Food preservative potential of gassericin A‐containing concentrate prepared from cheese whey culture supernatant of Lactobacillus gasseri LA39

Gassericin A (GA) is a circular bacteriocin produced by Lactobacillus gasseri LA39. In this study, GA‐containing concentrate was prepared using a cross‐flow membrane filtration device (30 kDa cut‐off) from the culture supernatant of Lb. gasseri LA39 cultivated in a cheese whey‐based food‐grade medium. The bacteriocin activity titer in the concentrate was 16 times as high as that of the culture supernatant and was completely maintained through each incubation at 4°C for 3 months, 37°C for 2 months, 60°C for 5 h, and 100°C for 30 min. The GA‐containing concentrate was used with glycine powder to make custard creams, and then four representative strains of custard cream spoilage bacteria (Bacillus cereus, Lactococcus lactis subsp. lactis, Achromobacter denitrificans and Pseudomonas fluorescens) were individually inoculated at c. 10³ colony forming units/g in the custard creams. Throughout 30 days of incubation at 30°C, all of the inoculated bacteria were completely inhibited by the combination of 5% (w/w) of the GA‐containing concentrate and 0.5% (w/w) glycine. This is the first highly practical application of GA to foods as a biopreservative, and the concentration method and the bacteriocin concentrate would contribute to biopreservation of several foods.     

Survival of spray‐dried and free‐cells of potential probiotic Lactobacillus plantarum 564 in soft goat cheese

A high viability of probiotics in food product, with a living cells threshold of 10⁷/cfu/g (colony‐forming units/g) is a challenge to achieve in food production. Spray drying is an efficient and economic industrial method for probiotic bacterial preservation and its application in food products. In this study, the survival of free and spray‐dried cells of potential probiotic strain Lactobacillus plantarum 564 after production and during 8 weeks of storage of soft acid coagulated goat cheese was investigated, as well as compositional and sensory quality of cheese. Total bacterial count of spray‐dried Lb. plantarum 564 cells were maintained at the high level of 8.82 log/cfu/g in cheese after 8 weeks of storage, while free‐cell number decreased to 6.9 log/cfu/g. However, the chemical composition, pH values and sensory evaluation between control cheese (C1 sample made with commercial starter culture) and treated cheese samples (C2 and C3, made with the same starter, with the addition of free and spray‐dried Lb. plantarum 564 cells, respectively) did not significantly differ. High viability of potential probiotic bacteria and acceptable sensory properties indicate that spray‐dried Lb. plantarum 564 strain could be successfully used in the production of soft acid coagulated goat cheeses.     

Heterologous expression of gassericin A,a bacteriocin produced by Lactobacillus gasseri LA39

Gassericin A, a bacteriocin produced by Lactobacillus gasseri LA39, has a cyclic structure linking N‐ and C‐terminal amino acids. Gassericin A was expressed in Escherichia coli JM109 as a biotinylated fusion protein on the basis of the DNA sequence of mature bacteriocin. A positive clone accumulated the bacteriocin, with no activity, as a soluble fusion protein in the cytoplasm. After release of an N‐terminal tag with factor Xa protease, gassericin A was converted into an active peptide having N‐ and C‐termini. The total amount of purified bacteriocins (expressed and native) was 480 µg/L and 370 µg/L, respectively. However, the specific activity of expressed gassericin A was 15 AU/mg lower than that of native bacteriocin (2600 AU/mg). Although the actual Mr (molecular weight) of the expressed bacteriocin should be 5666, the peptide showed the same mobility (Mr 3800) in sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) as native cyclic gassericin A, suggesting that the expressed peptide retains compact folding of the molecule similar to that of native gassericin A.     

