Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100–200 MPa, 7 min) and elevated temperature (80 °C, 10 min); spore germination at high temperatures (55, 60 or 65 °C); and inactivation of germinated spores with elevated temperatures (80 and 90 °C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 °C, 10 min). Low pressures (100–200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 °C, 10 min), and germinated at temperatures lethal for vegetative cells (≥55 °C) when incubated for 60 min with a mixture of l-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (∼4 decimal reduction) in meat by elevated temperatures (80–90 °C for 20 min) required a long germination period (55 °C for 60 min). However, similar inactivation level was reached with shorter germination period (55 °C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 °C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 °C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 °C in about 20 min and further incubation at 55 °C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 °C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.     

High Pressure Destruction Kinetics of Clostridium Sporogenes Spores in Salmon Slurry at Elevated Temperatures

Salmon slurry containing C. sporogenes spores was subjected to high pressure (HP) treatments (700–900 MPa; 80–100°C, and 0–24 min). Destruction rates (D value) and pressure/temperature sensitivity parameters (Z_P and Z_T ) were evaluated. Thermal treatment D values were an order of magnitude higher than those under HP. Higher pressures and temperatures accelerated the spore destruction rates. Z_P values were 14.5, 17.3 and 15.5°C at 700, 800 and 900 MPa respectively, while Z_T values (at constant temperature) were 440, 540, 550 MPa at 80, 90, and 100°C, respectively. The z value under thermal treatment was 8.8°C. The spores were relatively more sensitive to temperature than to pressure.     

Clostridium sporogenes-ATCC 7955 Spore Destruction Kinetics in Milk Under High Pressure and Elevated Temperature Treatment Conditions

Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R ² > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z _P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C), indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z _T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure.     

Addition of ethanol to supercritical carbon dioxide enhances the inactivation of bacterial spores in the biofilm of Bacillus cereus

Supercritical carbon dioxide (SC-CO₂) was used to inactivate Bacillus cereus spores inside biofilms, which were grown on stainless steel. SC-CO₂ treatment was tested using various conditions, such as pressure treatment (10–30 MPa), temperature (35–60 °C), and time (10–120 min). B. cereus vegetative cells in the biofilm were completely inactivated by treatment with SC-CO₂ at 10 MPa and at 35 °C for 5 min. However, SC-CO₂ alone did not inactivate spores in biofilm even after the treatment time was extended to 120 min. When ethanol was used as a cosolvent with SC-CO₂ in the SC-CO₂ treatment using only 2–10 ml of ethanol in 100 ml of SC-CO₂ vessel for 60–90 min of treatment time at 10 MPa and 60 °C, B. cereus spores in the biofilm were found to be completely inactivated in the colony-forming test. We also assessed the viability of SC-CO₂-treated bacterial spores and vegetative cells in the biofilm by staining with SYTO 9 and propidium iodide. The membrane integrity of the vegetative cells was completely lost, while the integrity of the membrane was still maintained in most spores. However, when SC-CO₂ along with ethanol was used, both vegetative cells and spores lost their membrane integrity, indicating that the use of ethanol as a cosolvent with SC-CO₂ is efficient in inactivating the bacterial spores in the biofilm.     

Inactivation of Bacillus stearothermophilus spores in egg patties by pressure-assisted thermal processing

The use of pressure-assisted thermal processing (PATP) to inactivate bacterial spores in shelf-stable low-acid foods, without diminishing product quality, has received widespread industry interest. Egg patties were inoculated with Bacillus stearothermophilus spores (10⁶ spores/g) and the product was packaged in sterile pouches by heat sealing. Test samples were preheated and then PATP-treated at 105 °C at various pressures and pressure-holding times. Thermal inactivation of spores was studied at 121 °C using custom-fabricated aluminum tubes; this treatment served as a control. Application of PATP at 700 MPa and 105 °C inactivated B. stearothermophilus spores, suspended in egg matrix rapidly, (4 log reductions in 5 min) when compared to thermal treatment at 121 °C (1.5 log reduction in 15 min). Spore inactivation by PATP progressed rapidly (3 log reductions at 700 MPa and 105 °C) during pressure-hold for up to 100 s, but greater holding times (up to 5 min) had comparatively limited effect. When PATP was applied to spores in water suspension or egg patties, D values were not significantly different. While thermal inactivation of spores followed first-order kinetics, PATP inactivation exhibited nonlinear inactivation kinetics. Among the nonlinear models tested, the Weibull model best described PATP inactivation of B. stearothermophilus spores in the egg product.     

