Combination Of High Hydrostatic Pressure Research Articles

Biotransformation of ginsenosides from Korean wild-simulated ginseng (Panax ginseng C. A. Mey.) using the combination of high hydrostatic pressure, enzymatic hydrolysis, and sonication

High hydrostatic pressure is a non-thermal processing technique for extracting functional compounds from herbal plants. This study aims to investigate the effectiveness of the combination of high hydrostatic pressure (HHP), enzymatic hydrolysis, and sonication for extracting wild-simulated ginseng (WSG) to improve yields of major and minor ginsenosides. By using LC-MS/MS analysis, the total ginsenoside yield was enhanced by 25.62% by increasing the pressure of HHP and sonication treatment (HHP-soni) extraction from 100 to 300 MPa. Furthermore, compared to HHP-soni at 100 MPa, adding two commercial food-grade enzymes (Viscozyme and Pectinex) resulted in a 1.23–1.43-fold increase in total ginsenoside contents, as well as a 1.09–1.95-fold increase in the contents of seven major ginsenosides. Similarly, HHP-soni with enzymes increased the yields of five minor ginsenosides (Ro, Rh1, F2, CO, and Rg3) by 1.76–30.24 times compared to extraction with Pectinex at 0.1 MPa. Ginsenoside compound K and protopanaxadiol were detected after extraction using Pectinex with HHP-soni, but not after extraction using Pectinex and sonication at 0.1 MPa. While the contents of the stereoisomers 20(S)-Rg3 and 20(R)-Rg3 were similar after extraction at pressures of 100 and 200 MPa, the 20(S)-Rg3 content was 1.87 times higher than the 20(R)-Rg3 content after HHP treatment at 300 MPa. From the analytical data, we inferred the hydrolytic pathways of the major to minor ginsenosides, and specifically the ginsenoside Rb1 standard, when using Pectinex under experimental conditions. These findings suggest that the combination process of HHP, sonication, and Pectinex treatment could improve the quality of WSG.

High hydrostatic pressure assisted by food-grade enzymes as a sustainable approach for the development of an antioxidant ingredient

Apple is one of the most important fruits in the world. The elaboration of apple-based products such as cider or apple juice generates around 3–4.2 million tonnes of apple by-product that are annually discarded. Apple by-product has been described as an interesting source of bioactive compounds, including polyphenols. These valuable components, once extracted, could enable the usage of the apple by-product as a natural antioxidant ingredient. The aim of the present work was to address the effect of high hydrostatic pressure (HHP), and HHP assisted by two alternative food-grade enzymes, Celluclast®, and Ultraflo®. For that purpose, the total phenolic content was measured by Folin-Ciocalteu and Fast-Blue BB assays. Furthermore, antioxidant capacity was determined by three analytical methods (DPPH, ORAC and FRAP) and the characterization of phenolic compounds was carried out by Chromatography and Mass Spectrometry analysis. Results indicated a significant increase of the total phenolic content and the antioxidant capacity after the HHP aided by Celluclast® or Ultraflo® treatment. Conversely, the exclusive application of HHP induced minor changes. Thus, the combination of HHP and the food-grade enzymes Celluclast® or Ultraflo®, has proved to be an effective strategy for the extraction of natural antioxidant compounds from the apple by-product.

High-Pressure Processing and Natural Antimicrobials Combined Treatments on Bacterial Inactivation in Cured Meat

The combination of high hydrostatic pressure (HHP) and natural antimicrobials can present an interesting efficiency in the decontamination process of cured meat. However, several factors, such as application method and antimicrobial type, must be better understood to improve the process and its total employment. Therefore, this study aimed to evaluate the combined effect (synergism or antagonism) of HHP and natural antimicrobials to inactivate pathogenic and spoilage bacteria in cured meat. After a systematic search of research articles in the databases (Web of Science, Scopus, PubMed, and Science Direct), 20 articles were eligible and resulted in 123 studies for meta-analysis. The effect on Listeria sp., Salmonella serovars, E. coli O157:H7, and total viable counts was investigated considering different application methods (spread onto the surface, incorporated into the product, and active packaging) and antimicrobial types (plant, bacterial and animal origins). Active packs showed the best synergy with HHP, exhibiting a mean effect of 0.78 (CI95: 0.25–1.32) log cfu/g. Antimicrobials of microbial origin (bacteriocins) were more effective in combination with HHP. In addition, Listeria sp. was the most sensitive bacterium considering all investigated combined methods. Hence, the use of natural antimicrobials has the potential to improve the decontamination process when HHP is applied.