Closantel plasma and milk disposition in dairy goats: assessment of drug residues in cheese and ricotta

Closantel (CLS) is currently used in programs for the strategic control of gastrointestinal nematodes. CLS is extralabel used in different dairy goat production systems. From available data in dairy cows, it can be concluded that residues of CLS persist in milk. The current work evaluated the concentration profiles of CLS in plasma and milk from lactating orally treated dairy goats to assess the residues pattern in dairy products such as cheese and ricotta. Six (6) female Saanen dairy goats were treated orally with CLS administered at 10 mg/kg. Blood and milk samples were collected between 0 and 36 days post‐treatment. The whole milk production was collected at 1, 4, 7, and 10 days post‐treatment to produce soft cheese and ricotta. CLS concentrations in plasma, milk, cheese, whey, and ricotta were determined by HPLC. The concentrations of CLS measured in plasma were higher than those measured in milk at all sampling times. However, the calculated withdrawal time for CLS in milk was between 39 and 43 days postadministration to dairy goats. CLS residual concentrations in cheese (between 0.93 and 1.8 μg/g) were higher than those measured in the milk used for its production. CLS concentrations in ricotta were sixfold higher than those in the milk and 20‐fold higher than those in the whey used for its production. The persistent and high residual concentrations of CLS in the milk and in the cheese and ricotta should be seriously considered before issuing any recommendation on the extralabel use of CLS in dairy goat farms.     

乳清干酪产品加工现状

为了解决干酪副产物综合利用问题,丰富干酪市场,本文对乳清干酪的加工进行阐述.介绍乳清干酪来源,各国乳清干酪的分类、营养价值,生产工艺及加热、酸化pH值、乳清浓缩方法、添加奶(鲜奶、脱脂奶、半脱脂或奶酪等)、发酵剂、非乳品蛋白质等因素对产品质地的影响.     

Selection of useful probiotic lactic acid bacteria from the Lactobacillus acidophilus group and their applications to functional foods

In the present review, a new mass screening system for selecting probiotic strains from Lactobacillus (L) acidophilus group lactic acid bacteria (LAB) with strong adhesion to the human intestinal tract is described. Characteristics of antimicrobial peptides (bacteriocin), lactose‐hydrolyzing enzymes and immunostimulative oligo DNA motifs in L. gasseri strains are also described. Finally, the use of L. acidophilus LAB, selected by our screening method, that have strong adhesion to the human colonic mucosa in functional yogurt products is described. Adhesiveness to the human intestine is one of the most important characteristics of probiotic LAB. A new screening system that involves a combination of three methods is proposed: rat colonic mucin (RCM)‐micro plate assay, Carnoy's histochemical staining method and carbohydrate probe binding assay. By using an RCM‐coated poly‐vinylidene‐diflouride membrane that mimics the human colonic mucous layer, a new lectin was isolated and its structure was clarified by gene cloning. Furthermore, the structures and functions of a new cyclic bacteriocin (gassericin A), new lactose‐hydrolyzing enzymes, and new immunostimulating oligo DNA motifs from Lactobacillus gasseri (B₁ subgroup) were clarified. A new functional yogurt ‘Fit down’ is proposed, that is fermented by an adhesive strain of L. acidophilus LA67 selected by our screening and contains antihypertensive peptides derived from whey proteins by protease digestion. In the future, superior functional foods containing more effective probiotic LAB are expected to be developed by the use of the proposed mass screening system.     

