藏北地区传统发酵乳中乳杆菌的多样性分析

摘要：【目的】针对藏北地区的乳杆菌来源及种属,对其多态性进行研究。【方法】采用ERIC-PCR技术和NTSYS-pc2.1软件对从藏北地区牧民家庭制作的发酵乳制品中分离出的77株乳杆菌进行多样性分析。【结果】ERIC-PCR扩增出的条带清晰,重复性好,多态性高。聚类分析表明,在0.73的水平上,77株乳杆菌共分为4大类群：干酪乳杆菌群A1、发酵乳杆菌群A2,瑞士乳杆菌群A3和植物乳杆菌群A4。其中,干酪乳杆菌群A1和发酵乳杆菌群A2分别占供试乳杆菌的35.06%和61.04%,为优势菌群。进一步对优势菌群     

Lactobacilli and dairy propionibacterium with potential as biopreservatives against food fungi and yeast contamination

Naturally fermented and raw foods contain a range of organisms that may have benefit as additives in some foods and food processing. In particular, potential antifungal properties of these organisms may be potentially utilised as natural alternatives to chemical additives used to delay and prevent spoilage by fungi and yeast. This study examined 12 novel bacteria previously isolated from food as possible biopreservatives. The bacteria from the lactobacilli and dairy propionibacterium groups were tested by agar overlay method for their ability to inhibit the growth of 10 fungi and one yeast commonly associated with food contamination. Eight among eleven tested lactic acid bacteria demonstrated broad spectrum of antifungal activity. Strong fungi inhibition was also demonstrated by the dairy propionibacterium, but efficacy was growth medium dependant. Only one fungi, Geotrichum candidum was highly resistant to the bacteria. Variation between the inhibition results for different bacteria identifies the importance of careful strain selection, and the benefits of strain combinations when selecting biopreservatives for foods. The article is published in the original.     

Occurrence of molds and yeasts in dairy products

Summary In the search for additional techniques for determining fungal populations of dairy products, 23 species of filamentous fungi and 25 species of yeasts were recovered from a variety of raw, pasteurized, and processed dairy products. The usefulness of media containing rose bengal and antibiotics is indicated. The occurrence of a number of the species found is discussed together with some of the results of physiological studies of yeasts used in species characterization.     

Bacteriophages in dairy products: pros and cons

Since the time bacteriophages were first identified as a major cause of fermentation failure in the dairy industry, researchers have been struggling to develop strategies to exclude them from the dairy environment. Over 70 years of research has led to huge improvements in the consistency and quality of fermented dairy products, while also facilitating an appreciation of the beneficial properties of bacteriophages with respect to dairy product development. With specific reference to Lactococcus lactis and cheese production, this review outlines some recently reported novel methods aimed at limiting the bacteriophage infection as well as highlighting some beneficial aspects of bacteriophage activity.     

Fate of aflatoxin B-1 in fermented dairy products

Polyacrylamide gel electropheresis and thin layer chromatography (TLC) were applied to detect the fate of aflatoxin B-1 in milk fermented with an active culture of Streptococcus lactis (ATCC-11454).TLC analysis revealed the formation of two fluorescent metabolites (B₂a and R₀) in fermented milk.Electropheretic analysis of both casein and whey protein showed fluorescent bands in the region of Kappa-casien and immunoglobulin which are glycoproteins in nature. The transformation of B-1 to the nontoxic metabolite B₂a and the less toxic compound aflatoxicol (R₀) reflects the preference for fermented dairy products in consumption in order to reduce chances of toxicity.     

Biodiversity of lactic acid bacteria in Romanian dairy products

Traditionally fermented dairy products are still a very important part of the daily food in Romania, especially for people living in the countryside. To study the biodiversity of lactic acid bacterium strains of these products, 110 samples (raw and fermented milk, sour cream, and cheese) were collected from farm houses, monasteries, and local markets throughout Romania. Lactic acid bacteria (LAB) were isolated using six different cultivation conditions. All 599 isolates were tested for their Gram reaction, catalase activity, and morphology. A rep-PCR fingerprinting technique with the (GTG)5 primer and, in some cases SDS-PAGE of total cell proteins and 16S rRNA gene sequencing were used to cluster and/or identify the LAB. The biodiversity of the isolated strains was correlated with the type of product and/or technology applied. The most frequent LAB found in Romanian raw milk and fermented dairy products were Lactococcus lactis, Leuconostoc spp., and Enterococcus spp. Among the latter, a new species E. saccharominimus was found.     