Effects of combined high hydrostatic pressure and pH-shifting pretreatment on the structure and emulsifying properties of soy protein isolates

The effects of high hydrostatic pressure (HHP) combined with pH-shifting treatment, on the structural and emulsifying properties of soy protein isolate (SPI) were investigated. SPI was subject to different pH solutions (pH 7, pH 3, and pH 11) with pressure levels ranging from 0.1 MPa to 400 MPa before being neutralized to pH 7. The combination of HHP and the pH-shifting process increased the protein solubility and the surface charge of the protein molecule, and induced the formation of smaller re-aggregated protein particles. Structural changes were characterized by free sulfhydryl groups, surface hydrophobicity, ultraviolet–visible spectroscopy, and circular dichroism spectra. Emulsions fabricated with SPI treated by the combined treatment were characterized by mean droplet size, zeta potential, emulsifying activity, emulsifying stability, and fluorescence microstructure. The results suggested that the increasing pressure enhanced the effect of pH shifting, and the protein structure could be significantly unfolded by the synergistic effect of HHP and pH-shifting, further improving the emulsifying performance of SPI. • Structural changes of soy protein isolate were induced by high pressure and pH shifting. • Enhanced unfolding in pH shifted SPI were observed after pressurization. • High pressure aided pH shifting improved the emulsifying properties of SPI.

Combined effect of thermosonication and high hydrostatic pressure on bioactive compounds, microbial load, and enzyme activities of blueberry juice.

The current study is aimed to evaluate the combined effect of thermosonication (TS) and high hydrostatic pressure (HHP) on enzyme activities (polyphenolase and peroxidase), microbial load and phenolic compounds (phenols, flavonoids, and anthocyanins) of blueberry juice. Blueberry juice has been treated with TS (40 kHz and 240 W) at different temperatures (25 °C and 45 °C) for 15 mins with subsequent different HHP (200, 400 and 600 MPa) for 5 mins at room temperature. The results revealed that a combined use of HHP of 400 MPa and 600 MPa with TS at 45 °C not only reduced microorganisms below 1 logCFU/mL, but also significantly inactivated enzymes. The treatments also increased the phenolic compounds, peroxyl radical scavenging capacity (PSC), and DPPH free radical scavenging activity to a higher level without causing any changes in soluble solids and pH. Therefore, the combination of HHP and TS can be used as a novel alternative nonthermal technology to improve the nutritional qualities of blueberry juice, which produces a desirable, healthy juice for consumers.

Effect of the Combination of High Hydrostatic Pressure and Alkaline Electrolyzed Water on the Reduction of Heat Resistance of Bacterial Spores.

The effect of combined use of alkaline electrolyzed water （AlEW） on the reduction of heat resistance of bacterial spores by high hydrostatic pressure processing（ HPP） was investigated in this study. No reduction of heat resistance of bacterial spores, which was defined as the spore survival by heat treatment at 80℃ for 15 min, was observed by the treatment of single HPP with 30MPa at 50℃ even for 6 hours. However, a 3-log decrease in the viable bacterial spores was obtained by the combination of AlEW pretreatment with 1 hour of HPP treatment. An additional 2 hours duration of HPP treatment could inactivate more 2 logs of the viable bacterial spores. The obtained D value of bacterial spores treated by HPP was decreased to one-eighth by the pretreatment with AlEW when compared with the control sample. In case of the temperature during HPP treatment was 70℃, bacterial spores did not reduce its heat resistance with lower pressuring levels. In case of the temperature during HPP treatment is high with lower pressure levels, bacterial spores did not reduce its heat resistance even when AlEW was combined as the pretreatment. It was considered that the decrease in heat resistance by AlEW was resulted from the weakening of surface layer of spores by protein dissolution with alkaline substance. No clear effect of high negative redox potential, which is a unique property of AlEW, on the reduction of heat resistance was recognized.