抑制奶牛乳房炎源金黄色葡萄球菌的乳酸菌的筛选

为获得抑制奶牛乳房炎源金黄色葡萄球菌(S. aureus)的乳酸菌(LAB),本研究从新疆巴音布鲁克牧区鲜牛乳和哈萨克族乳制品奶疙瘩样品中分离培养LAB,通过传统的分离鉴定与16S rDNA基因序列测序相结合的方法鉴定LAB种类,同时以临床奶牛乳房炎源金黄色葡萄球菌S. aureus N2为指示菌,采用双层琼脂扩散法检测分离株的抑菌能力。通过测定生长曲线确定分离株的生长稳定期,进而利用硫酸铵沉淀法透析提取稳定期内分离株的细菌素,并检测其细菌素抑菌效价。结果显示:从样品中筛选获得5株能够抑制指示菌生长的LAB,分别为希氏乳杆菌、干酪乳杆菌、粪肠球菌、戊糖片球菌和乳酸乳球菌亚种。生长规律曲线表明20 h^30 h为5株LAB的稳定期,此期培养液pH值维持在3.8~4.5。从培养20 h的5株LAB上清液中提取到了细菌素,经检测其具有抑菌活性,抑菌效价分别为457 IU/mL、1 023 IU/mL、676 IU/mL、1 862 IU/mL和1 023 IU/mL。本研究结果表明5株LAB通过在生长稳定期内维持较低酸性环境(pH<4.5),代谢产生细菌素对乳房炎源S. aureus发挥抑制生长作用。本研究为S. aureus性奶牛乳房炎的生物防治提供了实验依据。     

乳固形物浓度对新鲜软质干酪凝乳效果的影响

本研究以脱脂牛奶为原料制成的非成熟型新鲜软质干酪,其风味柔和、清淡,易被我国消费者接受;同时对乳固形物浓度对新鲜软质干酪凝乳效果及干酪品质的影响进行了研究,结果表明,随着乳固形物浓度的增加,凝乳时间延长,干酪口感粗糙变硬,乳清OD500值先降后升。     

细菌素及其应用的研究进展

细菌素是细菌自身生产的一类杀菌物质,由基因编码、核糖体合成,是自然界中细菌用于调节自身菌群结构的一类重要活性物质。细菌素的来源广泛、结构多样,对各种动物致病菌都具有高效抑杀作用,这些特点为细菌素开发成为一种新型抗菌药物提供了可能。作者对近年来在细菌素生物学特征的发展、分类更新及其应用研究等进行了综述,希望能为中国新型细菌素类动物药物的开发提供参考。     

干酪生产质量控制

干酪是液体乳为原料，经凝乳、排乳清，发酵成熟制成的产品。本文论述了干酪生产过程中原料乳及其均质、酸化、凝块切割等因素的影响。并对于酪成熟过程中酶类与微生物对其品质的影响进行了分析。     

乳清在奶酪制作中的应用

通过单因素对比试验结合Box-Behnken设计和响应面法研究乳清添加量、谷氨酰胺转氨酶（TG）添加量和TG作用时间对奶酪得率的影响,建立相应的回归模型。确定乳清的最适添加方式为不对其进行杀菌且在凝乳前加入到原料乳中,在乳清添加量30%、TG添加量1.4048g/100mL、TG作用时间89.955min的条件下,乳清奶酪得率的理论预测最大值为14.8463%,在此最佳条件下奶酪的实际平均得率为13.875%,与理论预测值差异不显著（P〉0.05）。乳清奶酪在成熟初期,其质构特性、蛋白水解程度和色泽与对照奶酪有差异,到成熟50d时,除弹性和咀嚼性差异显著（P〈0.05）外,其余指标差异均不显著（P〉0.05）。     

Flavour of goat's milk: A review of studies on the sources of its variations

The specific flavour of goat's milk is undesirable for direct consumption but for cheese production its presence can be advantageous.Norwegian trials have shown that unclean handling of the milk reduces the true flavour. The flavour was not influenced by the presence of a buck.The flavour is influenced by the free fatty acid content, especially the C₆ to C₁₀ acids, and also may be affected by the KCl content and the presence of three different cresols. The flavour is negatively correlated to the organic substances in the milk. A strong flavour in the milk causes a strong flavour in the product when making brown whey cheese as well as ordinary white cheese.In the Norwegian goat population there is a positive phenotypic, and maybe also a positive genetic, correlation between yield and strong flavour. The heritability for flavour is estimated to be about 0.25. A significant difference has been found between Norwegian and Saanen goat's milk, both in flavour intensity and free fatty acid content.The flavour was less pronounced at the start and the end of lactation. Small differences were found in the flavour when comparing milk produced by goats fed on pasture and indoors. High feeding intensity by means of concentrates generally increased the flavour of the milk. In general the method of feeding and different feedstuffs have little influence on the true flavour of the goat's milk.     

