Pressure-temperature Combinations Research Articles

On thermodynamics and heat and mass transfer aspects of CH4 adsorption onto coconut shell-based carbonaceous material

The current study investigates the equilibrium methane (CH4) adsorption capacity and the adsorption kinetics of a locally produced coconut shell-derived activated carbon (AC CARB 6X12 60) for pressure and temperatures ranging from 0 to 55 bar and -20 to 70 °C, respectively. The adsorption isotherms and kinetics are determined using an in-house developed adsorption test rig. A maximum methane adsorption uptake of 0.140 kg/kg is obtained at -20 °C and 40 bar pressure. The adsorption equilibrium isotherm data are fitted using Toth, Dubinin-Astakhov (DA), and Modified-DA isotherm models. Afterwards, the kinetics study is done considering pseudo first order, second order, Elovich, and intra-particle diffusion models. In continuation, based on the DA isotherm model, Clausius Clapeyron relation, and Maxwell's relations, the expressions for the crucial thermodynamic parameter of adsorbed phase, i.e., isosteric heat of adsorption, specific heat capacity, enthalpy, and entropy is derived, and same is estimated using DA isotherm parameters. Additionally, the activated carbon's thermophysical properties (i.e., thermal conductivity, thermal diffusivity, and specific heat) are determined using the TPS 2500 S analyzer, which works on the hot-disk principle. Using the most suitable isotherm (DA) and kinetic model (pseudo second order), heat and mass transfer analysis is carried out on novel reactor configuration with an external cooling jacket, double row of cooling pipes with external longitudinal fins for methane storage using a 3D transient model in Comsol Multiphysics. The charge characteristics are studied for gas charging pressure varying from 1 to 50 bar and cooling fluid temperature of -20 to 70 °C. Iso-concentration contours are plotted to identify the pressure-temperature combination resulting in identical storage capacity (i.e., including both gaseous and adsorbed phases). Further simulations are carried out for constant pressure charging and constant flow discharge conditions to expound upon the effects of the dormancy period, gas charging pressure, and cooling/heating fluid temperature. 14% improvement in total discharge amount is obtained with a dormancy period between charging and discharging compared to no dormancy case.

Predicting the essential oil composition in supercritical carbon dioxide extracts from hop pellets using mathematical modeling

Supercritical fluid extraction from hops (Humulus lupulus L.) can be used to extract essential oil for the flavoring of beer. With a special focus on the oil composition being linked to the hop aroma, the influence of pressure and temperature on the extraction kinetics of seven oil components (β-myrcene, α-humulene, β-caryophyllene, 2-methylbutyl isobutyrate, undecanone, linalool, and α-pinene) is analyzed and modeled in this article.Supercritical CO2 extraction from hop pellets was conducted at pressure-temperature combinations of 90/100/110 bar and 40/45/50 °C. The extract composition over time, analyzed by gas chromatography, was used for the parameterization of two existing mechanistic models: an internal-mass-transfer-control (IMTC), and a broken-and-intact-cells (BIC) model. The IMTC model was found to effectively describe most extraction kinetics and hence applied in this study. In contrast to previous studies, the IMTC model parameters were not only fitted to individual extraction curves from different experiments but also correlated to temperature and pressure as a further step towards model-based prediction. Using the parameterized model, the extract composition was predicted at 95 bar/48 °C, 105 bar/42 °C, and 105 bar/48 °C.Extraction yields were found to be higher at lower temperatures and higher pressures in general. The sensitivity towards pressure was observed to differ between components and to be particularly higher for β-myrcene compared with α-humulene. Changes of the essential oil composition with a variation in pressure and temperature were predicted correctly by the model with a mean relative deviation from experimental data of 11.7% (min. 1.2%, max. 36.2%).

