A Gompertz Model Approach to Microbial Inactivation Kinetics by High‐Pressure Processing (HPP): Model Selection and Experimental Validation

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 (N_lim), 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 (t_hold) ≤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 (μ_max), whereas the asymptote difference (A) was fixed as A = log₁₀(N₀/N_lim). 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 μ_max(P) were superior (R² ≥ 0.97). These GMPZ versions predicted that approximately 597 MPa is the theoretical pressure level (P_λ) at which microbial inactivation begins during CUT, mathematically defined as λ (P = P_λ) = t_CUT, 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.     

Continuous Versus Discontinuous Ultra‐High‐Pressure Systems for Food Sterilization with Focus on Ultra‐High‐Pressure Homogenization and High‐Pressure Thermal Sterilization: A Review

High‐pressure thermal sterilization (HPTS) and ultra‐high‐pressure homogenization (UHPH) are two emerging sterilization techniques that have not been implemented in the food industry yet. The two technologies apply different acting principles as HPTS uses isostatic pressure in combination with heat whereas UHPH uses dynamic pressure in combination with shear stress, cavitation, impingement, and heat. Both technologies offer significant benefits in terms of spore inactivation in food production with reduced thermal intensity and minimized effects on sensory and nutritional profiles. These benefits have resulted in relevant research efforts on both technologies over the past few decades. This state of the art of the discontinuous HPTS‐based and the continuous UHPH‐based sterilization concepts are assessed within this review. Further, various basic principles and promising future preservation applications of HPTS and UHPH for food processing, that are also applicable in the pharmaceutical, biochemical, and biotechnological sectors, are summarized. In addition, the applications and limitations of these technologies in terms of optimizations needed to overcome the identified challenges are emphasized.     

Microbial Inactivation Kinetics during High‐Pressure Carbon Dioxide Treatment: Nonlinear Model for the Combined Effect of Temperature and Pressure in Apple Juice

ABSTRACT: Isobaric and isothermal semi‐logarithmic survival curves of natural microflora in apple juice treated with high‐pressure carbon dioxide at 7, 13, and 16 MPa pressures and 35, 50, and 60 °C temperatures were fitted with a nonlinear equation to find the values of the coefficient b(P ), b(T ), n(P ), and n(T ). Profiles of the model parameters were obtained as a function of pressure and temperature. The model fitted with good agreement (R² > 0.945), the survival curves. An empirical equation was proposed to describe the combined effects of pressure and temperature. The equation, derived from a power law model, was written in the form: . The proposed model fitted the experimental data well. At 7 MPa and 50 and 60 °C, 13 MPa and 35 and 60 °C, 16 MPa and 35 °C, the model provided log₁₀ reduction residual values (observed value – fitted value) lower than 0.284 showing a good agreement between the experimental and the predicted survival levels.     

High-Pressure Processing of Orange Juice: Kinetics of Pectinmethylesterase Inactivation

ABSTRACT: A kinetic study of pectinmethylesterase (PME) inactivation in orange juice was conducted. Juice samples were subjected to combinations of high pressure (400, 500, 600 MPa) and thermal (25, 37.5, 50 °C) treatments for various time periods. PME inactivation followed a first-order kinetic model with a residual activity of pressure-resistant enzyme remaining. Calculated D-values ranged from 4.6 min to 117.5 min at 600 MPa/50 °C and 400 MPa/25 °C, respectively. Pressures in excess of 500 MPa resulted in sufficiently fast inactivation rates for economic viability of the process.     