Probiotic supplementation improves reproductive performance of unvaccinated farmed sows infected with porcine epidemic diarrhea virus

We investigated if probiotic supplementation could improve the health and reproductive performance of unvaccinated lactating sows infected with porcine epidemic diarrhea (PED) virus. Twenty unvaccinated pregnant sows were equally allocated to probiotic‐supplemented (P) and control (C) groups. For the experiment, 15 g/day of probiotic compound BIO‐THREE PZ was given to P sows. Reproductive performance was checked daily. The number of neonates fostered by each sow was maintained at eight throughout the experiment. Individual milk production post‐parturition was measured twice. Milk protein and fat ratios were determined by a milk analyzer. Total immunoglobulin (Ig) A and G concentrations were measured by ELISA. At day 7 post‐parturition, the body weight of P sows was 10 kg higher than that of C sows, and at day 3 post‐parturition, P sows produced more milk (+2 kg) and had a higher IgA concentration in whey than did C sows (p < .05). Finally, unlike C sows, P sows tended to return to estrus faster, and had larger piglets at birth with a lower mortality percentage during early days of suckling. In conclusion, probiotic compound BIO‐THREE PZ helped strengthen the immune system of unvaccinated, PED‐infected sows and improved their reproductive performance.     

Rapid activation of Mac-1(CD11b/CD18) molecules on macrophages by a new chemotactic factor 'Gasserokine' produced by Lactobacillus gasseri JCM1131T

The chemoattractant activity of a new chemotactic factor, 'Gasserokine' produced by Lactobacillus gasseri JCM1131^T, has been proposed as a novel immunological function of probiotic lactic acid bacteria. The focus of the present study was to understand the mechanism of the chemotaxis induced by Gasserokine, using activation of an adhesion molecule, Mac-1 (CD11b/CD18) on macrophages. The macrophage chemotaxis to Gasserokine was abolished by preincubation of macrophages with the anti-Mac-1 mAb. Gasserokine induced rapid serine phosphorylation of CD18 molecules within 1 min of stimulation, but the effect was short-lived. Substantial tyrosine phosphorylation was observed in CD18-associated protein of macrophages stimulated by Gasserokine. The tyrosine phosphorylation was confirmed in macrophages stimulated with Gasserokine and also serine/threonine phosphorylation was detected on CD18 molecules by laser microscopy using a double immunostaining method. These results suggest that selective activation of intracellular signaling cascades, such as the mitogen-activated protein kinase pathway, are related to the macrophage chemotaxis induced by Gasserokine.     

Characterization of bacteriocin produced by Streptococcus bovis J2 40-2 isolated from traditional fermented milk 'Dahi'

A bacteriocin-producing strain Streptococcus bovis J2 40-2 was isolated from traditional fermented milk 'Dahi' in Bangladesh. Despite its narrow antimicrobial spectrum, it showed strong antimicrobial activity against extremely challenging and problematic organisms in foods, such as Listeria monocytogenes . Bacteriocin was sensitive to several proteolytic enzymes and showed antimicrobial activity over a wide pH range of 2.0–10.0. It was stable when heated to 110°C for 20 min, but lost 25% of its activity when heated to 121°C for 15 or 20 min. Optimum bacteriocin production (5600 AU/mL) was achieved when the strain was cultured at 37°C for 24 h in MRS medium rather than in TYLG, GM17, or skim milk medium. Bacteriocin was partially purified by ammonium sulfate precipitation (80% saturation), dialysis (cut-off MW: 3500) and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that bacteriocin had a molecular weight of approximately 4.5 kDa.     

乳清饮料的研究进展

乳清是工业生产干酪和干酪素的副产品,含有多种营养成分,可以作为饮料的原料.介绍了乳清中的营养价值和乳清饮料的各种不同种类,并比较了各种饮料的特点,指出乳清发酵饮料是具有广阔发展前景的乳清饮料.     

