Effects of UV-C treatment on inactivation of Salmonella enterica and Escherichia coli O157:H7 on grape tomato surface and stem scars,microbial loads,and quality

The purpose of this study was to investigate the effectiveness of ultraviolet-C (UV-C) light inactivation as affected by the location of pathogens on the surface and at stem scars of whole grape tomatoes. A mixed bacterial cocktail containing a three strain mixture of Escherichia coli O157:H7 (C9490, E02128 and F00475) and a three serotype mixture of Salmonella enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) were used. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve a population of about 10^7±1 CFU/tomato. Additionally, the effects of treatment on color, texture, lycopene content, and background microbial loads during post UV-C storage at 4 °C for 21 days were determined. Results showed that UV-C doses of 0.60–6.0 kJ/m² resulted in 2.3–3.5 log CFU per fruit reduction of E. coli O157:H7 compared to 2.15–3.1 log CFU per fruit reduction for Salmonella on the surfaces. Under the same conditions, log reductions achieved at stem scar were 1.7–3.2 logs CFU for E. coli O157:H7 and 1.9–2.8 logs CFU for Salmonella. The treatment was effective in controlling native microbial loads during storage at 4 °C as the total aerobic mesophilic organisms (PCA) and anaerobic lactic acid bacteria (LAB) counts of treated tomatoes were significantly (p < 0.05) lower during storage compared to the control group and the yeast and mold populations were reduced significantly below the detection limit. Furthermore, the firmness of tomato and its color was not affected by the UV-C doses during storage. UV-C radiation could potentially be used for sanitizing fresh tomatoes and extending shelf-life. The results of this study indicate that the specific location of pathogens on the produce influences the effectiveness of UV-C treatment, which should be taken into consideration for the design of UV-C systems for produce sanitization.     

酵母菌纯种发酵普洱茶初探

酵母菌是普洱茶发酵过程中的优势菌种之一,含有极丰富的对人体有益的营养物质、丰富的酶系统和生理活性物质,此外还能代谢产生VB1、VB2、Vc等物质,是形成普洱茶甘、滑、醇品质风格的重要因子。对从普洱茶渥堆发酵样品中分离出的5株优势酵母菌进行纯菌接种发酵试验,并对发酵后的茶样进行化学成分检测和感官评价,结果发现,酵母菌株Y5能将生茶的多酚值由28.33%降至14.54%,将茶褐素值由2.45%增至6.86%,在5株酵母菌发酵的茶样中,其茶褐素增幅最为显著。另外Y5发酵的茶样有香甜味,其滋味略苦,生津,有回甘,可以用来提高普洱茶的香气和滋味。     

Transglutaminase cross-linking of milk proteins and impact on yoghurt gel properties

A novel yoghurt process was investigated in which milk proteins were covalently cross-linked by a microbial transglutaminase (TG) preparation containing glutathione (TG+GSH). As unheated milk is normally less reactive towards TG, TG+GSH was applied to enable non-inhibited cross-linking without requiring a pre-heat treatment beyond pasteurisation conditions. After the TG+GSH incubation phase, the enzyme was inactivated by heat treatment of the yoghurt milk prior to fermentation. During yoghurt fermentation, no negative effect of TG+GSH on fermentation time was found. Protein cross-linking by TG+GSH was enhanced, resulting in higher apparent viscosity and a higher degree of protein polymerisation than that given by TG without GSH. Furthermore, different ratios of casein to whey proteins (CWP ratios) were used to investigate the effect of both protein fractions on covalently cross-linked yoghurt gel structures. The results showed a relationship between extent of cross-linking, apparent viscosity and CWP ratio of the yoghurt gels. During storage for up to 6 weeks at 4 °C, no changes in rheological properties and degree of protein polymerisation were measurable for stirred yoghurt gels prepared from cross-linked milk proteins.     

酱香白酒中两种异嗅物质鉴定的研究

采用GC-MS技术与感官品评相结合的方法分析了某酱香型白酒的嗅味物质。通过谱图比对及统计学分析,找出高锰酸钾处理前后酒样中具有显著性差异的物质,最终确定了白酒中臭味物质的主要组成。结果表明,二甲基二硫和二甲基三硫是白酒中主要的臭味物质,在异味酒样中的浓度分别为439.26μg/L和547.16μg/L。另外,从生产工艺的角度提出了防止白酒中臭味产生的措施。     

枸杞果汁发酵过程复合乳酸菌的实时定量检测

利用植物乳植杆菌（Lactiplantibacillus plantarum）、发酵粘液乳杆菌（Limosilactobacillus fermentum）和瑞士乳杆菌（Lactobacillus helveticus）混合菌种进行枸杞果汁发酵。该研究对乳酸菌亚致死修复液的组成和修复温度进行优化,分别针对3株乳酸菌设计特异性引物,利用叠氮溴化丙锭（PMA）-荧光定量聚合酶链式反应（fqPCR）的方法,实时荧光定量检测枸杞果汁发酵过程中乳酸菌活菌数。结果表明,优化修复液的组成为蛋白胨1 g/L、牛肉浸出粉0.3 g/L、氯化钠0.5 g/L、吐温80 0.10 g/L、丙酮酸钠0.09 g/L、过氧化氢酶0.04 g/L、MgCl2 3 mmol/L、Na2HPO4 1 mmol/L、MnCl2 2 mmol/L和FeCl2 2 mmol/L。在27 ℃条件下培养15 min,乳酸菌亚致死细胞修复率达到97%。利用该方法实现了枸杞果汁发酵过程不同乳酸菌的实时定量检测,为今后枸杞果汁发酵生产过程中的微生物动态监测提供了方法。     

