Combined High Hydrostatic Pressure Research Articles

High-pressure pulses for Aspergillus niger spore inactivation in a model pharmaceutical lipid emulsion

High hydrostatic pressure (HHP) is a non-thermal process widely used in the food industry to reduce microbial populations. However, rarely its effect has been assessed in products with high oil content. This study evaluated the efficacy of HHP (200, 250, and 300 MPa) at different temperatures (25, 35, and 45 °C) by cycles (1, 2, or 3) of 10 min in the inactivation of Aspergillus niger spores in a lipid emulsion. After treatments at 300 MPa for 1 cycle at 35 or 45 °C, no surviving spores were recovered. All treatments were modeled by the linear and Weibull models. The presence of shoulders and tails in the treatments at 300 MPa at 35 or 45 °C resulted in sigmoidal curves which cannot be described by the linear model, hence the Weibull + Tail, Shoulder + Log-lin + Tail, and double Weibull models were evaluated to elucidate the inactivation kinetics. The tailing formation could be related to the presence of resistance subpopulations. The double Weibull model showed better goodness of fit (RMSE <0.2) to describe the inactivation kinetics of the treatments with the higher spore reductions. HHP at 200–300 MPa and 25 °C did not reduce the Aspergillus niger spores. The combined HHP and mild temperatures (35–45 °C) favored fungal spore inactivation. Spore inactivation in lipid emulsions by HHP did not follow a linear inactivation. HHP at mild temperatures is an alternative to the thermal process in lipid emulsions.

Effect of High Hydrostatic Pressure Combined with Sous-Vide Treatment on the Quality of Largemouth Bass during Storage.

In order to estimate the effects of high hydrostatic pressure treatment at 400 MPa for 0 min and 10 min (HHP-0, HHP-10) and high hydrostatic pressure in combination with sous-vide treatment (HHP-0+SV, HHP-10+SV) on the quality of largemouth bass stored at 4 °C for 30 days, the physicochemical changes were evaluated by microbiological determinations, pH, sensory evaluation and texture analysis, and the flavour changes were analysed by solid-phase microextraction–gas chromatography–mass spectrometry (SPME-GC-MS) and amino acid automatic analyser. The results show that HHP-0+SV and HHP-10+SV treatment effectively inhibited microbiological growth and attenuated physiochemical changes (pH, sensory evaluation, flesh and texture) of largemouth bass fillets. HHP+SV treatment prolonged the storage period of largemouth bass fillets for 24 days. The content of total free amino acids in control (CK) samples was high, but HHP+SV treatment caused the loss of free amino acid content. Especially when stored for 30 days, the total free amino acid content of HHP-0+SV and HHP-10+SV was only 14.67 mg/100 g and 18.98 mg/100 g, respectively. In addition, a total of 43 volatile compounds were detected and elucidated, among which hexanal, heptaldehyde, octanal and nonanal showed a decreasing tendency in HHP groups and an increasing trend in HHP+SV groups throughout the storage.

Synergistic antibacterial effect and mechanism of high hydrostatic pressure and mannosylerythritol Lipid-A on Listeria monocytogenes

