Characterization of psychrotrophic bacterial communities in modified atmosphere-packed meat with terminal restriction fragment length polymorphism

Characterization of psychrotrophic lactic acid bacteria (LAB) and Brochothrix thermosphacta communities is needed to understand the microbial ecology of spoilage of modified atmosphere-packed (MAP) meats. To overcome the limitations of the currently used methods for the characterization of psychrotrophic bacterial communities in meat, we developed a culture-independent, 16S rRNA gene-targeted terminal restriction fragment length polymorphism (T-RFLP) method. An identification library consisting of 100 Gram-positive and 30 Gram-negative meat-associated bacterial strains was set up to identify the terminal restriction fragments derived from the communities. The taxonomic resolution level of the T-RFLP method was in between genus and species within the investigated LAB strains and within family and genus within the investigated Gram-negative strains. The established library was applied to identify the members of bacterial communities in MAP minced meat at the end of the shelf life. The T-RFLP results and plate counts on Man-Rogosa-Sharpe, Violet Red Bile Glucose, and Streptomycin sulfate thallium acetate actidione agars indicated that LAB and B. thermosphacta predominated in meat. The bacterial taxa associated with the T-RFLP results were compared to those identified among plate-grown LAB isolates by numerical ribopattern analysis. Both methods agreed that Leuconostoc spp. and Carnobacterium spp. prevailed in the LAB community in minced meat followed by Lactobacillus algidus, Lactococcus spp. and Weissella spp. Colony identification revealed that Leuconostoc gasicomitatum, L. gelidum, Carnobacterium divergens and C. maltaromaticum were the predominant LAB species. The T-RFLP results were shown to correlate with viable counts of Leuconostoc spp. and B. thermosphacta. The T-RFLP method was found to be a useful tool enabling rapid and high-throughput characterization of psychrotrophic bacteria prevailing in MAP meat.     

助剂LAB在羊毛/涤纶混纺织物分散染料一浴法染色中的应用

研究了助剂LAB对分散染料染羊毛／涤纶混纺织物一浴法中上染率、染色牢度和同色性等的影响。实验结果表明：同常规染色方法相比，具有节约成本和湿牢度好等优点，是值得进一步研究的毛／涤混纺织物染色 新工艺。     

直投式泡菜乳酸菌发酵剂培养基的优化及离心条件的探索

根据番茄汁、马铃薯汁和胡萝卜汁的营养条件和乳酸菌的营养要求,通过正交试验,确定泡菜用肠膜明串珠菌和乳酸乳球菌的最佳培养基。试验结果为:肠膜明串珠菌的最佳培养基为:30%番茄汁、25%马铃薯汁、10%胡萝卜汁;乳酸乳球菌的最佳培养基为:25%番茄汁、35%马铃薯汁、15%胡萝卜汁。结果表明:肠膜明串珠菌和乳酸乳球菌分别以此培养基在34℃下培养24 h,其活菌数可达109cfu/mL以上,大大降低了培养基的成本。选择的最佳离心条件为:4 000 r/min的转速下离心20 min,在此条件下离心存活率最高,为制备直投式发酵剂提供了理论依据。     