Phenotypic and genetic characterisation of bacteriocin-producing strains of Staphylococcus aureus involved in bovine mastitis

Fifty strains of Staphylococcus spp. isolated from bovine mastitis cases in several herds from different Argentinian provinces were screened for antimicrobial substances. Twelve strains exhibited a high antagonistic activity against the indicator strain (Corynebacterium fimi) and were chosen for further characterisation. The antimicrobial substances were sensitive to proteolytic enzymes suggesting that they might be bacteriocins (Bac). These strains were identified as S. aureus by the amplification of the femA gene. Plasmid profile analysis of these strains revealed the presence of at least one plasmid. Eleven strains carried a plasmid with a size similar to that of pRJ6 (8.0kb), which encodes aureocin A70, a bacteriocin produced by the Brazilian S. aureus strain A70 isolated from commercial milk. The other strain harboured a much larger plasmid. PCR experiments, using specific primers for amplification of the bacteriocin operon found in pRJ6, showed that all strains had the expected 525bp amplicon, suggesting that the bacteriocin produced may be related to aureocin A70. The genomic DNA of all Bac(+) strains was then analysed by pulsed-field gel electrophoresis (PFGE) in order to investigate clonal relationships amongst strains. Based on the results of PFGE experiments, 10 out of the 12 Bac(+) strains belonged to the same clone. The remaining two strains are possibly related to the prevalent clone. The aureocin A70 producer-strain belonged to a distinct clone.     

乳过氧化物酶的特性及其在羊乳产业中的应用

羊乳富含维生素和蛋白质等营养物质,易被人体消化吸收,却也极利于微生物的生长,如何使用安全、便捷、成本低廉的保鲜方法促进羊乳产业的发展是必须要解决的现实难题。本文从乳过氧化物酶（lactoperoxidase,LP）的结构特性、组成成分、抑菌机理、热力学特性以及稳定性等方面进行论述,并综述了LP在羊乳产业中用于保鲜、检测对原料乳、干酪和发酵型乳制品的影响,为了解LP在羊乳产业的发展与应用提供参考。     

The inclusion of a daisy plant (Chrysanthemum coronarium) in dairy sheep diet. 1: Effect on milk and cheese fatty acid composition with particular reference to C18:2 cis-9, trans-11

An experiment was carried out to evaluate the effect on milk and cheese fatty acid composition of the inclusion of Chrysanthemum coronarium L., (Asteracea) into dairy sheep diet. Plots sown either with a binary mixture consisting of Lolium rigidum Gaudin and Medicago polymorpha (LM) or a ternary mixture including the above species and C. coronarium were (LMC) grazed by groups of Sarda dairy ewes during May. The botanical composition of diet, as measured by n-alkane method, showed that 34% of LMC group diet consisted of Chrysanthemum flowers and leaves. Exposure of sheep to this non-conventional forage did not affect animal performance and milk composition (fat and casein, P > 0.05) but resulted in different milk and cheese fatty acid composition. In particular conjugated linoleic acid, vaccenic acid and linoleic acid were all higher in LMC than LM groups (P < 0.05). The probable main reason was the higher proportion of linoleic acid in Chrysanthemum forage and hence in LMC than LM diet.     

Acid phosphatase in cheese

The combined action of proteinases/peptidases and acid phosphatases on phosphorylated proteins/peptides could be important for cheese quality. It seems that acid phosphatase activity in cheese originates from milk and microorganisms. Bovine milk contains more than one acid phosphatase, which are distributed between the cream and skim milk. The properties of two enzymes isolated from butter milk and skim milk are different. In general, acid phosphatase, especially that from starter organisms is very heat stable. The dephosphorylation of casein and phosphopeptides is of interest in cheese ripening. It has been suggested that acid phosphatases from both skim milk and lactic acid bacteria contribute to dephosphorylation of phosphopeptides in cheese, which are produced from casein by coagulant, indigenous milk proteinase and microbial proteinases during cheese ripening.