东北酸菜中产胞外多糖乳杆菌的分离筛选及其在酸乳中的应用

从东北酸菜中分离出97株乳杆茵菌株,并筛选出两株产酸快、产胞外多糖(EPS)的乳杆茵2号菌株和9号菌株.初步鉴定前者为干酪乳杆茵,后者为植物乳杆茵.在发酵剂(保加利亚乳杆菌和嗜热链球茵,LS)中混入等量的菌株2或9培养物(脱脂乳),所制备的酸乳中EPS质量浓度达34 mg/L.活茵总数可迭2×108mL-1以上.酸乳物性测定结果显示,产EPS菌株发酵的酸乳弹性好,相对粘度高,持水力强,乳清析出少.感官评定结果显示,与没有添加产EPS茵株发酵的酸乳相比,产EPS茵株LS+2与LS+9组合发酵酸乳风味分值较高,组织状态的分值差别较大,而酸度上没有显著差异.与物性测定结果一致.     

植物乳杆菌YW11胞外多糖对酸乳加工特性的影响

研究植物乳杆菌YW11胞外多糖（exopolysaccharide,EPS）对酸乳发酵过程中菌株生长、产酸速率和微流变特性,以及产品质构和风味特性的影响,结果表明,不同添加量（0.05、0.15、0.25 mg/g）的EPS对发酵过程菌株（保加利亚乳杆菌、嗜热链球菌）的生长和产酸速率无明显影响。添加EPS对发酵过程中样品的弹性指数（elasticity index,EI）、宏观黏度指数（microviscosity index,MVI）和流动性指数（fluidity index,FI）具有不同的影响,随着EPS添加量的增加,EI逐渐降低,MVI升高,而FI无明显变化。不同添加量的EPS均可提高酸乳的持水力,其中以EPS-0.25组样品的持水力最大,达57.93%;随着EPS添加量的增加,酸乳的硬度降低,最低值为10.08 g;黏力增加,最大值为9.57 g;而内聚性变化不大,在0.45～0.48之间。添加EPS使酸乳中蛋白交联结构增强,蛋白颗粒更小,网络结构中存在较大孔隙结构。添加适量的EPS能够促进酸乳风味物质如醛类、酸类和酯类等化合物的形成。本研究有助于进一步了解植物乳杆菌EPS对酸乳加工特性的影响,并基于EPS的应用提升酸乳品质。     

直投式发酵剂对酸乳产EPS影响的初步研究

采用两因素交叉重复试验对生产中常用的七种DVS发酵剂的产EPS能力及发酵条件进行了初步研究,研究结果表明:温度与发酵荆种类对酸乳产EPS都有极其显著影响(P＜0.001),各发酵剂在37℃发酵生产酸乳时EPS平均产量最高,不同的发酵剂之间在产EPS能力上存在差异,其中YC-Ⅻ发酵剂的产EPS能力最强.     

藏灵菇及其优势菌群的发酵性能研究

以藏灵菇为发酵剂生产酸乳的工艺条件为:发酵温度37℃,发酵时间10h。获得的酸乳产品pH较低。用MRS培养基、Elliker培养基、TYC培养基和SL培养基从藏灵菇中分离出乳球菌、乳杆菌、链球菌和明串珠菌。将优选的分离菌组合发酵鲜牛乳,产酸速度更快,黏度较高。     

用于发酵肉中菌种的优选

根据肉制品发酵剂的基本要求,对植物乳杆菌(Lp)、干酪乳杆菌(Lc)、瑞士乳杆菌(Lh)、嗜热链球菌(St)、乳酸乳球菌(Pl)、嗜酸乳杆菌(La)和德氏乳杆菌(Ld))进行了优选试验.结果表明:当NaCl的浓度达到6%时,植物乳杆菌、干酪乳杆菌、嗜酸乳杆菌和德氏乳杆菌还能正常生长,当耐亚硝酸盐浓度达到150mg/kg时,植物乳杆菌、干酪乳杆菌和嗜酸乳杆菌还能正常生长.但干酪乳杆菌的产酸性能要优于植物乳杆菌和嗜酸乳杆菌,所有供试的乳酸菌都没产气、产氨、产H2S的性质,也没有分解蛋白质和脂肪的性质.     