Coupling high hydrostatic pressure and ultrafiltration for fractionation of alpha-lactalbumin from skim milk

ABSTRACT The separation of α-lactalbumin (α-LAC) and β-lactoglobulin (β-LG) by ultrafiltration (UF) is a technological challenge due to their similar molecular size. As high hydrostatic pressure (HHP) treatment generates β-LG complexes of a larger molecular size than native β-LG, it was suggested that pressurization of skim milk could improve the separation of α-LAC by UF. The strategy was effective, but the pressurization affected UF performance, α-LAC recovery and purity. Hence, the combination of HHP and UF might not be the most efficient strategy for producing an enriched α-LAC fraction, but this study generated significant scientific knowledge about HHP in separation technology.

Effects of high hydrostatic pressure combined with heat treatment on the antigenicity and conformation of β-conglycinin

Soybean protein is considered as a main food allergen. This study illustrates the effects of a combination of high hydrostatic pressure (HHP) with heat treatment on soybean protein allergen. The main allergic protein β-conglycinin was isolated from low-temperature defatted soybean meal by the alkali-soluble acid precipitation method. The antigenicity and structure of β-conglycinin treated by HHP combined with heat treatment were analyzed by enzyme-linked immunosorbent assay (ELISA), western blot, non-reduced SDS-PAGE, Fourier transform infrared spectroscopy (FTIR), and fluorescence spectra. The antigenicity and immunogenicity of β-conglycinin was reduced significantly after HHP combined with heat treatment. Compared with the untreated protein, the antigenicity of β-conglycinin was lower, and it was reduced by 87.04% at 400 MPa and 100 °C for 20 min. The secondary structure of β-conglycinin changed after the combined treatment. The contents of α-helix and β-sheet decreased, but the contents of β-turn and random coils increased. The structure of the protein changed from order to disorder. Fluorescence spectroscopy showed that β-conglycinin exposed more hydrophobic groups after the combination treatment. HHP combined with heat treatment reduced the antigenicity of β-conglycinin by changing its conformation.

Combination of High Hydrostatic Pressure and Ultrafiltration to Generate a New Emulsifying Ingredient from Egg Yolk.

Egg yolk granule phosvitin (45 kDa) is a phosphoprotein known for its emulsifying properties. Recently, high hydrostatic pressure (HHP) treatment of granule induced the transfer of phosvitin to the soluble plasma fraction. This project evaluated the performance of the ultrafiltration (UF) used to concentrate phosvitin from the plasma fraction to produce a natural emulsifier. Phosvitin was characterized in plasma from a pressure-treated granule (1.73 ± 0.07% w/w) and in its UF retentate (26.00 ± 4.12% w/w). The emulsifying properties of both retentates were evaluated. The emulsion prepared with phosvitin-enriched retentate was more resistant to flocculation and creaming. Confocal laser scanning microscopy showed a network of aggregated protein similar to a gel, which encapsulated oil droplets in emulsions made with UF-retentate of plasma from pressure-treated granule. However, although sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that β-phosvitin is recovered in the cream, it is difficult to attribute the improved emulsifying properties of the UF-retentate of plasma from pressure-treated granules only to phosvitin.

