超高压杀菌效果及机制研究进展

超高压作为一种新型的食品非热加工技术, 处理过程温度低、对食品营养成分破坏小,能在有效杀菌的同时显著提升加工食品品质,是未来食品加工技术发展的热点方向。近年来,超高压技术被广泛应用于食品加工,并在国内外实现了商业化应用。杀菌作为超高压加工食品过程中最重要的环节,是保证食品安全、延长产品货架期的关键点,因此一直是本领域研究的重点。本文介绍了超高压技术的设备和作用原理, 总结了超高压或超高压联合其他手段对微生物营养体、细菌芽孢、真菌孢子及病毒的杀灭效果和杀菌机制, 归纳了超高压杀菌中存在的杀菌机制不清、缺乏杀菌指示菌以及深休眠芽孢等问题, 以期为进一步完善超高压杀菌理论、推动超高压技术在食品加工中的产业化应用指明方向。     

化学物质辅助超高压处理对枯草杆菌芽孢的作用

为研究化学物质辅助超高压处理(CAPS)对枯草杆菌芽孢的作用及其机理,采用150,350和550 MPa压力结合尼生素、溶菌酶、ε-聚赖氨酸或大蒜素处理枯草杆菌芽孢30 min,然后测定菌落总数变化。利用透射电镜和流式细胞仪研究超高压处理对枯草杆菌芽孢内部结构及内膜通透性的影响,结果表明:以上CAPS处理根本无法直接杀灭芽孢。在超高压处理下芽孢未彻底萌发,芽孢衣没有脱落,芽孢内膜未被损害。以上化学物质无法穿透芽孢衣或内膜这两个通透性屏障,进而杀灭芽孢。CAPS处理的芽孢在37℃培养3 h后,绝大部分芽孢彻底萌发,进而被化学物质杀灭。     

Spore inactivation on solid surfaces by vaporized hydrogen peroxide—Influence of carrier material surface properties

The aim of this study was to investigate the influence of surface hydrophobicity and roughness of carrier materials on the inactivation of bacterial spores with gaseous hydrogen peroxide whereas condensate formation is prevented. Spores of Bacillus subtilis and Bacillus atrophaeus were applied either as single spore culture or as a mixed spore population to simulate natural contamination with microorganisms of different characteristics. Inactivation with gaseous hydrogen peroxide was carried out at 5200 ppm hydrogen peroxide without condensate formation. The inactivation results of B. subtilis and B. atrophaeus spores on carrier materials with varying surface hydrophobicity differed significantly. However, inactivation of the mixed spore populations resulted in similar resistance compared to the single spore batches. The results of this study indicate that surface hydrophobicity most probably has an impact on the inactivation with gaseous hydrogen peroxide whereas surface roughness only plays a minor role.     

冷等离子体技术灭活细菌芽孢的研究进展

芽孢是某些细菌营养体在环境胁迫条件下形成的休眠体,广泛存在于自然界中。芽孢结构致密,对热、紫外线辐射等环境胁迫具有较强的抗性,很难被食品工业中常规的杀菌方法所杀灭,是影响食品安全的重要因素。近年来,非热加工技术在杀灭芽孢中的应用受到广泛关注。冷等离子体是一种新型非热杀菌技术,具有杀菌效率高、能耗低、无二次污染等优点,在食品工业中有广阔的应用前景。本文综述了冷等离子体杀灭食品中细菌芽孢的研究进展,总结了冷等离子体杀灭芽孢的作用机制,分析了影响冷等离子体作用效果的因素,并展望了今后的研究方向,以期为冷等离子体在食品安全控制领域的实际应用提供理论基础。     

酸浆豆腐直投式发酵剂制备和储存条件优化

目的 优化酸浆豆腐直投式发酵剂的制备和储存条件.方法 先以菌泥的离心收集率为指标,确定HCUL 1.1901-1912、乳酸链球菌乳亚种1.2472和嗜热链球菌1.2718的离心条件.再以冻干菌粉的存活率为指标,确定离心后菌泥的应激处理条件、冻干pH和菌粉的储存条件.最后检测直投式发酵剂的发酵性能和用其制备的酸浆豆腐品...     