Inhibitor‐Assisted High‐Pressure Inactivation of Bacteria in Skim Milk

The combined inactivation effects of high hydrostatic pressure (HHP) and antimicrobial compounds (potassium sorbate and ε‐polylysine [ε‐PL]) on 4 different bacterial strains present in skim milk and the effect of these treatments on milk quality were investigated in this study. HHP treatment at 500 MPa for 5 min reduced the populations of Escherichia coli, Salmonella enterica Typhimurium, Listeria monocytogenes, and Staphylococcus aureus from 6.5 log colony‐forming units (CFUs) or higher to less than 1 log CFU/mL. Compared to HHP alone, HHP with potassium or ε‐PL resulted in significantly higher reductions in the bacterial counts. After 5 min of treatment with HHP (500 MPa) and ε‐PL (2 mg/mL), no growth of E. coli, S. enterica Typhimurium, or L. monocytogenes in skim milk was observed during 15 d of refrigerated storage (4 ± 1 °C). Scanning electron microscopy analysis revealed that the synergistic treatments caused more serious damage to the bacterial cell walls. Quality assessments of the treated samples indicated that the combined treatments did not influence the color, the turbidity, the concentrations of –SH group of the proteins, or the in vitro digestion patterns of the milk. This study demonstrates that HHP with potassium or ε‐PL may be useful in the processing of milk or milk‐containing foods.     

Effects of High‐Hydrostatic Pressure on Inactivation of Human Norovirus and Physical and Sensory Characteristics of Oysters

The purpose of the study was to determine the effect of high‐hydrostatic pressure (HHP) on inactivation of human norovirus (HuNoV) in oysters and to evaluate organoleptic characteristics of oysters treated at pressure levels required for HuNoV inactivation. Genogroup I.1 (GI.1) or Genogroup II.4 (GII.4) HuNoV was inoculated into oysters and treated at 300 to 600 MPa at 25 and 0 °C for 2 min. After HHP, viral particles were extracted by porcine gastric mucin‐conjugated magnetic beads (PGM‐MBs) and viral RNA was quantified by real‐time RT‐PCR. Lower initial temperature (0 °C) significantly enhanced HHP inactivation of HuNoV compared to ambient temperature (25 °C; P < 0.05). HHP at 350 and 500 MPa at 0 °C could achieve more than 4 log₁₀ reduction of GII.4 and GI.1 HuNoV in oysters, respectively. HHP treatments did not significantly change color or texture of oyster tissue. A 1‐ to 5‐scale hedonic sensory evaluation on appearance, aroma, color, and overall acceptability showed that pressure‐treated oysters received significantly higher quality scores than the untreated control (P < 0.05). Elevated pressure levels at 450 and 500 MPa did not significantly affect scores compared to 300 MPa at 0 °C, indicating increasing pressure level did not affect sensory acceptability of oysters. Oysters treated at 0 °C had slightly lower acceptability than the group treated at room temperature on day 1 (P < 0.05), but after 1 wk storage, no significant difference in sensory attributes and consumer desirability was observed (P > 0.05).     

Effects of Rigor Status during High‐Pressure Processing on the Physical Qualities of Farm‐Raised Abalone (Haliotis rufescens)

High‐pressure processing (HPP) is used to increase meat safety and shelf‐life, with conflicting quality effects depending on rigor status during HPP. In the seafood industry, HPP is used to shuck and pasteurize oysters, but its use on abalones has only been minimally evaluated and the effect of rigor status during HPP on abalone quality has not been reported. Farm‐raised abalones (Haliotis rufescens) were divided into 12 HPP treatments and 1 unprocessed control treatment. Treatments were processed pre‐rigor or post‐rigor at 2 pressures (100 and 300 MPa) and 3 processing times (1, 3, and 5 min). The control was analyzed post‐rigor. Uniform plugs were cut from adductor and foot meat for texture profile analysis, shear force, and color analysis. Subsamples were used for scanning electron microscopy of muscle ultrastructure. Texture profile analysis revealed that post‐rigor processed abalone was significantly (P < 0.05) less firm and chewy than pre‐rigor processed irrespective of muscle type, processing time, or pressure. L values increased with pressure to 68.9 at 300 MPa for pre‐rigor processed foot, 73.8 for post‐rigor processed foot, 90.9 for pre‐rigor processed adductor, and 89.0 for post‐rigor processed adductor. Scanning electron microscopy images showed fraying of collagen fibers in processed adductor, but did not show pressure‐induced compaction of the foot myofibrils. Post‐rigor processed abalone meat was more tender than pre‐rigor processed meat, and post‐rigor processed foot meat was lighter in color than pre‐rigor processed foot meat, suggesting that waiting for rigor to resolve prior to processing abalones may improve consumer perceptions of quality and market value.     

