Behaviour of E. coli 0157:H7 strains in model system and in raw meat by hpp: Microbial and technological aspects

Abstract

Verotoxigenic Escherichia coli (VTEC) is an important pathogen which can cause serious illnesses in humans. It is of particular importance to the meat industry to be able to completely destroy E. coli. A technique used to destroy E. coli could be the high pressure process. For this reason a mixture of 8 strains of E. coli 0157:H7 was inoculated in raw minced meat and in broth. These samples were treated at pressures up to 700 MPa at WC, causing up to 5 decimal reductions. HP treatment is also effective in decreasing microbial contamination and increasing the shelf-life of raw minced meat under refrigerated conditions. The texture of raw minced meat improved with HP level, while the colour was less characteristic in HP-treated samples; a combined HP-treatment caused less colour change than an individual HP-treatment. No difference in colour of cooked minced meat was observed in untreated and HP-treated samples. The texture of cooked minced meat improved in HP-treated samples.     

Effect of high pressure processing on the preservation of frozen and re-thawed sliced cod (Gadus morhua) and salmon (Salmo salar) fillets

Cod and salmon are both widely found in the seafood market, but those products are easily spoiled. This work reports on the investigation of the effects of three moderate pressure values (150, 300 and 450?MPa) applied for 5?min at 20°C on crude sliced cod and salmon fillets. It was found that high pressure processing (HPP) significantly reduced the microbial load during refrigerated storage for up to 14 days. As expected, the most effective treatment was 450?MPa because it inhibited microbial growth. This process affected the hardness, lightness, lipid oxidation, protein denaturation and oxidation. The fish muscle composition (lipid amount and protein profile) played a main role in the changes promoted by pressure. HPP permits the shelf life of the raw product at 4°C to be increased with minimal changes in the organoleptic characteristics and to enable crude consumption.     

Effects of high pressure treatment on the quality of cooked pork ham prepared with different levels of curing ingredients

The aim of this study was to define the effects of high-pressure treatment (600 MPa, 10 min, 20 °C) on the quality of cooked pork ham prepared with two different levels of curing ingredients in brine. Physical, chemical, microbiological, and sensory tests were performed 24 h after high pressure processing (HPP), as well as after 6 and 8 weeks of storage in refrigerator conditions. The results indicate that HPP causes significant improvement of shelf life of vacuum packed ham, including the samples with reduced level of curing ingredients in brine to 8 weeks in refrigerator conditions (4–6 °C). HPP did not have significant effect on the texture or color of ham. However, it significantly increased the drip loss during storage in the packed samples. This may indicate that HPP has negative effects on water holding capacity of cooked products.     

Effect of high pressure processing on textural and microbiological quality of pink perch (Nemipterus japonicus) sausage during chilled storage

The non-thermal high pressure (HP) processing was studied on fish sausage to enhance the quality during chilled storage. Pink perch (Nemipterus japonicus) sausages, packed in poly amide casing under vacuum were subjected to 400, 500 and 600?MPa pressures (dwell time: 10?min and ramp rate: 300?MPa/min) and compared with heat-set samples for physico-chemical and microbial quality parameters. Pressurized samples formed softer and glossier gels with a slight reduction in water-holding capacity. HP made the texture of sausage softer, cohesive and less chewy and gummier than heat-treated ones. Folding test seen higher acceptance values in samples treated at 500 and 600?MPa, during storage. Maximum log reduction in microbial count was observed in 600?MPa immediately, and significant difference in cooked and pressurized sausages was seen only up to 7th day. This revealed the potential application of HP in replacing conventional heat treatment for sausages preparation with enhanced shelf-life.     

Combination of high pressure with nisin or lysozyme to further process mechanically recovered poultry meat

Abstract

The combined effect of high pressure processing (HPP) and nisin or lysozyme on aerobic mesophile and psychrotrophe populations of mechanically recovered poultry meat (MRPM) was evaluated. Nisin (0, 12.5, 100 and 200ppm) or lysozyme (0 and 150ppm) were added to MRPM, and vacuum-packaged samples were treated at 350 and 450 MPa for 5 and 15min at 20°C. In mesophiles, reductions above 4 log CFU/g were found in some samples. Psychrotrophes proved more sensitive; in MRPM containing 200 ppm of nisin treated at 450 MPa for 15min, no growth was detected (a lethality of more than 8 log units). There was no synergistic effect between HPP and lysozyme. In contrast, combination of HPP and nisin is a promising nonthermal preservation treatment.     

