食品中腐败酵母的实时荧光PCR鉴定

为研究食品中腐败酵母实时荧光PCR快速鉴定方法,设计和筛选出了可用于腐败酵母鉴定的多条探针和引物,并建立了针对酿酒酵母、鲁氏接合酵母、斯巴达克毕赤酵母和布鲁塞尔德克酵母等4种腐败酵母菌的实时荧光PCR鉴定方法。用文中建立的方法对从糕点、蜂蜜、饮料等市售食品中分离出的60余株酵母菌进行了鉴定,发现其中4株为酿酒酵母,21株为鲁氏酵母,其他为与上述4种不同的酵母。以实时荧光PCR方法鉴定酵母,全过程仅需约3 h,与常用的生化鉴定方法相比,简化了鉴定步骤,提高了鉴定准确性,缩短了鉴定时间。     

Technical note: A comparison of methods to determine pH in silages

The techniques used to assess pH in silages vary greatly. The aim of this study was to evaluate the effects of water-to-sample ratio, extraction procedure, and standing time on pH determination. Silage samples (n = 20 for each silage) were chosen to represent diverse crops (corn, elephant grass, sugarcane, and forage peanut) to have a varied ensilability index and thus a wide range in final pH. Three water-to-sample ratios and 2 extraction procedures were used to measure pH at 0, 5, 10, 15, 30, 60, and 120 min of standing time. The ratios (undried silage to water) were 9:60, 25:100, and 30:270. The samples with the first 2 ratios were manually extracted, using a glass beaker and a glass stirring rod. The samples with the 30:270 ratio were extracted by using a stomacher blender for 4 min at 200 rpm. An electrode was used to perform pH readings. Dry matter (DM), water-soluble carbohydrates, and lactic acid concentrations were determined. The experimental design was completely randomized using a mixed repeated-measures model. Mean separation was performed using the Tukey test at P < 0.10 using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). The DM concentrations ranged from 24.5 to 40.2, 15.8 to 25.9, 26.9 to 30.6, and 17.8 to 21.4% for corn, elephant grass, sugarcane, and forage peanut silages, respectively. The lactic acid concentrations ranged from 2.9 to 10.1, 1.8 to 4.4, 0.7 to 11.4, and 0.3 to 1.4% of DM for corn, elephant grass, sugarcane, and forage peanut silages, respectively. The pH values measured by the 9:60 method were greater than other techniques at any standing times. The pH values from the 25:100 and 30:270 methods did not differ for elephant grass and forage peanut silages at any standing times. However, the 30:270 method had greater pH values for corn and sugarcane silages than the 25:100 technique at any standing times. The pH values measured by the 30:270 method did not vary for any of the silages according to standing time. Nevertheless, the pH values of the 25:100 method were greater from 0 to 10 min than for other standing times for all silages. Thus, for this method, there was pH stabilization from 15 min of standing time on. Overall, the 25:100 and 30:270 methods are recommended for assessment of silage pH. Fifteen minutes of standing time should be used for the 25:100 method but the pH reading can be performed immediately after mixing for the 30:270 technique.     

腐乳源酵母分离鉴定及其极性脂质分析

从豆腐酸浆及毛坯中鉴定了23个分离菌株,测定了其脂肪酶酶活并利用超高效液相串联质谱对其中7个菌株的脂质进行了分析。结果表明,指纹图谱中包含2种鞘氨醇、16种酰胺、22种酯类和3种脂肪酸。其中,马克斯克鲁维酵母SP-1和挪威毕赤酵母SP-5中植物鞘氨醇、N,N-二甲基鞘氨醇的相对含量最高。此外,嗜酒假丝酵母ATW-1、库德里阿兹威毕赤氏酵母SP-4和阿米塞毕赤氏酵母Y的酯类化合物比较丰富,且其细胞结合型脂肪酶酶活力也比较高,PCA分析进一步表明这3个菌株脂质组成具有较大的相似性,表明酵母菌中丰富的代谢酯类物质可能与细胞结合型脂肪酶之间存在密切联系。     

高温高湿地区偏高水分玉米的筒仓储藏试验

针对高温高湿地区筒仓中粮食储藏安全的问题,进行了偏高水分玉米控温的试验.结果表明:偏高水分玉米初春入仓后,应首先将粮食水分降至14.5％左右;然后启动内环流系统将内圈筒仓的粮温维持在20℃以下、外围筒仓维持在25℃左右;盛夏期间当偏高水分粮或杂质分级点引起局部发热时,可利用谷冷机进行降温散湿.另外,可将偏高水分玉米储于不受外部环境影响的内圈筒仓,配以加强入仓粮食清杂和提前进行预防性熏蒸等措施,以提高湿粮储藏的稳定性.     