以嗜酸乳杆菌和植物乳杆菌为发酵剂发生发酵香肠

本文研究了嗜酸乳杆菌和植物乳杆菌在发酵香肠中的适应性，确定了嗜酸乳杆菌和植物乳杆菌的最佳组合比例，并对产品的理化指标了分析。     

利用纯种乳酸菌制作泡萝卜的技术研究

研究了不同纯种乳酸菌即肠膜明串珠菌、发酵乳杆菌、嗜热链球菌、嗜酸乳杆菌、保加利亚乳杆菌的组合发酵制作泡菜的变化和风味。结果表明,与传统发酵制作工艺相比,嗜酸乳杆菌+肠膜明串珠菌+发酵乳杆菌组合发酵(添加量为发酵液的5%),发酵速度快、产品风味好、亚硝酸盐含量为0.385×10-6mg/kg低于传统工艺生产的产品(1.55×10-6mg/kg),产品质量稳定。     

新疆传统乳制品中优良乳酸菌的筛选及多菌株发酵剂的研究

从新疆地区采集的46份传统乳制品中分离获得的612株乳酸菌,根据菌株来源、培养条件,形态特征、凝乳状态和产酸特性,选择其中20株乳酸菌进行生理生化鉴定和酸奶发酵试验,结果表明,分离株中3株为链球菌,4株为乳球菌,13株为乳杆菌,平均发酵产酸速率在8.11~12.43oT/h,不同菌株在酸乳冷藏期间表现出不同的后酸化活性,冷藏15d滴定酸度提高了6.3%~55.7%。不同菌株凝乳时黏度在272~1085cp,多数菌株发酵乳在冷藏期间黏度呈上升趋势,球菌的产黏能力普遍低于杆菌。气相色谱分析结果显示不同菌株发酵乳中丁二酮在3.51~68.74mg/L,乙醛在3.51~68.74mg/L,丙酮在0.87~48.35mg/L,乙酸乙酯在0~103.68mg/L,异戊醇都未检出。经过混合菌株发酵生产酸乳比较,发现以S.thermophilusX1、S.thermophilusX5、L.plantarumY5和L.delbrueckii bulgaricussubsp.Y10按1∶1∶1∶1比例组合作为发酵剂,生产的酸乳组织状态较好、风味独特、后酸化弱。     

嗜酸乳杆菌和乳酸乳球菌单独发酵对菊芋泡菜的影响

主要对抗菌性嗜酸乳杆菌LA和乳酸乳球菌LL在菊芋泡菜中的应用进行了研究。以亚硝酸盐含量、总酸含量、氨基酸态氮含量为指标,研究发酵温度、接种量、加糖量、发酵时间等因素对嗜酸乳杆菌LA和乳酸乳球菌LL分别单独发酵菊芋的影响。结果表明,嗜酸乳杆菌LA和乳酸乳球菌LL对大肠杆菌、金黄色葡萄球菌具有抑菌性。发酵7d,嗜酸乳杆菌LA产酸较快且亚硝酸盐含量较低的发酵温度为34℃,接种量5%;发酵7～14d,乳酸乳球菌LL产酸较快且亚硝酸盐含量较低的适宜温度为37℃,接种量5%。采用嗜酸乳杆菌LA和乳酸乳球菌LL分别发酵,白砂糖的添加量对菊芋发酵液中总酸含量的变化均无显著影响,白砂糖添加量为5g/kg时,亚硝酸盐含量最低。采用嗜酸乳杆菌LA发酵,发酵液中氨基酸态氮含量要高于乳酸乳球菌LL发酵。发酵过程中菊芋的总酸含量、亚硝酸盐含量、氨基酸态氮含量等各项指标主要受发酵时间的影响,随着发酵时间延长,各指标值趋于稳定。发酵14d时,不同条件发酵,亚硝酸盐含量均降低至5mg/kg以下。抗菌性乳酸菌发酵有利于菊芋泡菜的安全生产。     

嗜热链球菌和乳杆菌最佳促生长剂的选择

本文研究了七种不同添加剂对嗜酸乳杆菌、嗜热链球菌和保加利亚乳杆菌产酸及凝乳的影响。结果表明：７％番茄汁可作为这三种菌的促生长剂；嗜酸乳杆菌的最佳促生长剂为７％番茄汁或１０％胡萝卜汁；７％五星啤酒是嗜热链球菌的最佳促生长剂，１０％的信阳毛尖茶次之；７％番茄汁是保加利亚乳杆菌的最佳促生长剂。     