Catalytic activity and stabilization of phenyl-modified glucose oxidase at high hydrostatic pressure

Glucose oxidase (GOx) was modified by attaching phenyl groups to either carboxyl or amino side chains on the enzyme. High hydrostatic pressure (HHP) stabilized the aniline-, and benzoate-modified GOx at 69.1–80 °C compared to atmospheric pressure. At 240 MPa and 80.0 °C, the first order rate constant of inactivation kinact. of aniline-modified GOx was 20 × 10−2 min−1, or 3.7 times smaller than for the native GOx, while the kinact for benzoate-modified GOx was 26 × 10−2 min−1, or 2.8 times smaller than for the native GOx at the same temperature. Furthermore, at 240 MPa and 80.0 °C, the kinact of the aniline-modified GOx was 69 times smaller than the kinact of native GOx (1530 × 10−2 min−1) at 0.1 MPa and 80.0 °C. Similar results were obtained for benzoate-modified GOx. At each temperature in this study (25–69.1 °C), the catalytic activity of the native, aniline-, or benzoate-modified GOx increased with HHP, and reached a maximum at around 180 MPa. At 180 MPa and 69.1 °C, aniline-modified GOx produced the fastest catalytic rate, followed by benzoate-modified GOx, and then native GOx. An increase in temperature increased the activation volume of the reaction. Similarly, the activation energy increased with pressure. The combination of HHP and hydrophobic modification made GOx more thermostable and increased the effect of temperature in enzyme activity.

Stabilization of Glucose Oxidase and Alcohol Oxidase Based Biosensors By Immobilization in Electrochemically Generated Poly-o-Phenylenediamine Under High Hydrostatic Pressure

Electrochemical biosensors have applications in medical diagnostic, agriculture, and food. In the food industry, glucose oxidase (GOX) and alcohol oxidase (AOX) based biosensors can be valuable for real-time detection and quality control of glucose and ethanol. The global market for electrochemical biosensors are expected to reach $23.7 billion by 2022 and thousands of research papers have been published annually since 2011. However, compared to the number of publications, there are very few commercial electrochemical enzyme-based biosensors currently available on market. Glucose and lactic acid biosensors are the most common commercial devices. High price and low stability of other enzymes are arguably the two main limiting factors. Therefore, it is critical to improve the biosensor stability. Enzyme covalent immobilization, addition of solutes like sugars and polyols, and crosslinking have been used for stabilization of enzyme biosensors. High hydrostatic pressure (HHP) has also been used to stabilize enzymes but not for biosensor fabrication because upon depressurization, enzymes return to their native, less stable state. Here we report the fabrication of stabilized of GOX and AOX based biosensors using entrapment under HHP. An electrochemical cell was fabricated to fit for the HHP reactor with a custom-made electrical feed-through connectors rated to up to 700 MPa (model U111, Warsaw, Poland). Two platinum wires (diameter 0.8128 mm) were inserted into a piece of Teflon rod to be the working and counter electrode. One Ag|AgCl electrode pellet was held in a heat shrinking tube (filled with 3 M KCl) with a porous glass frit to be the reference electrode. The platinum electrodes were polished and platinized before using. GOX or AOX was entrapped by electrochemical polymerization in 5 mM o-phenylenediamine at 650 mV vs. Ag|AgCl (3 M KCl) at 0.1 to 420 MPa or 0.1 to 240 MPa, respectively. The GOX biosensors were heated at 70 °C for 180 min and amperometric response was measured at 700 mV vs. Ag|AgCl (3 M KCl) every 20 min in 20 mM glucose solution. The AOX biosensors were heated at 50 °C for 10 min and amperometric response was measured at 700 mV vs. Ag|AgCl (3 M KCl) every 2 min in 100 mM ethanol solution. The amperometric response was measured using a commercial potentiostat (Reference 600, Gamry, Warminster, PA) or a low-cost portable wireless (Bluetooth) potentiostat developed in house (ABE-stat, University of Hawaii). After 180 min, the measured current decreased to 18.8% for GOX biosensors immobilized at 0.1 MPa, while to 47.3% for those immobilized at 420 MPa. After 10 min, the measured current decreased to 23.3% for AOX biosensors immobilized at 0.1 MPa, while to 34.8% for those immobilized at 240 MPa. Electrochemical impedance spectroscopy results showed no significant difference of the charge transfer resistance between GOX biosensors immobilized at 0.1 MPa and 180 MPa. To our knowledge, this is the first report of using HHP to improve the stability of enzyme-based biosensors. In the range of 0.1 to 420 MPa or 0.1 to 240 MPa, GOX and AOX biosensor stability increased with increasing pressure, respectively. The combination of HHP with cross-linking or chemical modification to further increase the stability of enzyme based biosensors is presented as well.