灰树花海棠果发酵饮料研制及其抗疲劳活性研究

该试验以灰树花、海棠果为原料,以植物乳杆菌（Lactobacillus plantarum）MA2、保加利亚乳杆菌（Lactobacillus bulgaricus）717和嗜热链球菌（Streptococcus thermophiles）176为发酵剂,制备灰树花海棠果发酵饮料,并采用正交试验对其发酵工艺进行优化。结果表明,灰树花海棠果发酵饮料最佳发酵工艺为白砂糖添加量6%,MA2∶717∶176接种比例为2∶1∶1,发酵时间3 d,发酵温度为37 ℃。在此优化条件下制得饮料酸甜可口,风味良好,感官评分为89分。通过跑笼试验、负重游泳试验、爬杆试验探究灰树花海棠果发酵饮料对大鼠抗疲劳的作用。结果表明,灰树花海棠果发酵饮料具有良好的抗疲劳效果,可显著提高大鼠机体耐力,缓解疲劳。     

金属-多酚网络的组装、功能特性及其在食品领域中的应用研究进展

多酚与金属离子形成的金属-多酚网络（metal-polyphenol network,MPN）能发挥金属与多酚的协同效应,既具有金属离子赋予的特定功能,又具有多酚结构对各种表面的高亲和力,能吸附在纳米材料和生物界面等多种表面上,且结构更加稳定。近年来MPN发展迅猛,在很多领域都得到了广泛的应用。本文首先概述了MPN的组装机制和组装原材料（主要是单宁酸和铁离子）,简要介绍了一步共混沉积法和层层组装法两种组装方法及常见的表征方法,详细论述了MPN的抗菌性、抗氧化性、吸附性和pH值响应性等功能特性及其在食品领域的应用等,并对MPN的未来发展趋势进行了展望。     

玉米油精炼过程氯离子含量变化及其对3-氯丙醇酯和缩水甘油酯含量的影响

对取自安徽、河北、山东等地玉米油加工厂的玉米油毛油、待脱臭油和成品油中的氯离子、3-氯丙醇（3-monochloro-1,2-propanediol,3-MCPD）酯和缩水甘油酯（glycidyl esters,GEs）含量进行检测,并在实验室明确可控的条件下对玉米毛油进行精炼,检测精炼过程氯离子、3-MCPD酯和GEs含量,与玉米油加工厂实际精炼过程的含量变化情况进行对比分析,研究玉米油精炼过程中氯离子含量变化及其对3-MCPD酯和GEs含量变化的影响。结果表明：所检测的所有玉米油样品中均含有氯离子、3-MCPD酯和GEs,其中毛油中氯离子含量最高,为0.628～2.029 mg/kg,毛油中3-MCPD酯和GEs含量分别为0.547～1.083 mg/kg和0.246～0.721 mg/kg;待脱臭玉米油中氯离子含量为0.110～0.374 mg/kg,较毛油中含量明显降低,3-MCPD酯和GEs含量分别为0.933～1.422 mg/kg和0.246～0.432 mg/kg,3-MCPD酯较毛油中含量有所升高,GEs含量变化不明显。脱臭油中3-MCPD酯和GEs含量分别为3.523～4.541 mg/kg和1.501～13.584 mg/kg,较待脱臭油中含量大幅升高,其中一个油样中含量分别增加3.5 倍和32.1 倍,同时该油样中氯离子含量的降幅也最大（0.287 mg/kg）。对实验室精炼过程及工厂精炼过程的玉米油样品检测分析显示,无论是实验室精炼还是工厂实际生产,氯离子含量均随精炼过程逐渐减少,其中降幅最大的是水化脱胶和碱炼脱酸工序（降幅为76.1%～81.3%）;3-MCPD酯和GEs在水化脱胶、碱炼脱酸及吸附脱色过程的含量变化不大,经脱臭后含量大幅升高,同时伴随脱臭过程氯离子含量的降低,并且氯离子含量降幅越大3-MCPD酯的升幅越高。研究结果明确了玉米油精炼过程氯离子和3-MCPD酯及GEs含量的变化规律,以及待脱臭玉米油中氯离子含量对脱臭油脂中3-MCPD酯和GEs含量的影响,对玉米油精炼乃至其他植物油生产中3-MCPD酯和GEs的风险防范和控制都具有指导意义。     

Heat transfer from a spinning disk during semi-confined axial impingement from a rotating nozzle

Conjugate heat transfer from a uniformly heated spinning solid disk of finite thickness and radius during a semi-confined liquid jet impingement from a rotating nozzle is studied. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the spinning confinement plate and free surface flow after exposure to the ambient gaseous medium. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The solution is made under steady state and laminar conditions. The study considered various plate materials such as aluminum, copper, silver, constantan and silicon. Ammonia, water, flouroinert FC-77 and MIL-7808 oil were used as working fluids. The range of parameters covered included Reynolds number (220–900), Ekman number (7.08 × 10^?5–∞), nozzle-to-target spacing (β = 0.25–1.0), disk thicknesses to nozzle diameter ratio (b/d_n = 0.25–1.67), Prandtl number (1.29–124.44) and solid to fluid thermal conductivity ratio (36.91–2222). It was found that a higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire disk surface. The rotational rate also increased local heat transfer coefficient under most conditions. An engineering correlation relating the Nusselt number with other dimensionless parameters was developed for the prediction of the system performance.