Heat Inactivation Kinetics of Trypsin Inhibitors During High Temperature-Short Time Processing of Soymilk

Heat treatment of soymilk was studied in the conventional batch boiling process and under High Temperature-Short Time (HTST) conditions. Reduction in total trypsin inhibitor was assayed enzymatically, and individual inhibitors, the Kunitz and the Bowman-Birk inhibitor, were assayed by ELISA technique. Standard first-order reaction kinetics and thermodynamics were applicable for inactivation, and results indicated that the mechanism was not protein unfolding, because entropy changes were zero or negative. The two inhibitors were inactivated at the same rate around 137°C. Therefore, a simple first-order kinetic model which gave a good, slightly conservative estimate of residual anti-trypsin activity under HTST conditions could be established.     

Heat Inactivation of Pectinesterase in Orange Juice Pulp

Heat inactivation of pectinesterase in juice pulp was nonlinear suggesting the presence of fractions of pectinesterase with differing heat stabilities. The residual activity rapidly decreased to 4% upon heating for 19 sec at 80°C and decreased very little upon subsequent heating for up to 180 sec at 80°C. The D values (time to inactivate 90% of the enzyme) at 90°C of the heat sensitive and heat stable fractions were estimated to be 0.225 and 32 sec, respectively. The Z values (change in temperature to achieve a 10-fold change in time of inactivation) were estimated to be 10.8°C and 6.5°C for the sensitive and stable fractions, respectively.     

Stochastic and Deterministic Model of Microbial Heat Inactivation

ABSTRACT: Microbial inactivation is described by a model based on the changing survival probabilities of individual cells or spores. It is presented in a stochastic and discrete form for small groups, and as a continuous deterministic model for larger populations. If the underlying mortality probability function remains constant throughout the treatment, the model generates first-order (“log-linear”) inactivation kinetics. Otherwise, it produces survival patterns that include Weibullian (“power-law”) with upward or downward concavity, tailing with a residual survival level, complete elimination, flat “shoulder” with linear or curvilinear continuation, and sigmoid curves. In both forms, the same algorithm or model equation applies to isothermal and dynamic heat treatments alike. Constructing the model does not require assuming a kinetic order or knowledge of the inactivation mechanism. The general features of its underlying mortality probability function can be deduced from the experimental survival curve's shape. Once identified, the function's coefficients, the survival parameters, can be estimated directly from the experimental survival ratios by regression. The model is testable in principle but matching the estimated mortality or inactivation probabilities with those of the actual cells or spores can be a technical challenge. The model is not intended to replace current models to calculate sterility. Its main value, apart from connecting the various inactivation patterns to underlying probabilities at the cellular level, might be in simulating the irregular survival patterns of small groups of cells and spores. In principle, it can also be used for nonthermal methods of microbial inactivation and their combination with heat.     

Heat Inactivation of the Ethylene-Forming Enzyme System in Cucumbers

Heat inactivation of the ethylene-forming enzyme system (EFE) in cucumbers was biphasic and both phases followed first order kinetics. The activation energies for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFE's were 77.67 and 68.92 kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both HS and HR are as follows: enthalauv. 68.27 (HS) and 77.03 (HR) kcal/mole; free energy; 21.2 (HS) and 22.9 (HR) kcal/mole; entropy, 146.1 (HS) and 168.2 (HR) cahdeg-mole. The heat resistant EFE appears to comprise 2535% of the total EFE activity     

Heat Inactivation of Native Plasminogen Activators in Bovine Milk

Inactivation of plasminogen activators appeared to follow first-order kinetics in the temperature range tested. The Arrhenius plot was linear (correlation coefficient 0.990). The Arrhenius equation for heat inactivation was deduced, from which the rate of inactivation at any temperature in the range 60–140°C could be calculated. The decimal reduction time (D-value) was 109 min at 70°C and 32 set at 140°C. This indicated that native plasminogen activators in bovine milk are not affected by pasteurization, and to a large extent are not inactivated by UHT dairy processing conditions.     

热与超声波对多聚半乳糖醛酸酶的钝化动力学

以多聚半乳糖醛酸酶（polygalacturonase,PG）为研究对象,探讨了在热与超声波作用下PG的钝化动力学。采用3,5-二硝基水杨酸比色法测定酶活力。结果表明：单独的热（≤45 ℃）或超声波（频率20 kHz,温度0 ℃,功率密度242、605、968 W/cm2）处理对PG钝化作用不明显,残留活力均在80%以上,并且处理15 min后,酶活力基本不变,动力学符合部分转化模型。但两者同时处理能使PG显著失活,钝化效果符合一级动力学模型。在20 kHz、35 ℃、605 W/cm2条件下处理16 min可使酶活力降至13.72%。先进行热处理（35 ℃、5 min）再进行超声波处理（0 ℃、605 W/cm2、0～10 min）或先进行超声波处理（0 ℃、605 W/cm2、5 min）再进行热处理（35 ℃、0～10 min）均不能有效钝化PG,表明只有在两者同时作用的前提下,才能表现出协同效应,达到更好的钝酶效果。PG是影响果蔬汁品质的主要酶之一,本实验不仅为超声波钝化PG提供了理论数据,也为果蔬汁加工提供了研究参考。     

