共查询到20条相似文献，搜索用时 15 毫秒
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Volatile formation in milk subjected to pressure-assisted thermal processing (PATP) was investigated from a reaction kinetic analysis point of view to illustrate the advantages of this technology. The concentration of 27 volatiles of different chemical class in milk subjected to pressure, temperature, and time treatments was fitted to zero-, 1st-, and 2nd-order chemical reaction models. Temperature and pressure effects on rate constants were analyzed to obtain activation energy (E(a)) and activation volume (deltaV*) values. Hexanal, heptanal, octanal, nonanal, and decanal followed 1st-order kinetics with rate constants characterized by E(a) values decreasing with pressure reflecting negative deltaV* values. Formation of 2-methylpropanal, 2,3-butanedione, and hydrogen sulfide followed zero-order kinetics with rate constants increasing with temperature but with unclear pressure effects. E(a) values for 2-methylpropanal and 2,3-butanedione increased with pressure, that is, deltaV* > 0, whereas values for hydrogen sulfide remained constant, that is, deltaV* = 0. The concentration of all other volatiles, including methanethiol, remained unchanged in pressure-treated samples, suggesting large negative deltaV* values. The concentration of methyl ketones, including 2-pentanone, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone, 2-decanone, and 2-undecanone, was independent of pressure and pressure-holding time. PATP promoted the formation of few compounds, had no effect on some, and inhibited the formation of volatiles reported to be factors of the consumer rejection of \"cooked\" milk flavor. The kinetic behavior observed suggested that new reaction formation mechanisms were not likely involved in volatile formation in PATP milk. The application of the Le Chatelier principle frequently used to explain the high quality of pressure-treated foods, often with no supporting experimental evidence, was not necessary. 相似文献
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Vinicio Serment‐Moreno Claudio Fuentes José Antonio Torres Jorge Welti‐Chanes 《Journal of food science》2017,82(8):1885-1891
A recently proposed Gompertz model (GMPZ) approach describing microbial inactivation kinetics by high‐pressure processing (HPP) incorporated the initial microbial load (N0) and lower microbial quantification limit (Nlim), and simplified the dynamic effects of come‐up time (CUT). The inactivation of Listeria innocua in milk by HPP treatments at 300, 400, 500, and 600 MPa and pressure holding times (thold) ≤10 min was determined experimentally to validate this model approach. Models based on exponential, logistic‐exponential, and inverse functions were evaluated to describe the effect of pressure on the lag time (λ) and maximum inactivation rate (μmax), whereas the asymptote difference (A) was fixed as A = log10(N0/Nlim). Model performance was statistically evaluated and further validated with additional data obtained at 450 and 550 MPa. All GMPZ models adequately fitted L. innocua data according to the coefficient of determination (R2 ≥ 0.95) but those including a logistic‐exponential function for μmax(P) were superior (R2 ≥ 0.97). These GMPZ versions predicted that approximately 597 MPa is the theoretical pressure level (Pλ) at which microbial inactivation begins during CUT, mathematically defined as λ (P = Pλ) = tCUT, and matching the value observed on the microbial survival curve at 600 MPa. As pressure increased, predictions tended to slightly underestimate the HPP lethality in the tail section of the survival curve. This may be overseen in practice since the observed microbial counts were below the predicted log10 N values. Overall, the modeling approach is promising, justifying further validation work for other microorganisms and food systems. 相似文献