果蔬产品超高压加工的研究进展

采用超高压技术能在较低温度下达到一定的杀菌、灭酶作用,避免高温处理对食品营养物质造成的损失,受到越来越多的研究人员的关注。基于对大量外文资料的综合分析,本文综述了超高压对果蔬产品中微生物、内源酶、产品质地、感官品质、营养等方面影响的研究进展,分析超高压在果蔬产品加工中的应用前景。     

Effects of High‐Pressure Processing on Inactivation of Salmonella Typhimurium,Eating Quality,and Microstructure of Raw Chicken Breast Fillets

Abstract: High‐pressure inactivation of Salmonella Typhimurium DMST 28913, eating quality, and microstructure of pressurized raw chicken breast meat was determined. The inoculated samples (approximately 7 log CFU/g initial load) were processed at 300 and 400 MPa, using pressurized medium of 25 to 35 °C during pressurization. Weibull model was well fitted to the survival curves with tailing. Least severe conditions with acceptable inactivation levels were 300 MPa, 35 °C, 1 min (approximately 2 log reduction) and 400 MPa, 30 °C, 1 min (approximately 4 log reduction). Based on these 2 conditions, the 400 MPa treatment yielded the raw chicken meat with higher L* value, greater cooking loss, and lower water holding capacity. Cooked chicken breast meat prepared from the pressurized samples had firmer texture than the control. Scanning electron microscopic images showed that higher pressure resulted in increasing extent of protein coagulation and the contraction of the muscle bundles. Practical Application: For raw chicken breast fillet, 300 MPa, 35 °C, 1 min was the condition that reasonably reduced the load of Salmonella Typhimurium. However, the pressurized samples had greater cooking loss. Marination with brine containing sodium chloride and phosphate prior to pressurization might help improve this eating quality.     

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。     

Combined effect of high pressure,temperature and holding time on polyphenoloxidase and peroxidase activity in banana (Musa acuminata)

Polyphenoloxidase and peroxidase enzyme activities were evaluated following combined pressure, temperature and holding time treatment in banana (Musa acuminata). Using pressures of up to 110 MPa, temperatures of up to 70 °C and holding times of up to 25 min, based on a 2³ central composite design, the interactive effects were found to significantly influence the activity of both enzymes in prepared banana pulp. Temperature and pressure were found to influence the inactivation of polyphenoloxidase separately, while temperature, pressure and holding time were found to influence the loss of peroxidase in the banana, although no significant interactive effects were found. The reduction in polyphenoloxidase activity was found to be less influenced by the combined treatment than peroxidase activity, thought to be due to solubilisation of the enzyme and effects of the soluble solids content. © 2000 Society of Chemical Industry     

Kinetic Study of Antibrowning Agents and Pressure Inactivation of Avocado Polyphenoloxidase

Pressure inactivation at room temperature (25 °C) of avocado polyphenoloxidase (pH 5.0) in absence or presence of 10 mM ethylene diaminetetraacetic acid (EDTA), NaCl, or benzoic acid or 0.05 mM 4-hexylresorcinol or glutathione could be described by a fractional conversion model. There appeared to be a resistant enzyme fraction (∼10% to 20%), necessitating about 825 MPa for inactivation in absence of antibrowning agents. EDTA addition resulted in sensitization of the pressure-sensitive enzyme fraction, which was attributed to the acid effect. Benzoic acid or NaCl addition resulted in a marked stabilization, whereas addition of glutathione resulted only in a minor stabilization of the pressure-sensitive enzyme fraction. 4-Hexylresorcinol displayed a sensitizing effect below and a stabilizing effect above 700 MPa. The pressure dependency of the inactivation rate constant was altered (p < 0.05) by addition of 4-hexylresorcinol or benzoic acid.     