Thermal inactivation of Yersinia enterocolitica in pork slaughter plant scald tank water

The objective of this study was to establish the time–temperature combinations required to ensure the thermal inactivation of Yersinia enterocolitica during scalding of pork carcasses. A 2 strain cocktail of Y. enterocolitica (bioserotypes 2/O:5,27 and 1A/O:6,30) was heat treated at 50, 55 and 60 °C in samples of scald tank water obtained from a commercial pork slaughter plant. Samples were removed at regular intervals and surviving cells enumerated using (i) Cefsulodin–Irgasan–Novobiocin Agar (CIN) supplemented with ampicillin and arabinose and (ii) Tryptone Soya Agar (TSA), overlaid with CIN agar with ampicillin and arabinose. The data generated was used to estimate D- and z-values and the formula D_x = log^− 1(log D₆₀ − ((t₂ − t₁)/z)) was applied to calculate thermal death time–temperature combinations from 55 to 65 °C. D₅₀, D₅₅ and D₆₀-values of 45.9, 10.6 and 2.7 min were calculated from the cell counts obtained on CIN agar, respectively. The corresponding D-values calculated from the TSA/CIN counts were 45.1, 11 and 2.5 min, respectively. The z-value was 7.8. It was concluded that a time–temperature combination of 2.7 min at 60 °C is required to achieve a 1 log reduction in Y. enterocolitica in pork scald tank water. The predicted equivalent at 65 °C was 0.6 min. This study provides data and a model to enable pork processors to identify and apply parameters to limit the risk of carcass cross-contamination with Y. enterocolitica in pork carcass scald tanks.     

Kinetics of the formation of radicals in meat during high pressure processing

The kinetics of the formation of radicals in meat by high pressure processing (HPP) has been described for the first time. A threshold for the radicals to form at 400 MPa at 25 °C and at 500 MPa at 5 °C has been found. Above this threshold, an increased formation of radicals was observed with increasing pressure (400–800 MPa), temperature (5–40 °C) and time (0–60 min). The volume of activation (ΔV^#) was found to have the value −17 ml mol⁻¹. The energy of activation (E_a) was calculated to be 25–29 kJ mol⁻¹ within the pressure range (500–800 MPa) indicating high independence on the temperature at high pressures whereas the reaction was strongly dependent at atmospheric pressure (E_a = 181 kJ mol⁻¹). According to the effect of the processing conditions on the reaction rate, three groups of increasing order of radical formation were established: (1) 55 °C at 0.1 MPa, (2) 500 and 600 MPa at 25 °C and 65 °C at 0.1 MPa, and (3) 700 MPa at 25 °C and 75 °C at 0.1 MPa. The implication of the formation of radicals as initiators of lipid oxidation under HPP is discussed.     

Evaluation of high pressure (HP) treatment for rapid and uniform pH reduction in carrots

Acidification (pH < 4.6) of marginally low acid foods allows them to be treated like high acid foods and, hence, has the potential to improve quality and reduce energy costs by lowering the severity of processing conditions. The objective of this study was to evaluate high pressure (HP) treatment for rapid and uniform pH reduction of low acid foods using carrot. Three organic acids (citric, malic and glucono-delta-lactone) were used in the study. Conventional acidification tests were carried out at atmospheric pressure at different temperatures (36–48 °C) and different treatment times (0–36 min). HP treatments were given at room temperature (maximum process temperature <32 °C) with different pressures (200–300 MPa) and treatment times (0–14 min). Time dependent acid infusion and the resulting pH reduction were used to evaluate the acidification kinetics. Results showed that the pH reduction rates were described by a first order kinetic model. No significant differences (p > 0.05) in acidification rates were observed between the acidifying agents either in conventional or HP acidification process. Pressure (HP acidification) and temperature (conventional acidification) significantly (p < 0.05) reduced decimal reduction time (D) for pH drop. The associated D values were 2.4–4.4 times higher in conventional (slower) as compared with HP acidification. For conventional acidification, the z values (temperature sensitivity) were 34–44.8 °C and for HP acidification, the z values (pressure sensitivity) were 206–222 MPa. HP acidification provided more rapid and uniform pH reduction as compared to conventional method.     