Solution enhanced dispersion by supercritical fluids (SEDS): An approach in particle engineering to modify aqueous solubility of andrographolide from Andrographis paniculata extract

The objective of study is to improve aqueous solubility of andrographolide through particle engineering using Solution Enhanced Dispersion by Supercritical Fluids (SEDS) approach. The precipitation pattern of sticky crude Andrographis paniculata extract from CO2-acetone system and CO2-acetone:ethanol (v/v) 1:1 system as well as the aqueous solubility of andrographolide precipitated were first studied at different pressure (100, 150bar) and temperature (40, 50°C) combination (full factorial design). The modification of aqueous solubility of andrographolide was then attempted by manipulating its precipitation process from CO2-solvent systems consisting of single solvent and solvent mixture at different proportions (v/v) at the appropriate pressure-temperature combination. A. paniculata powder precipitated from CO2-acetone system at 150bar, 40°C was found to be large, irregularly shaped, less crystalline with the highest andrographolide aqueous solubility (twofold increment compared to crude extract) and recovery compared to those precipitated from CO2-ethanol system and other CO2-solvent mixture systems. Complete dissolution of andrographolide from A. paniculata powder precipitated from CO2-acetone system had been achieved within 90min. For SEDS precipitation under solvent mixture system, with increment of proportion of ethanol from 25% to 75%, larger particles and change of powder morphology from stripes into plates were resulted. Based on the higher aqueous solubility and dissolution of andrographolide, recovery as well as a different morphology observed from the less crystalline A. paniculata powder precipitated from CO2-acetone system, less impurities could have co-precipitated with andrographolide.

Thermal-assisted high hydrostatic pressure extraction of nutraceuticals from saffron (Crocus sativus): Process optimization and cytotoxicity evaluation against cancer cells

The extraction of nutraceuticals (crocin, picrocrocin, and safranal) from saffron was conducted using high hydrostatic pressure. A pressure range of 100–600 MPa in combination with elevated temperatures (30–70 °C) was studied. Extract quality was determined by an ISO (the international organization for standardization) method, and also compared with HPLC analysis. The results showed a significantly (P < 0.05) positive effect of pressure on the extract quality with an increase of 52–63%, 54–85%, and 55–62% in crocin, picrocrocin, and safranal content, respectively, as the pressure increased. However, a highly significant decrease (25–36%) in crocin content was observed with the increase in temperature. Moreover, the effect of pressure on saffron components varied with the change in temperature which was observed from the response surfaces. A third-order model showed a good fit (R2 > 0.9) of these data including pressure effect on crocin, picrocrocin, and safranal content. An optimum pressure-temperature combination of 580 MPa and 50 °C with an extraction time of 5 min (dwell time) was obtained, predicting 100, 50, and 92 units of crocin, safranal, and picrocrocin content, respectively. A <5% error was found between the predicted and experimental values. Anti-cancer activity of the optimized extract obtained under high hydrostatic pressure was evaluated using MTT (3,(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide) based assay, which showed a 28% higher anti-cancer activity as compared to the conventionally extracted sample. High hydrostatic pressure proved to be a better technology than conventional process for extraction of bioactive components from saffron, the highest valued spice in the world. Pressure-extracted components of saffron can be used to formulate functional foods or directly applied for clinical trials.

Modeling the Combined Effect of Pressure and Mild Heat on the Inactivation Kinetics of Escherichia coli, Listeria innocua, and Staphylococcus aureus in Black Tiger Shrimp (Penaeus monodon)

The high-pressure inactivation of Escherichia coli, Listeria innocua, and Staphylococcus aureus was studied in black tiger shrimp (Penaeus monodon). The processing parameters examined included pressure (300 to 600 MPa) and temperature (30 to 50°C). In addition, the pressure-hold period (0 to 15 min) was investigated, thus allowing both single-pulse pressure effects (i.e., zero holding time) and pressure-hold effects to be explored. E. coli was found to be the most sensitive strain to single-pulse pressure, followed by L. innocua and lastly S. aureus. Higher pressures and temperatures resulted in higher destruction rates, and the value of the shape parameter (β′) accounted for the downward concavity (β′ > 1) of the survival curves. A simplified Weibull model described the non-linearity of the survival curves for the changes in the pressure-hold period well, and it was comparable to the original Weibull model. The regression coefficients (R2), root mean square error (RMSE), accuracy factor (Af), bias factor (Bf), and residual plots suggested that using linear models to represent the data was not as appropriate as using non-linear models. However, linear models produced good fits for some pressure–temperature combinations. Analogous to their use in thermal death kinetics, activation volume (Va) and activation energy (Ea) can be used to describe the pressure and temperature dependencies of the scale parameter (δ, min), respectively. The Va and Ea values showed that high pressure and temperaturefavored the inactivation process, and S. aureus was the most baro-resistant pathogen.