8种乳酸菌发酵荔枝汁-大豆蛋白的氨基酸代谢特征研究

本文目的在于探究8种乳酸菌发酵荔枝汁-大豆蛋白的氨基酸代谢差异,分析不同乳酸菌的氨基酸代谢特征。本研究以荔枝汁-大豆蛋白为培养基,选择8种乳酸菌在37 ℃温度下培养18 h,测定发酵前后乳酸菌发酵液活菌数及氨基酸含量。结果表明,发酵前后共检测到17种氨基酸,发酵后氨基酸总量从582.79 mg/100 g下降至427.97 mg/100 g。不同乳酸菌发酵后的氨基酸总量差异明显,副干酪乳杆菌FJAT-13741(365.95 mg/100 g)<嗜热链球菌FJAT-43774(369.36 mg/100 g)<发酵乳杆菌FJAT-13771(411.03 mg/100 g)<植物乳杆菌FJAT-13737(417.54 mg/100 g)<短乳杆菌FJAT-43776(438.14 mg/100 g)<鼠李糖乳杆菌FJAT-13807(462.38 mg/100 g)<嗜酸乳杆菌FJAT-13772(477.65 mg/100 g)<德氏乳杆菌FJAT-43773(481.52 mg/100 g)。聚类分析结果显示,8种乳酸菌的氨基酸代谢特征分为3组,高含量组含1种氨基酸、中含量组含5种氨基酸、低含量组含11种氨基酸;根据氨基酸含量,8种乳酸菌可分为三类,高含量组含3种乳酸菌,中含量组含3种乳酸菌,低含量组含2种乳酸菌。进一步构建了乳酸菌的氨基酸代谢特征指数(AAMCI),表示功能性氨基酸占氨基酸总量的比值,其中比值最高的为德氏乳杆菌FJAT-43773(54.32%),最低的为嗜热链球菌FJAT-43774(47.82%)。研究结果将为荔枝乳酸菌饮品研制菌株的筛选提供理论依据。     

A novel bacteriocin against Staphylococcus aureus from Lactobacillus paracasei isolated from Yunnan traditional fermented yogurt: Purification,antibacterial characterization,and antibiofilm activity

Staphylococcus aureus and its biofilm have emerged as a significant threat to the safety of dairy products. In recent years, lactic acid bacteria (LAB) bacteriocins have been widely acknowledged as the potential natural antibacterial substance in food biopreservation due to their excellent antibacterial effects. However, few LAB bacteriocins with antibacterial and antibiofilm activity against S. aureus have been reported in dairy products. In the present study, a novel bacteriocin LSX01 of Lactobacillus paracasei LS-6 isolated from a traditional fermented yogurt produced in Yunnan, China, was purified and characterized extensively. The LSX01 possessed a molecular weight of 967.49 Da and an AA sequence of LDQAGISYT. The minimum inhibitory concentration of LSX01 against S. aureus_45 was 16.90 μg/mL, which was close to or lower than the previously reported bacteriocins. The LSX01 exhibited an extensive antimicrobial spectrum against both gram-positive and gram-negative bacteria. Moreover, LSX01 exhibited excellent tolerance to heat and acid-base treatments, and sensitivity to the proteolytic enzymes, such as pepsin and proteinase K. Furthermore, the treatment of S. aureus_45 planktonic cells with LSX01 significantly reduced their metabolic activity and disrupted the cell membrane integrity. Scan electron microscopy results demonstrated that LSX01 induced cytoplasmic content leakage and cell deformation. Additionally, biofilm formation of S. aureus_45 was also significantly inhibited by LSX01. Overall, the results suggested that the novel LAB bacteriocin LSX01 possessed antibacterial activity and antibiofilm activity against S. aureus and, hence, could have potential for improving safety of dairy products.     

16S rRNA基因序列方法分析传统发酵菜中乳酸菌多样性

以发酵甘蓝卤水中微生物的总DNA为模板,用扩增革兰氏阳性菌16S rRNA基因的方法研究中国发酵甘蓝菜卤中乳酸菌的多样性。获得了42种含有1.5kb的16S rRNA基因插入核苷酸片段的克隆菌。利用克隆菌落核苷酸的部分序列和NCBI数据库中搜索到的相似序列进行对比后作出鉴定,结果得出4种独特的菌落,鉴定为Lactobacillus acidifarinae、植物乳杆菌(Lactobacillus Plantarum)、融合乳杆菌(Weissella confusa)和足球菌属(Pediococcus sp.)。此外,还发现两种非核糖体序列。用这种分子方法发现了常规分离培养技术未鉴定的乳酸菌,如Lactobacillus acidifarinae。     

Taxonomic and molecular characterization of lactic acid bacteria and yeasts in nunu,a Ghanaian fermented milk product