Response of Bacillus cereus spores to high hydrostatic pressure and moderate heat

The effects of high pressure (400-600 MPa) and moderate heat (60-80 °C) treatments at various process times (10-20 min) on the reduction of Bacillus cereus As 1.1846 spores, suspended in milk buffer were investigated. In the present work, response surface methodology (RSM) was employed, and a quadratic equation of high hydrostatic pressure inactivation was built with RSM. By analyzing response surface plots and corresponding contour plots and by solving the quadratic equation, experimental values were shown to be significantly in agreement with predicted values, since the adjusted determination coefficient was 0.9752 and the level of significance was P < 0.0001. Optimum process parameters for a six-log cycle reduction of B. cereus spores were obtained: pressure, 540.0 MPa; temperature, 71 °C; and pressure-holding time, 16.8 min. The adequacy of the model equation in predicting optimum response values was verified effectively using experimental test data that was not used in the development of the model.     

A comparison between E-beam irradiation and high pressure treatment for cold-smoked salmon sanitation: microbiological aspects

The effectiveness of electron beam irradiation and high pressure treatment for the sanitation of cold-smoked salmon from two points of view, microbial safety and shelf-life extension, was compared. From the response of L. monocytogenes INIA H66a to irradiation, a D value of 0.51 kGy was calculated. For samples stored at 5 °C, 1.5 kGy would be sufficient to attain a Food Safety Objective (FSO) of 2 log₁₀cfu/g L. monocytogenes for a 35-day shelf-life, whereas 3 kGy would be needed in the case of a temperature abuse (5 °C + 8 °C). Pressurization at 450 MPa for 5 min was considered to be an insufficient treatment, since the FSO of 2 log₁₀cfu/g L. monocytogenes was only attained for a shelf-life of 21 days at 5 °C. However, treatment at 450 MPa for 10 min achieved this FSO for samples held during 35 days at 5 °C, or during 21 days under temperature abuse (5 °C + 8 °C) conditions. Irradiation at 2 kGy kept the microbial population of smoked salmon below 6 log₁₀cfu/g after 35 days at 5 °C, with negligible or very light changes in its odor. Pressurization at 450 MPa for 5 min also kept the microbial population below 6 log₁₀cfu/g after 35 days at 5 °C and did not alter odor, but affected negatively the visual aspect of smoked salmon.     

“Cold” electroporation in potato tissue induced by pulsed electric field

This work compares PEF-induced effects in potato tissue at temperatures below and above ambient (T = 2–45 °C). The potato (Agata) was selected for investigation. The PEF treatment using electric field strength E = 200–800 V/cm and bipolar pulses of near-rectangular shape with pulse duration t_p (=100 μs) was applied. The PEF experiments were done under non-isothermal conditions with temperature increase owing to the effect of ohmic heating. The linear temperature dependencies of electrical conductivity of potato tissue with different values of the electrical conductivity disintegration index, Z, were observed. However, the values of the conductivity temperature coefficient, α, at the reference temperature T_r = 25 °C were noticeably different for the intact (α_i = 0.0255 ± 0.0003 °C⁻¹) and completely damaged (α_d = 0.031 ± 0.009 °C⁻¹) potato tissues. This difference was explained by the impact of temperature on the structure of the damaged tissue. The non-isothermal PEF treatment was shown to be an effective tool for electroporation at low temperatures (below ambient). For initial temperature T_i = 2 °C, the most power saving was the PEF treatment at E = 200 V/cm (W ≈ 20–30 kJ/kg), and the PEF treatment at E = 400–800 V/cm required more power consumption (W ≈ 50–80 kJ/kg). The PEF treatment at the fixed value of E (=400 V/cm) showed that the total power consumptions (accounting for PEF treatment and thermal heating), required for high level of tissue disintegration, Z ≈ 0.9, were comparable for initial temperatures T_i = 2 °C (W ≈ 50–80 kJ/kg) and T_i = 20 °C (W ≈ 80 kJ/kg) and were noticeably higher for initial temperature T_i = 40 °C (W ≈ 150 kJ/kg).     

