INHIBITORY ACTIVITY OF LACTIC ACID BACTERIA ISOLATED FROM THAI FERMENTED FOOD AGAINST PANDEMIC STRAINS OF VIBRIO PARAHAEMOLYTICUS

Since 1996, Vibrio parahaemolyticus serotype O3:K6 and its clones have been reported to cause human infections worldwide. In Thailand, infections caused by these pandemic strains are still high. In order to control these infections, an attempt has been made to use probiotic bacteria. In this study, 327 strains of lactic acid bacteria were isolated from 22 types of fermented Thai foods. They were screened for probiotic properties. One isolate designated as PSU-LAB 71 strongly inhibited the pandemic strains of V. parahaemolyticus and also Vibrio cholerae. PSU-LAB71 was isolated from naturally fermented pork and was identified as Lactobacillus plantarum. The mechanism of its ability to inhibit V. parahaemolyticus was most likely caused by acid production. PSU-LAB71 showed high adhesion to an enterocyte-like Caco-2 cell line. This study highlighted the possibility of using PSU-LAB71 as a probiotic strain to control infections by pandemic V. parahaemolyticus.

PRACTICAL APPLICATIONS

Asian countries use many fermented foods containing lactic acid bacteria. This study describes a method to isolate potential probiotic bacteria from fermented foods that have inhibitory properties against pathogenic Vibrio species, especially pandemic strains of Vibrio parahaemolyticus . This report may initiate other countries that face problems caused by this pathogen to isolate their local lactic acid bacteria that have the potential to act as probiotics to control infections.     

CHANGES IN FLAVOR ATTRIBUTES DURING RIPENING OF FERMENTED SAUSAGES

Production of flavor-related compounds (amines and short-chain fatty acids) was followed throughout the ripening of a fermented sausage, and related to populations of two spoilage microorganisms (pseudomonds and Brochothrix thermosphacta) and lactic acid bacteria (LAB). Changes in pH, acidity, degree of oxidation and water activity were observed. Although spoilage microorganisms were present through ripening to 30 days, no off-odor was detected. The antibacterial activity of LAB, including Lactobacillus plantarum, was caused by a lower pH, as well as lactic acid, bacteriophage, and bacteriocin-like compounds synthesized by the strain. The concentration of short-chain fatty acids, mainly acetic acid, increased toward the end of the study time as a consequence of microbial metabolism. Putrescine and cadaverine, produced by Bacillaceae, increased during the first six days of storage, remaining constant through 30 days of ripening. Tyramine, a metabolic product of lactic acid baceria decreased after 24 days of storage.     

发酵香肠发酵剂菌种筛选的研究

从近年发酵肉制品中涉及到的有益微生物中，筛选出能够快速发酵并使发酵肠风味品质俱佳、质量稳定的发酵剂。并且通过正交试验确定发酵香肠组合发酵剂的最优配比，对香肠成熟过程和贮藏过程中的pH值、乳酸菌数量的变化、感官品质等方面进行分析，研究结果表明，植物乳杆菌（Lp）、嗜酸乳杆菌（La）和戊糖片球茼（Pp）是良好的发酵肉制品发酵剂；它们作为发酵香肠发酵剂的最优配比是0.6％，0.6％，0.3％；此组合发酵剂发酵的香肠的pH值，乳酸菌数，感官特征等指标均优于单一菌种发酵的香肠.     

BIOGENIC AMINES IN FINNISH DRY SAUSAGES

A study was conducted to determine the biogenic amine levels of Finnish dry sausages and to compare the results with those of other surveys of different types of fermented sausages. Sausages with high amine concentration were analyzed microbiologically in order to identify amine-producing microorganisms. Tyramine was the most common amine: the mean of 68 samples was 82 mg/kg and the mode 110 mg/kg. Other vasoactive amines found were histamine (<1–200 mg/kg), phenylethylamine (<1–48 mg/kg) and tryptamine (<10–91 mg/kg). Increased amounts of the spoilage indicator amines putrescine and cadaverine were found from most of the samples containing vasoactive amines. The formation of amines can be linked with problem(s) in hygienic conditions of raw materials and manufacturing practices and it is thus proposed that the sum of tyramine, histamine, putrescine and cadaverine could serve as an indicator of quality in fermented meat products.     

EVALUATION OF BIOGENIC AMINES FORMATION BY PROTEOLYTIC ENTEROCOCCI STRAINS ISOLATED FROM RAW DROMEDARY MILKS FROM SOUTHERN ALGERIA

Twenty-three strains of lactic acid enterococci isolated from dromedary raw milks in Southern Algeria were investigated for their proteolytic activity and ability to produce biogenic amines by decarboxylating amino acids: histidine, tyrosine and ornithine. All strains tested displayed proteolytic activities, but none of them were able to produce detectable biogenic amines in the usual adequate laboratory media, namely, Joosten and Northolt medium and Leuschner medium. Polymerase chain reaction experiments indicate a positive correlation between the absence of the hdc and odc genes and the lack of histamine and putrescine production for all tested strains. By contrast, all strains appeared to possess tdc gene, but no correlation was found with a negative expression of tyrosine decarboxylase.

PRACTICAL APPLICATIONS

In foods, biogenic amines are mainly generated by decarboxylation of the corresponding amino acids through substrate-specific enzymes of the microorganisms present in this environment, particularly histidine, tyrosine, lysine, ornithine and arginine, and the capability of enterococci and some other lactic acid bacteria to produce biogenic amines has been described. For this purpose, several qualitative and quantitative methods to determine biogenic amines production by these microorganisms have been developed. There is great interest to identify and to characterize the bacteria strains intended for an industrial use and to verify if they are potentially able to produce biogenic amines in order to prevent it's synthesis and limit the poisoning risk.     

