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.     

Food processing by high hydrostatic pressure

The use of high hydrostatic pressures (HHP) for food processing is finding increased application within the food industry. One of the advantages of this technology is that because it does not use heat, sensory, and nutritional attributes of the product remain virtually unaffected, thus yielding products with better quality than those processed traditional methods. HHP have the ability to inactivate microorganisms as well as enzymes responsible for shortening the life of a product. In addition to lengthening the shelf-life of food products, HHP can modify functional properties of components such as proteins, which in turn can lead to the development of new products. Equipment for large-scale production of HHP processed products are commercially available nowadays. Guacamole, sliced ham, oysters, and fruit juices are some of the products currently available on the market. HHP technology is one of the most promising nonthermal processes.     

超高压对食品中微生物的影响

超高压是一种新型食品加工技术,已广泛应用于食品的非热加工。在超高压条件下微生物的细胞壁、细胞膜被破坏,引起细胞形态结构的改变;微生物细胞内的结构蛋白、酶等在超高压条件下被钝化,导致微生物正常的代谢功能和增殖能力被破坏;在超高压条件下微生物的蛋白组和基因组也产生了一定的变化,许多与抗逆有关的蛋白质和基因表达上调。     

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.     

Anthocyanin condensation reactions under high hydrostatic pressure

The effects of temperature and/or high hydrostatic pressure on anthocyanin condensation reactions were studied. For this purpose, model solutions containing cyanidin-3-O-glucoside (Cy3gl) and pyruvate, in excess, were subjected to different combined temperature/pressure treatments. After a high hydrostatic pressure treatment of 600 MPa, at 70 °C during 30 min, about 25% of Cy3gl was degraded. Parallel to this decrease, a vitisin A-type derivative was formed. By contrast, the rate of condensation was only 5% when samples were heated (70 °C, 30 min). In both cases, the degradation kinetics fitted well to a first order reaction (R² = 0.99). The decrease in Cy3gl was correlated with a decrease in the antioxidant activity. Moreover, the chemical stability of wine subjected to a temperature/pressure treatment of 600 MPa, at 70 °C during 1 h was investigated. After this treatment, a decrease in the concentration of malvidin-3-O-glucoside (Mv3glu) was found. As a consequence, an increase in the concentration of several products of high molecular weight at 370 nm was observed. When wine was subjected to pasteurization conditions (600 MPa, 70 °C, 10 min), no significant changes in the chemical composition were found (P < 0.05).     

Physical properties of surimi sausages subjected to high hydrostatic pressure treatment

Food Science and Biotechnology - We aimed to investigate the effect of high pressure treatment (HPT) on the physical properties of surimi sausages. For protein gelation, high hydrostatic pressure...     

Factors affecting the resistance of listeria monocytogenes to high hydrostatic pressure

Several factors relevant to food preservation had large effects on the resistance of L. monocytogenes to high hydrostatic pressure. Cells in the stationary phase of growth were much more resistant to pressures above 200MPa than those in the exponential phase. Following treatment for 10 min at 400 MPa viable numbers of stationary phase cells were reduced by only 1.3 log₁₀ units compared with more than 7 log₁₀ units for exponentially growing cells. Stationary phase cells were sensitised to pressure by butylated hydroxyanisole, potassium sorbate and by acid conditions. The most effective sensitiser was BHA which, at 1.55 mM, caused a 10⁴‐fold enhancement of killing by treatment at 300 MPa for 10 min. Propyl hydroxybenzoate, butylated hydroxytoluene and sodium ascorbate were without effect. Xylitol (15%) protected log phase cells against inactivation by pressure: after treatment at 350 MPa for 10 min viable numbers were reduced by only 0.24 log₁₀ units compared with 2.4 log₁₀ units in the absence of xylitol. The physicochemical environment can substantially increase or decrease resistance to pressure and these effects will require quantification if the microbiological effects of pressure are to be predicted.     

Effect of high hydrostatic pressure on Cryptosporidium parvum infectivity

The incidence of foodborne disease outbreaks caused by contaminated low-pH fruit juices is increasing. With recent mandatory pasteurization of apple juice and the industry's concerns of food safety, fruit juice processors are showing more interest in alternative nonthermal technologies that can kill >99.99% of microbial pathogens present in foods. The association of the coccidian protozoan, Cryptosporidium, with diarrheal disease outbreaks from contaminated tap water and fruit juice raises a safety concern in the food and beverage industries. The objective of this study was to evaluate the effects of high hydrostatic pressure (HHP) on C. parvum oocysts. Oocysts were suspended in apple and orange juice and HHP treated at 5.5 x 10(8) Pa (80,000 psi) for 0, 30, 45, 60, 90, and 120 s. Oocyst viability was assessed by excystation using bile salts and trypsin while the cell culture foci detection method was used to assess infectivity. Results indicated that HHP inactivated C. parvum oocysts by at least 3.4 log10 after 30 s of treatment. No infectivity was detected in samples exposed to > or =60 s of HHP and >99.995% inactivation was observed. This study demonstrated that HHP efficiently rendered the oocysts nonviable and noninfectious after treatment at 5.5 x 10(8) Pa.     

