Screening of strains of Lactococci isolated from Egyptian dairy products for their proteolytic activity

A collection of cocci isolates (293) obtained from traditional Egyptian dairy products collected from four Egyptian regions yielded 151 lactic acid bacteria (LAB) cocci isolates. Among them, 24 isolates were characterised as highly proteolytic. SDS–PAGE showed that 6 isolates were the most proteolytically active, which were classified into Enterococcus faecalis HH22 (4 isolates) and Enterococcus faecium DO623 (2 isolates). The proteolytic activity of E. faecalis was higher than that of E. faecium (particularly on β-casein). The maximal degradation of milk proteins was achieved at pH 6.5–7.2 (E. faecalis) or pH 6.5 (E. faecium) and at 42 °C for both strains. The proteolytic activities of the two strains were inhibited mostly by the presence of EDTA, showing that their proteases belong mainly to metalloproteases. A slight inhibition of proteolysis by PMSF in the case of E. faecalis HH22 suggests a limited inclusion of serine proteases in its protease system.     

Assessment of the safety and applications of bacteriocinogenic Enterococcus faecium Y31 as an adjunct culture in North-eastern Chinese traditional fermentation paocai

Enterococcus faecium Y31 is a class IIa bacteriocin producer found in traditional Chinese fermented foods. The bacteriocin produced by Y31 (bacteriocin Y31) has a broad inhibitory spectrum. Here, we investigated the safety and behaviours of E. faecium Y31 in North-eastern Chinese traditional fermentation paocai (NCTFP) to assess its suitability as an adjunct culture. E. faecium Y31 showed interesting features, such as the absence of virulence determinants (aggregation substance [agg], enterococcal surface protein [esp], endocarditis antigen [efaAfm], gelatinase [gelE], hemolysin [cylA, cylB, cylM], sex pheromone [cpd, cob, ccf], adhesion of collagen [ace], and hyaluronidase [hyl] genes), sensitivity to various antibiotics, lack of haemolytic compounds, and lack of biogenic amine production. E. faecium Y31 could propagate in raw Chinese cabbage and produce bacteriocin Y31. To evaluate its performance as an adjunct culture for NCTFP, changes in the overall quality of control (noninoculated) and experimental NCTFP (inoculated with E. faecium Y31 under previously optimised fermentation conditions) were determined in duplicate fermentations of Chinese cabbage using chemical, microbiological, texture, and sensory evaluations. In the presence of E. faecium Y31, faster fermentation and higher bacteriocin Y31 production were observed than in the control. Additionally, the nitrite concentration of the fermentation solution decreased more rapidly, the total viability of the culture increased, and the lactic acid bacterium population was higher than those in NCTFP produced by spontaneous fermentation. No yeasts and moulds were detected in NCTFP produced by inoculation fermentation or spontaneous fermentation, and the textural properties of these two products were similar. Sensory evaluation results for NCTFP produced by inoculation fermentation were superior to those produced by spontaneous fermentation. Therefore, E. faecium Y31 was sufficient as an adjunct culture to enhance both the hygienic and sensory attributes of NCTFP and its use may help to address the issues inherent in commercial production of NCTFP.     

Fermentation characteristics of a low‐oxygen inducible hmp promoter system in Bacillus subtilis LAB1886

In an attempt to find a low‐cost promoter system which could be used for producing recombinant proteins, a low oxygen inducible hmp promoter system in Bacillus subtilis (LAB1886) was characterized by studying the effects of cell density (OD₆₀₀), glucose concentration, pH, dissolved oxygen (DO) level, nitrate and nitrite concentration on cell growth and β‐galactosidase expression. The optimal cultivation strategy was found to be to grow the cells in the presence of nitrate to OD₆₀₀ = 0.2 at a high DO level (80%), and then to induce the hmp promoter by lowering the DO level to 1–2%. As a result, the specific β‐galactosidase activity increased continuously to the maximal value of 1750 Miller Units. Nitrite, as the apparent inducer of the hmp promoter, was produced from nitrate reduction, and had profound effects on cell growth and β‐galactosidase expression. Copyright © 2006 Society of Chemical Industry     

Probiotic Fermented Sausages: Myth or Reality?

Experts view the development of functional foods as an opportunity for innovation for the meat industry in line with consumers’ concerns on food nutrition, well being and food safety. The main microbiota of fermented sausages consists of lactobacilli, which suggests that properly characterized strains could be selected as starter cultures. The selection of strains from human origin was considered in order to promote their survival in the host. Lactobacillus rhamnosus CTC1679 dominated during the ripening process and temporarily colonized the gastrointestinal tract of healthy volunteers, confirming that this strain could be delivered as a potential probiotic in fermented sausages.     