Listeria monocytogenes is an important food-borne pathogen that can cause fatal listeriosis. High hydrostatic pressure (HHP) in combination with antimicrobial agent is a potential antibacterial strategy for controlling L. monocytogenes in the food industry. The aim of this study was to investigate the antibacterial effect and the underlying mechanisms of HHP alone and HHP in combination with Mannosylerythritol Lipid-A (MEL-A), an antimicrobial biosurfatant, on L. monocytogenes . The results of antibacterial rate and morphological changes showed that a combined HHP (100, 200, 300 MPa) and MEL-A (16 μg/mL, 32 μg/mL) treatment had a synergistic bactericidal effect on L. monocytogenes . The synergistic treatment caused severe damage to the cell membrane structure of L. monocytogenes . To further explore the antibacterial mechanism of the synergistic treatment of HHP and MEL-A on L. monocytogenes , genome-wide transcriptome analysis was carried out and identified 1392 differentially expressed genes (DEGs). Enrichment analysis of the DEGs showed that HHP induced significant down-expression of membrane-related genes and up-regulation of ribosome-related pathways (50 S and 30 S ribosomal proteins). Interestingly, ribosome was also the most significantly enriched pathway in the synergistic treatment group. Moreover, compared to HHP treatment alone, synergistic treatment also affected pathways related to the PTS system. In addition, the good safety performance in vivo and in vitro indicates that MEL-A could be potentially used as a potential additive for controlling L. monocytogenes in the food industry. This study reveals the synergistic bactericidal effect and mechanisms of a combined HHP and MEL-A treatment against L. monocytogenes , which may provide potential strategies for prevention and control of food-borne pathogens. • High hydrostatic pressure (HHP) and mannosylerythritol lipids-A (MEL-A) exhibited synergistic bactericidal effect. • Severe damage in cell membrane structure were observed by SEM and TEM. • Ribosome related pathways were significantly enhanced in both HHP and MH treatment groups. • In vitro and in vivo safety assessment experiments revealed the safety of MEL-A.

A Novel Strategy to Produce a Soluble and Bioactive Wheat Bran Ingredient Rich in Ferulic Acid.

Wheat bran (WB) is a byproduct from the milling industry that contains bioactive compounds beneficial to human health. The aim of this work was on the one hand, increasing extractability of antioxidant and anti-inflammatory compounds (specifically ferulic acid, FA), through enzymatic hydrolysis combined with hydrothermal treatment (HT) and high hydrostatic pressure (HHP). On the other hand, enhancing the stability of final ingredient applying spray-drying (SPD) and microencapsulation (MEC). The use of HT increased FA, total phenolics (TP), and antioxidant capacity (AC) in WB hydrolysates, regardless the HT duration. However, the HT tested (30 min, HT30) produced a loss in anti-inflammatory activity (AIA). The combination of HT (15 min, HT15) with HHP increased AIA of the WB. SPD enhanced the TP yield in WB with no significant effect of inlet temperature (up to 140 °C) on phenolic profile mainly composed of trans-FA and smaller amounts of cis-FA and apigenin diglucosides. SPD caused a temperature-dependent increase in AC (160 °C > 140 °C > 130 °C). SPD inlet temperatures affected total solids yield (from 22 to 36%), with the highest values at 140 °C. The use of HHP in combination with HT resulted in >2-fold increase in total solids yield.

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.

Effects of combined HHP and heat treatment on viscosity attributes and microbiological condition of liquid egg yolk

AbstractMinimal processing technologies, like High Hydrostatic Pressure (HHP), heat treatments at low temperatures have an increasing role in food industry. Eggs are considered as functional foods, but for high retention of biological active compounds adequate minimal processing technologies are needed during preservation procedure. In our study, liquid egg yolk (LEY) was examined to meet consumer's expectations.Combinations of pasteurization (57–63 °C, 5–7 min) and HHP (350–400 MPa, 5 min) were used to provide microbiological stability of LEY. After these treatments samples were examined for mesophyll aerobes and Enterobacteriaceae cell counts (using Nutrient agar an incubation of 30 °C, 48 h) and viscosity attributes (Anton Paar MCR 92).Our results show that microbiological stability is significantly influenced by the different parameters of heat treatments and HHP. Heat treatment effected at least 3 orders of magnitude decrease in cell count. Viscosity attributes point out that higher pressure of HHP have a stronger effect on viscosity than the temperature of pasteurization.The results point out a great opportunity for industrial use of minimal processing technologies for LEY. Microbiological safety is strongly influenced by the order of treatments, but viscosity may be independent from the order of the treatments.