Bacterial inactivation by high-pressure homogenisation and high hydrostatic pressure

The resistance of five gram-positive bacteria, Enterococcus faecalis, Staphylococcus aureus, Lactobacillus plantarum, Listeria innocua and Leuconostoc dextranicum, and six gram-negative bacteria, Salmonella enterica serovar typhimurium, Shigella flexneri, Yersinia enterocolitica, Pseudomonas fluorescens and two strains of Escherichia coli, to high-pressure homogenisation (100-300 MPa) and to high hydrostatic pressure (200-400 MPa) was compared in this study. Within the group of gram-positive bacteria and within the group of gram-negative bacteria, large differences were observed in resistance to high hydrostatic pressure, but not to high-pressure homogenisation. All gram-positive bacteria were more resistant than any of the gram-negative bacteria to high-pressure homogenisation, while in relative to high hydrostatic pressure resistance both groups overlapped. Within the group of gram-negative bacteria, there also existed another order in resistance to high-pressure homogenisation than to high hydrostatic pressure. Further it appears that the mutant E. coli LMM1010, which is resistant to high hydrostatic pressure is not more resistant to high-pressure homogenisation than its parental strain MG1655. The preceding observations indicate a different response of the test bacteria to high-pressure homogenisation compared to high hydrostatic pressure treatment, which suggests that the underlying inactivation mechanisms for both techniques are different. Further, no sublethal injury could be observed upon high-pressure homogenisation of Y. enterocolitica and S. aureus cell population by using low pH (5.5 7), NaCl (0 6%) or SDS (0-100 mg/l) as selective components in the plating medium. Finally, it was observed that successive rounds of high-pressure homogenisation have an additive effect on viability reduction of Y. enterocolitica and S. aureus.     

超高静压对食品热力学特性的影响

超高静压技术是21世纪食品工业大力提倡和发展的高新技术之一。在食品的超高静压处理中,由于压缩做功使其温度发生改变,导致压致升温现象的产生,而要了解食品在超高静压下的温度变化,须知道与压力有关的这些食品的热力学特性。本文综述了在超高静压处理中食品热力学特性的测定方法及高静压对这些热力学特性的影响。     

Effect of high hydrostatic pressure on starches: A review

Various strategies have been employed to enhance starch property, including thermal processing, chemical modification. The application of high hydrostatic pressure (HHP) may be a complementary, synergistic, or an additive starch enhancement technique. While most current applications of HHP are in starch processing, over 25 starches had been investigated by HHP, which can induce gelatinization and modification of some starches. Different starch responds differently to high pressure depending on the pressure range, starch source, pressurization temperature and time, different solvent and starch concentration. We have re‐examined the information on the various factors that influence the HHP‐induced structure, gelatinization, retrogradation, and modification of starches from different plant sources, with an emphasis on the HHP‐induced gelatinization. The compiled evidence of high pressure starch enhancement in this paper indicates that HHP is an effective technology with potential for greater utilization in starch application.     

Maillard-type reactions under high hydrostatic pressure: Formation of pentosidine

Application of hydrostatic pressure up to 600 MPa on a solution consisting of N ^α -acetylarginine, N ^α -acetyllysine and ribose in equimolar ratios (pH 7.4, T=60 °C, t=2 h) resulted in a pressure-dependent increase of the pentosidine content. This marker for the advanced Maillard reaction could also be found protein-bound in enhanced yields by increasing pressure on β-casein incubated with ribose in solution. Received: 4 January 2000     

Physiological damages of Listeria monocytogenes treated by high hydrostatic pressure

A fluorescent glucose analogue, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG), which had been developed previously for the analysis of glucose uptake activity by living cells, was investigated to evaluate its applicability for assaying the viability of yeasts. Fluorescence intensities of the yeast population were measured by fluorescence spectrophotometry upon exposure to antifungal agents after staining with 2-NBDG and were compared to the number of colony forming units (CFU). A good correlation was obtained between the yeast viability, determined by the CFU, and the accumulation of 2-NBDG by yeast cells (correlation constant: r=0.98). Susceptibility testing of amphotericin B and miconazole against yeast strains by plate count and 2-NBDG fluorescence method yielded corresponding results. In conclusion, we found that staining with 2-NBDG is a rapid and sensitive method for the assessment of yeast cell viability.     

Pasteurization of food by hydrostatic high pressure: chemical aspects

Food pasteurized by hydrostatic high pressure have already been marketed in Japan. There is great interest in this method also in Europe and USA. Temperature and pressure are the essential parameters influencing the state of substances including foods. While the influence of temperature on food has been extensively investigated, effects of pressure, also in combination with temperature, are attracting increasing scientific attention now. Processes and reactions in food governed by Le Chatelier's principle are of special interest; they include chemical reactions of both low- and macromolecular compounds. Theoretical fundamentals and examples of pressure affected reactions are presented.