The application of high pressure–mild temperature processing for prolonging the shelf-life of strawberry purée

The aim of this study was to monitor the shelf-life and quality of strawberry purée preserved using combined high pressure processing (HPP)–mild temperature processing at 300 and 600?MPa for 15 min during cold storage (6°C). Increasing the pressure resulted in a prolonged shelf-life of from 4 to 28 weeks for HPP-preserved purée at 300 and 600?MPa, respectively. The highest inactivation of peroxidases, pectinesterases and polygalacturonases was noted when a higher pressure was used, whereas a lower pressure was more efficient for polyphenoloxidases. The degradation of vitamin C and anthocyanins was 20% and 5% higher at 600?MPa than at 300?MPa, respectively. Significantly fewer changes in the colour coefficient, expressed as ΔE, and the browning index, were observed in purée preserved at 600?MPa. Oxidative and hydrolytic enzymes are highly pressure-resistant, which suggests other inhibitors should be used to increase the shelf-life of good-quality fruit products.     

Hydrostatic high pressure applied to food sterilization III: Application to spices and spice mixtures

Abstract

The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography.     

High pressure processing and storage of blueberries: effect on fruit hardness

Non-thermal preservation technologies such as high pressure processing (HPP) have low impact in original fruit flavours. The objective of this study was to process the whole blueberries by HPP and investigate the effect on its hardness after processing and during 7 and 28 days storage. Whole blueberry immersed in water was the best packaging option. The blueberries submitted to 200 and 600?MPa for 5–60?min and were stored at 3°C for 1 week. In another experiment, HPP blueberries (200 and 600?MPa for 10?min) were stored for 28 days. No difference in sensorial texture was observed between HPP and fresh unprocessed blueberry, although the instrumental hardness decreased significantly. Hardness was not affected by the processing time and was similar just after HPP and one-week storage. The hardness of HPP-processed blueberries was kept along 28 days storage without considerable weight loss as opposed to fresh fruits which collapsed.     

Nonthermal pasteurization of beer by high pressure processing: modelling the inactivation of saccharomyces cerevisiae ascospores in different alcohol beers

The industrial production of beer ends with a process of thermal pasteurization. In this research, the nonthermal pasteurization of beer by high pressure processing (HPP) was carried out. First, the effect of alcohol content on Saccharomyces cerevisiae ascospore inactivation at 400?MPa was studied. The number of ascospores in 0.0%, 4.8%, and 7.0% alc/vol beers for 10?min processing time decreased by 3.1, 4.9, and ≥?6.0 log, respectively. The Weibull model fitted the ascospore inactivation by HPP in 0.0%, 4.8%, and 7.0% alc/vol beers. At 400?MPa, 7.2?s could ensure the minimum pasteurization of beers and for 600?MPa 5?s were enough for ≥?7 log reductions. The overall flavour of HPP vs. untreated beers was evaluated for a lager and an ale, with no significant differences between the untreated and HPP beers. Thus, nonthermal HPP is a feasible technology to pasteurize beer with different alcohol contents without heat.     

Effects of high pressure treatment on the quality of chicken patties

The effects of high pressure treatment (500 MPa, 10 min, 20 °C) on the quality of commercial chicken patties (breaded and unbreaded) were evaluated. Physical, chemical and microbiological tests were performed 24 h after high pressure processing (HPP), as well as after 14 and 21 days of storage in refrigerated conditions. It was concluded that the use of high pressures extends the shelf life of vacuum-packaged chicken patties by up to 3 weeks, based on the condition of storage during refrigeration. After this period, the number of mesophilic, psychrotrophic and lactic acid bacteria in the pressure-treated patties was five to six logarithmic cycles lower than that in the control products. HPP did not considerably influence the amount of storage drip loss, texture or colour of the patties; however, it quickened the process of lipid oxidation.     