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The enhanced quasi-chemical kinetics (EQCK) model is presented as a methodology to evaluate the nonlinear inactivation kinetics of baro-resistant Listeria monocytogenes in a surrogate protein food system by high-pressure processing (HPP) for various combinations of pressure (P= 207 to 414 MPa) and temperature (T= 20 to 50 °C). The EQCK model is based on ordinary differential equations derived from 6 \"quasi-chemical reaction\" steps. The EQCK model continuously fits the conventional stages of the microbial lifecycle: lag, growth, stationary phase, and death; and tailing. Depending on the conditions, the inactivation kinetics of L. monocytogenes by HPP show a lag, inactivation, and tailing. Accordingly, we developed a customized, 4-step subset version of the EQCK model sufficient to evaluate the HPP inactivation kinetics of L. monocytogenes and obtain values for the model parameters of lag (λ), inactivation rate (μ), rate constants (k), and \"processing time\" (tp). This latter parameter was developed uniquely to evaluate kinetics data showing tailing. Secondary models are developed by interrelating the fitting parameters with experimental parameters, and Monte Carlo simulations are used to evaluate parameter reproducibility. This 4-step model is also compared with the empirical Weibull and Polylog models. The success of the EQCK model (as its 4-step subset) for the HPP inactivation kinetics of baro-resistant L. monocytogenes showing tailing establishes several advantages of the EQCK modeling approach for investigating nonlinear microbial inactivation kinetics, and it has implications for determining mechanisms of bacterial spore inactivation by HPP. Practical Application: Results of this study will be useful to the many segments of the food processing industry (ready-to-eat meats, fresh produce, seafood, dairy) concerned with ensuring the safety of consumers from the health hazards of Listeria monocytogenes, particularly through the use of emerging food preservation technologies such as high-pressure processing. 相似文献
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M. A. Cheeseman 《Food Additives & Contaminants》2005,22(10):900-906
The scientific basis for the US Food and Drug Administration (FDA) threshold of regulation is discussed in relation to its toxicological testing recommendations for food contact substances and the existing methods it employs for exposure estimation. A case is made that the FDA's threshold of regulation is a natural extension of its toxicity testing regime. The genetic toxicity tests recommended in the exposure-based toxicological testing framework for food contact substances are examined regarding their ability to predict positively carcinogens of varying potency. In addition, the computational toxicology program MULTICASE v. 3.1 is also examined for its ability to predict positively carcinogens of varying potency. It is concluded that MULTICASE can provide equivalent results to genetic toxicity tests at the lowest dietary concentrations. 相似文献
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紫外辐照是一种非热杀菌技术,汞蒸气紫外灯是现阶段用于食品卫生处理的主要设备,但受某些因素影响,汞灯的生产使用将逐渐变少,被环保节能的紫外发光二极管（UV-LED）取代是一种不可避免的趋势。本文根据UV-LED发光原理和多波长耦合应用的特点,综述了对微生物灭活的机理、探究了影响灭活效果的因素（波长、紫外剂量和物料特性）、处理食品的灭菌效果以及对部分食品品质的影响,为UV-LED在食品领域的杀菌处理工艺和设备参数优化提供参考。 相似文献
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Micha Peleg Robert Engel Consuelo Gonzalez‐Martinez Maria G Corradini 《Journal of the science of food and agriculture》2002,82(12):1346-1355
The classic Arrhenius and WLF equations are commonly used to describe rate–temperature relations in food and biological systems. However, they are not unique models and, because of their mathematical structure, give equal weight to rate deviations at the low‐ and high‐temperature regions. This makes them particularly useful for systems where what happens at low temperatures is of interest, as in spoilage of foods during storage, or where the effect is indeed exponential over a large temperature range, as in the case of viscosity. There are systems, however, whose activity is only noticeable above a certain temperature level. A notable example is microbial inactivation, for which these two classical models must be inadequate simply because cells and spores are not destroyed at ambient temperature. For such systems a model that identifies the temperature level at which the rate becomes significant is required. Such an alternative model is Y = ln{1 + exp[c(T ? T c)]} m, where Y is the rate parameter in question (eg a reaction rate constant), Tc is the marker of the temperature range where the changes accelerate, and c and m are constants. (When m = 1, Y at T ? Tc is linear. When m ≠ 1, m is a measure of the curvature of Y at T ? Tc.) This model has at least a comparable fit to published rate–temperature relationships of browning and microbial inactivation as well as viscosity–temperature data previously described by the Arrhenius or WLF equation. This alternative log logistic model is not based on the assumption that there is a universal analogy between totally unrelated systems and simple chemical reactions, which is explicitly assumed when the Arrhenius equation is used, and it has no special reference temperature, as in the WLF equation, whose physical significance is not always clear. It is solely based on the actual behaviour of the examined system and not on any preconceived kinetics. © 2002 Society of Chemical Industry 相似文献