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.     

Inactivation Kinetics of Listeria monocytogenes by High-Pressure Processing: Pressure and Temperature Variation

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.     

High‐Pressure Thermal Sterilization: Food Safety and Food Quality of Baby Food Puree

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.     

超高静压对非浓缩还原杨梅果汁中氧化酶的钝化作用

该研究以非浓缩还原（not from concentrate,NFC）杨梅果汁为研究对象,研究不同超高静压（high hydrostatic pressure,HHP）处理（300~600 MPa/0~30 min）对NFC杨梅汁中多酚氧化酶（polyphenol oxidase,PPO）和过氧化物酶（peroxidase,POD）的影响。对比传统高温灭酶,拟合建立HHP压力与酶活性的一级动力学回归方程,分析得到相关参数（压力脉冲效应PE、压力脉冲数值ND、等效破坏值Dp及酶的失活速率K）。结果表明,较高压力（400~600 MPa）对PPO与POD均起到钝化效果,其中600 MPa/10 min能钝化90%的PPO活性,600 MPa/20 min钝化80%的POD活性。600 MPa/30 min条件下,重复加压不能明显加强钝化效果。将PPO和PPO活性与压力进行一级动力学拟合,得到相应线性回归方程（R2>0.8）。随着压力从300 MPa升高到600 MPa,PPO的K值从3.03×10-2升高到12.12×10-2,POD的K值从1.23×10-3上升到7.67×10-3。600 MPa条件下,PPO和POD的ND分别为1.04和1.59,Dp值都为19。同时,压力和保压时间及其相互作用对PPO和POD活性的影响均有极高的显著性（p<0.001）。因此,HHP对杨梅果汁中关键的氧化酶能起到较好的钝化作用,能够为NFC杨梅汁加工技术的应用提供科学依据。     

Inactivation of Lactobacillus brevis in Beer Utilizing a Combination of High‐Pressure Homogenization and Lysozyme Treatment

Inactivation of Lactobacillus brevis in beer by high‐pressure homogenization (HPH) and lysozyme addition was evaluated. The minimum inhibitory concentration of lysozyme against L. brevis was determined and found to be 100 mg.L^?1. The effects of the homogenization process on lysozyme antimicrobial activity and muramidase activity, and the microbial reduction promoted by HPH, and by HPH associated with lysozyme, were evaluated. A significant reduction in lysozyme muramidase activity was observed under 250 MPa, however, no reduction in antimicrobial activity was observed after homogenization up to 300 MPa. The HPH at 100, 140 and 150 MPa promoted 1, 3 and 6 decimal reductions in L. brevis microbial counts, respectively. The HPH and lysozyme association had an additive effect on microbial inactivation, immediately after homogenization, and the lysozyme remained active during 10 days of storage, increasing the inactivation of L. brevis up to a 6 decimal reduction. Therefore, the application of lysozyme with HPH has the potential to reduce the level of pressure required for beer processing, improving the economic costs when utilizing HPH.     

High Pressure Inactivation Kinetics of Saccharomyces cerevisiae Ascospores in Orange and Apple Juices

High pressure inactivation kinetics (D and z values) of Saccharomyces cerevisiae ascospores were determined in fruit juices and a model juice buffer at pH 3.5 to 5.0. Approximately 0.5 to 1.0 × 10⁶ ascospores/mL were pressurized at 300 to 500 MPa in juice or buffer. D-values ranged from 8 sec to 10.8 min at 500 and 300 MPa, respectively. The range for z-values was 115 to 121 MPa. No differences (P≥0.05) in D (at constant pressure) or z-values among buffers or juices at any pH were determined, indicating little influence of pH in this range and absence of protective or detrimental effects of juice constituents.