Effect of high hydrostatic pressure processing and squeezing pressure on some quality properties of pomegranate juice against thermal treatment

The aim of this study was to investigate the effect of high hydrostatic pressure (HHP) treatment (200, 300, 400?MPa; 5°C, 15°C and 25°C; 5 and 10 min) on some quality properties of pomegranate juice. Juice samples are obtained under industrial conditions at two different squeezing pressure levels (100 and 150?psi – 0.689 and 1.033?MPa, respectively). Results are compared against conventional thermal treatment (85°C/10 min) and raw sample. For all three processing temperature, HHP combinations at 400?MPa for 10 min were sufficient to decrease the microbial load around 4.0 log cycles for both squeeze levels. All HHP treatments showed no significant decrease at antioxidant activity, total phenolic content and monomeric anthocyanin pigment concentrations, while there was a significant decrease (p?≤?.05) in thermal-treated samples. Being the highest sugar alcohol in pomegranate juice, mannitol content must be considered for determining the authenticity, and mannitol content increased with squeezing pressure and thermal treatment.     

High pressure and thermal pasteurization effects on sweet cherry juice microbiological stability and physicochemical properties

This study evaluated high pressure processing (P1 – 400?MPa/5?min; P2 – 550?MPa/2?min) and thermal pasteurization (TP – 70°C/30?s) effects on sweet cherry juice's microbiological and physicochemical parameters, during four weeks of refrigerated storage. All treatments reduced the microbiological load to undetectable levels not affecting total soluble solids and titratable acidity. The pH increased with all treatments, however, it decreased during storage. Phenols were differently affected: TP increased them by 6%, P1 had no effect while P2 decreased them by 11%. During storage, phenols in control and TP samples decreased by 26% and 20%, P1 samples decreased them by 11% whereas P2 showed no variation. TP had no effect on anthocyanins, while pressure treatments increased them by 8%. Anthocyanins decreased during storage, particularly in the control and P1 (decreasing 41%). All treatments had no effect on antioxidant activity until the 14th day, thereafter high pressure processing samples showed the highest antioxidant activity.     

The determination of the parameters of sub- and supercritical extraction of plant raw materials

The extraction of biologically active substances by carbon dioxide from various plant raw materials (amaranth seeds, Sophora japonica flower buds, Stephania rotunda stems, and Stevia rebaudiana leaves) was studied at sub- and supercritical parameters. A laboratory unit for the extraction of plant raw materials by liquefied gases and supercritical fluids at 5–35 MPa pressures and 285–350 K temperatures was developed. The maximum yield of the extracted substances from plants specified was obtained at temperature and pressure exceeding the critical parameters of CO₂ (320–330 K, 28–30 MPa).     

Effects of High Pressure Treatment on the Microbiological Quality,Texture and Colour of Vacuum Packed Pork Meat Products

The aim of the study was to define usefulness of high pressure treatment for inactivation of microorganisms and prolongation of shelf life of two types of cooked pork ham and raw smoked pork loin. The samples of ham and loin in the presentation of standard 200 g pieces were vacuum packed in polylayer polyethylene bags and exposed to high pressure treatment in the range of 300-600 MPa and time of exposure of 10-30 minutes. Results indicate that 300 MPa and 400 MPa pressure applied for 10 minutes was insufficient for prolongation of storage period of ham. Pressure of 500 MPa, applied for 10 minutes caused significant decrease of microbiological parameters studied such as: total bacterial count, psychrophylic bacteria, acidophylic bacteria and enterococci in investigated samples, stored in refrigarator conditions for 4 weeks. Pressure of 600 MPa applied for 10 minutes reduced the number of all investigated microorganisms by 10 5 -10 6 fold. Application of this pressure prolonged storage period of traditionally produced ham to 6-8 weeks. Physico-chemical characteristics of ham, measured 24 h after high pressure treatment and after 4, 6 and 8 weeks of storage, did not change when compared to the initial samples. High pressure treatment caused increase in the colour lightness parameters only in pork smoked loin.     

On the nature and the practical relevance of the molecular modifications induced in wheat proteins by high pressure treatment

Abstract

Modifications induced by the combined application of pressure (up to 800 MPa) and temperature (up to 80° C) were studied on wet and dry semolina, and on fresh pasta as such and after cooking. Rheological and immunochemical properties of the treated products were investigated, along with parameters indicating the extent of protein denaturation. No modification occurs in semolina treated at less than 45% water, below 60°C/800MPa for 10min. Egg noodles prepared from pressure/heat treated semolina had increased protein digestibility and low recognition by anti-gliadin antibodies either before or after cooking. The same effects were observed in heat/pressure treated pasta, but were lost upon subsequent cooking, although we found decreased immunochemical reactivity after heat/pressure treatment of cooked pasta. No sensory difference was found between cooked and pressure-treated semolina products.     

Effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites

This paper investigates the effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites at operating frequencies between 0.1 and 10 kHz. The magnetic and electrical properties of samples were measured by an LCR meter and morphology of the samples was characterized by scanning electron microscopy. It was shown that the compacted sample prepared at 800 MPa and 550 °C had the lowest magnetic loss and electrical resistivity, and highest magnetic induction and effective permeability in comparison with other samples compacted at 800 MPa and room temperature, 150, 250, 350 and 450 °C.     

High Pressure Processing at Subzero Temperature: Effect on Spoilage Microbiota of Poultry

Mechanically recovered poultry meat (MRPM) was treated at 350 and 450 MPa for 5 and 15 min at m 20 °C and then stored at 2 °C. Counts of mesophilic, psychrotrophic and lactic acid bacteria were determined at 1, 4 and 15 days of storage. Initial counts were ca. 7 log CFU/g for the three populations. High pressure induced lethalities of ca. 1.5 log CFU/g for mesophiles and psychrotrophs and, in some cases, ca. 2.5 log CFU/g for lactic acid bacteria. At 4 days, counts in pressurized samples increased less for mesophiles and psychrotrophs ( h 0.5 CFU/g) than for lactic acid bacteria ( S 1 log CFU/g). At 15 days, counts of the three populations were ca. 9 log CFU/g in all samples. High pressure processing at subzero temperature does not extend shelf-life of MRPM.     

In situ studies of microbial inactivation during high pressure processing

High pressure processing (HPP) has been shown to reduce microbial concentration in foods. The mechanisms of microbial inactivation by HPP have been associated with damage to cell membranes. The real-time response of bacteria to HPP was measured to elucidate the mechanisms of inactivation, which can aid in designing more effective processes. Different pressure cycling conditions were used to expose Enterobacter aerogenes cells to HPP. Propidium iodide (PI) was used as a probe, which fluoresces after penetrating cells with damaged membranes and binding with nucleic acids. A HPP vessel with sapphire windows was used for measuring fluorescence in situ. Membrane damage was detected during pressurization and hold time, but not during depressurization. The drop in fluorescence was larger than expected after pressure cycles at higher pressure and longer times. This indicated possible reversible disassociation of ribosomes resulting in additional binding of PI to exposed RNA under pressure and its release after depressurization.     

The usage of high hydrostatic pressure (HHP) to control food-borne pathogens in hummus

ABSTRACT

With the increasing demand for fresher, higher quality, minimally processed and safer food, there is a strong necessity to develop non-thermal processing techniques. Also for hummus, which is popular all around the world. In this work, the effect of refrigerated storage on the survival of pathogens in hummus treated by high hydrostatic pressure (HHP) (500?MPa/10?min/room temperature) was evaluated. The cocktail of two Salmonella, four Listeria monocytogenes and two Escherichia coli strains was used in this study. All pathogen types were able to survive in hummus during 60 days of refrigerated storage. HHP-treated samples plated on day 0 successfully achieved a?>?5 log cfu/g reduction for all pathogen types. No residual survivors were present after 30 and 60 days in any of the HHP-treated samples. These results demonstrate that HHP may be a useful technique for the inactivation of pathogens and therefore helpful in designing non-thermal HHP conditions for pressurization of hummus.     

High-pressure effects on cooking loss and histological structure of beef muscle

In this study, we investigate the effects of high pressures (up to 600 MPa) applied at room temperature for 10 min on beef cooking loss and structure. The data on cooking loss, pH and protein solubility, as well as the electron microscopy, illustrate the changes in cooking loss and structure with high pressure processing (HPP). There is a significant reduction in cooking loss of beef with HPP. When the beef sample is imposed upon by 300 or 400 MPa, the cooking loss reduction is about 12%. Further, the pH of beef is dramatically increased as the pressure increases, and the pH increases by about 5% when imposed upon by 500 MPa. When a high pressure was applied at room temperature, the structure of the beef tissue apparently changed. Muscle fiber fragments gradually became slender and sarcomeres became lengthened. Our data indicated that high-pressure treatment on beef leads to stretching of the muscle fiber and an increase in the water-holding capacity.