Identification of yeasts isolated from wine-related environments and capable of producing 4-ethylphenol

The ability to produce 4-ethylphenol from the substrate p-coumaric acid in synthetic media was evaluated for several yeast species associated with wine production. Molar conversion rates as high as 90% were found by only Dekkera bruxellensis, D. anomala and by some unidentified strains isolated from wine-related environments. Other unidentified strains produced traces of 4-ethylphenol. All unidentified strains showed the same cultural characteristics as D. bruxellensis when grown on DBDM (Dekkera/Brettanomyces differential medium) agar. The determination of long-chain fatty acid compositions and the utilization of peptide nucleic acid (PNA) probes specific for D. bruxellensis showed that the unidentified strains did not belong to this species. Further identification, by restriction pattern generated from PCR-amplification of the 5.8S rRNA gene and the two internal transcribed spacers (ITS), assigned the unidentified strains to Candida cantarelli, C. wickerhamii, Debaryomyces hansenii, Kluyveromyces lactis and Pichia guilliermondii. However, only some strains of P. guilliermondii were capable of converting p-coumaric acid into 4-ethylphenol with efficiencies close to those observed in D. bruxellensis and D. anomala.     

Culture independent methods to assess the diversity and dynamics of microbiota during food fermentation

Culture independent methods first appeared in the food microbiology field at the end of the 90s and since then they have been applied extensively. These methods do not rely on cultivation and target nucleic acids (DNA and RNA) to identify and follow the changes that occur in the main populations present in a specific ecosystem. The method that has most often been used as a culture independent method in food microbiology is denaturing gradient gel electrophoresis (DGGE). The number of papers dealing with DGGE grew exponentially in the late nineties and, by analysing the studies available in the literature, it is possible to describe a trend in the subjects that have been investigated. DGGE was first used as a tool to monitor the ecology of fermented food, such as fermented sausage, cheese and sourdough, and later it also showed its potential in microbial spoilage process. In the last few years, the main application of DGGE has been to study fermented food from Asia, Africa and South America.     

Antimicrobial susceptibility of Staphylococcus aureus isolated from bovine mastitis in Europe and the United States

Minimum inhibitory concentrations were determined for 811 strains of Staphylococcus aureus isolated from cases of bovine mastitis in 11 countries. The countries and number of isolates included Denmark (105), England (92), Finland (95), Germany (103), Iceland (22), Ireland (42), Norway (101), Sweden (123), Switzerland (69), United States (53), and Zimbabwe (6). The antimicrobial agents tested were penicillin, ampicillin, oxacillin, cephalothin, ceftiofur, amoxicillin + clavulanate, penicillin + novobiocin, enrofloxacin, premafloxacin, erythromycin, clindamycin, lincomycin, pirlimycin, neomycin, lincomycin + neomycin, and sulfamethazine. The MIC90 for these antimicrobial agents for all strains were 0.5, 1.0, 1.0, 0.5, 1.0, < or =0.06, 0.125, 0.125, < or =0.0078, 0.5, 1.0, 16.0, 1.0, 2.0, 0.5, and 4.0 microg/ml, respectively. Overall, only small variations between countries were seen in the MIC90 for the majority of compounds tested. Of the strains tested, 35.6% were positive for beta-lactamase production on initial testing, with an additional 21.3% positive after induction by penicillin. In conclusion, the overall level of resistance was generally low for all antimicrobial agents tested regardless of country. Given the differences in antimicrobial use in various countries, the widespread adoption of mastitis control programs to prevent infections limits the exposure of S. aureus infected animals to antimicrobial drugs.     

Comparison of lactococcal bacteriophage isolated in the United States and Argentina

Bacteriophage of Lactococcus lactis ssp. lactis and ssp. cremoris, isolated in the United States and Argentina, were compared with respect to host range, adsorption, latent period, burst size and immunological cross-reactivity. Only 1 out of 13 U.S. culture isolates was sensitive to Argentinian phage. Argentinian L. lactis ssp. lactis C2 mutants were resistant to 13 U.S. phage isolates (4 prolate and 9 isometric). While Argentinian phage Stl-3 multiplied on U.S. culture isolate 59-1, low adsorption (38%) and insignificant burst size and latent period data were evident. Antisera prepared against U.S. phage D59-1 (prolate) and F4-1 (isometric) neutralized the lytic activities of all Argentinian prolate phage although the F4-1 antiserum was less effective. The data suggest homology especially between U.S. phage D59-1 and the Argentinian phage.     