High-Pressure Cold Pasteurization of Gilthead Seabream Fillets: Selection of Process Conditions and Validation of Shelf Life Extension

The objective of this study was to identify and kinetically study the most high-pressure (HP) resistant deteriorative factor of gilthead seabream (Sparus aurata) fillets aiming in their shelf life extension using in pack cold pasteurization technology. Fillets were HP processed (600 MPa, 25 °C, 5 min) and stored at 15 °C for 15 days, until spoilage. Lactobacilli were isolated from the spoiled fillets and were identified and classified as Pediococcus spp. The necessary HP process conditions for Pediococcus spp. cells inactivation were studied at various combinations of pressure (150–600 MPa) and temperature (20–40 °C) for appropriate time. The D values were calculated at all pressure–temperature combinations. The effect of temperature (z T) and pressure (z P) was estimated at all pressures and temperatures, respectively. According to the developed model for Pediococcus spp. inactivation, HP treatment of seabream fillets at 600 MPa and 25 °C for 5 min seemed to be capable for a 6-log10 reduction of the initial microbial load, potentially providing shelf life extension. Shelf-life experiments were conducted for validation. Untreated and HP treated at 600 MPa for 5-min samples were stored at 0, 5, 10 and 15 °C. Quality indices (colour, texture, microbial growth, sensory scoring) were monitored and kinetically modelled. Temperature dependence of quality loss rates was modelled by the Arrhenius equation. Microbial growth was well correlated with the sensory indices. HP treatment led to significant shelf life extension of fillets. Based on sensory scoring, the shelf life of the untreated samples was 11, 7, 4 and 3 days while for the HP-treated fillets 37, 27, 17 and 10 days after storage at 0, 5, 10 and 15 °C, respectively.

Selection of Process Conditions for High Pressure Pasteurization of Sea Buckthorn Juice Retaining High Antioxidant Activity

Sea buckthorn berries juice is a nutritious beverage, rich in vitamin C and carotenoids with high antioxidant activity. The main requirements for a freshly squeezed sea buckthorn juice production are the cloud stability and antioxidant activity retention after processing. Appropriate process technologies and conditions have to be applied in order to inactivate pectin methyl esterase (PME), responsible for cloud loss, while maintaining the nutritional characteristics and antioxidant activity of the juice. The objectives of the present work were to study and model the effect of thermal treatment and high pressure (HP) processing on the inactivation kinetics of endogenous PME and on total antioxidant activity alteration. Thermal treatment significantly affected PME inactivation and residual antioxidant activity. Processing even at mild process conditions (60 °C for 1 min) resulted in 2.5-fold antioxidant activity reduction and 50 % PME inactivation compared to untreated sample. Pressure and temperature acted synergistically for PME inactivation that followed first-order kinetics with a residual PME activity at all pressure–temperature combinations used (200–600 MPa and 25–35 °C). The effect of temperature and pressure on the inactivation rate constants was expressed through the activation energy and activation volume, respectively. Values of 163 kJ/mol and −17 mL/mol at reference pressure of 600 MPa and reference temperature of 35 °C were estimated, respectively. Antioxidant activity of the samples was expressed through the determination of the effective concentration (EC50). A slight increase in sea buckthorn antioxidant activity when applying pressures (200–600 MPa) at ambient temperature (25 °C) was observed compared to the corresponding value of untreated juice. Processing at higher temperatures did not significantly alter the total antioxidant activity of sea buckthorn juice. For sample treated at 600 MPa–35 °C for 5 min, a 5 % reduction of total antioxidant activity was observed. These conditions are proposed as effective process conditions for sea buckthorn juice cold pasteurization, based on the higher antioxidant activity retention and simultaneous PME inactivation.