Fatty acid composition and oxidative stability of oils recovered from acid silage and bacterial fermentation of fish (Sea bass – Dicentrarchus labrax) by‐products

Lipid quality and fatty acid compositions of fish oils recovered from fish (Sea bass – Dicentrarchus labrax) waste silages produced with formic acid (FA) and five different LAB strains (Lactobacillus plantarum (LP), Pediococcus acidilactici (PA), Enterococcus gallinarum (EG), Lactobacillus brevis (LB) and Streptococcus spp. (ST)) were assessed to ensure for the usage for human consumption. Generally, it was observed that there were no significant differences between PUFA contents (23.27–23.64%). Peroxide (PV) (2.12 meq active O₂/per kg of oil) and TBA values (1.07 mg malonaldehyde (MA) g^?1 oil) of fish oils from acid silage were significantly higher than those of the fermented ones (1.14–1.91 meq active O₂ kg^?1, 0.67–0.81 mgMA g^?1 oil, respectively). Anisidine values (AV) were determined in range of 8.04–11.14 for fermented silages and 13.08 from acid silage. The highest totox value (17.33 ± 0.88) was also detected in acid silage oil whereas fermented groups gave totox value in the range of 10.40–13.88. It can be concluded that the initial lipid quality of fermented fish waste silages was better than the initial lipid quality of acid fish waste silage. Therefore, fish oils recovered from fermented silages can be used as food additives or supplements for animal and human diets.     

彩色图像数字水印新算法的研究

为了解决电子产品印刷盗版的问题,提出了基于LAB色彩空间和DWT的彩色图像数字水印算法,算法将水印置乱后嵌入到LAB色彩空间的亮度L分量的小波分解系数,实验证明,所提出的算法对常用的图像处理如JPEG压缩、加噪、剪切和滤波等攻击具有较好的鲁棒性、不可见性和安全性.     

Probiotics,prebiotics, and microencapsulation: A review

The development of a suitable technology for the production of probiotics is a key research for industrial production, which should take into account the viability and the stability of the organisms involved. Microbial criteria, stress tolerance during processing, and storage of the product constitute the basis for the production of probiotics. Generally, the bacteria belonging to the genera Lactobacillus and Bifidobacterium have been used as probiotics. Based on their positive qualities, probiotic bacteria are widely used in the production of food. Interest in the incorporation of the probiotic bacteria into other products apart from dairy products has been increasing and represents a great challenge. The recognition of dose delivery systems for probiotic bacteria has also resulted in research efforts aimed at developing probiotic food outside the dairy sector. Producing probiotic juices has been considered more in the recent years, due to an increased concern in personal health of consumers. This review focuses on probiotics, prebiotics, and the microencapsulation of living cells.     

Bread wastes to energy: Sequential lactic and photo-fermentation for hydrogen production

One third of the World's entire food production is lost or wasted every year. Biohydrogen production offers a possibility to re-use this resource; in particular, bread and bakery products wastes, due to their composition (up to 70% of carbohydrates, mostly starch), represent an appropriate source of nutrients for microorganisms. The aim of this work was to convert bread wastes into hydrogen with a sequential system composed of lactic fermentation and photofermentation, with a minimum number of treatments to the substrate. The best results were provided by Lactobacillus amylovorus DSM 20532, followed by photofermentation by Rhodopseudomonas palustris 42OL, supplemented with ferric citrate and magnesium sulfate. The process led to 3.1 mol H₂ mol^?1 glucose, among the highest yields obtained on starch containing substrates, with an energy recovery of 54 MJ t^?1 dry waste. This study promotes the re-use of energy-containing food wastes for improving circular economy.     

腊鱼加工中的乳酸菌及其特性

以白鲢为原料,对腊鱼加工过程的乳酸菌进行分离鉴定,并分析了其特性,为腊鱼加工及其品质控制提供实验数据。结果表明,腊鱼加工中存在植物乳杆菌、弯曲乳杆菌、食品乳杆菌、乳酸片球菌、戊糖片球菌,且不同加工阶段乳酸菌菌种分布不同。原料鱼、腌制结束时鱼体和成品中杆菌分别占乳酸菌的88%、56%和94%,是腊鱼加工中的优势乳酸菌。所有分离的乳酸菌都具有一定的耐盐、耐低温能力和蛋白酶活性,其中弯曲乳杆菌、乳酸片球菌的耐盐和耐低温能力较高;乳酸片球菌的蛋白酶活性最高。     

乳酸菌细菌素分类与作用机制

乳酸菌细菌素作为天然的食品防腐剂,可抑制或杀灭食品中致病微生物和腐败微生物从而保护食品的安全。文中介绍了乳酸菌细菌素传统分类方法和新提出的分类方法,并且综述了乳酸菌细菌素的作用机制。