High Hydrostatic Pressure Assisted by Celluclast® Releases Oligosaccharides from Apple By-Product

A novel and green procedure consisting of high hydrostatic pressure (HHP) aided by a commercial cellulase (Celluclast®) has been applied to valorise the apple by-product, a valuable source of dietary fibre but mainly composed by insoluble fibre. Optimal conditions for solubilisation of dietary fibre were first determined at atmospheric pressure as 2% (w/v) of substrate concentration and 20 Endo-Glucanase Units of cellulase. Monitoring of polysaccharides and oligosaccharides released from apple by-product was carried out by means of a newly validated HPLC method with refractive index detector. A synergistic effect was observed when the combined HHP plus cellulase treatment was used. Thus, the application of 200 MPa at 50 °C for 15 min enabled a significant increase in the release of water-soluble polysaccharides (1.8-fold) and oligosaccharides (3.8-fold), as well as a considerable decrease in the time required (up to 120-fold), compared to control at 0.1 MPa. Therefore, this technology could be a promising alternative approach to transform an industrial by-product into a novel rich-in-oligosaccharide food ingredient and a step forward into shaping the world of prebiotics.

Phenolic and Aroma Changes of Red and White Wines during Aging Induced by High Hydrostatic Pressure.

The aim of this study was to investigate use of high hydrostatic pressure (HHP) along with different antioxidants (glutathione and SO2) as an alternative method for wine preservation and production of low-SO2 wines. In the first phase of the study, low-SO2, young red and white wines were pressurized at three pressure levels (200, 400 and 600 MPa) for 5, 15 and 25 min at room temperature, and analyzed immediately after treatments. Additionally, for the wine aging experiment, red and white wines with standard-SO2, low-SO2+glutathione and low-SO2 content were treated with HHP treatment (200 MPa/5 min) and stored for 12 months in bottles. Color parameters, phenolic and aroma compounds were determined. The sensory evaluation was also conducted. HHP showed very slight, but statistically significant changes in the chemical composition of both red and white wine right after the treatment, and the main variations observed were related to the different pressures applied. Furthermore, during aging, most of the differences observed in chemical composition of pressurized wines, both red and white, were statistically significant, and greater in wines with a lower content of antioxidants. However, after 12 months of aging, some differences between unpressurized and pressurized samples with standard SO2 content were lost, primarily in aroma compounds for red wine and in color and phenolics for white wine. Additionally, similar values were obtained for mentioned characteristics of red and white wines in pressurized samples with standard SO2 and low SO2+glutathione, indicating that HHP in combination with glutathione and lower doses of SO2 might potentially preserve wine. The sensory analysis confirmed less pronounced changes in the sensory attributes of pressurized wines with higher concentration of antioxidants. Furthermore, the treatments applied had a slightly higher effect on the sensory properties of white wine.

Effect of high hydrostatic pressure in combination with low salt content for the improvement of texture and palatability of meat gels

The effect of high hydrostatic pressure (HHP) treatment of 200 MPa for 10 min at room temperature in combination with salt (sodium chloride) and phosphate (sodium pyrophosphate) addition on the microstructure and sensory characteristics of beef gels were investigated. Sensory evaluation was involving students and staff of the Niigata University, using Scheffe’s paired comparison method with grade. Gel microstructure was observed using scanning electron microscopy (JSM-6510LA, JEOL LTD., Japan). The free amino acid content of beef gels was analyzed by an amino acid analyzer (JLC-500/V, JEOL LTD., Japan). The results of sensory evaluation revealed that high pressure at 200 MPa improved the cohesiveness and springiness (elasticity) while significantly decreasing the softness in low salt and/or low phosphate beef gels (p < 0.05). Irrespective of the salt and/or phosphate content in the beef samples, panellists noted that the pressurized beef gels were firmer, more elastic, and more pleasant to bite. The scanning electron microscopy images revealed that high pressure treatment at 200 MPa produced a dense, homogeneous networked structure with small cavities for water retention in low salt beef gels. The total free amino acid content of low salt and/or low phosphate beef gels was increased by high pressure at 200 MPa (p < 0.05). The present study confirmed that high hydrostatic pressure at 200 MPa was effective in producing low salt and/or low phosphate beef gels while providing high quality textural and organoleptic properties.