High hydrostatic pressure inactivation kinetics of the endogenous lipoxygenase in crude silver carp (Hypophthalmichthys molitrix) extract

SummaryInactivation kinetics of endogenous lipoxygenase in crude silver carp (Hypophthalmichthys molitrix) extract was studied for thermal (50–80 °C, ambient pressure) and high hydrostatic pressure combined with heat treatment (300–700 MPa at 50–80 °C) process conditions. Lipoxygenase (LOX) inactivation followed first‐order kinetics at all pressure–temperature combinations used. Moreover, LOX inactivation rates became less pressure dependent with increasing pressure at all temperatures studied and also showed less temperature dependence of the enzyme inactivation rate at various high pressure levels tested. It is evident that inactivation kinetics is complex affected by both pressure and temperature. Therefore, response surface methodology (RSM) was attempted to investigate combined temperature–pressure processing conditions on LOX inactivation kinetics in crude silver carp extract samples. In conclusion, the LOX inactivation rate constant was modelled as a function of both temperature and pressure conditions by a quadratic polynomial equation as follows: .

High pressure–temperature degradation kinetics of polyacetylenes in carrots

The present study assessed the effect of high pressure–temperature (HPT) processing on the levels of three polyacetylenes in carrot disks immediately after processing in comparison to sous-vide processing. The degradation kinetics of these compounds following processing at HPT was also investigated. The highest pressure–temperature combination which gave maximum retention during the time 10–30min, for falcarinol it was 400MPa, at 50 and 60°C for 10min; for falcarindiol it was 400MPa, at 50°C for 10min and for falcarindiol-3-acetate was 400MPa, at 50°C for 10min, respectively. Falcarindiol-3-acetate was found to be most barosensitive and falcarindiol was found to be most thermosensitive of the three polyacetylenes studied. When compared with sous-vide (SV) processed carrot disks, HPT processed samples showed higher retention of polyacetylenes. The changes in the levels of polyacetylenes during HPT treatment were adequately described by Weibull model function.

Effect of non-thermal processing by High Hydrostatic Pressure on the survival of probiotic microorganisms: Study on Bifidobacteria spp.

High Hydrostatic Pressure (HP) processing has been suggested as an alternative method to improve textural attributes of dairy products. Since, the global market seeks improved functional foods, it is important to investigate whether HP processing can be applied to fermented dairy probiotic products. The inactivation kinetics of Bifidobacterium spp. in a model system of acid pH value under high pressure (100–400 MPa) combined with moderate temperature (20–35 °C) was investigated. Bifidobacterium spp. inactivation followed first order kinetics at all pressure–temperature combinations used. Pressure and temperature were found to act synergistically on the viability loss of the bacterium. The corresponding z T and z P values of inactivation were also estimated and, values of 41.5 °C and 93.5 MPa at reference pressure of 200 MPa and reference temperature of 25 °C were estimated, respectively. HP treatment of 200 MPa at 20–25 °C for 10–15 min, recommended for textural modification, is not detrimental to the viability of the studied probiotic culture and would be suitable for respective fermented probiotic products.

Kinetic study of high pressure microbial and enzyme inactivation and selection of pasteurisation conditions for Valencia Orange Juice

SummaryKeeping quality of fresh orange juice is highly dependent on pectinolytic enzyme activity and the growth of spoilage microorganisms. The inactivation kinetics of indigenous pectin methylesterase (PME) and of the two more pressure resistant species of spoilage lactic acid bacteria (LAB) Lactobacillus plantarum and L. brevis in freshly squeezed Valencia orange juice under high hydrostatic pressure (100–500 MPa) combined with moderate temperature (20–40 °C) was investigated. PME inactivation followed first order kinetics with a residual PME activity (15%) at all pressure–temperature combinations used. The values of activation energy and activation volume were estimated at each pressure and at each temperature, respectively. Values of 90 kJ/mol and −30 mL/mol at reference pressure of 300 MPa and reference temperature of 35 °C were estimated respectively. The corresponding zT and zP values of LAB inactivation were also estimated at all conditions tested. Values of 19.5 °C and 95 MPa at reference pressure of 300 MPa and reference temperature of 30 °C were estimated respectively for L. plantarum, while the corresponding values for L. brevis were 40 °C and 82 MPa, respectively, at the same reference conditions. Pressure and temperature were found to act synergistically both for PME and LAB inactivation. The PME and LAB inactivation rate constants were expressed as functions of the temperature and pressure process conditions. These functions allow the determination of the pressure/temperature conditions that achieve the target enzyme and microbial inactivation at a selected processing time. The process conditions of 350 MPa at 35 °C for 2 min are proposed as effective for Valencia orange juice cold pasteurisation.