Listeria Inactivation by the Combination of High Hydrostatic Pressure and Lactocin AL705 on Cured-Cooked Pork Loin Slices

The effect of the bacteriocin lactocin AL705 in combination with high hydrostatic pressure (HHP) on the inactivation of Listeria innocua 7, a nonpathogenic indicator for Listeria monocytogenes, deliberately inoculated (ca. 6.4 log CFU/g) onto the surface of ready-to-eat (RTE) sliced cured-cooked pork loin, was evaluated. Nontreated pork slices (control) and treatments subjected to lactocin AL705 (105 AU/ml) and/or HHP (400 or 600 MPa) were prepared. L. innocua 7 was monitored at days 1, 20, and 40 of storage at 4 °C. The results showed a complete inhibition of L. innocua 7 after the combined treatment with lactocin AL705 and 600 MPa and no regrowing of cells up to 40-day storage. The treatment at 600 MPa alone was not enough to avoid regrowth of L. innocua. Ultrastructural cell damage was observed at the cytoplasm and cell membrane/wall levels with all treatments; however, complete cell lysis was observed only with the combined treatment. HHP in combination with lactocin AL705 provided a wider margin of safety as post-processing listericidal treatment of RTE cured-cooked meat products.

High hydrostatic pressure aided by food-grade enzymes as a novel approach for Okara valorization

Abstract Okara is a cheap, abundant and valuable by-product from soybean but it needs an easy industrial method to maximize its soluble dietary fibre (SDF) content. A novel combination of high hydrostatic pressure (HHP) assisted by the food-grade enzyme Viscozyme ® L was simultaneously used for this purpose. Viscozyme ® L (0.025%) was able to degrade Okara at atmospheric pressure in 120–180 min, and the most effective conditions were found at pH 7 and 37 °C (9.3% SDF). Synergy between HHP and Viscozyme ® L was observed, in terms of SDF release and molecular weight decrease, as determined by direct High Performance Liquid Chromatography - Evaporative Light Scattering Detector analysis (HPLC-ELSD). In fact, at 600 MPa, 0.025% Viscozyme ® L and 30 min treatment, SDF and polysaccharides content were 2.50 and 3.20-times higher than in native Okara, achieving a concentration of 13.53 ± 0.30% (SDF), which improved its nutritional value and applicability in functional foods. Industrial relevance HHP is a novel technological process which is useful for increasing the added value of by-products like Okara by solubilizing their dietary fibre. Some enzymes increase their activity when they are under HHP. A simultaneous method with Viscozyme ® L and HHP on Okara has been optimized for reducing the industrial cost of the process.

Anti-Inflammatory and Antioxidant Properties of Peptides Released from β-Lactoglobulin by High Hydrostatic Pressure-Assisted Enzymatic Hydrolysis.

Background: β-lactoglobulin hydrolysates (BLGH) have shown antioxidant, antihypertensive, antimicrobial, and opioid activity. In the current study, an innovative combination of high hydrostatic pressure and enzymatic hydrolysis (HHP–EH) was used to increase the yield of short bioactive peptides, and evaluate the anti-inflammatory and antioxidant properties of the BLGH produced by the HHP–EH process. Method: BLG was enzymatically hydrolyzed by different proteases at an enzyme-to-substrate ratio of 1:100 under HHP (100 MPa) and compared with hydrolysates obtained under atmospheric pressure (AP-EH at 0.1 MPa). The degree of hydrolysis (DH), molecular weight distribution, and the antioxidant and anti-inflammatory properties of hydrolysates in chemical and cellular models were evaluated. Results: BLGH obtained under HHP–EH showed higher DH than the hydrolysates obtained under AP-EH. Free radical scavenging and the reducing capacity were also significantly stronger in HHP-BLGH compared to AP-BLGH. The BLGH produced by alcalase (Alc) (BLG-Alc) showed significantly higher antioxidant properties among the six enzymes examined in this study. The anti-inflammatory properties of BLG-HHP-Alc were observed in lipopolysaccharide-stimulated macrophage cells by a lower level of nitric oxide production and the suppression of the synthesis of pro-inflammatory cytokines. Peptide sequencing revealed that 38% of the amino acids in BLG-HHP-Alc are hydrophobic and aromatic residues, which contribute to its anti-inflammatory properties. Conclusions: Enzymatic hydrolysis of BLG under HHP produces a higher yield of short bioactive peptides with potential antioxidant and anti-inflammatory effects.