Lactobacilli isolated from vaginal vault of dairy and meat cows during progesteronic stage of estrous cycle

Lactobacilli have been barely studied in cows. We proposed isolate and characterize lactic acid bacteria from dairy cows as compared to those raised for meat production and elucidate the presence of strains with evident probiotic employment's potential. For this, isolation and quantification of LAB mainly lactobacilli were realized from vaginal cattle samples in MRS medium. Each selected microorganism was then briefly characterized. The MATH method was employed using hexadecane, xilene an toluene as solvent. According to the hydrophobic characteristics, strains were classified into three categories: high (71-100%), medium (36-70%) and low (0-35%). Hydrogen peroxide qualitative production was studies too, lactobacilli were streaked onto an MRS agar plate containing 5 mg of 3,3',5,5'-tetramethylbenzidine and 0.20 mg of horseradish peroxidase. Twenty-one sampled cows (78%) were positive for lactic acid microflora, 12 belonging to the dairy group and 17 of the meat group. Total LAB counting including dairy and meat cows were log 2,41 CFU/ml. Of overall identified strains, an 83% corresponded to lactobacilli. Most strains belonged to the heterofermentative facultative group (75%), with L. plantarum as the most frequent specie. The highest proportion of isolated vaginal strains (69%) had low hydrophobicity, the LAB with highest hydrophobic characteristics (3 strains) were found only in meat cows. In the qualitative evaluation of H(2)O(2) production, a positive reaction was observed in 13 of 29 strains (45%). The role of lactobacilli in vaginal microbiota is limited, and therefore the present work is interesting in incorporate knowledge of normal microflora of progesteronic healthy cows, in this case in production animals. The isolation and characterization data obtained are consistent in consider the study of particular strains with great potential in the development of a probiotic for production cows.     

Lactobacilli on Plants

The distribution, enumeration, and identification of lactobacilli on vegetable plants were studied in an area described geographically as being subtropical and moist. The lactobacilli were obtained, by means of quantitative enrichment procedures in Rogosa''s SL broth, from 35.3% of all samples incubated at 32 C, and from 15.4% of the samples incubated at 45 C. Less than 10 lactobacilli/g of plant material were enumerated in 54% of all positive samples. The lactobacilli were found much less frequently and in lower numbers than were streptococci or Leuconostoc mesenteroides. The most frequently isolated lactobacillus was very simular to, but not identical with, Lactobacillus fermenti. It was aerogenic, grew well at both 15 and 45 C, fermented arabinose, lactose, and sucrose, and liberated ammonia from arginine. Of the identified species, L. plantarum, L. fermenti, and L. brevis were the most frequently isolated, whereas L. casei, L. viridescens, L. cellobiosus, L. salivarius, and L. buchneri were obtained from small numbers of samples. The widespread but sporadic distribution of lactobacilli in low numbers seems to indicate that these organisms do not normally thrive on plant surfaces. A ternary cycle, beginning with intestinal waste, followed by mechanical distribution to and among plants, and return to the host via the oral cavity, is suggested.     

Membrane filtration of dairy products for microbiological analysis

Incubation with protease or Tween 80 or both dramatically improved the membrane filterability of liquid milks, powdered skim milk, and frozen dairy products without reducing the viability of five common species of bacteria. The technique can permit isolation and enumeration of microorganisms from test samples of these foods as large as 5 g. Flow direction through the filter was an important factor in filterability of dairy products.     

Promotion of Autolysis in Lactobacilli

The conditions of promotion of autolysis of three strains of Lactobacilli were investigated. The autolysis of L. acidophilus, L. helveticus and L. casei at exponential phase was remarkably enhanced by freezing storage at ?20°C overnight.

The turbidity decrease of L. acidophilus’ cell suspension corresponds to the increase of cell free nitrogen compounds, glucosamine and DNA component. All these compounds were more rapidly released from the cells stored at ?20°C than those stored at 3°C. The cells which were harvested at the exponential phase had higher autolytic activity than those at stationary phase. The storage of the cells at ?20°C for 2 days or more could effectively promote the autolysis.

The activity was increased by Ca²⁺ or Mg²⁺. Optimum pH of the autolytic enzyme of L. acidophilus was 6~7.     

Lactobacilli on Plants

The distribution, enumeration, and identification of lactobacilli on vegetable plants were studied in an area described geographically as being subtropical and moist. The lactobacilli were obtained, by means of quantitative enrichment procedures in Rogosa's SL broth, from 35.3% of all samples incubated at 32 C, and from 15.4% of the samples incubated at 45 C. Less than 10 lactobacilli/g of plant material were enumerated in 54% of all positive samples. The lactobacilli were found much less frequently and in lower numbers than were streptococci or Leuconostoc mesenteroides. The most frequently isolated lactobacillus was very simular to, but not identical with, Lactobacillus fermenti. It was aerogenic, grew well at both 15 and 45 C, fermented arabinose, lactose, and sucrose, and liberated ammonia from arginine. Of the identified species, L. plantarum, L. fermenti, and L. brevis were the most frequently isolated, whereas L. casei, L. viridescens, L. cellobiosus, L. salivarius, and L. buchneri were obtained from small numbers of samples. The widespread but sporadic distribution of lactobacilli in low numbers seems to indicate that these organisms do not normally thrive on plant surfaces. A ternary cycle, beginning with intestinal waste, followed by mechanical distribution to and among plants, and return to the host via the oral cavity, is suggested.