Heat resistance of Listeria species to liquid whole egg ultrapasteurization treatment

The lethality of ultrapasteurization treatments (70 °C/1.5 min.) applied at constant temperature (isothermal condition) and at a constantly raising temperature of 2 °C/min (non-isothermal condition) in liquid whole egg (LWE) against two strains of Listeria monocytogenes (STCC 5672 and 4032) and one of Listeria innocua has been investigated. Isothermal survival curves up to 71 °C were obtained, which followed first-order inactivation kinetics. The obtained D_t values indicated that L. innocua was significantly (p < 0.05) more heat resistant than L. monocytogenes strains. Non-significant (p > 0.05) differences were observed among z values (12.4 ± 0.4 °C, 13.1 ± 0.4 °C and 12.2 ± 0.7 °C for L. innocua and L. monocytogenes 5672 and 4032, respectively). Based on obtained D_t and z values, isothermal ultrapasteurization treatment (70 °C/1.5 min.) would provide 3.5-, 5.0-, and 6.5-Log₁₀ cycles of L. innocua and L. monocytogenes 5672 and 4032, respectively. Non-isothermal heating lag phase increased the thermotolerance of Listeria species in LWE. The simulated industrial pasteurization treatment for LWE (heating-up phase from 25 to 70 °C followed by 1.5 min. at 70 °C) would attain 5-Log₁₀ reductions of L. monocytogenes 5672 and 4032, and 3.7-Log₁₀ reductions of L. innocua. Therefore, the safety level of industrial ultrapasteurization concerning L. monocytogenes could be lower than that estimated with data obtained under isothermal conditions.     

Inactivation of Saccharomyces cerevisiae in conference pear with high pressure carbon dioxide and effects on pear quality

This work explores the use of high pressure carbon dioxide (HPCD) for the inactivation of Saccharomyces cerevisiae in fresh-cut conference pears. This fruit was chosen as an example of a ready to eat and minimally processed food. Assays were carried out with continuous CO₂ flow at different pressures (6–30 MPa), temperatures (25–55 °C), and exposure times (10–90 min). Heat treatments at similar temperatures and times were compared to the use of HPCD, wherein it was observed that HPCD was more effective. The total inactivation (5 log₁₀ cycles) of the yeast took place at 55 °C with HPCD while it was necessary to reach 70 °C when only heat was applied. Required pressures and exposure times were relatively low (?6 MPa and on the order of minutes) because of the direct contact between the CO₂ and the pear. The pH and °Brix were not affected by the HPCD treatment; however, the pears lost their texture and became darker due to a decrease in vitamin C and enzymatic browning. Peroxidase activity was only partially reduced. The addition of an antioxidant did not help to prevent darkening. Therefore, HPCD could be a low temperature conservation method that is superior to conventional thermal treatments for the preparation of fruit preserves where a firm texture is not essential.     

Effects of high pressure/thermal treatment on lipid oxidation in beef and chicken muscle

Lipid oxidation was studied in beef and chicken muscle after high pressure treatment (0.1–800 MPa) at different temperatures (20–70 °C) for 20 min, prior to storage at 4 °C for 7 days. Pressure treatment of beef samples at room temperature led to increases in TBARS values after 7 days storage at 4 °C; however, the increases were more marked after treatment at pressures ?400 MPa (at least fivefold) than after treatment at lower pressures (less than threefold). Similar results were found in those samples treated at 40 °C, but at 60 °C and 70 °C pressure had little additional effect on the oxidative stability of the muscle. Pressure treatments of 600 MPa and 800 MPa, at all temperatures, induced increased rates of lipid oxidation in chicken muscle, but, in general, chicken muscle was more stable than beef to pressure, and the catalytic effect of pressure was still seen at the higher temperatures of 50 °C, 60 °C and 70 °C. The addition of 1% Na₂EDTA decreased TBARS values of the beef muscle during storage and inhibited the increased rates of lipid oxidation induced by pressure. The inhibition by vitamin E (0.05% w/w) and BHT (0.02% w/w), either alone or in combination, were less marked than seen with Na₂EDTA, suggesting that transition metal ions released from insoluble complexes are of major importance in catalysing lipid oxidation in pressure-treated muscle foods.     

Response surface optimisation for the extraction of phenolic compounds and antioxidant capacities of underutilised Mangifera pajang Kosterm. peels

The optimum extraction conditions for highest recovery of total phenolics content (TPC) and antioxidant capacities (AC) were analysed for Mangifera pajang peels (MPP), using response surface methodology. The effects of ethanol concentration (X₁: 20–80%), extraction temperature (X₂: 30–65 °C) and liquid-to-solid ratio (X₃: 20–50 mL/g) on the recovery of total phenolics (Y₁) and antioxidant capacity (Y₂) were investigated. A second order polynomial model produced a satisfactory fitting of the experimental data with regard to total phenolic content (R² = 0.9966, p < 0.0001) and antioxidant capacity (R² = 0.9953, p < 0.0001). The optimum extraction conditions for TPC were 68%, 55 °C and 32.7 mL/g, and for AC were 68%, 56 °C and 31.8 mL/g, respectively. Predicted values for extraction of TPC and AC agreed well with the experimental values. Liquid chromatography–mass spectrometry of the optimally obtained extracts from MPP revealed the major phytochemicals as mangiferin, gallic acid, catechin and epicatechin.     

