Quantitative Evaluation of Thermal Inactivation Kinetics of Free-Floating Versus Surface-Attached Listeria innocua Cells

Surface pasteurization is one of the decontamination treatments that can contribute to better preservation of meat products retaining most of their quality characteristics relatively intact if compared with the raw products. The current research compares the kinetics of free-floating and surface attached Listeria innocua cells by using integrated microbial and heat transfer modelling approaches. Surface pasteurization treatments are applied on a (abiotic) Teflon® model system in a novel steam surface decontamination rig. The experimental set-up prevented following four technological aspects to occur, (1) cold purge migration to the surface during the heating process, (2) inactivation kinetics of a cocktail of microbes, (3) protective effect of food components, and (4) physical distribution of bacteria throughout the depth of the product skin. Microbial load predictions are performed based on the inactivation parameters obtained during free-floating cell experiments. These predictions, when compared with the microbial data of the surface treatments, prove that the surface attached cells were much more heat resistant, despite the experimental set-up preventing the aforementioned (technological) events to occur. Indeed, surface attached cells can have different physiological/phenotypical/genetical characteristics, such as cell aggregations, colony formations, presence of flagella. In a final step, three techniques are implemented to evaluate mathematically the kinetics of the surface attached cells. Overall, this research’s significance is lying in the quantitative assessment of microbial heat resistance. The technological reasons underlying the increased microbial heat resistance on biotic and abiotic surfaces should be reevaluated, taking into account possible physiological/phenotypical/genetical characteristics.     

副溶血弧菌在低温贮藏过程中的失活动力学特征

本实验对在4℃和-20℃贮藏温度下接种于带鱼样品中的4株副溶血弧菌的失活动力学特征进行了研究,结果表明：在4℃冷藏过程中,60d贮藏期内带鱼样品中副溶血弧菌的残活细胞数降低了6.55～8.22lgCFU,在起始20d内失活速度缓慢,平均下降速率为0.06～0.1lgCFU/d,在第25～35d内失活速度变快,平均下降速率为0.16～0.2lgCFU/d,而在第35～60d的平均下降速率为0.11～0.12lgCFU/d,不同菌株之间下降速度有所差异,其中菌株Vp06001下降速度显著快于其它3个菌株（p〈0.01）。在-20℃冷冻过程中,在开始5d内下降速度最快（0.39lgCFU/d）,在10～60d下降速度缓慢（0.027lgCFU/d）,菌株之间没有显著差异（p〉0.05）。应用线性模型、Weibull模型和Log-logistic模型对残活曲线进行了拟合,通过拟合方程计算分析预测值与实测值之间的精确因子（Af）、偏差因子（Bf）、均方根差（RMSE）和相关系数平方（R2）4个评价参数,结果表明：在4℃冷藏过程中Log-logistic模型拟合的精确度显著高于线性模型和Weibull模型（p〈0.01）;而在-20℃贮藏温度下Weibull模型可以较好的描述Vp的失活动力学特征。     

Pulsed electric field technology in the manufacturing processes of wine,beer, and rice wine: A review

Pulsed electric field (PEF) technology is an alternative to traditional food processing because this application can ensure good product quality and energy use efficiency. In PEF applications, the functional compounds extracted from food products can be enhanced, and the microorganisms contaminating the food products during processing can be inactivated. These properties are considered advantageous by alcoholic beverage producers. In this review, studies on the PEF treatment of wine, beer, and rice wine are summarized. The PEF technology is used in the pretreatment in grape wine and control of microbial growth in grape wine, beer, and rice wine. In grape wines, the PEF pretreatment can increase phenolic compound and anthocyanin contents and can enhance color intensity; this pretreatment slightly influences the organoleptic characteristics of samples. The PEF technology is also an effective tool to sterilize grape wine, beer, and rice wine. With this application, the quality of these three alcoholic beverages can be ensured because the PEF technology can be applied in the absence of heat. In addition, the main negative effect of PEF technology is discussed as well.     

稠油极性四组分与其黏度及乳状液反相点的关联研究

介绍了环丁砜抽提蒸馏工艺在中国石油庆阳石化10×10^4 t/a苯抽提装置的应用情况。运行结果表明,苯产品纯度达到99.95%,结晶点大于5.4℃,苯回收率99.81%,装置能耗810.15MJ/t,均达到设计要求。此外针对运行中出现的抽提蒸馏塔液泛、脱C6塔底热量没有充分利用、白土失活等问题进行了分析,提出了解决方法。     

