Cold storage of porcine plasma treated with microbial transglutaminase under high pressure. Effects on its heat-induced gel properties

The objective of this work was to study the heat-induced gelling properties, at acid pH, of porcine plasma previously treated with microbial transglutaminase (MTGase) under high pressure (HP), when kept under refrigeration conditions for different times (setting time). The results indicated that, although the cross-linking activity of MTGase was enhanced under pressure, consequently, improving the thermal gel texture, the most significant effects, particularly on gel hardness, were obtained by keeping the treated plasma solutions under refrigeration for at least 2 h before gelation. On the whole, under such conditions, increases of approximately 60% of this textural parameter, calculated on the basis of the values corresponding to the heat-induced non-treated plasma gels at pH 5.5, were achieved. However, from the SDS–PAGE profiles, it can be suggested that mechanisms other than polymerisation by MTGase explain the beneficial effects of the treated plasma cold storage on gel texture. In contrast, the setting time had no effects on the water-holding capacity of heat-induced plasma gels at acid pH value, although this gel property was slightly enhanced by submitting porcine plasma solutions to the combined treatment (MTGase plus HP), with improvements being in accordance with the better-structured network of these heat-induced plasma gels.     

Improvement of gelling properties of porcine blood plasma using microbial transglutaminase

The effect of microbial transglutaminase (MTGase) on the texture and water-holding capacity (WHC) of heat-induced gels prepared from porcine blood plasma at pH 5.5 was investigated. Different concentrations of commercial MTGase were added to plasma and incubated for several times under specific conditions of temperature and pH. From the results obtained, it can be postulated that enzymatic treatment enhances textural properties and WHC of plasma gels at pH 5.5, especially when incubated with 3% of the commercial product for 3 h at 30 °C and pH 7. This treatment increased by 0.4 N the hardness of gels and reduced by 3% the water released after gel centrifugation with respect to the control samples. SDS–PAGE confirmed that cross-linking took place when MTGase was added to plasma solutions. However, the results suggest that the sole addition of MTGase was not effective enough to improve the gelling properties of plasma proteins under acidic conditions.     

Studies of the effect of hydrostatic pressure pretreatment on thermal gelation of chicken myofibrils and pork meat patty

The structures and characteristics of pressure–heat-induced gels of chicken myofibrils and pork patty were investigated. The M-line and Z-line in the chicken myofibril in 0.2 M NaCl were disrupted, and both of the thin and thick filaments were dissociated by pressure treatment. The microstructure of pressure–heat-induced chicken myofibrillar gel was composed of three-dimensional fine strands. Pressurization, at 200 MPa, prior to heating, increased the apparent elasticities of chicken myofibrillar gel and pork patty; however, pressure treatment above 200 MPa decreased it. The apparent elasticity of the pressure-treated (200 MPa) thermal myofibrillar gel was three times higher, and that of pork patty was twice higher than those of the unpressurized ones. The rheological properties of the low salt (1% NaCl) pork sausage can be improved by pressure treatment at 200 MPa prior to heating.     

超高压与转谷氨酰胺酶协同对碎猪肉凝胶成型的研究

研究了超高压与TGase协同对碎猪肉凝胶成型的影响,采用Box-Behnken实验设计获得的碎猪肉凝胶成型最佳工艺条件为:TGase添加量4.5g/kg,压力水平240MPa,保压时间10min。最佳工艺条件下的碎猪肉凝胶成型制品与鲜猪肉的硬度、粘着性、内聚性、胶凝性差异不显著。超高压与TGase结合的技术,实现了碎猪肉的凝胶成型,为碎猪肉边角料的利用提供了新方法。     

Individual and combined application of dry heat with high hydrostatic pressure to inactivate Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Alfalfa sprouts are recurrently implicated in outbreaks of food-borne illnesses as a result of contamination with Salmonella or Escherichia coli O157:H7. In the majority of these outbreaks, the seeds themselves have been shown to be the most likely source of contamination. The aims of this study were to comparatively assess the efficacy of dry heat treatments alone or in conjunction with high hydrostatic pressure (HHP) to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Dry heat treatments at mild temperatures of 55 and 60 °C achieved ≤1.6 and 2.2 log CFU/g reduction in the population of Salmonella spp. after a 10-d treatment, respectively. However, subjecting alfalfa seeds to more aggressive temperatures of 65 °C for 10 days or 70 °C for 24 h eliminated a ∼5 log population of Salmonella and E. coli O157:H7. We subsequently showed that the sequential application of dry heating followed by HHP could substantially reduce the dry heating exposure time while achieving equivalent decontamination results. Dry heating at 55, 60, 65 and 70 °C for 96, 24, 12 and 6 h, respectively followed by a pressure treatment of 600 MPa for 2 min at 35 °C were able to eliminate a ∼5 log CFU/g initial population of both pathogens. Finally, we evaluated the impact of selected treatments on the seed germination percentages and yield ratios and showed that dry heating at 65 °C for 10 days did not bring about any considerable decrease in the germination percentage. However, the sprout yield of treated alfalfa seeds was reduced by 21%. Dry heating at 60 and 65 °C for 24 and 12 h respectively followed by the pressure treatment of 600 MPa for 2 min at 35 °C did not significantly (P > 0.05) affect the germination percentage of alfalfa seeds although a reduction in the sprouting yield was observed.     