Carotenoids of yeasts isolated from the Brazilian ecosystem

The carotenoid composition of pigmented yeasts isolated in Brazil was studied. The yeasts were cultured in yeast malt broth at 200 rpm, 25 °C, for 5 days, without illumination. Open column, thin layer and high performance liquid chromatography were used to separate, identify and quantify the carotenoids. The major pigments found in these yeasts were torulene and β-carotene. β-Carotene predominated in Rhodotorula graminis-125, Rhodotorula glutinis and Sporobolomyces roseus, while torulene was the principal carotenoid in Rhodotorula mucilaginosa. The yeast R. glutinis had the highest total carotenoid production (881 μg/l), followed by R. graminis (594 μg/l), Rhodotorula mucilaginosa-137 (590 μg/l), Rhodotorula mucilaginosa-108 (562 μg/l) and Rhodotorula mucilaginosa-135 (545 μg/l). Rhodotorula minuta and S. roseus had the lowest carotenoid contents (168 and 237 μg/l, respectively). In μg/g of dry cells, R. glutinis had a total carotenoid concentration of 132 μg/g.     

黄淮流域高水分玉米就仓干燥技术优化研究

以现行的国家储粮技术规范为基础,结合黄淮流域储粮生态和粮情,采用精准检测水分、合理布置风网、机械通风降水、倒仓平衡水分的方法,通过优化试验,解决了在具体的干燥实践过程中出现的粮食过度干燥,通风降水过程存在"瓶颈现象"造成干燥效果下降,以及粮堆各部位水分梯度较大等问题。     

Occurrence of non-lactic acid bacteria populations involved in protein hydrolysis of cold-stored high moisture Mozzarella cheese

The aim of this study was to analyse non-lactic acid bacteria populations (NLABPs) and evaluate their role in proteolysis of cold-stored high moisture (HM) Mozzarella cheese. NLABPs reached values close to 8 log cfu mL⁻¹ after seven days of cold storage. Sequencing of 16 rDNA and rpoB genes and molecular biotyping allowed to identify 66 bacterial strains belonging to 25 species from 15 genera, mainly represented by Pseudomonas, Acinetobacter, and Rahnella. Fifteen strains showed proteolytic activity values higher than 1000.00 μg Gly mL⁻¹ after 24 h of growth in skimmed milk. Moreover, as shown by Urea-PAGE, 11 proteolytic strains caused partial or total disappearance of at least one of the caseins. Their proteolytic behaviour was assessed even when they grew inside the governing liquid together with HM Mozzarella cheese at 4 °C for 12 days. This is the first report that throws light on the complexity of NLABPs in HM Mozzarella cheese, demonstrating that some strains caused the partial hydrolysis of α, β, and γ caseins on its outer surface where a concomitant wrinkling and successive exfoliation became visible without significant changes in texture characteristics.     

旋转通风干燥仓高水分玉米降水实验研究

采用自主研发的旋转通风干燥仓,进行高水分玉米降水工艺研究。实验期间,对仓内粮堆不同位置的温度和湿度,及环境温湿度进行定时监测,并定时取样检测玉米水分和真菌孢子。结果表明:粮堆中各监测点的温湿度随环境变化而变化,相同层或相同列的检测点温湿度基本一致;在有降雪的情况下(实验第6天,雨转雪),18天内玉米水分由27.12%降至14.60%;玉米携带真菌孢子数保持在真菌生长的临界范围内,达到短期安全储存目标。因此,采用旋转通风干燥仓对高水分玉米进行降水的工艺是可行的,降水效果均匀、高效,有效保证粮食不发热霉变。同时,旋转通风干燥的方法不使用燃煤、燃气,符合我国当前环境保护和可持续发展的新要求,有显著的经济社会效益,可在大农户玉米干燥和短期安全储存中推广应用。     

利用低场核磁分析玉米干燥过程中内部水分变化

采用低场核磁共振的横向弛豫时间(T_2)反演谱技术,研究了玉米在不同热风干燥温度下(60、75、90、105、120、135℃)内部水分的变化。干燥处理改变了玉米内部水分的迁移特性,使得与玉米淀粉相结合的结合水和仅次于自由水的结合水的自由度增加,玉米内部水分逐渐向外迁移,干燥速率随着干燥温度升高而渐增,干基含水率与核磁共振信号幅值之间存在十分显著的线性关系。     

