Bacillus cereus and Bacillus stearothermophilus Spore Inactivation in Batch and Continuous Flow Systems

Thermal inactivation kinetics were evaluated in batch and continuous flow systems using phosphate buffer between 99 and 107°C for Bacillus cereus T and 128.5 and 139°C for Bacillus stearothermoohilus ATCC 12980 spores. z_D-Values for B. cereus spores in batch aid continuous flow systems were not significantly different; the continuous flow system was more lethal than the batch system. z_D-Values obtained using B. stearothermophilus spores in batch and continuous flow systems were different; the batch system was more lethal than the continuous flow system. Thus, use of batch generated data to predict or design continuous flow processes may not be accurate.     

Model of the Inactivation of Bacterial Spores by Moist Heat and High Pressure

ABSTRACT: Formulae for the prediction of inactivation and accumulated lethality of bacterial spores under moist heat and high pressures were derived on the basis of classic thermodynamic and kinetics principles. The capability of the model to describe the inactivation of bacterial spores was verified using 2 independent data sets corresponding to Clostridium botulinum processed at 60°C to 75°C and Bacillus stearothermophilus processed at 92°C to 110°C. Both sets included pressures between 5 × 10⁸ Pa and 7 × 10⁸ Pa. The equation fit explained more than 86% of the variation of the rate constant data. The developed equations establish a strong foundation on which to compare high-pressure processing treatments of different systems. This is especially useful because most systems have different transient temperature-pressure conditions.     

BP网络对凝结芽孢杆菌芽孢热压协同灭活条件的优化

通过BP网络对超高静压协同热处理灭活凝结芽孢杆菌芽孢的条件(压力、温度和保压时间)进行优化,结果表明,经过训练的BP网络具有良好的预测能力;经训练的BP网络能够对超高静压协同热处理灭活凝结芽孢杆菌芽孢的条件进行优化,得到的最优组合为：压力550MPa,温度80℃、时间20min,此组合可达到的灭活效果为芽孢数下降了4.97个数量级,此结果比正交试验结果提高了0.16个数量级。     

Inactivation Kinetics of Geobacillus stearothermophilus Spores in Water Using High-pressure Processing at Elevated Temperatures

ABSTRACT: Establishment of a high-pressure sterilization process requires data on pressure and temperature-dependent inactivation kinetics of target pathogenic, spoilage, or surrogate spore-forming bacteria in the food being tested. The objective of this study was to examine the response of Geobacillus stearothermophilus ATCC10149 spores to various temperature, time, and pressure combination treatments (500 to 700 MPa; 92°C to 111°C, 0.01 to 360 s). The pressure inactivation of spores was characterized at elevated temperatures under isobaric and isothermal conditions during the holding time using a laboratory-scale high-pressure unit. The inactivation kinetics was well described by the log-linear regression model. As expected, the rate of spore inactivation increased with increasing pressure and temperature. Decimal reduction times at constant pressure ( D _T,P values) varied from 29.4 to 108.8 s at 92°C, 17.4 to 76 s at 100°C, and 6.1 to 51.3 s at 111°C within the pressure range of 500 to 700 MPa. The resistance of spores to temperature and pressure was characterized with z_T and z_P values and compared with their resistance to conventional steam heating. The conventional thermal resistance of G. stearothermophilus species did not correlate to the thermal resistance at high pressure. The study provides kinetic data on the effects of pressure and temperature on the inactivation of a heat-resistant bacterial spore species under conditions applicable to the commercial processing of low-acid foods.     

热协同超高压对不同介质中嗜热脂肪芽孢杆菌芽孢的灭活作用

以磷酸缓冲液及经过人工接种的牛乳、鸡腿菇和卤牛肉为对象,考察超高压协同热处理对嗜热脂肪芽孢杆菌灭活的影响,测定处理前后的细菌菌落总数。结果表明,嗜热脂肪芽孢杆菌的失活率依次为:牛乳>磷酸缓冲液>鸡腿菇>卤牛肉。处理组500/60℃、500/90℃、600/80℃,5min、10min,牛乳中失活率(-2.18,-2.82,-3.32)高于磷酸缓冲液中的失活率(-1.62,-2.78,-2.98);卤牛肉中的失活率低于鸡腿菇中的失活率。说明在热协同超高压杀灭嗜热脂肪芽孢杆菌过程中,牛乳中存在利于诱导芽孢发芽的物质,使芽孢失去原有的对热的抵抗力,而在鸡腿菇和卤牛肉中失活率较牛乳低是由于其水分活度较低,卤牛肉中的失活率低于鸡腿菇中的失活率是由于NaCl对芽孢有保护作用,增加了其对压力的耐受性。     