Inactivation of Morganella morganii by high hydrostatic pressure combined with lemon essential oil.

The inactivation and damage of histamine‐forming bacterium, Morganella morganii, in phosphate buffer and tuna meat slurry by high hydrostatic pressure (HHP) alone or in combination with 0.2% lemon essential oil (LEO) treatments were studied using viability measurement and scanning electron microscopy (SEM). HHP alone or in combination with LEO treatments showed first‐order destruction kinetics to M. morganii during pressure holding period. The D values of M. morganii (200 to 600 MPa) in phosphate buffer ranged from 16.4 to 0.08 min, whereas those in tuna meat slurry ranged from 51.0 to 0.10 min, respectively. M. morganii in tuna meat slurry had higher D values and were more resistant to HHP treatments than in phosphate buffer. In addition, the D values of HHP in combination with LEO treatment were lower than those of HHP treatment alone at <400 MPa of pressure, indicating that it is more effective to inactivate M. morganii under the same pressure. The results showed the M. morganii at HHP in combination with LEO treatment was more susceptible to pressure treatment alone. HHP with or without LEO treatments can be used to inactivate M. morganii by causing disruption to bacterial cell membrane and cell wall as demonstrated by SEM micrographs.

Structural properties of lotus seed starch prepared by octenyl succinic anhydride esterification assisted by high hydrostatic pressure treatment

This paper describes a new method for combining high hydrostatic pressure (HHP) and octenyl succinic anhydride (OSA) esterification for starch modification. The degree of substitution (DS) was 0.0148–0.0389 when the OSA concentration increased from 3% to 9%, whereas after HHP treatment, the DS decreased, especially for H-OSA-9%, from 0.0389 to 0.0125. Scanning electron microscopy indicated that OSA with combined HHP treatment destroyed the surface morphology of the starch. FTIR spectroscopy revealed two new absorption peaks at 1526 cm−1 and 1728 cm-1. The particle size of OSA-LS and H-OSA-LS increased significantly (P < 0.05), except H-OSA-9%, owing to the hydrophobic groups introduced into the starch during the esterification reactions; consequently, the starch powders tended to swell and aggregate in aqueous solution. The Mw, Mn, and Mw/Mn of amylose decreased slightly with OSA treatment. The X-ray diffraction patterns confirmed that the crystalline patterns of OSA-LS and H-OSA-LS were preserved, but the crystallinity decreased to different degrees. These results indicated that H-OSA-LS provided conditions for encapsulating lipophilic substances, thus providing a potential direction for further research.

(Invited) Application of High Hydrostatic Pressure and Nanofilms to the Fabrication of Enzyme Biosensors

Fabrication of enzyme biosensors has evolved since they were first conceived in the late 1950s. Increased sensitivity and reproducibility have been perhaps the two main driving forces for the development of such sensors. Increased sensitivity enables miniaturization and the development of implantable sensors for in-vivo applications. Because most oxidoreductases used in the fabrication of enzyme biosensors quickly lose their activity over time, most enzyme biosensors either are one-use disposable strips or require periodic change of membrane and frequent calibration, which makes them impractical for industrial applications. With the nanotechnology boom, several research reports have focused on increased sensitivity by creating porous nanostructures. There are also several reports on the effects of immobilization, cross-linking, and additions of solutes to stabilize enzymes and extend the operational life of enzyme biosensors. Here we summarize our research for the last 10 years on the effects of platinization conditions, including the use of high hydrostatic pressure (HHP) up to 500 MPa on the fabrication of microporous platinum black structures that maximize electrode sensitivity. In our early research we reported a 60-fold increase in sensitivity of glucose biosensors. We also report the effect of enzyme entrapment in poly-o-phenylenediamine (PoPD) nanofilms and their impact on electrode sensitivity and stability on glucose oxidase, alcohol oxidase, and galactose oxidase. High pressure and immobilization in PoPD resulted in two orders of magnitude increase in glucose oxidase biosensors. In contrast, while HHP increased the stability of AOx by a factor of ~15, immobilization only increased its stability by a factor of ~5 stability and combined HHP and immobilization only increased the stability by a factor of 6.4 relative to the enzyme in solution.