豆腐乳中乳酸菌的分离鉴定与发酵特性研究

目的分离鉴定农家自制传统发酵豆腐乳中的乳酸菌,探讨其作为豆类乳酸菌发酵饮品菌株的可行性。方法利用MRS(man rogosa sharp)培养基分离豆腐乳中的乳酸菌,通过形态学观察、生理生化特性和16S rDNA基因序列分析进行鉴定,并将所分离到的乳酸菌与适合于豆类植物发酵的植物乳杆菌FJAT-7926(Lactobacillus plantarum FJAT-7926)和干酪乳杆菌FJAT-7928 (Lactobacillus casei FJAT-7928)进行发酵特性的对比研究。结果从豆腐乳中分离出1株乳酸菌,命名为FJAT-46777,该菌株菌体细胞为圆端直杆状或圆端弯曲杆状,无芽孢,革兰氏阳性,过氧化氢酶阴性,生理生化特征与发酵乳杆菌(Lactobacillus fermentum)一致,对菌株的16S rDNA基因进行扩增测序、分子系统发育树分析,也表明其为发酵乳杆菌。发酵乳杆菌FJAT-46777发酵的豆乳中乳酸菌增殖速度最快,最终活菌数最高,为9.42 lg(CFU/mL); pH值下降最快,最终pH值最低,为3.91;滴定酸度上升速度最快,最终滴定酸度最高,为62~ΟT。结论分离自豆类自然发酵食品中的发酵乳杆菌FJAT-46777,对豆类植物为主的基质具有更优良的发酵特性,发酵时间快,乳酸菌含量高,产酸能力强,适用于发酵豆乳的开发。     

草莓果酒酵母菌的筛选、鉴定及耐受性研究

从自然发酵的草莓果酒中分离得到野生酵母菌,根据其菌落形态特征、生理生化实验及酒精、二氧化硫、葡萄糖、pH的耐受性实验,筛选出性能最优2株菌株（RL4和RL6）进行分子生物学鉴定。结果表明,初步鉴定菌株RL4和RL6分别为Hanseniaspora thailandica和葡萄汁有孢汉逊酵母（Hanseniaspora uvarum）。该研究为草莓果酒研制提供了优良酵母菌。     

高酸度水果果酒酿造产酯酵母的鉴定及发酵特性研究

采用脱氧核糖核酸（DNA）鉴定比对、生长特性和耐受性实验对从蓝莓果皮及特香型白酒酒醅中筛选得到的6株产酯酵母进行菌种亲缘性鉴定和发酵特性比较。结果表明,6株产酯酵母（E1～E6）分别被鉴定为异常毕赤酵母（Pichia anomala）、库德里阿兹威毕赤酵母（Pichia kudriavzevii）、异常威克汉姆酵母（Wickerhamomyces anomalus）、光滑假丝酵母（Candida glabrata）、戴尔凯氏有孢圆酵母（Torulaspora.delbrueckii）和德巴利汉逊酵母（Debaryomyces hanseni）。通过发酵特性和耐受性实验分析发现,菌株E1（P. anomala）生长速度最快,发酵性能俱佳,总酯产量为3.71 g/L,且在酒精度9%vol、SO2质量浓度200 mg/L、pH 3.0及蔗糖含量＜70%的发酵液中都能有良好的生长状态,是一株蓝莓等高酸度水果果酒酿造的优良产酯酵母菌株。     

Incidence, concentration and effectiveness of malathion residues in wheat and maize (corn) exported from the United States

The incidence, concentration, and effectiveness of malathion treatments were measured in wheat and maize samples obtained from 79 port terminals in the United States. The presence of biologically active residue levels of malathion was inferred by bioassay assessment in 28% of 2058 wheat samples and in 8.4% of 2383 maize samples examined during the 2-year period, January 1977–December 1978. Malathion occurred most often in wheat from port terminals in the Pacific and Gulf regions where treatments were frequently part of the grain sale agreement and where grain was often treated immediately prior to sampling. At terminals where the grain was not treated just prior to sampling, the incidence of malathion on grain arriving at the ports was only 11.6% for wheat and 7.7% for maize.

Average malathion residues were 2.50 ppm in 210 samples of wheat and 1.03 ppm in 139 samples of maize and ranged from 2.71 ppm in Gulf wheat to 0.66 ppm in Pacific maize. Residues on wheat treated just prior to sampling, show inconsistent and generally inadequate malathion deposits resulting from port terminal treatments. No consistent relationship was evident between grain handling capacities and malathion residues.     

Comparison of the microflora isolated from spoiled cold-smoked salmon from three smokehouses

The microflora on spoiled, sliced and vacuum packed, cold-smoked salmon from three smokehouses was quantified and characterized in two independent experiments. Large variations in the microflora were observed both within (i.e. among vacuum packs from the same batch) and among the smokehouses. Lactic acid bacteria dominated the microflora, which reached 10⁷ cfu g⁻¹. Total viable counts of microorganisms alone were not related to quality, though spoilage characteristics were typical for microbiological spoilage. Among the lactic acid bacteria, Lactobacillus curvatus (ca 52–55%) was the most common species in both experiments with Lactobacillus saké, Lactobacillus plantarum, Carnobacterium spp. and Leuconostoc spp. present in smaller numbers. In some cases, large numbers of Enterobacteriaceae were also present and identified species were Serratia liquefaciens, Enterobacter agglomerans and Hafnia alvei. The microflora on cold-smoked salmon appeared to be related to the source of contamination i.e. the raw material and/or the smokehouse rather than being specific for the product, thus rendering the identification of the specific spoilage organisms difficult.