Reduction of counts of Listeria monocytogenes in cheese by means of high hydrostatic pressure

Inactivation of Listeria monocytogenes (strains NCTC 11994 and Scott A) was evaluated in model cheeses submitted to 10 min HHP treatments of 300, 400 or 500 MPa at 5 or 20 degrees C. Counts were measured immediately after high hydrostatic pressure (HHP) treatment (day 1) and after 2, 15 and 30 days of storage at 8 degrees C. Both strains behaved significantly different after 400 and 500 MPa, being NCTC 11994 more sensitive. Scarce differences were found among final values at both HHP treatment temperatures. Initial reductions (log cfu/g) for 400 MPa at 20 degrees C were 2.9 +/- 0.2 for strain NCTC 11994 and 1.5 +/- 0.2 for Scott A. They reached after 30-day storage 5.3 +/- 0.2 and 4.6 +/- 0.4 log cfu/g for NCTC 11994 and Scott A, respectively. For 500 MPa treatments, day-1 reductions of both strains were around 5-log cfu/g, and counts fell below quantification limit after 30 days. Injured cells (around 0.8-log cfu/g) were mostly observed in 400 MPa treated samples on days 1 and 2. Starter cells suffered higher inactivation and injury. For 20 degrees C treatments, its final counts (log cfu/g) at 300, 400 and 500 MPa were: 8.5 +/- 0.2, 5.4 +/- 0.3 and 2.5 +/- 0.1, respectively. These figures evidence the HHP potential to improve safety of cheese products.     

Simultaneous application of transglutaminase and high pressure to improve functional properties of chicken meat gels

Low-fat protein gels obtained by pressure are softer than those processed by conventional heat treatment. In this study, microbial transglutaminase (MTGase) (0.3%) was added to chicken batters in order to investigate the combined effect of pressure and enzyme on the functional properties of gels. Batters of meat with egg proteins were treated at 500 MPa for 30 min at 40 °C and then heated at 75 °C for 5 min to inactivate the enzyme. Treated samples showed, under confocal microscopy, a more compact and homogeneous microstructure and exhibited a notable increase in hardness and chewiness as compared to controls that were pressurized but contained no MTGase. They were also harder, more chewy and springy but had a similar cohesiveness and cutting force to those obtained by heat alone.     

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.     

Effects of combining microbial transglutaminase and high pressure processing treatments on the mechanical properties of heat-induced gels prepared from arrowtooth flounder (Atheresthes stomias)

The objective of this study was to evaluate the effect of setting conditions (25 °C for 2 h or 40 °C for 30 min) and combining of microbial transglutaminase (MTGase) and high pressure processing (HPP) on the mechanical properties of heat induced gels obtained from paste from arrowtooth flounder (Atheresthes stomias). Treatments included fish paste control without added MTGase, fish paste incubated with MTGase but not pressurized (MTGase + cooking), fish paste incubated with MTGase and pressurized at 600 MPa for 5 min (MTGase + HPP + cooking) and fish paste pressurized at 600 MPa for 5 min and incubated with MTGase (HPP + MTGase + cooking). The controls and the treated samples were then subjected to one of two thermal treatments: 90 °C for 15 min or 60 °C for 30 min before cooking at 90 °C for 15 min. Samples of fish paste heated at 60 °C before cooking could not be used to prepare gels for texture profile analysis (TPA). TPA showed that pressurization improved the mechanical properties of gels made from paste treated with MTGase and set at 25 °C. The opposite was observed for samples set at 40 °C. Setting at 40 °C appeared to induce proteolytic degradation of myofibrillar proteins.     