Changes in Chemical Constituents of Kiwifruit During Post-Harvest Ripening

Kiwifruit (Actinidia chinensis Planch, Hayward cultivar) were ripened at 20°C under a stream of water-vapor saturated air containing 5 ppm ethylene gas. A remarkable rapid softening in the texture and rising of the soluble solids were observed in 24 hr. The total acidity, starch and amylose content decreased during ripening. Both fructose and glucose increased from 2.7% to 5.0% after 5 days of ripening. Sucrose content increased from 0.45% to 2.22% on the second day, then decreased to 1.19% after 5 days. No significant change in chlorophyll and total solids were observed throughout the experiment. There were stepwise decreases in the L and b_L values during ripening. The ascorbic acid content decreased from 210 to 190 mg per 100g fresh fruit after 5 days of ripening.     

Salmonella Inactivation During Extrusion of an Oat Flour Model Food

Little research exists on Salmonella inactivation during extrusion processing, yet many outbreaks associated with low water activity foods since 2006 were linked to extruded foods. The aim of this research was to study Salmonella inactivation during extrusion of a model cereal product. Oat flour was inoculated with Salmonella enterica serovar Agona, an outbreak strain isolated from puffed cereals, and processed using a single‐screw extruder at a feed rate of 75 kg/h and a screw speed of 500 rpm. Extrudate samples were collected from the barrel outlet in sterile bags and immediately cooled in an ice–water bath. Populations were determined using standard plate count methods or a modified most probable number when populations were low. Reductions in population were determined and analyzed using a general linear model. The regression model obtained for the response surface tested was Log (N_R/N_O) = 20.50 + 0.82T ? 141.16a_w – 0.0039T² + 87.91a_w² (R² = 0.69). The model showed significant (p < 0.05) linear and quadratic effects of a_w and temperature and enabled an assessment of critical control parameters. Reductions of 0.67 ± 0.14 to 7.34 ± 0.02 log CFU/g were observed over ranges of a_w (0.72 to 0.96) and temperature (65 to 100 °C) tested. Processing conditions above 82 °C and 0.89 a_w achieved on average greater than a 5‐log reduction of Salmonella. Results indicate that extrusion is an effective means for reducing Salmonella as most processes commonly employed to produce cereals and other low water activity foods exceed these parameters. Thus, contamination of an extruded food product would most likely occur postprocessing as a result of environmental contamination or through the addition of coatings and flavorings.     

Heat Inactivation of Trypsin Inhibitors in Soymilk at Ultra-High Temperatures

Soymilk samples at pH 7.5, 6.5 and 2 were subjected to heat treatment at 93°C and indirect ultra-high temperature. When heated at 93°C, 121°C and 132°C, trypsin inhibitor activity (TIA) in soymilk was more heat-labile at high pH than at lower pH. However, the effect of pH on rate of thermal inactivation was less pronounced when the holding temperature was increased to 143°C and 154°C. The point on a curve relating holding temperature and holding time, indicating inactivation of 90% of the TIA in soymilk at pH 6.5 in the range 93–154°C, coincided with the thermal-death-time curve of the organism putrefactive anacrobe 3679 at about 125°C.     

Cellular Automata Modeling of Hesperetin Release Phenomenon from Lipid Nanocarriers

Release behavior of encapsulated food bioactives is an important issue which has not been befittingly studied. Cellular automaton is a mathematical model that shows complex systems can be simulated based on interactions of their constructing components. In this research, cellular automata were proposed for simulating encapsulant release through lipid nanocarriers via diffusion mechanism in order to know effects of different parameters, e.g., encapsulant load, kind of neighborhood, probability of encapsulant solubility, encapsulant distribution, and type of release medium in two and three dimensions. The simulation results were validated using experimental hesperetin release data which showed good agreement indicating the ability of cellular automata to enhance the resolution over the complexity of the diffusion phenomenon during encapsulant release from nanocarriers.     

Heat Inactivation Kinetics of Apple Polyphenoloxidase and Activation of its Latent Form

Heat inactivation kinetics of crude polyphenoloxidase (PPO) from six apple cultivars (Golden Delicious, Starking Delicious, Granny Smith; Gloster, Starcrimson and Amasya) were studied at three temperatures (68°, 73° and 78°C). PPO activity initially increased and then decreased with heat, following a first order kinetic model. Increase in activity indicated presence of latent PPO. Regression coefficients for the linear portions of inactivation curves were computed to determine inactivation parameters. Reaction data at 78°C revealed that PPO in Amasya was the least and Starking Delicious the most heat-stable. Rate constants for heat inactivation at 78°C ranged from 15.99–28.27. 10^?2 min^?1. Activation energies varied between 54.7–77.2 kcal. mol^?1 with z values of 7.1–10.0C°.PPO in apples was generally more heat-stable than PPO in most fruits.     