Short communication: Quantification of the transmission of microorganisms to milk via dirt attached to the exterior of teats

Pathogens and spoilage microorganisms can be transmitted to milk via dirt (e.g., feces, bedding material, soil, or a combination of these) attached to the exterior of the cows’ teats. To determine the relevance of this pathway and to perform quantitative microbial risk analysis of the microbial contamination of farm tank milk (FTM), it is important to know the amount of dirt transmitted to milk via the exterior of teats. In this study at 11 randomly selected Dutch farms the amount of dirt transmitted to milk via the exterior of teats is determined using spores of mesophilic aerobic bacteria as a marker for transmitted dirt. The amount of transmitted dirt to milk varied among farms from ∼3 to 300 mg/L, with an average of 59 mg/L. The usefulness of the data for microbial risk analyses is briefly illustrated using the contamination of FTM with spores of butyric acid bacteria as a case study. In a similar way the data can be used to identify measures to control the contamination of FTM with other microorganisms or chemical residues.     

Effects of High-Pressure Processing (HPP) on Bacterial Spores: An Overview

High pressure processing (HPP) at high temperatures has been investigated to inactivate bacterial spores. By improving HPP using cyclic/oscillatory/pulsed pressure applications or combination with other treatments (such as thermal), and agents (such as antibacterial), bacterial spores can be inactivated, resulting in shelf-stable foods with natural sensory, quality, and nutritional attributes. This paper reviews literature on the recent advances in inactivation of bacterial spores by HPP, including its combination with high temperature, and oscillatory processing. The mechanisms of HPP-induced bacterial spore germination and inactivation are also discussed.     

Quantification of Factors Which Influence Nisin's Inhibition of CIostridium botulinum 56A in a Model Food System

We modeled nisin's anticlostridial activity and assessed the antagonistic or potentiating influences of food ingredients. The model systems contained yeast extract, proteose peptone, and glucose; were supplemented with protein (0.075, 0.75, 7.5% w/v), phospholipid (0.075, 0.75, 7.5% w/v), or soluble starch (5, 17.5, 30% w/v); and were adjusted to pH 5.5, 6.0, or 6.5. Samples inoculated with 10⁴/mL spores were incubated at 15, 25, or 35°C. Statistical analysis developed an equation (r²= 0.76) that modeled the response and identified temperature as the most significant (α 0.001) variable. Nisin lost effectiveness with increasing temperature. Nisin concentration had significant positive and phospholipid negative, linear effects. Many interactive effects were significant (α 0.20). Nisin inhibited C. botulinum until its residual level dropped below a threshold, which decreased from 154 IU/mL at 35°C to 12 IU/mL at 15°C.     

Comparison of Predictive Models for Bacterial Spore Population Resources to Sterilization Temperatures

Comparisons of characteristics of recent models and the conventional model of bacterial spore populations during thermal sterilization showed the conventional model was inadequate for general representation because it lacks activation of dormant spores. New models accounting for activation differed in other assumptions but obviated heat shock of indicator spores required when using the conventional model in validations of thermal sterilization. Comparisons of rate constants and simulated and experimental responses of models of B. stearother-mophilus spores in constant and dynamic temperatures showed one new model was more general, more accurate and preferred. Arrhenius equations accurately described temperature dependencies of all rate constants of that model.     