Combined effect of enterocin AS-48 and high hydrostatic pressure to control food-borne pathogens inoculated in low acid fermented sausages

The single and combined effects of enterocin AS-48 and high hydrostatic pressure (HHP) on Listeria monocytogenes, Salmonellaenterica, and Staphylococcus aureus was investigated in fuet (a low acid fermented sausage) during ripening and storage at 7 °C or at room temperature. AS-48 (148 AU g⁻¹) caused a drastic 5.5 log cfu g⁻¹ decrease in L. monocytogenes (P < 0.001) and a significant (P < 0.01) inhibition (1.79 logs) for Salmonella at the end of ripening (10 d). After pressurization (400 MPa) and storage Listeria counts remained below 5 cfu g⁻¹ in all fuets containing AS-48 (pressurized or not). HHP alone had no anti-Listeria effect. HHP treatment significantly reduced Salmonella counts, with lowest levels in pressurized fuets with AS-48. S. aureus showed similar growth for all treatments and storage conditions. These results indicate that AS-48 can be applied alone to control L. monocytogenes and combined with HHP treatment to control Salmonella in fuets.     

Fate of Staphylococcus aureus in cheese treated by ultrahigh pressure homogenization and high hydrostatic pressure

We evaluated the influence of ultrahigh pressure homogenization (UHPH) treatment applied to milk containing Staphylococcus aureus CECT 976 before cheese making, and the benefit of applying a further high hydrostatic pressure (HHP) treatment to cheese. The evolution of Staph. aureus counts during 30 d of storage at 8°C and the formation of staphylococcal enterotoxins were also assessed. Milk containing approximately 7.3 log₁₀ cfu/mL of Staph. aureus was pressurized using a 2-valve UHPH machine, applying 330 and 30 MPa at the primary and the secondary homogenizing valves, respectively. Milk inlet temperatures (T_in) of 6 and 20°C were assayed. Milk was used to elaborate soft-curd cheeses (UHPH cheese), some of which were additionally submitted to 10-min HHP treatments of 400 MPa at 20°C (UHPH+HHP cheese). Counts of Staph. aureus were measured on d 1 (24 h after manufacture or immediately after HHP treatment) and after 2, 15, and 30 d of ripening at 8°C. Counts of control cheeses not pressure-treated were approximately 8.5 log₁₀ cfu/g showing no significant decreases during storage. In cheeses made from UHPH treated milk at T_in of 6°C, counts of Staph. aureus were 5.0 ± 0.3 log₁₀ cfu/g at d 1; they decreased significantly to 2.8 ± 0.2 log₁₀ cfu/g on d 15, and were below the detection limit (1 log₁₀ cfu/g) after 30 d of storage. The use of an additional HHP treatment had a synergistic effect, increasing reductions up to 7.0 ± 0.3 log₁₀ cfu/g from d 1. However, for both UHPH and UHPH+HHP cheeses in the 6°C T_in samples, viable Staph. aureus cells were still recovered. For samples of the 20°C T_in group, complete inactivation of Staph. aureus was reached after 15 d of storage for both UHPH and UHPH+HHP cheese. Staphylococcal enterotoxins were found in controls but not in UHPH or UHPH+HHP treated samples. This study shows a new approach for significantly improving cheese safety by means of using UHPH or its combination with HHP.     

The effects of high hydrostatic pressure at subzero temperature on the quality of ready-to-eat cured beef carpaccio

We compared the application of high hydrostatic pressure (HHP) on unfrozen carpaccio (HHP at 20°C) and on previously-frozen carpaccio (HHP at -30°C). HHP at 20°C changed the color. The pressure increase from 400 to 650MPa and the time increment from 1 to 5min at 400MPa increased L* and b*. a* decreased only with 650MPa for 5min at 20°C. The prior freezing of the carpaccio and the HHP at -30°C minimized the effect of the HHP on the color and did not change the shear force, but increased expressible moisture as compared to the untreated carpaccio. HHP at 20°C was more effective in reducing the counts of microorganisms (aerobic total count at 30°C, Enterobacteriaceae, psychrotrophs viable at 6.5°C and lactic acid bacteria) than HHP at -30o C. With HHP at 20°C, we observed a significant effect of pressure and time on the reduction of the counts.     