Optimization of high pressure processing to reduce the safety risk of low-salt ready-to-eat sliced turkey breast supplemented with carvacrol

Purpose The purpose of this paper is to evaluate the optimization of high hydrostatic pressure (HHP) processing for the microbial inactivation on low-sodium sliced vacuum-packaged turkey breast supplemented with a natural antimicrobial compound (carvacrol). Design/methodology/approach A response surface methodology was used to model and describe the effects of different pressures (200–650 MPa) and holding times (30–300 s) during HHP processing of low-salt ready-to-eat turkey breast supplemented with 200 mg/kg of carvacrol on survival of the target pathogen (Listeria sp.) and spoilage microflora and on the quality attributes, including pH, syneresis, CIE color and lipid oxidation. Findings The HHP parameters influenced (p&lt;0.05) the lethality rates and syneresis but did not affect the pH values and lipid oxidation of the products evaluated. According to the required performance criteria for Listeria post-lethality treatment, a treatment at 600 MPa/180 s (at 25°C) appears to be suitable for the studied low-sodium product. The HHP bacterial inactivation effects can notably be potentiated via the presence of carvacrol, and is useful at sensory acceptable sub-inhibitory levels. Originality/value This study shows that combined HHP plus additives may produce similar safety and shelf-life extension effects with mild HHP treatments, creating a global increase in the quality of HHP-processed food in addition to reducing costs on equipment maintenance and increasing industry productivity.

Thermograms of the combined High Hydrostatic Pressure and Sous-vide treated Longissimus dorsi of pork

In this work, slices of Longissimus dorsi of pork was used as raw material to establish the effects of the sous-vide technology and the high hydrostatic pressure treatments (and their combinations) on meat. The state of the proteins in meat has a very important effect on several quality parameters of the product, such as weight loss, water holding capacity, organoleptic properties. Therefore it is important to follow and analyse the denaturation of the protein content during food processing. The samples were cooked sous-vide (60 °C, 5-480 minutes) or pressurized (100-600 MPa, 5 minutes, room temperature). Also two steps treatments were studied combining both technologies, applying high hydrostatic pressure treatment (300 or 600 MPa, 5 minutes, room temperature) after or previous to sous-vide cooking (60 °C, 30 minutes). The changes in the condition of meat proteins were followed by a differential scanning calorimeter. The DSC curves were analysed using the unit’s own software where denaturation heat was determined. Thermograms show through the change of the sample’s protein state the dissimilar effect of the treatments. Using the Polar Qualification System -previously proved to be effective with NIR measurements- the spectral information was reduced to a two dimensional polar co-ordinate system where each DSC curve is represented by a “quality point”. As a new experiment the applied PQS data reduction method compared to the traditional thermal analysis data processing gave us less information on the differences of our samples although the results are promising as we were able to detect the same trends and characteristics.

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.

Combined high hydrostatic pressure and thermal treatments fully inactivate trypsin inhibitors and lipoxygenase and improve protein solubility and physical stability of calcium-added soymilk

Abstract The objective of this work was to assess the possibility of obtaining calcium-added soymilk with acceptable characteristics regarding protein solubility and physical stability, and inactivation of trypsin inhibitors and lipoxygenase, through a combined thermal-high hydrostatic pressure treatment. A Doehlert design was applied to study the effect of combining pressure levels (500–700 MPa), initial temperatures (45–65 °C) and CaCl 2 concentrations (5–15 mmol L − 1 ). Results showed that protein solubility was a function of CaCl 2 concentration (p Industrial relevance An analysis of the effect of the combination of high hydrostatic and thermal treatments on calcium-added soymilk is introduced in the present study. Some processing conditions were found to allow the obtention of a product with improved protein solubility and physical stability, and with inactivated trypsin inhibitors and lipoxygenase enzyme. This information could be beneficial considering the reduction of process time and energetic costs, because the assayed combination of thermal and high pressure treatments takes advantage of the instantaneous compression heating. Thus, the results provided in the present work could be useful to prepare an acceptable calcium-added soymilk.