The allergenic potential of walnuts treated with high pressure and heat in a mouse model of allergy

Abstract This study investigates the effects of high hydrostatic pressure (HHP) and/or thermal treatment on walnut immunoreactivity. The residual immunoreactivity of processed walnuts was assessed by competitive inhibition enzyme-linked immunosorbent assays (ci-ELISA). Compared to HHP or boiling treatment, walnut allergens (WA) subjected to HHP and thermal treatment at 650 MPa, 100 °C for 15 min (WAH), were able to diminish the IgE binding capacity more efficiently with the highest reduction up to 86.37%. The effects of processed walnut on the BALB/c mouse model of allergy were characterized using IgE binding capacity, histamine levels in serum, cytokine mRNA expressions. The results showed that significant reductions of 41.04% and 19.76% were observed in serum specific IgE binding capacity and histamine levels, respectively, in mice fed with WAH, accompanied by a repression of both IL-4 (36.79%) and IFN-γ (34.39%) mRNA expressions in ileums. Consequently, clinical signs for allergic reactions were significantly alleviated in WAH treated mice, which indicated that the combination of HHP and thermal treatment HHP could be a potential strategy for the reduction of walnut allergens. Industrial relevance Allergic reactions to walnuts were serious. High hydrostatic pressure (HHP) processing was reported to decrease allergenic activity in rice, fish, milk, peanut and celery through changing allergen conformation. In the study, high pressure and thermal were used to reduce the allergic properties of walnut. Furthermore, a BALB/c mouse model of walnut allergy was adopted to analyze the immunoreactivity of walnut allergens treated with HHP and thermal, which indicated that HHP has great potentiality for industrialization to eliminate or decrease allergenicity of food protein.

INACTIVATION OF SHIGA-TOXIN PRODUCING Escherichia coli (STEC) O157:H7 IN MILK BY COMBINED TREATMENT WITH HIGH HYDROSTATIC PRESSURE AND AQUEOUS POMEGRANATE EXTRACT

The aim of this work was to evaluate the synergistic effect of combined treatment with high hydrostatic pressure (HHP) and an aqueous extract of Punica granatum (pomegranate) peels on the survival of Shiga toxin-producing Escherichia coli (STEC). Our results showed that HHP (250 MPa, 60 min, 25 ºC) reduced the STEC bacterial load in milk and tryptic soy broth culture medium by about 2.5 and 3.5 logs, respectively. Under these conditions, HHP did not alter the cytotoxicity of Shiga toxins in Vero and human umbilical vein endothelial cells. Treatment with up to 30 mg of pomegranate extract/mL caused negligible inactivation, but a combination of HHP and pomegranate extract (3 mg/mL) produced bacterial inactivation from 109 CFU/mL to undetectable levels of viable bacteria. These findings suggest that a combination of HHP and pomegranate extract may be potentially effective in bacterial inactivation during food processing, particularly in the elimination of important foodborne pathogens such as STEC. a

Enrichment of ginsenoside Rd in Panax ginseng extract with combination of enzyme treatment and high hydrostatic pressure