大豆胰蛋白酶抑制剂失活方法探讨

胰蛋白酶抑制剂是大豆食品与饲料的主要抗营养因子 ,大豆胰蛋白酶抑制剂的失活能明显提高大豆食品与饲料的营养价值和食用安全性。大豆胰蛋白酶抑制剂的钝化方法有物理、化学、生物还原、酶解、发酵以及天然化合物络合法等。文中介绍了大豆胰蛋白酶抑制剂失活诸方法与技术 ,并对其发展前景作了初步探讨     

Inactivation of Neosartorya fischeri and Paecilomyces variotii on paperboard packaging material by hydrogen peroxide and heat

This study reports on the influence of heat and hydrogen peroxide combination on the inactivation kinetics of two heat resistant molds: Neosartorya fischeri and Paecilomyces variotii. Spores of different ages (1 and 4 months) of these molds were prepared and D-values (the time required at certain temperature/hydrogen peroxide combination to inactivate 90% of the mold ascospores) were determined using thermal death tubes. D-values found for P. variotii ranged from 1.2 to 25.1 s after exposure to different combinations of heat (40 or 60 °C) and hydrogen peroxide (35 or 40% w/w) while for N. fischeri they varied from 2.7 to 14.3 s after exposure to the same hydrogen peroxide concentrations and higher temperatures (60 or 70 °C). The influence of temperature and hydrogen peroxide concentration on the d-values varied with the genus of mold and their ages. A synergistic effect of heat and hydrogen peroxide in reducing D-values of Paecilomyces variotti and N. fischeri has been observed. In addition to strict control of temperature, time and hydrogen concentration, hygienic storage and handling of laminated paperboard material must be considered to reduce the probability of package’s contamination. All these measures together will ensure package’s sterility that is imperative for the effectiveness of aseptic processing and consequently to ensure the microbiological stability of processed foods during shelf-life.     

Effects of high pressure treatment on the quality and storage of kimchi

The effects of high pressure treatment on the microflora and storage of kimchi were investigated. In a bacterial suspension, numbers of Lactobacillus plantarum were reduced by 6 logs by 500 MPa, at 25 °C for 10 min. Kimchi juice did not alter the rate of inactivation of lactic acid bacteria by high pressure treatment. There was no change in the texture of kimchi subjected to a pressure of 400 MPa, but an increase in cutting force was observed at 600 MPa. When kimchi was pressurized at 400 MPa for 10 min at 25 °C and subsequently stored at 20 °C for 4 weeks, the total number of viable cells stayed at 10³ CFU mL⁻¹. High pressure treatment above 400 MPa prevented excessive acidification that typically occurs during the extended storage of kimchi. The inflation of pouches as a result of accumulated carbon dioxide was also prevented by high pressure treatment. Although colour changes were accelerated by high pressure treatment, this study demonstrates that high pressure treatment can be used to control overripening during the distribution and storage of kimchi products.     

Solar disinfection of wild Salmonella sp. in natural water with a 18 L CPC photoreactor: Detrimental effect of non-sterile storage of treated water

For the first time solar disinfection of liters of water containing wild Salmonella sp. and total coliforms was carried out in a compound parabolic collector (CPC) photoreactor at temperatures of almost 50 °C. Using surface water with high turbidity, this treatment was efficient in completely inactivating Salmonella sp. without regrowth during the subsequent 72 h of dark sterile storage. However if the solar treated water is poured in a non- sterile container, bacteria regrowth occurs even if 10 mg L⁻¹ of H₂O₂ is added before the storage. On the other hand, 30 mg L⁻¹ of H₂O₂ added when the irradiation started was completely depleted within 2 h and did not prevent bacterial regrowth during post-irradiation storage in non-sterile containers, demonstrating that storage of large volumes of water treated by solar irradiation was not optimal. Finally, total coliforms (Escherichia coli included) showed a far higher sensitivity than Salmonella sp. and demonstrated to be an inappropriate indicator for monitoring bacterial contamination in water during solar disinfection processes.     

Kinetic compensation relations for ascorbic acid degradation and pectinesterase inactivation during orange juice pasteurisations

The thermal degradation kinetics of ascorbic acid and the inactivation kinetics of pectinesterase were studied experimentally with pH-adjusted orange juice. No simple trends were observed in variation of the kinetic parameters with pH, but both kinetic functions agreed with kinetic compensation relations. An isokinetic temperature was observed for ascorbic acid degradation at pH 2.5, 3.0, and 3.5 implying that the same degradation mechanism was valid at these pH values. A large deviation at pH 4.0 from this isokinetic reaction rate implied that the degradation mechanism was different at this pH. There was no isokinetic temperature for pectinesterase inactivation reactions, indicating that pectinesterase was inactivated by different mechanisms at different pH values. The variation of the inactivation mechanism of pectinesterase with pH was attributed to its more complex molecular structure.     

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.