High Pressure Inactivation of Polyphenoloxidases

Pressure stabilities of polyphenoloxidases (PPO) from apples, avocados, grapes, pears and plums were determined at pH 6-7. These PPOs differed in pressure stability, but all were rather pressure-stable. Inactivation of PPO from apple, grape, avocado and pear at room temperature (25°C) became noticeable at 600, 700, 800 and 900 MPa respectively, and followed first-order kinetics. Plum PPO was not inactivated at room temperature by pressures up to 900 MPa. For the two most pressure-stable PPOs, we investigated whether pressure stability would be reduced by the simultaneous application of mild heat. In case of plum PPO, activity reduction was detectable at 900 MPa and 50°C. Further temperature increase resulted in increase of the inactivation rate constant (E_a 63 kJ/mol). In case of pear PPO, temperature increase up to 35°C resulted in a 3-fold reduction of the inactivation rate constant. Only at higher temperatures, increase of the inactivation rate constant with increasing temperature was noted (Ea 120 kJ/mol).     

超高压提取灵芝孢子粉多糖的工艺研究

采用超高压技术提取灵芝孢子粉多糖,通用正交试验法,以多糖得率为指标,考察料液比、温度、压力、保压时间等因素对多糖提取的影响,并与水浸提法比较.超高压提取灵芝多糖最优工艺条件为:压力为400MPa,温度为50℃,固(g)液(mL)比1:40,保压时间应低于6min;提取得率为2.762%,高出水浸提提取37.1%,超高压提取具有得率高,提取温度低,提取时间短、节能等优点,为灵芝多糖的提取提供了一种新技术.     

Enzyme Inactivation in Food Processing using High Pressure Carbon Dioxide Technology

High pressure carbon dioxide (HPCD) is an effective non-thermal processing technique for inactivating deleterious enzymes in liquid and solid food systems. This processing method avoids high temperatures and exerts a minimal impact on the nutritional and sensory properties of foods, but extends shelf life by inhibiting or killing microorganisms and enzymes. Indigenous enzymes in food such as polyphenol oxidase (PPO), pectin methylesterase (PME), and lypoxygenase (LOX) may cause undesirable chemical changes in food attributes, showing the loss in color, texture, and flavor. For more than two decades, HPCD has proved its effectiveness in inactivating these enzymes. The HPCD-induced inactivation of some microbial enzymes responsible for microbial metabolism is also included. This review presents a survey of the published knowledge regarding the use of HPCD for the inactivation of these enzymes, and analyzes the factors controlling the efficiency of HPCD and speculates on the underlying mechanism that leads to enzyme inactivation.     

微热协同超高压处理杀灭芽孢杆菌芽孢效果的研究

采用比色法研究了微热协同超高压处理对枯草芽孢杆菌与嗜热脂肪芽孢杆菌芽孢的影响。结果表明,微热协同超高压处理芽孢能够显著提高芽孢2,6-吡啶二羧酸(DPA)的泄漏率(p<0.05)。处理组550、600MPa,50、60、70℃作用于枯草芽孢杆菌与嗜热脂肪芽孢杆菌芽孢,破坏芽孢结构,通透性屏障破坏,导致DPA的泄漏。所泄漏的DPA与灭菌对照组(121℃,30min)相比差异不显著(p>0.05),主要是芽孢质中的DPA。说明微热处理协同超高压杀灭枯草芽孢杆菌与嗜热脂肪芽孢杆菌芽孢的原因可能是其物理结构的破坏。     

High Hydrostatic Pressure as a Hurdle for Zygosaccharomyces bailii Inactivation

The combined effects of high hydrostatic pressure (HHP, 172, 345, 517 or 689 MPa), duration of HHP treatment (0, 2, 4, or 10 min), water activity (a_w 0.98 or 0.95), and potassium sorbate (PS) concentration (0 or 1000 ppm) on Zygosaccharomyces bailii inactivation were evaluated at pH 3.5 and 21°C in laboratory model systems. Inactivation of the initial inoculum (? 1.0 times; 10⁵ CFU/mL) occurred when the pressure was 689 MPa regardless of a_w PS or duration of treatment. Lower pressure was required for Z. bailii inactivation in the presence of PS.     