Pressure and temperature combination for inactivation of soymilk trypsin inhibitors

High hydrostatic pressure (HHP) processing, an emerging technology for food preservation, in combination with thermal treatment (250/50, 550/19, 550/65, and 550/80 MPa/°C) was applied to soymilk made from previously soaked soybeans (in distilled water or 0.5% sodium bicarbonate solution). First order kinetics constants ranging from 0.081 to 0.217 min−1, for residual trypsin, were estimated in soymilk from soaked soybeans at selected pressure–temperature combinations. Residual trypsin, at 550 MPa and 80 °C, was high at higher HHP holding times. The highest percentage of residual trypsin (76%) was estimated after a 15 min holding time. The use of sodium bicarbonate for soaking of soybeans synergistically decreased the trypsin inhibitor activity in soymilk in comparison with residual trypsin using distilled water alone.

High-pressure treatments induce folate polyglutamate profile changes in intact broccoli ( Brassica oleraceae L. cv. Italica) tissue

In plant matrices, folates exist largely as folylpoly-γ-glutamates requiring deglutamylation to monoglutamates prior to absorption, which might impair dietary folate bioavailability. This study investigated folylpoly-γ-glutamate stability and conversions in broccoli tissue during thermal (25–90 °C, 30 min) and high-pressure treatments (0.1–600 MPa, 25–45 °C, 30 min) after vacuum packaging. Folates were analyzed based on poly-γ-glutamate side chain length by RP-HPLC. During thermal treatments, folates were stable up to 90 °C, whereas differences in folylpoly-γ-glutamate profiles towards higher conjugated folylpoly-γ-glutamates were observed at elevated temperatures (70–90 °C). High-pressure treatments resulted in significant folate losses (48–78%). Depending on the pressure–temperature combinations studied, folylpoly-γ-glutamates were converted to folylmono- and folyldi-γ-glutamates, which was shown to occur mainly during the initial stages of the high-pressure treatments, i.e. during pressure build-up and subsequent equilibration. Targeted application of high-pressure treatments can hence be applied to obtain broccoli with higher monoglutamate folate content. Implications towards folate bioavailability in relation to the observed folate degradation, however, requires further investigation.

High pressure inactivation of lipoxygenase in soy milk and crude soybean extract

The high pressure inactivation of lipoxygenase (LOX) in soy milk and crude soybean extract was studied in the pressure range 0.1–650 MPa with temperature varying from 5 to 60 °C. For both systems, the isobaric–isothermal inactivation of LOX was irreversible and followed a first-order reaction at all pressure–temperature combinations tested. In the entire pressure–temperature area studied, the LOX inactivation rate constants increased with increasing pressure at constant temperature for both systems; the rate constants were somewhat smaller in soy milk system than in crude soybean extract. At constant elevated pressure, LOX exhibited the greatest stability around 20 °C in both systems, indicating that the Arrhenius equation was not valid over the entire temperature range. For both systems, the temperature dependence of the LOX inactivation rate constants at high temperature decreased with increasing pressure, while the highest sensitivity of the LOX inactivation rate constants to pressure was observed at about 30 °C. The pressure–temperature dependence of the LOX inactivation rate constants was successfully described either using an empirical mathematical model or using a thermodynamic kinetic model for both systems. On a kinetic basis, neither the reaction order of inactivation nor the pressure and temperature sensitivities of the inactivation rate constants were influenced by the different levels of food complexity between the two systems.