Effects of exopolysaccharide-producing strains of thermophilic lactic acid bacteria on the texture of stirred yoghurt

Summary Rheological and sensory properties of yoghurts prepared from commercially available cultures that had ropy and non-ropy characteristics were compared. Our results from both instrumental and sensory data suggest that it may not be the amount of polysaccharide that is important to rheological properties, but the type of exopolysaccharide (EPS)-producing strains and consequently the interaction of the polymer with the milk proteins during the fermentation. Data also suggest that the interaction and co-operative growth that occurs in mixed cultures also influences the yield of EPS production in the fermentation, as combining two ropy strains does not lead to an increase in total polysaccharide, although the viscosity can be improved. Texture measurements for viscosity correlated with sensory evaluation of viscosity and with slipperiness.     

Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy

Cryo-scanning electron microscopy was used to visualize the microstructure of two types of cheese (Karish and Feta) and milk fermented with different ropy and non-ropy strains of lactic acid bacteria. Specimen frozen in liquid nitrogen slush were transferred in a frozen state and under vacuum into the preparation chamber where they were fractured, etched and coated with gold. Specimen were then transferred under vacuum onto the cold stage and imaged using scanning electron microscopy (SEM). Milk fat and exopolysaccharide (EPS) were visible in pores within the protein network. Cheese and fermented milk made with EPS-producing cultures exhibited a porous structure in which the largest pores were associated with visible EPS. A compact structure with small pores was seen in cheese and milk fermented with EPS non-producing cultures. EPS and protein appeared to be segregated in both cheese and fermented milk. EPS formed a network-like structure. Differences were observed in the microstructure of EPS between moderately ropy and highly ropy strains. A relatively long etching (sublimation) time caused EPS to appear as thin filaments similar to those seen with conventional SEM.     

Effect of various starter cultures on the viscoelastic properties of bovine and caprine yogurt gels

Bovine and caprine yogurt gels made using 'ropy' (extracellular polysaccharide-producing starters) and 'non-ropy' starter cultures were examined using dynamic (oscillatory) testing. The storage (G¸) and loss (G˝) moduli of the ropy gels were found to be lower than those of the equivalent non-ropy ones. Both moduli of the ropy gels declined on storage (at 4°C). On the other hand, the loss tangents of the gels made using the ropy starters were higher than those of the non-ropy gel systems. Caprine yogurt gels were some eight times weaker than the equivalent bovine systems, the ropy gels again being weaker that the non-ropy systems. These data suggest that the secreted polysaccharide may well interfere with the gel structure and development.     

Influence of heat impact in reconstituted skim milk on the properties of yoghurt fermented by ropy or non-ropy starter cultures

The paper describes studies on the influence of heat impact in reconstituted skim milk on chemical and functional properties of yoghurt products. Reconstituted skim milk was heated for 20 min at 85 degrees C, 90 degrees C, or 95 degrees C. Ropy (producing exopolysaccharides, EPS) or non-ropy strains of S. thermophilus and L. delbrueckii subsp. bulgaricus were used as starter culture for yoghurt manufacture. The studies have shown that the fermentation times decreased with increasing heat impact when the ropy starter culture was used, while they remained to a far extent unchanged if the non-ropy starter culture was applied. The lactic acid contents of the yoghurt products were in the same range when the milk was heated at 85 degrees C or 90 degrees C, while they were different when milk was heated at 95 degrees C. There was a tendency visible that an increase in preheating leads to increased L(+)- and decreased D(-)-lactic acid contents if the non-ropy culture was applied. Using the ropy culture, it was vice versa. A slightly decrease in proteolysis with increasing heat impact was to be noted with both starter cultures. Concerning the relation of proteolysis to acidification, the fermentation process could be subdivided into three sections with different slopes if the non-ropy starter culture was used, while a linear relation was found if the ropy starter culture was applied. Regarding final product characteristics it was found that the functional properties of yoghurt decreased with increasing heat impact when the ropy starter culture was applied, while they remained to a far extent unchanged when the non-ropy starter culture was used. It can be concluded from these studies that a preheating of milk at a temperature of 85 degrees C (20 min) is optimal in regard to final yoghurt product characteristics.     