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研究了丙烯腈与涤纶纤维的接枝共聚反应。从实验结果得出了聚合反应速率与引发剂浓度、单体浓度、纤维用量及反应温度的关系,并由此求出反应的表观速率方程和表观活化能。还对接枝纤维的性能进行了研究。 相似文献
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M.G. Corradini M.D. Normand C. Newcomer D.W. Schaffner M. Peleg 《Journal of food science》2009,74(1):R1-R11
ABSTRACT: Theoretically, if an organism's resistance can be characterized by 3 survival parameters, they can be found by solving 3 simultaneous equations that relate the final survival ratio to the lethal agent's intensity. (For 2 resistance parameters, 2 equations will suffice.) In practice, the inevitable experimental scatter would distort the results of such a calculation or render the method unworkable. Averaging the results obtained with more than 3 final survival ratio triplet combinations, determined in four or more treatments, can remove this impediment. This can be confirmed by the ability of a kinetic inactivation model derived from the averaged parameters to predict survival patterns under conditions not employed in their determination, as demonstrated with published isothermal survival data of Clostridium botulinum spores, isobaric data of Escherichia coli under HPP, and Pseudomonas exposed to hydrogen peroxide. Both the method and the underlying assumption that the inactivation followed a Weibull-Log logistic (WeLL) kinetics were confirmed in this way, indicating that when an appropriate survival model is available, it is possible to predict the entire inactivation curves from several experimental final survival ratios alone. Where applicable, the method could simplify the experimental procedure and lower the cost of microbial resistance determinations. In principle, the methodology can be extended to deteriorative chemical reactions if they too can be characterized by 2 or 3 kinetic parameters. 相似文献
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This paper deals with kinetics of quality changes during food frying. The quality parameters of interests include color, texture, viscoelastic properties, volume/density, and nutraceuticals (Omega 3 fatty acids). The kinetic theory and determination methodology under isothermal/non-isothermal conditions are also reviewed. This paper presents the reported reaction rate constant, order of reaction, and activation energy for specific quality changes including phenomenological observations and important speculations. The changes of color, textural, and viscoelastic properties generally followed a first order reaction. In some studies, activation energy analysis could have been improved by applying corresponding system temperatures for the quality change reactions of interest. The kinetic information on volume/density changes and thermal degradation of nutraceutical is still limited to experimental observations of the changes. 相似文献
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Direct experimental identification and quantification of the pressure contribution to a pressure-assisted sterilization process efficacy is difficult. However, dynamic kinetic models of thermal inactivation can be used to assess the lethality of a purely thermal process having the same temperature profile. Thus, a pressure-assisted process' temperature record can be used to generate a corresponding purely thermal survival curve with parameters determined in conventional heating experiments. Comparison of the actual final survival ratio with that calculated for the purely thermal process would reveal whether the hydrostatic pressure had synergistic or antagonistic effect on bacterial spores survival. The effect would be manifested in the number of log cycles subtracted or added to the survival ratio, and in the length of time at the holding temperature needed to produce the final survival ratio of the combined process. A set of combined treatments would reveal how the temperature and pressure profiles affect the pressure's influence on the process' lethality to either vegetative cells or spores. The need to withdraw samples during the thermal and combined processes would be avoided if the thermal survival parameters could be calculated by the \"three endpoints method,\" which does not require the entire survival curve determination. Currently however, this method is limited to thermal inactivation patterns characterized by up to 3 survival parameters, the Weibull-Log logistic (WeLL) model, for example. 相似文献