Biogenic Amine Formation and Nitrite Reactions in Meat Batter As Affected by High-Pressure Processing and Chilled Storage

Changes in biogenic amine formation and nitrite depletion in meat batters as affected by pressure-temperature combinations (300 MPa/30 min/7, 20, and 40 degrees C), cooking process (70 degrees C/30 min), and storage (54 days/2 degrees C) were studied. Changes in residual nitrite concentration in raw meat batters were conditioned by the temperature and not by the pressure applied. Cooking process decreased (P < 0.05) the residual nitrite concentration in all samples. High-pressure processing and cooking treatment increased (P < 0.05) the nitrate content. Whereas protein-bound nitrite concentration decreased with pressure processing, no effect was observed with the heating process of meat batters. High-pressure processing conditions had no effect on the rate of residual nitrite loss throughout the storage. The application of high pressure decreased (P < 0.05) the concentration of some biogenic amines (tyramine, agmatine, and spermine). Irrespective of the high processing conditions, generally, throughout storage biogenic amine levels did not change or increased, although quantitatively this effect was not very important.

Evaluation of Chemical and Physical (High-Pressure and Temperature) Treatments To Improve the Safety of Minimally Processed Mung Bean Sprouts during Refrigerated Storage

The objective of this study was to compare the effects of combined high hydrostatic pressure and temperature treatments with different chemical sanitation treatments (water, sodium hypochlorite, and hydrogen peroxide) on the microbiological properties of mung bean sprouts. In a first study, the raw product was subjected to several combined high-pressure and temperature treatments for calculating a mathematical model by a response surface methodology. The number of pressure-temperature (150 to 400 MPa; 20 to 40°C) combinations was limited to 10. In addition, a model system consisting of mung bean sprout juice was inoculated with Listeria monocytogenes (CECT 4032). Microbial inactivation with this model system was also investigated by a response surface methodology. The highest aerobic mesophilic bacteria and L. monocytogenes inactivation was achieved at maximum pressure and temperature (5.5 and 1.8 log cycles, respectively). In a second study, the effect of five different processing lines on the microbial load reduction of minimally processed mung bean sprouts during refrigerated storage was studied. All treatments reduced the initial population of aerobic mesophilic bacteria and fecal coliforms, with the physical treatment of 400 MPa and 40°C being the most effective, showing initial reductions of 5.8 and 7.8 log CFU/g, respectively. Recovery of bacteria from sprouts treated under these conditions was not observed during storage. However, the sprouts that received washing treatments with water, sodium hypochlorite, and hydrogen peroxide exhibited increases in aerobic mesophilic and fecal coliform counts after 3 days of storage at 4°C.

Stability and catalytic activity of α‐amylase from barley malt at different pressure–temperature conditions

The impact of high hydrostatic pressure and temperature on the stability and catalytic activity of alpha-amylase from barley malt has been investigated. Inactivation experiments with alpha-amylase in the presence and absence of calcium ions have been carried out under combined pressure-temperature treatments in the range of 0.1-800 MPa and 30-75 degrees C. A stabilizing effect of Ca(2+) ions on the enzyme was found at all pressure-temperature combinations investigated. Kinetic analysis showed deviations of simple first-order reactions which were attributed to the presence of isoenzyme fractions. Polynomial models were used to describe the pressure-temperature dependence of the inactivation rate constants. Derived from that, pressure-temperature isokinetic diagrams were constructed, indicating synergistic and antagonistic effects of pressure and temperature on the inactivation of alpha-amylase. Pressure up to 200 MPa significantly stabilized the enzyme against temperature-induced inactivation. On the other hand, pressure also hampers the catalytic activity of alpha-amylase and a progressive deceleration of the conversion rate was detected at all temperatures investigated. However, for the overall reaction of blocked p-nitrophenyl maltoheptaoside cleavage and simultaneous occurring enzyme inactivation in ACES buffer (0.1 M, pH 5.6, 3.8 mM CaCl(2)), a maximum of substrate cleavage was identified at 152 MPa and 64 degrees C, yielding approximately 25% higher substrate conversion after 30 min, as compared to the maximum at ambient pressure and 59 degrees C.

High-pressure-mediated survival of Clostridium botulinum and Bacillus amyloliquefaciens endospores at high temperature.