Characterisation of the exopolysaccharide (EPS)-producing Lactobacillus paraplantarum BGCG11 and its non-EPS producing derivative strains as potential probiotics

Traditional fermented foods are the best source for the isolation of strains with specific traits to act as functional starters and to keep the biodiversity of the culture collections. Besides, these strains could be used in the formulation of foods claimed to promote health benefits, i.e. those containing probiotic microorganisms. For the rational selection of strains acting as probiotics, several in vitro tests have been proposed. In the current study, we have characterized the probiotic potential of the strain Lactobacillus paraplantarum BGCG11, isolated from a Serbian soft, white, homemade cheese, which is able to produce a "ropy" exopolysaccharide (EPS). Three novobiocin derivative strains, which have lost the ropy phenotype, were characterized as well in order to determine the putative role of the EPS in the probiotic potential. Under chemically gastrointestinal conditions, all strains were able to survive around 1-2% (10(6)-10(7)cfu/ml cultivable bacteria) only when they were included in a food matrix (1% skimmed milk). The strains were more resistant to acid conditions than to bile salts and gastric or pancreatic enzymes, which could be due to a pre-adaptation of the parental strain to acidic conditions in the cheese habitat. The ropy EPS did not improve the survival of the producing strain. On the contrary, the presence of an EPS layer surrounding the strain BGCG11 hindered its adhesion to the three epithelial intestinal cell lines tested, since the adhesion of the three non-ropy derivatives was higher than the parental one and also than that of the reference strain Lactobacillus rhamnosus GG. Aiming to propose a potential target application of these strains as probiotics, the cytokine production of peripheral blood mononuclear cells (PBMC) was analyzed. The EPS-producing L. paraplantarum BGCG11 strain showed an anti-inflammatory or immunosuppressor profile whereas the non-ropy derivative strains induced higher pro-inflammatory response. In addition, when PBMC were stimulated with increasing concentrations of the purified ropy EPS (1, 10 and 100μg/ml) the cytokine profile was similar to that obtained with the EPS-producing lactobacilli, therefore pointing to a putative role of this biopolymer in its immune response.     

Ropy exopolysaccharide-producing Bifidobacterium longum YS108R as a starter culture for fermented milk

Bifidobacteria are generally inferior compared to traditional starter lactic acid bacteria (LAB) in terms of fermentation properties. The results of this study showed that the use of a ropy EPS producing strain Bifidobacterium longumYS108R during fermentation improved the physicochemical properties of fermented milk, including decreased whey syneresis and increased water-holding capacity and apparent viscosity, however, another non-ropy EPS producing strain B. longum C11A10B did not exert such effects. Furthermore, we found that synergistically fermented milk with YS108R and commercial starter could reduce the production of acetic acid, a metabolite of bifidobacteria, and scored better in terms of sensory evaluation, especially with regards to mouthfeel texture. Comparative genomic analysis revealed a single mutation in the protein-tyrosine kinase gene of strain YS108R, which may relate to ropy phenotype. Our results indicate that ropy-EPS producing B. longumYS108R is suitable as an adjunct culture for the manufacture of novel fermented dairy products.     

Effect of 'ropy' strains of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus on rheology of stirred yogurt

The TA-TX2 Texture Analyser and the Brookfield RVT Viscometer have been used to investigate the contribution of ropiness to the texture of stirred yogurts made using ropy strains of bacteria. Back extrusion and texture profile analysis, not commonly used to quantify rheological properties of semi-solid foods, have been found useful in distinguishing the contribution of exopolysaccharides to different texture attributes (Toba et al ., 1990). Thus ropiness, a characteristic which is imparted to the product as a result of fermentation with particular polysaccharide-producing strains, contributes to 'adhesiveness', while 'firmness' and 'elasticity' are likely to be influenced more by the protein matrix of the yogurt than by secretion of the polysaccharide by the ropy strains. Effects on viscosity and ability to recover viscosity after disruption were apparent, although the contribution of ropiness was not always positive. Ropy strains increased viscosity of stirred yogurts when compared to yogurt made with non-ropy cultures. But, whilst a ropy Lactobacillus delbrueckii ssp. bulgaricus (Lb r⁺) combined with a non-ropy Streptococcus thermophilus (St r⁻) produced a viscous product which recovered its viscosity well, a yogurt made by combining both ropy strains did not recover its viscosity as well as yogurt made by combining two non-ropy cultures and lost its structure more rapidly during the destructive testing. These results show therefore that inclusion of a ropy strain will not always lead to improved texture attributes, that while ropy strains may increase viscosity they may not influence 'firmness' and lend support to the view that this latter attribute is more influenced by protein–protein interactions.     