APPLICATION OF α-TOCOPHEROL IN DRY CHINESE POWCHICKEN SAUSAGES

Chicken breast at 8%, 17% and 25% levels was used to replace pork fat in a low-fat dry Chinese sausage. This replacement resulted in more lipid and oxymyoglobin oxidation; also pH values declined (P<0.05) during 4C storage. Cooking loss decreased with increasing chicken cantent in sausaga (P<0.05). The addition of α-tocopherol to pork/chicken sausages delayed lipid and oxymyoglobin oxidation (P<0.05) but did not influence pH value or cooking loss.     

无花果、牛蒡乳酸菌发酵饮料的研制

以优质无花果酱和牛蒡原汁为原料,用保加利亚乳杆菌和嗜热链球菌为菌种,开发研制无花果、牛蒡混合汁乳酸菌发酵饮料。采用四因素三水平正交实验,确定发酵液及发酵饮料口感稳定性的最佳工艺配方。结果:用保加利亚乳杆菌和嗜热链球菌按1:1比例作为菌种;发酵液最佳配方:无花果、牛蒡混合汁配比7:3,发酵温度41℃,发酵时间24h,接种量4%;发酵饮料调配最佳配方:发酵原液中添加蔗糖5%,柠檬酸0.02%,耐酸羧甲基纤维素钠(CMC-Na)0.2%,黄原胶0.03%。     

CYTOTOXICITY ASSESSMENT OF BACILLUS STRAINS ISOLATED FROM STREET-VENDED FOODS IN JOHANNESBURG, SOUTH AFRICA

Twenty-one isolates each of Bacillus (B.) cereus, B. licheniformis and B. subtilis from street foods, collected in central Johannesburg, were randomly selected to test for cytotoxicity against McCoy 5A Mouse cells using a 3-(4,5-dimethylthizol-2-yl)-2,5-diphenyltetrazolium bromide assay, and observation by confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM). Forty-eight percent of B. cereus, 33% of B. licheniformis and 19% of B. subtilis strains produced cytotoxic compounds. For B. cereus strains, all supernatants exhibiting cytotoxic effects were inactivated by heat treatment at 121C for 15 min. By contrast, 24% of B. licheniformis and 10% of B. subtilis supernatants exhibited cytotoxic effects following heat treatment. CSLM and SEM showed that McCoy cells treated with cytotoxic supernatants exhibited leakage and necrosis. Presence of B. cereus, B. licheniformis and B. subtilis in street foods in high numbers may pose potetnial safety risks due to production of cytotoxic compounds.     

HYDROLYSIS OF ISOFLAVONE PHYTOESTROGENS IN SOYMILK FERMENTED BY LACTOBACILLUS AND BIFIDOBACTERIUM COCULTURES

This study evaluated the hydrolysis of isoflavones in soymilk fermented at 37C for 48 h by four different Lactobacillus and Bifidobacterium cocultures. The hydrolysis of isoflavone β-glucosides significantly increased ( P <  0.05) the bioactive aglycones from 36 to over 90% of total isoflavones in soymilk fermented with any of the four Lactobacillus and Bifidobacterium cocultures as compared with unfermented soymilk. Compared with three other cocultures of Lactobacillus and Bifidobacterium, fermentation of soymilk with the Lactobacillus paracasei/Bifidobacterium longum cocultures yielded better isoflavone hydrolytic potential (Otieno-Shah index) and the highest β-glucosidase activity after 12 h of incubation.

PRACTICAL APPLICATIONS

Isoflavones are known as phytoestrogens because they are present in soy products and have estrogen-like activity. During fermentation, the majority of glucoside isoflavones in soymilk are converted to bioactive aglycones via microorganism-derived β-glucosidase. In human intestines, aglycone isoflavones are absorbed faster and in greater amounts than their glucosides. Using probiotic Lactobacillus and Bifidobacterium cocultures to ferment soymilk efficiently increases the bioactive aglycone concentrations. Hence, fermenting soymilk with this coculture could enhance the nutritional value of the product.     

乳酸菌发酵红薯清汁饮料的研制

利用提取淀粉后的红薯浆液，采用保加利亚乳酸杆菌和嗜热链球菌共同发酵生产出一种发酵红薯饮料，当加入α-淀粉酶、纤维素酶和果胶酶并接入适量保加利亚乳酸杆菌和嗜热链球菌，在40℃发酵20h，料液pH值为4．0，经调配，制备的饮料外观清亮、酸甜可口。     

类植物乳杆菌抑菌物质的性质及其在猪肉保鲜中的作用

类植物乳杆菌Ⅱ32能够抑制沙门氏菌等革兰氏阴性腐败菌和其它细菌的生长.其菌液的正丁醇萃取液,通过阳离子交换层析、凝胶过滤、反相高效液相层析等分离纯化,获得纯度较高的抑菌物质.该物质耐热性强,耐酸,但在碱性条件下不稳定,对蛋白酶不敏感.初步研究表明,该菌的发酵液能抑制冷却猪肉中腐败菌的生长、延长冷却猪肉的货架期,而且对猪肉的品质没有不良影响.     

瑞士乳杆菌TUST005发酵乳ACE抑制活性的研究

通过正交试验确定瑞士乳杆菌TUST005制备具有抑制血管紧张素转换酶(ACE)发酵乳的最佳工艺条件.脱脂复原乳浓度为13%,经灭菌后,接种3%(体积百分数)的发酵剂,在不同的温度和时间组合下培养,超滤发酵乳的乳清,测定滤液的ACE抑制活性.42℃,6h发酵乳样品ACE抑制活性最高,为35.71%.4℃下后发酵3d的抑制活性最佳,为45.91%.