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Zusammenfassung Mit Hilfe hydrostatischen Hochdrucks pasteurisierte Lebensmittel werden in Japan bereits vermarktet. Auch in Europa und USA ist das Interesse an dieser Methode groß. Temperatur und Druck sind die wichtigsten Parameter, die den Zustand der Materie -auch von Lebensmitteln — beeinflussen. Während die Einwirkung von Temperatur auf Lebensmittel seit langem Gegenstand von Untersuchungen ist, ist der Einfluß des Druckes auch in Kombination mit Temperatur auf Lebensmittel ein relativ junges Forschungsgebiet. Generell sollten Vorgänge und Reaktionen in Lebensmitteln untersucht werden, die dem Prinzip von Le Chatelier unterliegen. Hierzu gehören chemische Reaktionen niedermolekularer und makromolekularer Verbindungen. Es werden theoretische Grundlagen und Beispiele für durch Druck beeinflußte Reaktionen vorgestellt.

     

Application of high hydrostatic pressure to eliminate Listeria monocytogenes from fresh pork sausage.

Ground pork patties were inoculated separately with 10(9) CFU/g each of three strains of Listeria monocytogenes obtained from the National Animal Disease Center (NADC). Inoculated patties were packaged under vacuum and treated at 414 megapascals (60,000 lb/in2) for up to 60 min by high hydrostatic pressure (HHP). Survivors were determined by surface plating onto modified Oxford agar and trypticase soy agar with yeast extract, as well as by the most probable number method using Listeria enrichment broth. Average D values ranged from 1.89 to 4.17 min, depending on the strain, with the most virulent strain (reported by the NADC) having the highest D value. We tested the usefulness of applying a mild heat treatment at 50 degrees C, simultaneously with HHP, to lower these values. Average D values ranged from 0.37 to 0.63 min, depending on the strain. Thus, a 10-log10 reduction could be achieved even in the most pressure-resistant strain of L. monocytogenes by a 6-min application of heat and HHP. Shelf life studies were also conducted, with spoilage levels reached after 5 days of storage at 4 degrees C for controls versus 28 days for treated samples. Sensory evaluation of uninoculated grilled patties showed that panelists could not distinguish between those treated by heat and HHP and untreated controls (P<0.05). Thus, treatment by HHP in combination with mild heating can be used successfully to produce safer, longer-lasting fresh pork without affecting quality.     

Effect of high hydrostatic pressure on quality parameters of lager beer

Unpasteurized lager beer samples from a commercial brewery were treated either by high hydrostatic pressure (HHP; 200, 250, 300, 350 MPa for 3 and 5 min at 20 °C) or by conventional heat pasteurization (60 °C for 15 min). The main attributes of the beer, such as ethanol content, extract and pH, were not affected by either treatment; however HHP and heat pasteurization affected colour, chill haze, protein sensitivity and bitterness. Change in bitterness was higher in conventional heat pasteurization, but pressures up to 300 MPa had no significant affect on bitterness. Although more studies should be carried out to investigate the effects of HHP treatment on different types of lagers and ales, our results revealed that HHP could be successfully used to process beer, even at temperatures well below those required for heat pasteurization, without affecting some of the quality attributes. Copyright © 2005 Society of Chemical Industry     

Effects of high hydrostatic pressure on shelf life of lager beer

Filtered bright lager beer samples were either treated with high hydrostatic pressure (HHP, 350 MPa for 3 and 5 min at 20 °C) or conventional heat pasteurization (60 °C for 15 min). A storage period of 56 days showed that HHP and heat pasteurization had similar results in terms of pH and color (p<0.05). However HHP-treated samples had lower bitterness and protein sensitivity and higher chill haze values than the heat pasteurized samples at the end of the storage period. The microbiological stability of HHP-treated beers was the same as that of heat-treated beers, and the development of both lactic and acetic acid bacteria was inhibited for 56 days of storage. Although more studies should be carried out to investigate the effects of HHP treatment on different types of lagers and ales, our results revealed that HHP could be successfully used to increase the shelf life of beer even at temperatures well below those required for heat pasteurization.     

Effects of high hydrostatic pressure on membrane proteins of Salmonella typhimurium

Salmonella typhimurium is a leading cause of foodborne diseases. Today high hydrostatic pressure treatments are considered as alternative methods of preservation. To select optimal conditions of treatment, we have to characterize the cell targets of pressure. In this study the action of pressure on the bacterial membrane proteins is analysed. The total membrane extract is obtained by lysis of cells separated by equilibrium density gradient centrifugation. Protein content is analysed by electrophoresis SDS-PAGE and visualised by silver stain. Electrophoretic profiles reveal the presence of three major outer membrane proteins and 12 minor proteins in control bacteria outer membranes. Outer membrane protein content is drastically modified after treatments. In some cases, except for the major proteins OmpA and LamB, other outer membrane proteins seem to totally disappear. LamB is more resistant to hyperbaric exposure when the pH of the media is acidic. This behaviour could be explained by a different conformation adopted by the LamB protein depending on the extracellular pH. This work allows us to define membrane proteins as a target of high hydrostatic pressure treatments. Knowledge of the behaviour of these bacterial membrane proteins subjected to pressure under different conditions (pH, temperature, a(w)...) could allow an increase in the efficiency of treatments.