高压二氧化碳杀灭细菌芽胞的作用机制和影响因素

细菌芽胞对于外界物理或化学处理抗性很强,如何有效杀灭细菌芽胞是食品灭菌的重要难题。高压二氧化碳(high pressure carbon dioxide,HPCD)杀菌技术协同热处理对细菌芽胞有很好的杀灭作用。此外,辅助试剂的加入可以大幅增强其杀灭作用,并保持HPCD的处理条件温和、对食品破坏作用小和易于操控等优点。本文主要从芽胞结构与抗性关系、HPCD杀灭芽胞的机理以及影响因素三个方面,介绍了HPCD杀灭芽胞作用研究的进展。     

高压处理对鲜牛乳中枯草杆菌芽孢致死效应的研究

采用压力、时间、循环处理次数相结合的方法,在较低的温度下,对鲜乳中枯草杆菌芽孢激活及致死效应进行了研究。在40℃条件下,200MPa低压处理5min,停压1min,再升至700MPa下处理5min,循环处理7次,可将鲜乳中枯草杆菌芽孢数减少到102～103cells/ml。     

Kinetics of Tomato Pectin Methylesterase Inactivation by Temperature and High Pressure

ABSTRACT: In this study we investigated the inactivation of endogenous pectin methylesterase (PME) in tomato juice during combined high-hydrostatic pressure (ambient to 800 MPa) and moderate temperature (60 to 75 °C) treatments under isobaric and isothermal processing conditions. PME inactivation rates increased with increasing processing temperature, with the highest rate obtained during processing at 75 °C and ambient pressure. Inactivation rates were dramatically reduced as soon as processing pressure was raised. High inactivation rates were again attained when processing pressure exceeded a value of about 700 MPa. Such a behavior was described by considering two parallel mechanisms of inactivation, each one following first order kinetics with its own kinetic parameters.     

脉冲强光对枯草芽孢杆菌NG-2灭活机理

采用脉冲强光对枯草芽孢杆菌NG-2及芽孢进行灭活并研究其机理。在脉冲强光辐照枯草芽孢杆菌NG-2菌体及其芽孢后,利用扫描电子显微镜和透射电子显微镜观察形态特征变化,利用紫外分光光度法测定细胞内物质含量,利用荧光光谱法检测细胞内Ca~(2+)浓度和非特异性酯酶活力。结果表明,辐照距离为5 cm,闪照频率为5次/s,辐照15 s时,脉冲强光对NG-2菌体及其芽孢灭活率超过50%;辐照40 s时,脉冲强光对NG-2菌体及其芽孢灭活率超过99.98%。辐照枯草芽孢杆菌及芽孢后菌体结构损伤,芽孢壁破裂,细胞内核酸、蛋白质、Ca~(2+)和2,6-吡啶二羧酸含量显著减少,非特异性酯酶活力降低,研究结果为脉冲强光对枯草芽孢杆菌及芽孢灭活机理提供理论依据。     

High Pressure and Temperature Effects on Enzyme Inactivation in Strawberry and Orange Products

High hydrostatic pressure treatment (50-400 MPa) combined with heat treatment (20–60°C) effects on peroxidase (POD), polyphenoloxidase (PPO) and pectin methylesterase (PME) activities of fruit-derived products were studied. Assays were carried out on fresh orange juice and strawberry puree. Pressurization/depressurization treatments caused a significant loss of strawberry PPO (60%) up to 250 MPa and POD activity (25%) up to 230 MPa, while some activation was observed for treatments carried out in 250–400 MPa range for both enzymes. Optimal inactivation of POD was using 230 Mpa and 43°C in strawberry puree. Combinations of high pressure and temperature effectively reduced POD activity in orange juice (50%) to 35°C. The effects of high pressure and temperature on PME activity in orange juice were very similar to those for POD.     