Ginsenoside Rd, a minor ginseng saponin, has several pharmacological activities. Traditionally, saponins are extracted using organic solvents or hot water extraction. However, both of these methods have disadvantages such as formation of artefacts and compound decomposition. Additionally, the use of organic solvents for extraction is hazardous to the environment. Therefore, we aimed to produce ginsenoside Rd without using organic solvents or hot extraction. We developed a simultaneous extraction and transformation process for higher yields of ginsenoside Rd using a combination of high hydrostatic pressure (HHP) and enzymes. Several commercial glycosidases in various combinations were studied for the enrichment of ginsenoside Rd from major ginsenosides by enzymatic transformation and HHP. We found that treatment with a combination of cellulase (2 U/mL), cellobiase (4 U/mL) and HHP of 100 Mpa at pH 4.8 and 45°C for 24 h resulted in a ginsenoside Rd content of 3.47 ± 0.35 mg/g of fresh ginseng. This yield is 2.1-fold higher than that of the corresponding enzyme treatment at atmospheric pressure (AP, 0.1 Mpa) at pH 4.8, 45°C and for 24 h. This simultaneous extraction and transformation process can be used for the preparation of Rd enriched ginseng beverage without using hazardous organic solvents.

Biocontrol of Shigella flexneri in Ground Beef and Vibrio cholerae in Seafood with Bacteriophage-Assisted High Hydrostatic Pressure (HHP) Treatment

Virulent bacteriophages (VP) and high hydrostatic pressure (HHP) were studied for the inactivation of Shigella flexneri in ground beef and Vibrio cholerae in salmon and mussels. Inoculated foods were treated individually with HHP (150-450 MPa for 5 and 9 min, 300 MPa for 13 min, and 550 MPa for 5 min), with phages (cocktail of 3 S. flexneri or single V. cholerae phages, both applied at 109 PFU/mL) or combinations thereof (HHP/VP, VP/HHP). Stand-alone treatments with VP, HHP below 450 MPa (seafood) or 550 MPa (meat), and combined treatments of VP and HHP at 250 MPa for 5 min did not reduce bacterial counts below the detection limit. By contrast, complete inactivation of S. flexneri and V. cholerae (P < 0.05) was achieved at 550 MPa for 5 min or, more energy-efficient, at 350 MPa for 5 min followed by addition of phages, thus, indicating a combination of HHP and VP as an efficacious hurdle technology for meat and seafood processing.

Pressure-Based Strategy for the Inactivation of Spores.

Since the first application of high hydrostatic pressure (HHP) for food preservation more than 100 years ago, a wealth of knowledge has been gained on molecular mechanisms underlying the HHP-mediated destruction of microorganisms. However, one observation made back then is still valid, i.e. that HHP alone is not sufficient for the complete inactivation of bacterial endospores. To achieve "commercial sterility" of low-acid foods, i.e. inactivation of spores capable of growing in a specific product under typical storage conditions, a combination of HHP with other hurdles is required (most effectively with heat (HPT)). Although HPT processes are not yet industrially applied, continuous technical progress and increasing consumer demand for minimally processed, additive-free food with long shelf life, makes HPT sterilization a promising alternative to thermal processing.In recent years, considerable progress has been made in understanding the response of spores of the model organism B. subtilis to HPT treatments and detailed insights into some basic mechanisms in Clostridium species shed new light on differences in the HPT-mediated inactivation of Bacillus and Clostridium spores. In this chapter, current knowledge on sporulation and germination processes, which presents the basis for understanding development and loss of the extreme resistance properties of spores, is summarized highlighting commonalities and differences between Bacillus and Clostridium species. In this context, the effect of HPT treatments on spores, inactivation mechanism and kinetics, the role of population heterogeneity, and influence factors on the results of inactivation studies are discussed.

Enhancing the thermal stability of inulin fructotransferase with high hydrostatic pressure

The thermal stability of inulin fructotransferase (IFTase) subjected to high hydrostatic pressure (HHP) was studied. The value of inactivation rate of IFTase in the range of 70–80°C decreased under the pressure of 100 or 200MPa, indicating that the thermostability of IFTase under high temperature was enhanced by HHP. Far-UV CD and fluorescence spectra showed that HHP impeded the unfolding of the conformation of IFTase under high temperature, reflecting the antagonistic effect between temperature and pressure on IFTase. The new intramolecular disulfide bonds in IFTase were formed under a combination of HHP and high temperature. These bonds might be related to the stabilization of IFTase at high temperature. All the above results suggested that HHP had the protective effect on IFTase against high temperature.