Properties of Low-Fat Ground Beef Containing Potassium Lactate During Aerobic Refrigerated Storage

Low-fat patties containing water, carrageenan, encapsulated salt and hydrolyzed vegetable protein (carrageenan-based patties) with 0, 1, 2 or 3% potassium lactate were compared to low-fat all-beef patties with no additives. Carrageenan-based patties had enhanced (P<0.05) sensory properties (juiciness, tenderness, mealiness and beef flavor intensity) compared to all-beef patties. The bacterial populations of low-fat, carrageenan-based patties did not differ (P<0.05) from low-fat all-beef patties. Bacterial growth in low-fat, carrageenan-based patties was reduced through the use of 2 or 3% potassium lactate with no deleterious effects on the sensory properties of the low-fat, ground beef. However, low-fat, carrageenan-based patties underwent greater (P<0.5) discoloration and lipid oxidation during aerobic refrigerated storage than all-beef patties.     

Ripeness and Tissue Depth Effects on Heat Inactivation of Papaya Ethylene-Forming Enzyme

Heat inactivation studies were conducted on the ethylene-forming enzyme system (EFE) in papayas of different maturities, and at three tissue depths. D-values showed EFE in the mesocarp and endocarp were more heat sensitive than EFE in the exocarp. Within the mesocarp and endocarp, EFE in ¼ and ½ ripe papayas were more heat labile than in mature green and color break fruits. Ion leakage increased concomitantly with increased mesocarp and endocarp ripeness confirming that papayas ripen differentially from the innermost tissues outwards. Membrane integrity as determined by ion leakage may explain the increase in heat sensitivity of EFE in riper tissues.     

Biologically Active Components Inactivation and Protein Insolubilization during Heat Processing of Soybeans

Inactivation of lipoxygenase, trypsin inhibitor, urease and retention of protein solubility during water blanching of dehulled soybeans at 90°, 95° and 100°C were investigated. Lipoxygenase was the most heat labile, followed by urease and then trypsin inhibitor. Processing time based on “acceptable inactivation time” (AI) was proposed. AI value was longest for trypsin inhibitor, followed by urease and then lipoxygenase. The combined effect of heat on protein solubility and biologically active components inactivation was expressed as “PDI at acceptable inactivation time” (PDIAI). PDIAI value for the processing “limiting factor,” trypsin inhibitor inactivation, at the three temperatures were 36.7%, 42.5%, and 34.8%, respectively.     

Heat Inactivation of Catalase from Cod Muscle and from Some Psychrophilic Bacteria

Catalase from Pseudomonas sp. and Micrococcus sp. bacteria is inactivated at 93°C and 73°C, respectively, while cod muscle catalase is inactivated at 41°C. This implies that a suitable thermal treatment of a mixture of cod muscle and bacterial catalases will destroy only the cod catalase and leave the bacterial catalase unaltered. The activity of the remaining bacterial catalase is then measured using the disc flotation method.     

Release of Iron from Phosvitin by Heat and Food Additives

Most of the iron in egg yolk is bound by phosvitin. Heating whole egg or yolk in a double boiler does not release this iron. Also, heating a 0.125 mg/ml solution of phosvitin in distilled water for 20 and 40 min at 110°C did not free iron. A second phosvitin solution mixed equally with 0.04M citric acid, 2 M NaCl and 0.03M Na₂ EDTA. Only EDTA released (ca) iron from phosvitin without heating.     

Heat Transfer During Brining of Cuartirolo Argentino Cheese

The heat transfer which occurs during the brining of Cuartirolo Argentino cheese is mathematically modelled as a conduction process. The thermal diffusivity of the cheese was determined experimentally and shown to agree with the value calculated from thermal conductivity, density and heat capacity measurements. The theoretical and experimental temperature profiles in the time and spatial domains showed good agreement, thus demonstrating the applicability of the proposed model.     

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.     

Influence of Sugars on Heat Inactivation, Injury and Repair of Saccharomyces cerevisiae

The type of sugar in the heating and recovery media affected the rate of inactivation and repair capability of a Chablis strain of Saccharomyces cerevisiae. The rate of heat inactivation decreased with decreasing a_w in glucose and fructose but not in sucrose solutions. At any a_w the order of susceptibility to inactivation of yeast cells was consistently: fructose, glucose, and sucrose. In fructose, a major proportion of the survivors exhibited sublethal injury. When suspended in solutions containing the various sugars after heating and incubated for up to 18 hr prior to plating, the type of sugar in the solution influenced the ability of cells to repair injury.