Extraction of fish oil from the skin of Indian mackerel using supercritical fluids

The total oil was extracted from the ground skin of Indian mackerel (Rastrelliger kanagurta) using various techniques of supercritical fluid extraction (SFE) at 20–35 MPa and 45–75 °C and by the Soxhlet method for comparison. The oil yield increased with pressure and temperature and the highest yields were 24.7, 53.2, 52.8, and 52.3/100 g sample (dry basis) for the continuous, cosolvent, soaking, and pressure swing techniques, respectively, at 35 MPa and 75 °C. The yield from the Soxhlet extraction was 53.6/100 g sample (dry basis). The CO₂ consumption was 581.8, 493.6, 484.9 and 290.9 g for the continuous, cosolvent, soaking and pressure swing techniques, respectively, at 35 MPa and 75 °C. The largest recoveries of PUFA, especially the ω-3 family, were achieved from the soaking and pressure swing techniques at 35 MPa and 75 °C. Thus, the pressure swing and soaking techniques are the most effective at extracting the oil from fish skin.     

Effects of supercritical carbon dioxide extraction parameters on virgin coconut oil yield and medium-chain triglyceride content

The extraction of coconut oil has been performed using supercritical carbon dioxide (SC-CO₂). The extractions were performed at pressure and temperature ranges of 20.7–34.5 MPa and 40–80 °C, respectively. It was observed that almost all (more than 99%) of the total oil could be extracted. Response surface methodology (RSM) was applied to evaluate the effects of the parameters (pressure, temperature and CO₂ consumption) on the extraction yield and medium-chain triglycerides (MCTs), in terms of the fatty acid content in the extracted oil. A correlation was established with p-values for both responses significant at the 95% confidence level.     

Estimating pressure induced changes in vegetable tissue using in situ electrical conductivity measurement and instrumental analysis

Pressure-induced textural changes in selected vegetables (carrot, potato, and red radish) were investigated using in situ electrical conductivity measurement. Electrical conductivity of the vegetables was recorded in situ up to 10 min under elevated pressures (200, 400, 600 MPa at 25 °C) using a custom-fabricated experimental setup. The tissue disintegration index (Z) was determined for raw, processed and freeze–thawed samples. The hardness and stiffness of the samples were evaluated using the instrumental texture analyzer. This information was related to the crunchiness index (CI). Pressure treatment increased electrical conductivity values of all the samples as a function of pressure and holding time. Beyond a certain threshold of pressure holding time, the electrical conductivity did not change further. In situ electrical conductivity measurement is a useful tool to document the extent of textural changes during high pressure processing.     

Effects of light,temperature and water activity on the kinetics of lipoxidation in almond-based products

Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (a_w) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at a_w 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the a_w increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol⁻¹ to 60 kJ mol⁻¹. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q₁₀) decreased from 3.3 to 1.6.     

Inactivation kinetics of Bacillus spores in batch- and continuous-heating systems

Kinetic parameters for the thermal inactivation of Geobacillus stearothermophilus ATCC 7953 and Bacillus flexus 1316 spores were determined for temperatures ranging from 100 to 130 °C and 100 to 125 °C, respectively. Ringer's solution (pH = 7.1) was used as the heating medium. A batch-heating system, in which the samples are kept in small tubes that are heated with steam, and a continuous-heating system, which is based upon a heat exchanger and enables high temperature short time heating, were used. Experiments were conducted in both systems and the heat resistances of the two species were determined. Additionally, a comparison of the two heating systems was carried out. The reaction rate constant at the reference temperature, k_ref, the activation energy, E_a, the D-value and the z-value were calculated for the two species. The D-values at 121 °C for G. stearothermophilus and for B. flexus in the batch-heating system were found to be 42 and 4.2 s, respectively. The z-values were calculated as 13 K for G. stearothermophilus and 16 K for B. flexus in the batch-heating system. The results from both systems differed significantly, wherein the continuous-heating system had been more lethal than the batch-heating system.