,乳糖发酵阳性的茵种,即为保加利亚乳杆菌.在Elliker琼脂培养基上分离出的菌种,镜检细菌形状为球状.葡萄糖、蔗糖发酵呈阳性,麦芽糖发酵阴性且能在45℃条件下生长的茵种即为嗜热链球茵.     

乳酸菌增菌培养基的营养因子优化

以改良MRS发酵培养基为基础,选择玉米浆、牛肉膏、乳糖、番茄汁、眎蛋白胨等7个营养因子增菌培养乳酸菌进行优化。利用L8(27)正交实验,优化出培养基营养因子最佳组成是:玉米浆3%、牛肉膏1%、乳糖1%。研究结果表明,嗜酸乳杆菌、嗜热链球菌、保加利亚乳杆菌、嗜酸乳酸菌,在优化后的MRS培养基发酵液中,37℃培养20 h,菌落数均高于原MRS培养基发酵液的菌落数,达到109cfu/mL以上,乳酸菌发酵液得到了浓缩,大大降低了乳酸菌发酵培养基的成本,原料成本降低了约40%。     

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.     

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.     

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.     

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.