Antioxidant effect of Majorana syriaca extract in bulk corn oil and o/w emulsion after applying high hydrostatic pressure

Bulk oils and oil-in-water emulsions were subjected to high hydrostatic pressure (HHP) (200, 650 MPa) treatment so as to estimate the effect of applied pressures on lipid oxidation. HHP-treated and non-treated samples were left to autoxidise under accelerated conditions (2 weeks, 70 °C) and their oxidative status was periodically estimated by measurement of conjugated dienes and peroxide value. Total changes of thiobarbituric acid-reactive substances were recorded as additional oxidative markers for emulsions. Results showed an increase in oxidation as pressure was increased especially at 650 MPa. Lipid oxidation rates that were more pronounced for HHP-treated samples can be correlated to measured dissolved oxygen that was also higher. HHP did not seem to have an effect on emulsion droplet size. The addition of Majorana syriaca (200 ppm) ethyl acetate extract led to protection against lipid oxidation under HHP and atmospheric conditions, 20.9–38.7% and 28.9–43.2%, respectively. It was observed that the antioxidant effect of M. syriaca extract under HHP was weaker.     

The effect of high hydrostatic pressure on the microbiological quality and safety of carrot juice during refrigerated storage

The microbial quality of untreated and pressure-treated carrot juice was compared during storage at 4, 8 and 12 °C. High pressure treatment at 500 MPa and 600 MPa (1 min/20 °C) reduced the total counts by approximately 4 log CFU ml⁻¹ and there was very little growth of the survivors during storage at 4 °C for up to 22 days. Total counts increased during storage of pressure-treated juice at 8 °C and 12 °C but took significantly longer to reach maximum levels compared to the untreated juice. The microflora in the untreated juice consisted predominantly of Gram-negative bacteria, identified as mostly Pantoea spp., Erwinia spp. and Pseudomonas spp. Initially the pressure-treated juice contained low numbers of spore-forming bacteria (Bacillus spp. and Paenibacillus spp.) and Gram-positive cocci; the spore-formers continued to dominate during storage.     

Environmental factors influencing the inactivation of Cronobacter sakazakii by high hydrostatic pressure

The effect of High Hydrostatic Pressure (HHP) on the survival of Cronobacter sakazakii was investigated. Deviations from linearity were found on the survival curves and the Mafart equation accurately described the kinetics of inactivation. Comparisons between strains and treatments were made based on the time needed for a 5-log₁₀ reduction in viable count. The ability of C. sakazakii to tolerate high pressure was strain-dependent with a 26-fold difference in resistance among four strains tested. Pressure resistance was greatest in the stationary growth phase and at the highest growth temperatures tested (30 and 37 °C). Cells treated in neutral pH buffer were 5-fold more resistant than those treated at pH 4.0, and 8-fold more sensitive than those treated in buffer with sucrose added (a_w = 0.98). Pressure resistance data obtained in buffer at the appropriate pH adequately estimated the resistance of C. sakazakii in chicken and vegetables soups. In contrast, a significant protective effect against high pressure was conferred by rehydrated powdered milk. As expected, treatment efficacy improved as pressure increased. z values of 112, 136 and 156 MPa were obtained for pH 4.0, pH 7.0 and a_w = 0.98 buffers, respectively. Cells with sublethal injury to their outer and cytoplasmic membranes were detected after HHP under all the conditions tested. The lower resistance of C. sakazakii cells when treated in media of pH 4.0 seemed to be due to a decreased barostability of the bacterial envelopes. Conversely, the higher resistance displayed in media of reduced water activity may relate to a higher stability of bacterial envelopes.     

不同温度培养诱导金黄色葡萄球菌对超高压失活的抗性及其建模

探讨不同培养温度处理诱导金黄色葡萄球菌(ATCC 6538)对超高压的抗性,并建立不同培养温度下金黄色葡萄球菌的超高压抗性模型。金黄色葡萄球菌经不同温度培养,在100~500 MPa的超高压条件下,选用线性、Weibull和Gompertz三种模型来拟合超高压抗性曲线,以决定系数(R2),均方误差(RMSE),精确因子(Af)和偏差因子(Bf)作为模型拟合度优劣的评判指标。实验结果表明,在100~500 MPa压力的作用下,线性模型的拟合效果不佳,R2最小值达到0.8870,Weibull和Gompertz模型对超高压的抗性具有较好的拟合性(R2≥0.9467),且Weibull模型的拟合效果最好,R2最大值达到0.9956,RMSE最小值为0.0312。因此,Weibull模型可以很好地拟合金黄色葡萄球菌以不同的培养温度胁迫后在超高压作用下的抗性曲线,随着培养温度的升高,金黄色葡萄球菌的超高压抗性呈增加趋势。      

Evaluation of atmospheric pressure plasma to improve the safety of sliced cheese and ham inoculated by 3-strain cocktail Listeria monocytogenes