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以蓝莓、草莓和苹果为原料,通过感官评价分析,研制出一款蓝莓复合果泥。利用超高压（UHP）和热杀菌（TS）处理果泥,分析处理前后和4 ℃贮藏40 d内其微生物、理化指标、色泽、花青素、香气和流变特性的变化。结果表明,两种处理后果泥菌落总数、大肠菌群和霉菌均未检出,贮藏40 d时仍符合食品标准限量。pH值在处理后和贮藏期内都显著降低（P<0.05）。可溶性固形物在UHP处理后无显著变化（P>0.05）,TS处理后显著增大（P<0.05）,贮藏结束时均为7.80 °Brix。TS处理后果泥花青素含量显著降低（P<0.05）,UHP组无显著变化（P>0.05）,贮藏期间,UHP组花色苷含量显著高于TS组。UHP和TS组果泥贮藏期间ΔE最大值分别为1.26和3.47,TS组果泥贮藏时出现明显颜色变化。电子鼻结果表明UHP比TS能更好地保留果泥的香气成分。流变仪结果表明UHP组果泥贮藏期间具有更好的稳定性。综上,UHP对蓝莓复合果泥的品质保存效果好,是一种适用于蓝莓复合果泥加工的杀菌方式。 相似文献
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Robert Sevenich Elke Kleinstueck Colin Crews Warwick Anderson Celine Pye Katerina Riddellova Jaromir Hradecky Eliska Moravcova Kai Reineke Dietrich Knorr 《Journal of food science》2014,79(2):M230-M237
The benefits that high‐pressure thermal sterilization offers as an emerging technology could be used to produce a better overall food quality. Due to shorter dwell times and lower thermal load applied to the product in comparison to the thermal retorting, lower numbers and quantities of unwanted food processing contaminants (FPCs), for example, furan, acrylamide, HMF, and MCPD‐esters could be formed. Two spore strains were used to test the technique; Geobacillus stearothermophilus and Bacillus amyloliquefaciens, over the temperature range 90 to 121 °C at 600 MPa. The treatments were carried out in baby food puree and ACES‐buffer. The treatments at 90 and 105 °C showed that G. stearothermophilus is more pressure‐sensitive than B. amyloliquefaciens. The formation of FPCs was monitored during the sterilization process and compared to the amounts found in retorted samples of the same food. The amounts of furan could be reduced between 81% to 96% in comparison to retorting for the tested temperature pressure combination even at sterilization conditions of F0‐value in 7 min. 相似文献
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为研究膨胀型阻燃剂对棉纤维热降解行为的影响,采用聚磷酸铵APP/三聚氰胺MEL/季戊四醇（PER）构成的复合膨胀型阻燃体系对棉织物浸轧阻燃整理。采用热失重法分析阻燃整理后棉织物在氮气氛围中不同升温速率下的热降解动力学行为。利用Kissinger、Flynn-Wall-Ozawa和Friedman 3种方法研究膨胀型阻燃棉纤维的动力学参数,并对比探讨膨胀阻燃剂加入前后棉织物的热降解行为。结果表明：APP/MEL/PER膨胀型阻燃剂的加入使棉织物的初始分解温度提前,有效地促进棉织物分解成炭,起到良好的隔热隔氧作用;提高了棉织物的活化能;Kissinger法和Flynn-Wall-Ozawa法求得的活化能值相接近,可靠度较高;但用Friedman法计算的活化能比前二者偏高。 相似文献
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Synthetic fibers are used in various industrial applications such as packaging, protective coating, and biomedical and sealing materials. However, these polymers have few polar groups. As a result, they have a weak capacity to form hydrogen bonds with water (hydrophilic groups). Hence, low‐pressure plasma treatments have been proposed to modify their surface properties (hydrophobicity and wettability) by introducing polar groups or by increasing the surface roughness. In this study, we focused on a new approach to increase the hydrophilicity of poly(ethylene terephthalate) (PET) fabrics by a low‐pressure plasma technique under three oxidizing atmospheres (oxygen [O2] 100%, carbon dioxide [CO2] 100%, and a mixture of O2 (50%) and CO2 (50%)). The plasma processes used in the study aimed to modify the superficial structure of polyester fibers, in particular PET, by forming new carboxyl, hydroxyl, and other polar groups on the surface. The increase in hydrophilicity was evaluated by the contact angles, the best results being 43.48° for the 100% CO2 atmosphere and 44.56° for the combined CO2 + O2 atmosphere. It was also confirmed by the rising height, which was determined according to the International Standard DIN 53924. The results showed an important improvement in the hydrophilicity using both the combined CO2 + O2 atmosphere and the 100% CO2 atmosphere. The surface energies of the fabrics were estimated using the contact angles. The presence of new carboxyl and hydroxyl groups was evaluated by staining methods using a cationic and a reactive dye, respectively. The results revealed an improvement in the water adsorption capacity due to the formation of carboxyl groups. Scanning electron microscope analysis of the surface morphology of the fibers showed an important cleaning action and oligomer elimination. 相似文献