Nano-TiO 2 particles and high hydrostatic pressure treatment for improving functionality of polyvinyl alcohol and chitosan composite films and nano-TiO 2 migration from film matrix in food simulants

Abstract This study investigated the impact of nano-TiO 2 and high hydrostatic pressure (HHP) treatment on microstructure, water vapor and gas barrier, antibacterial and mechanical properties of polyvinyl alcohol (PVA)–chitosan (CHI) biodegradable films and determined the migration behavior of TiO 2 nanoparticles from the films to food simulants. Apart from the effect of filler, TiO 2 nanoparticles also could improve the antibacterial activity of the films and play a role as a plasticizer in the films. HHP treatment promoted the interaction between PVA and chitosan molecules, resulting in the formation of more compacted network structures in PVA–CHI films. The migration of TiO 2 from the films was investigated in food simulants including distilled water, acetic acid, ethanol and olive oil, in which the trace amount of TiO 2 ( − 3 ‰) was only detected in olive oil. HHP treatment at 200–400 MPa significantly reduced migration of TiO 2 nanoparticles from the films. Industrial relevance Results from this study provide a new application direction of high hydrostatic pressure (HHP) in the field of food packaging materials for improving the functionality of materials. Due to the non-thermal characteristic, HHP in combination with nano-TiO 2 not only improved the mechanical and barrier properties of the biodegradable PVA–CHI composite films (polyvinyl alcohol and chitosan based materials), but also enhanced the antibacterial activity of the films. The HHP treated PVA–CHI–TiO 2 films are very stable in food simulants, such as olive oils. Therefore, the utilization of HHP and nano-TiO 2 is promising in the preparation of food packaging materials with desirable functionalities.

Effects of Combined High Hydrostatic Pressure and Dense Phase Carbon Dioxide on the Activity, Structure and Size of Polyphenoloxidase.

High hydrostatic pressure (HHP) may activate undesirable enzymes such as polyphenoloxidase (PPO). Carbon dioxide (CO2 ) addition to HHP could increase enzyme inactivation. We investigated the inactivation of combined HHP and dense phase carbon dioxide process on activity, secondary conformation and size of pure PPO from mushroom. Solutions (2.35μM, in phosphate buffer pH 6.8) were treated with HHP alone (HHP), or 3.6% w/w of CO2 was injected into the package (HHP+CO2). Treatment conditions were 600 MPa, 20 °C, for 1, 3, 5, 7, and 9 min. HHP+CO2 treatment significantly decreased residual enzyme activity (REA) to 30% to 12% after 1 to 9 min, respectively, whereas only HHP had no significant effect. Both HHP and HHP+CO2 treatments caused changes in secondary conformations, however HHP+CO2 changes were more extensive. Alpha-helix fractions were reduced by 32% and 41%, while β sheet, turn and unordered increased by 63% and 213%, 100% and 71%, and 118% and 82% for HHP and HHP+CO2, respectively after 9 min. The protein size in HHP+CO2 samples was 5- to 6-fold larger than that of Control and HHP treatment, and this increase was inversely correlated with REA. The best inactivation kinetics of HHP+CO2 model was the 2-fractional model with 2 simultaneous 1st-order steps, contributing 70% and 30% to original enzyme activity, with k(labile) = 12.15 min(-1) and k(stable) = 0.07 min(-1), respectively. No recovery in activity, secondary conformation and size in all samples were observed after 1-mo storage. Addition of CO2 in HHP treatment can improve enzyme inactivation, and therefore product shelf-life and quality. High hydrostatic pressure (HHP) achieves the safety of foods as a nonthermal method, but it may activate undesirable enzymes resulting in short shelf life due to, for example flavor and color changes. Our study determined that addition of CO2 to HHP has significant effects on enzyme inactivation, secondary conformational and molecular size changes of mushroom PPO. No recovery in activity, secondary conformation and size in all samples were observed after 1 mo storage at 4 °C. This combined process increases product shelf life, in addition to safety and nutrient preservation.