Inactivation Kinetics of Lactobacillus plantarum by High Pressure Carbon Dioxide

Inactivation kinetics of Lactobacillus plantarum by high pressure CO₂ was investigated to understand the mechanism of microbial inactivation. The inactivation rates increased with pressure, temperature and exposure time, and with decreasing pH of media. Microbial inactivation was governed essentially by penetration of CO₂ into cells and its effectiveness could be improved by the enhanced transfer rate. Microbial reduction of 8 log cycles was observed within 120 min under CO₂ pressure of 70 kg/cm² at 30°C. We hypothesized that the cell death resulted from the lowered intracellular pH and damage to the cell membrane due to penetration of CO₂. Pressurized CO₂ treatment is a potential nonthermal technology for food preservation.     

高静压对桃汁杀菌、钝化酶活性的效果

研究在不同处理压力和时间条件下,高静压加工技术对桃汁中微生物(细菌总数、霉菌、酵母菌、大肠菌群)以及酶(多酚氧化酶、果胶甲基酯酶、脂肪氧化酶)的影响。结果表明:经400MPa、5min高静压处理即可完全杀灭桃汁中的微生物;在400MPa和500MPa条件下,桃汁中的多酚氧化酶和脂肪氧化酶的活性出现了不同程度的激活现象,但在600MPa时,随着处理时间的延长,其活性逐渐降低,经30min处理后,分别被钝化了0.7662和0.641。而果胶甲基酯酶在400、500、600MPa条件下,出现了不规律的激活或钝化现象。另外,研究表明在高静压加工前增加漂烫工艺,可以有效杀灭桃汁中的微生物及钝化酶活性。     

Mechanism of inactivation of heat-tolerant spores of Bacillus stearothermophilus IFO 12550 by Rapid Decompression

The effect of three rapid decompression methods to clear the mechanism of inactivation of heat tolerant spores of Bacillus stearothermophilus IFO 12550 was investigated. Pressurization of the spores at 200 MPa and 75°C for 60 min caused a kill of 10⁴ CFU/mL by the link-motion system but the nonrotational rod valve and E.G. seal methods gave a kill of about 10³ CFU/mL. Sterilization was due to the physical breakdown of spore coat, and was induced by its physical permeability of water at high pressure and temperature. Rapid decompression by the link-motion system at 200 MPa decreased the D-value of the spores from 3000 min (100°C, one atmosphere) to 6 min, 11 min, and 17 min at 95, 85, and 75°C, respectively.     

Inactivation Kinetics of Food Poisoning Microorganisms by Carbon Dioxide and High Hydrostatic Pressure

The inactivation kinetics of food poisoning microorganisms using a combined treatment of carbon dioxide (CO₂) with high hydrostatic pressure (HHP) was investigated. Staphylococcus aureus, Fusarium oxysporum, and Fusarium sporotrichioides were totally inactivated by a combined treatment of carbonation and HHP at 500 MP_a. Bacillus subtilis, a spore forming bacteria, were not completely inactivated after the combined treatment. The microorganisms treated by carbonation and HHP were exponentially reduced in a pressure range and the D_p ‐value, the Z^p‐value, and the activation volume were determined. UV absorbing materials leaked from injured cells. Morphological changes of the cells were observed by scanning and transmission electron microscopy.     

超高压对泡萝卜的杀菌效果及其动力学研究

研究300～600 MPa超高压条件下处理四川泡萝卜5～25 min,对其细菌总数的影响、对霉菌、酵母菌及大肠菌群的杀灭效果的影响。并采用3 种模型对不同压力条件下杀菌动力学过程进行分析比较。结果表明：随处理压力和时间的增加,超高压对泡萝卜的杀菌效果增强;霉菌和酵母菌对压力较为敏感,500 MPa处理5 min可被全部杀死;Weibull模型能很好地拟合泡萝卜超高压杀菌的动力学过程（决定系数R2＞0.99）,且相较Log-logistic模型更简洁、灵活实用。尺度参数b随处理压力的增加而增大,形状参数n则随压力的增加而减小。