The objective of this study was to evaluate the efficacy of atmospheric pressure plasma (APP), which is capable of operating at atmospheric pressure in air, in sliced cheese and ham inoculated by 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111, LMC). The process parameters considered were input power (75, 100, 125, and 150 W) and plasma exposure time (60, 90, and 120 s). Microbial log reduction increased with increases of input power and plasma exposure time. After 120 s APP treatments at 75, 100, and 125 W, the viable cells of LMC were reduced by 1.70, 2.78, and 5.82 log in sliced cheese, respectively. More than 8 log reductions can be achieved in 120 s at 150 W. In contrast, reductions after 120 s ranged from 0.25 to 1.73 log CFU/g in sliced ham. Calculated D values, the exposure time required to inactivate 90% of a population, from the survival curves of 75, 100, 125, and 150 W of APP treatments were 71.43, 62.50, 19.65, and 17.27 s for LMC in sliced cheese, respectively, and those in sliced ham were 476.19, 87.72, 70.92, and 63.69 s. No viable cells were detected at 125 and 150 W of APP treatment in sliced cheese, irrespective of plasma exposure time, after 1 week at a detection limit of 10¹ CFU/g. These results indicate that the inactivation effects of APP on L. monocytogenes are strongly dependent on the type of food.     

Effectiveness of high pressure processing on the hygienic and technological quality of porcine plasma from biopreserved blood

The effects of a high hydrostatic pressure (HHP) treatment (450MPa, 15min at 20°C) on both the microbiological quality and the functional properties of plasma from biopreserved porcine blood were evaluated. Blood was inoculated with Enterococcus raffinosus-PS99 (10(7)ufcmL(-1)) and stored at 5°C. After 72-h storage, bacterial counts in inoculated samples decreased by 52, 70, 81 and more than 99% for coliforms, Pseudomonas spp, hemolytic and proteolytic bacteria, respectively. Counts of these bacterial groups were undetectable in the final product after pressurization, whereas total lactic acid bacteria were detected at levels up to 10(2)ufcmL(-1). Gelling, foaming and emulsifying properties of the plasma proteins were not noticeably affected by HHP. The results show that it is possible to obtain high-quality and microbiologically stable blood derivatives as functional ingredients, by combining biopreservation and HHP.     

Response of two Salmonella enterica strains inoculated in model cheese treated with high hydrostatic pressure

The aim of this work was to determine the response to high hydrostatic pressure and the ability for survival, recovery, and growth of 2 strains of Salmonella enterica (Salmonella enteritidis and Salmonella typhimurium) inoculated in a washed-curd model cheese produced with and without starter culture. Inoculated samples were treated at 300 and 400 MPa for 10 min at room temperature and analyzed after treatment and after 1, 7, and 15 d of storage at 12° C to study the behavior of the Salmonella population. Cheese samples produced with starter culture and treated at 300 and 400 MPa showed maximum lethality; no significant differences in the baroresistant behavior of both strains were detected. Nevertheless, when starter culture was not present, the maximum lethality was only observed in cheese samples treated at 400 MPa, in the case of S. enteritidis. Ability to repair and grow was not observed in model cheese produced with starter culture and cell counts of treated samples decreased after 15 d of storage at 12° C. In cheese produced without starter culture, Salmonella cells showed the ability to repair and grow during the storage period, reaching counts over 3 log₁₀ (cfu/mL) in both applied treatments and serotypes. These results suggest that high hydrostatic pressure treatments are effective to reduce Salmonella population in this type of cheese, but the presence of the starter culture affects the ability of this microorganism to repair and grow during the storage period.     

Scale-up unit of a unique moderately high pressure unit to enhance microbial inactivation

The efficacy of a scale-up of a moderately high pressure unit built in this work was investigated with regards to inactivation of Geobacillus stearothermophilus spores suspended in pumpkin soup, and effect of the process on l-ascorbic acid. In this design saturated steam was used as a heating medium. The treatment unit is a double pipe heat exchanger in which the food is pumped in its inner tube, while steam is passed in the annular region to heat the sample. This technology comprises a unique approach of generating a mild pressure (80-100 MPa) utilizing thermal expansion of the liquid being treated. The results show that this unique application decreased the D-values of Geobacillus stearothermophilus ATCC 7953 spores suspended in soup samples in comparison to thermal treatment alone. The improvement was more significant at lower treatment temperatures. The D-values obtained were in a good agreement with that of the small unit built earlier in which oil was used as a heating medium. The effect of treatment on l-ascorbic acid was similar to that of thermal treatment. The treated samples were subjected to shelf life study by storing them at two different temperatures. No evidence of spore recovery was noted during the post-treatment storage period.