邵武烟田土壤微生物群落结构变化与烟草青枯病发生关系初报

为了研究健康和发病烟田土壤微生物群落结构的差异,分别在烟株不同生长时期采取健康和发病烟田土壤,对土壤微生物进行16S rRNA和18S rRNA基因测序,分析其群落结构和多样性的变化。结果表明:与移栽前相比,烟株旺长期土壤微生物群落结构已发生了较大变化,旺长期土壤中酸杆菌门（Acidobacteria）相对丰度平均减少了5.4%,放线菌门（Actinobacteria）增多了8.0%,子囊菌门（Ascomycota）增多了22.8%;健康土壤中unclassifed_f__Micrococcaceae相对丰度是发病土壤的2倍,而发病土壤中假霉样真菌属（Pseudallescheria）相对丰度是健康土壤的2倍;健康土壤微生物多样性较高于发病土壤。微生物群落结构在健康和发病土壤之间存在较大差异,unclassifed_f__Micrococcaceae、假霉样真菌属（Pseudallescheria）等土壤微生物是造成差异的主要物种。      

鲟鱼发酵过程中微生物的演替变化分析

为了解鲟鱼发酵中细菌群落多样性及动态演替规律,为发酵鲟鱼的品质提供理论数据,利用Illumina HiSeq测序平台,采集鲟鱼发酵过程中的7个阶段的样品,对样品中的细菌16S rDNA V4~V5区进行测序和系统发育分析。结果表明,样品获得序列数平均为46 463条,各个发酵阶段的操作分类单元数目分别为新鲜鱼样1 064,腌制鱼样952;发酵5 d 454,发酵10 d 442,发酵20 d 327,发酵25 d 372和发酵35 d 356。7组样品中总体细菌组成较为复杂,含有38个门、196个科,在新鲜鱼样中,厚壁菌门(Firmicutes)和变形菌门(Proteobacteria)占主要优势;在腌制阶段,蓝藻门(Cyanobacteria)占主要优势;从发酵开始至结束,厚壁菌门(Firmicutes)占绝对优势。在科水平上,新鲜鱼样中的主要优势菌科为肠杆菌科(Enterobacteriaceae),腌制样品中的主要优势菌科为肠球菌科(Enterococcaceae);从发酵开始至结束,主要的优势菌科为明串珠菌科(Leuconostocaceae),其次是乳杆菌科(Lactobacillaceae)和链球菌科(Streptococceae)。通过HiSeq测序能够更全面解析鲟鱼发酵过程中的细菌多样性;从测序平台提供的微生物多样性信息中发现,各样品间的菌属丰度存在一定的差异性,说明菌群组成与发酵环境密切相关,这为传统腌鱼发酵提供了理论依据和数据支撑。     

Ruminal metabolism of grass silage soluble nitrogen fractions

The present study was conducted to investigate ruminal N metabolism in dairy cows using ¹⁵N-labeled N sources and dynamic models. The data summarized in this study were obtained from 2 of 4 treatments whose effects were determined in a 4 × 4 Latin square design. Soluble N (SN) isolated from timothy grass silage labeled with ¹⁵N and ammonia N (AN) labeled with ¹⁵N were administered into the rumen contents of 4 ruminally cannulated dairy cows. Ruminal N pool sizes were determined by manual evacuation of rumen contents. The excess ¹⁵N-atom% was determined in N-fractions of rumen digesta grab samples that were collected frequently between 0 to 72 h and used to determine ¹⁵N metabolism in the rumen. Calculations of area under the curve ratios of ¹⁵N were used to estimate proportions of N fractions originating from precursor N pools. A model including soluble nonammonia N (SNAN), AN, bacterial N, and protozoal N pools was developed to predict observed values of ¹⁵N atomic excess pool sizes. The model described the pool sizes accurately based on small residuals between observed and predicted values. An immediate increase in ¹⁵N enrichment of protozoal N suggests physical attachment of bacteria pool to protozoa pool. The mean proportions of bacterial N, protozoal N, and feed N in rumen solid phase were 0.59, 0.20, and 0.21, respectively. These observations suggest that protozoal N accounted for 0.25 of rumen microbial N. About 0.90 of the initial dose of AN was absorbed or taken up by microbes within 2 h. Faster ¹⁵N enrichment of bacterial N with SN than with AN treatment indicates a rapid adsorption of SNAN to microbial cells. Additionally, the recovery of ¹⁵N as microbial and feed N flow from the rumen was approximately 0.36 greater for SN than for the AN treatment, indicating that SNAN was more efficiently used for microbial growth than AN. The present study indicated that about 0.15 of microbial N flowing to the duodenum was of protozoal origin and that 0.95 of the protozoal N originated from engulfed bacterial N. The kinetic variables indicated that 0.125 of SNAN escaped ruminal degradation, which calls into question the use of in situ estimations of protein degradation to predict the flow of rumen undegradable protein.     