Microbial and Sensory Effects of Combined High Hydrostatic Pressure and Dense Phase Carbon Dioxide Process on Feijoa Puree.

High hydrostatic pressure (HHP) is used for microbial inactivation in foods. Addition of carbon dioxide (CO2) to HHP can improve microbial and enzyme inactivation. This study investigated microbial effects of combined HHP and CO2 on Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae, and evaluated sensory attributes of treated feijoa fruit puree (pH 3.2). Microorganisms in their growth media and feijoa puree were treated with HHP alone (HHP), or saturated with CO2 at 1 atm (HHPcarb), or 0.4%w/w of CO2 was injected into the package (HHPcarb+CO2). Microbial samples were processed at 200 to 400 MPa, 25 °C, 2 to 6 min. Feijoa samples were processed at 600 MPa, 20 °C, 5 min, then served with and without added sucrose (10%w/w). Treated samples were analyzed for microbial viability and sensory evaluation. Addition of CO2 enhanced microbial inactivation of HHP from 1.7-log to 4.3-log reduction in E. coli at 400 MPa, 4 min, and reduction of >6.5 logs in B. subtilis (vegetative cells) starting at 200 MPa, 2 min. For yeast, HHPcarb+CO2 increased the inactivation of HHP from 4.7-log to 6.2-log reduction at 250 MPa, 4 min. The synergistic effect of CO2 with HHP increased with increasing time and pressure. HHPcarb+CO2 treatment did not alter the appearance and color, while affecting the texture and flavor of unsweetened feijoa samples. There were no differences in sensory attributes and preferences between HHPcarb+CO2 and fresh sweetened products. Addition of CO2 in HHP treatment can reduce process pressure and time, and better preserve product quality. A higher microbial inactivation of Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae by combining dense phase carbon dioxide and high hydrostatic pressure was observed. For sweetened products there were no significant differences in sensory attributes and preferences between samples treated by the combined method and the fresh samples. In conclusion, addition of CO2 in HHP treatment of juices could reduce process severity and improve product quality.

Effects of high hydrostatic pressure on Escherichia coli ultrastructure, membrane integrity and molecular composition as assessed by FTIR spectroscopy and microscopic imaging techniques.

High hydrostatic pressure (HHP) is a novel food processing technology that is considered as an attractive alternative to conventional heat treatments for the preservation of foods, due to its lethal effects on pathogenic and spoilage microorganisms, while causing minor effects on food quality and sensorial attributes. This study is aimed at investigating how HHP treatments at varying intensities in the range 50–900 MPa affect the viability, membrane integrity, ultrastructure and molecular composition of Escherichia coli. Results of membrane integrity tests (measurement of cellular leakage and monitoring of propidium iodide uptake through fluorescence microscopy) and ultrastructural observations by transmission electron microscopy demonstrated that HHP gave rise to cellular enlargement, membrane damage or detachment, DNA and protein denaturation and loss of intracellular contents. Fourier-transform infrared (FTIR) spectroscopy analyses evidenced minor changes in molecular composition in response to high pressures, which were mostly observed on the spectral region w4 (1200–900 cm−1), mainly informative of carbohydrates and polysaccharides of the cell wall. These findings suggest that exposure of E. coli cells to HHP causes alterations in their physical integrity while producing minor modifications in biochemical cellular composition. The current study increases the knowledge on the mechanisms of E. coli inactivation by HHP and provides valuable information for the design of more effective food preservation regimes based on the integration of mild HHP in combination with other food preservation strategies into a multi-target hurdle technology approach.