Endospores of proteolytic type B Clostridium botulinum TMW 2.357 and Bacillus amyloliquefaciens TMW 2.479 are currently described as the most high-pressure-resistant bacterial spores relevant to food intoxication and spoilage in combined pressure-temperature applications. The effects of combined pressure (0.1 to 1,400 MPa) and temperature (70 to 120 degrees C) treatments were determined for these spores. A process employing isothermal holding times was established to distinguish pressure from temperature effects. An increase in pressure (600 to 1,400 MPa) and an increase in temperature (90 to 110 degrees C) accelerated the inactivation of C. botulinum spores. However, incubation at 100 degrees C, 110 degrees C, or 120 degrees C with ambient pressure resulted in faster spore reduction than treatment with 600 or 800 MPa at the same temperature. This pressure-mediated spore protection was also observed at 120 degrees C and 800, 1,000, or 1,200 MPa with the more heat-tolerant B. amyloliquefaciens TMW 2.479 spores. Inactivation curves for both strains showed a pronounced pressure-dependent tailing, which indicates that a small fraction of the spore populations survives conditions of up to 120 degrees C and 1.4 GPa in isothermal treatments. Because of this tailing and the fact that pressure-temperature combinations stabilizing bacterial endospores vary from strain to strain, food safety must be ensured in case-by-case studies demonstrating inactivation or nongrowth of C. botulinum with realistic contamination rates in the respective pressurized food and equipment.

Kinetics of (6R,S) 5-formyltetrahydrofolic acid isobaric–isothermal degradation in a model system

Isothermal and isobaric–isothermal degradation kinetics of (6R,S) 5-formyltetrahydrofolic acid (5-CHOH4PteGlu) was studied at different pH levels in the temperature range from 80 to 110 °C and different pressure–temperature combinations (100–800 MPa and 30–70 °C). The thermal degradation of 5-CHOH4PteGlu followed first-order kinetics at all pH levels (in the range of pH 3–9.2) studied. 5-CHOH4PteGlu at pH 7–9.2 was quite stable up to 5–7 h of heating at 80 °C but less stable in more acidic conditions (pH 3.38 and 5). Pressure–temperature degradation of 5-CHOH4PteGlu could be adequately described by a first-order reaction. In the whole pressure–temperature area studied, the degradation rate constants of 5-CHOH4PteGlu were enhanced by increasing pressure or increasing temperature. Significant reductions in 5-CHOH4PteGlu concentration were noticed when pressures above 400 MPa were combined with temperatures above 40 °C. A model to describe the effect of combined pressure and temperature on the 5-CHOH4PteGlu destruction rate constant was presented.

Low Pressure CO2 Storage of Raw Milk: Microbiological Effects

The effects of holding raw milk under carbon dioxide pressures of 68 to 689 kPa at temperatures of 5, 6.1, 10, and 20°C on the indigenous microbiota were investigated. These pressure-temperature combinations did not cause precipitation of proteins from the milk. Standard plate counts from treated milks demonstrated significantly lower growth rate compared with untreated controls at all temperatures, and in some cases, the treatment was microcidal. Raw milk treated with CO2 and held at 6.1°C for 4 d exhibited reduced bacterial growth rates at pressures of 68, 172, 344, and 516 kPa; and at 689 kPa, demonstrated a significant loss of viability in standard plate count assays. The 689-kPa treatment also reduced gram-negative bacteria and total Lactobacillus spp. The time required for raw milk treated at 689 kPa and held at 4°C to reach 4.30 log10 cfu/mL increased by 4 d compared with untreated controls. Total coliform counts in the treated milk were maintained at 1.95 log10 cfu/mL by d 9 of treatment, whereas counts in the control significantly increased to 2.61 log10 cfu/mL by d 4 and 2.89 log10 cfu/mL by d 9. At d 8, Escherichia coli counts had not significantly changed in treated milk, but significantly increased in the control milk. Thermoduric bacteria counts after 8 d were 1.32 log10 cfu/mL in treated milk and 1.98 log10 cfu/mL in control milk. These data indicated that holding raw milk at low CO2 pressure reduces bacterial growth rates without causing milk protein precipitation. Combining low CO2 pressure and refrigeration would improve the microbiological quality and safety of raw milk and may be an effective strategy for shipping raw single strength or concentrated milk over long distances.