Predicting Growth of Weissella Viridescens in Culture Medium under Dynamic Temperature Conditions

The lactic acid bacteria (LAB) are among the main spoilage microorganisms of foods, and the Weissella viridescens (formerly Lactobacillus viridescens) is well known to cause deterioration on the meat surface in vacuum packed meat products, even under refrigerated conditions. Therefore, this study evaluated the predictive ability of Baranyi and Roberts dynamic model to describe W. viridescens growth in culture medium (which simulates a food rich in nutrients), subjected to dynamic temperature conditions. Baranyi and Roberts primary model was fitted to the growth curves of W. viridescens in culture medium under six different isothermal temperatures (4, 8, 12, 16, 20 and 30°C) previously obtained in our laboratory. Four secondary models (linear, square root, exponential and Arrhenius type) were assessed to describe the influence of temperature on the growth parameters. The square root was the best model to describe temperature influence on μ_max parameter. For Y_max parameter, the secondary model was considered the mean values obtained experimentally in the studied temperature range. Experimental data were used to evaluate the model predictions under dynamic conditions for two different temperature profiles, NIP-1 (12-16-20-25°C) and NIP-2 (16-12-8-4°C). According to the statistical indexes, the model showed better predictive ability for NIP-1, with RMSE of 0.3341, R² of 0.9939, bias factor of 1.0046 and accuracy factor of 1.0197; the growth of W. viridescens under NIP-2 conditions was underestimated, indicating a fail dangerous prediction. The results showed that the predictive model can be used to predict the shelf life of meat products spoiled by W. viridescens.     

Estimation of the Temperature Dependent Growth Parameters of Lactobacillus Viridescens in Culture Medium with Two-step Modelling and Optimal Experimental Design Approaches

In predictive microbiology, the model parameters has been estimated using the traditional two-step modeling approach (TS), in which primary models are fitted to the microbial growth data and secondary models represent the dependence of model parameters with environmental variables. The optimal experimental design approach (OED) has been used as an alternative to TS, mainly because the improvement of model identifiability and reduction of the experimental workload and costs. The fitting of mathematical model to experimental data in TS is sequential, whereas in OED is simultaneous. Lactobacillus viridescens is a lactic acid bacteria that is of great interest to the meat products preservation. The objective of this study was to estimate the growth parameters of L. viridescens in culture medium with TS and OED. For TS, the experimental data were obtained in six temperatures; for OED, the data were obtained in four optimal non-isothermal experiments, two experiments with increasing temperatures (ITOED) and two with decreasing temperatures (DTOED). The Baranyi and Roberts, and the Square Root models were used to describe the microbial growth, in which the b and T_min parameters (± 95% confidence intervals) were estimated from the experimental data. The parameters obtained for TS were b = 0.0290 (±0.0020) h^-0.5°C^-1 and T_min = -1.33 (±1.26) °C, with R² = 0.991; for ITOED were b = 0.0314 (±0.0019) h^-0.5°C^-1 and T_min = 0.12 (±0.71) °C, with R² = 0.995; for DTOED were b = 0.0295 (±0.0019) h^-0.5°C^-1 and T_min = -1.57 (±1.05) °C, with R² = 0.999. The parameters obtained in the OED approach presented smaller confidence intervals, higher R² and less experimental time than the parameters obtained in the traditional TS approach. In this way, it is possible to answer positively that OED approach is feasible and could be widely applied in predictive microbiology.