Physical characteristics of yoghurts made using exopolysaccharide-producing starter cultures and varying casein to whey protein ratios

This study investigated the physical characteristics of set and stirred yoghurts made at 9% (w/w) total solids with various casein (CN)-to-whey protein (WP) ratios and with exopolysaccharide (EPS)-producing starter cultures (capsular or ropy) during storage. The yoghurt was evaluated for composition, firmness and syneresis of set yoghurt, and for the flow curve and the area of hysteresis loop between the upward and downward curve of stirred yoghurt. Viable counts of starter bacteria and concentrations of lactic acid and EPS in the yoghurt were also determined. EPS concentration did not decrease during storage for 28 d. Firmness and syneresis of set yoghurt decreased when the CN-to-WP ratio was reduced from ratio 4:1 to 1:1 and when EPS starter cultures (especially ropy EPS) were used. Stirred yoghurt with a CN-to-WP ratio of 3:1 and made using ropy EPS-producing starter cultures had a higher shear stress and hysteresis loop area than yoghurt made using capsular EPS- or non-EPS-producing starter cultures. The results suggested that the physical characteristics of set and stirred yoghurts can be improved by varying CN-to-WP ratio and by the use of EPS-producing starter cultures.     

Scanning electron microscopic and texture studies on characteristic consistency of Nordic ropy sour milk

The characteristic consistency of Nordic ropy sour milk was studied. Skim milk, reconstituted from non-fat dry milk, was fermented at 20 degrees C for 24 h by addition of 5% (v/v) inoculum of slime-producing (ropy) strain of Lactococcus lactis ssp. cremoris SBT 0495, isolated from Finnish ropy sour milk 'viili' starter culture, and its non-ropy variant SBT 1275. Measurements of texture showed that milk gel prepared by the ropy strain exhibited remarkably increased adhesiveness as compared to that by the non-ropy variant. Milk gel prepared by the ropy strain also exhibited decreased syneresis (wheying-off) as compared to that by the non-ropy variant. Scanning electron micrographs of milk gel prepared by the ropy strain showed that slime was in the form of a network attaching the bacterial cells to the protein matrix. A thick network of slime attached the casein micelle clusters to each other to make casein conglomerates, which is likely to result in the characteristic consistency of 'viili'.     

Texture characteristics and pizza bake properties of low-fat Mozzarella cheese as influenced by pre-acidification with citric acid and use of encapsulated and ropy exopolysaccharide producing cultures

Low-fat Mozzarella cheeses containing 6% fat were made by pre-acidification of milk with citric acid to pH 6.1 and using encapsulated ropy or non-ropy exopolysaccharide (EPS) producing Streptococcus thermophilus. Moisture retention, changes in texture profile analysis (TPA), meltability and stretchability of cheese, and changes in colour, surface scorching and shred fusion were analysed after baking over 90 days (d). Control cheeses and those made from pre-acidified milk without EPS cultures had the lowest moisture content at 54.84% and 55.28%, respectively. Control cheeses were hardest and their meltability and stretchability were initially low. Hardness was reduced and the melt and stretch distances increased with time. When baked, control cheeses showed incomplete shred fusion. Pre-acidification reduced hardness and increased meltability. Capsular- and ropy-EPS were quantified at 30.42 and 30.55 mg g⁻¹ of cheese, respectively, and increased moisture retention in pre-acidified cheese to 56.67% and 56.21%, respectively. These cheeses were softer and exhibited lower springiness. Greater meltability was observed initially but became similar to control cheeses after 90 d of storage. When baked after 45 d of storage, cheeses containing EPS producing cultures showed improved shred fusion, meltability and a reduction in surface scorching.