Produced from raw unpasteurized milk, nunu is a spontaneously fermented yoghurt-like product made in Ghana and other parts of West Africa. Despite the importance of nunu in the diet of many Africans, there is currently only limited information available on the microorganisms associated with nunu processing. With the aim of obtaining a deeper understanding of the process and as a first step towards developing starter cultures with desired technological properties for nunu production, a microbiological characterization of nunu processing in three different towns in the Upper East region of Ghana, namely Bolgatanga, Paga and Navrongo, was carried out. Lactic acid bacteria (LAB) and yeasts associated with nunu processing were isolated and identified using a combination of pheno- and genotypic methods including morphological and carbohydrate fermentation tests, (GTG)₅-based rep-PCR, multiplex PCR, and 16S and 26S rRNA gene sequencing. The LAB counts during nunu processing increased from 4.5 ± 0.4 log cfu/ml at 0 h to 8.7 ± 1.8 log cfu/ml at 24 h of fermentation while yeasts counts increased from 2.8 ± 1.2 log cfu/ml at 0 h to 5.8 ± 0.5 log cfu/ml by the end of fermentation. Lactobacillus fermentum was the dominant LAB throughout the fermentations with Lactobacillus plantarum and Leuconostoc mesenteroides playing prominent roles during the first 6–8 h of fermentation as well. Less frequently isolated LAB included Lactobacillus helveticus, Enterococcus faecium, Enterococcus italicus, Weissella confusa and a putatively novel Lactococcus spp. The yeasts involved were identified as Candida parapsilosis, Candida rugosa, Candida tropicalis, Galactomyces geotrichum, Pichia kudriavzevii and Saccharomyces cerevisiae with P. kudriavzevii and S. cerevisiae being the dominant yeast species.     

Comparison of the anti‐obesity and hypocholesterolaemic effects of single Lactobacillus casei strain Shirota and probiotic cocktail

This study compared the efficacy of Lactobacillus casei strain Shirota (LAB13) and a probiotic cocktail for their anti‐obesity and other lipid profile modulating effects. Diet‐induced obese rats were supplemented with two different probiotics which are LAB13 (1 × 10⁹ CFU day^?1 per rat) and cocktail of five bacterial strains (1 × 10⁹ CFU day^?1 per rat) for 12 weeks. Comparative data on weight gain, energy intake, liver weight, subcutaneous fat, total fat weights, total cholesterol and leptin levels in both treatment groups showed significant reduction in probiotic‐treated groups compared to the obese control group. Both probiotics have the anti‐obesity and hypocholesterolaemic effects and are able to reduce body weight and fats via reduction in energy intake. Only LAB13 was able to reduce the level of triglyceride significantly. Therefore, the LAB13 is equally effective compared to the probiotic cocktail in weight reduction. LAB13 is more effective in improving lipid profile which is a common medical complication of obesity.     

Source Tracking and Succession of Kimchi Lactic Acid Bacteria during Fermentation

This study aimed at evaluating raw materials as potential lactic acid bacteria (LAB) sources for kimchi fermentation and investigating LAB successions during fermentation. The bacterial abundances and communities of five different sets of raw materials were investigated using plate‐counting and pyrosequencing. LAB were found to be highly abundant in all garlic samples, suggesting that garlic may be a major LAB source for kimchi fermentation. LAB were observed in three and two out of five ginger and leek samples, respectively, indicating that they can also be potential important LAB sources. LAB were identified in only one cabbage sample with low abundance, suggesting that cabbage may not be an important LAB source. Bacterial successions during fermentation in the five kimchi samples were investigated by community analysis using pyrosequencing. LAB communities in initial kimchi were similar to the combined LAB communities of individual raw materials, suggesting that kimchi LAB were derived from their raw materials. LAB community analyses showed that species in the genera Leuconostoc, Lactobacillus, and Weissella were key players in kimchi fermentation, but their successions during fermentation varied with the species, indicating that members of the key genera may have different acid tolerance or growth competitiveness depending on their respective species.     

乳酸菌代谢工程的研究与应用

综述了乳酸菌代谢工程的研究与应用，阐述了利用基因工程技术改良乳酸菌发酵剂产双乙酰能力、蛋白质水解能力、胞外多糖的合成能力以及抗杂菌病原菌污染能力4个方面的最新研究进展。