High Pressure Processing Conditions Research Articles

Combined effects of high pressure processing and sous-vide cooking on the tenderization of proteolytic enzyme-injected chicken breast

The combined effects of high pressure processing (HPP), sous-vide cooking (SV), and their processed sequence on papaya extract (PaExt) tenderized chicken breast were investigated. Chicken breasts were injected with 0.05% PaExt and then divided into HPP + SV or SV + HPP where the HPP conditions were 250 or 450 MPa for 10 min and meats were SV cooked at 61 °C for 100 min. The cooking loss, pH value, meat color, texture, and microstructure of treated chicken breasts were determined. PaExt treated chicken breast with HPP + SV had the lowest values in all texture parameters and the highest cooking loss among all treatments. Microstructural images further explained the tenderization of PaExt + HPP + SV treatments which caused severe degradation and denaturation of muscle fibers and connective tissues. Therefore, the application of PaExt + HPP + SV may lead to tender meat texture which is easier for the elderly to consume and also shows the potential of elderly care food development.

Se-Pair Search for Deciphering Selenium-Encoded Peptide and a Pyrolysis-Thermolysis Dietary Model for Minimizing Loss of "KKSe(M)R" during Processing.

Dietary deficiency of selenium is a global health hazard. Supplementation of organic selenopeptides via food crops is a relatively safe approach. Selenopeptides with heterogeneous selenium-encoded isotopes or a poorly fragmented peptide backbone remain unidentified in site-specific selenoproteomic analysis. Herein, we developed the Se-Pair Search, a UniProtKB-FASTA-independent peptide-matching strategy, exploiting the fragmentation patterns of shared peptide backbones in selenopeptides to optimize spectral interpretation, along with developing new selenosite assignment schemes (steps 1-3) to standardize selenium-localization data reporting for the selenoproteome community and thereby facilitating the discovery of unexpected selenopeptides. Using selenium-biofortified rice under cooking, fermentation, and high-temperature and high-pressure processing conditions as a pyrolysis-thermolysis dietary model, we probed the single-molecule-level kinetic evolution of the novel selenopeptide "KKSe(M)R" with qual-quantitative information on graph-theory-oriented localization calculations, abundance patterns, activation energy, and rate constants at a selenoproteome-wide scale. We ground-truth-annotated thirteen pyrolysis-thermolysis products and inferred four pyrolysis-thermolysis pathways to characterize the formation reactivity of the main intermediate variables of KKSe(M)R and constructed an advanced probe-type ultrasound technique prior to pyrolysis-thermolysis conditions for minimizing loss of KKSe(M)R during processing. Importantly, we reveal the unappreciated pyro-excitation diversion of KKSe(M)R at pyrolysis-thermolysis time and temperature matrices. These findings provide pioneering theoretical guidance for controlling dietary selenium supplementation within the safety thresholds.

Exploring the effect of high-pressure processing conditions on the deaggregation of natural major royal jelly proteins (MRJPs) fibrillar aggregates

High pressure processing is a safe and green novel non-thermal processing technique for modulating food protein aggregation behavior. However, the systematic relationship between high pressure processing conditions and protein deaggregation has not been sufficiently investigated. Major royal jelly proteins, which are naturally highly fibrillar aggregates, and it was found that the pressure level and exposure time could significantly promote protein deaggregation. The 100–200 MPa treatment favoured the deaggregation of proteins with a significant decrease in the sulfhydryl group content. Contrarily, at higher pressure levels (>400 MPa), the exposure time promoted the formation of disordered agglomerates. Notably, the inter-conversion of α-helix and β-strands in major royal jelly proteins after high pressure processing eliminates the solvent-free cavities inside the aggregates, which exerts a 'collapsing' effect on the fibrillar aggregates. Furthermore, the first machine learning model of the high pressure processing conditions and the protein deaggregation behaviour was developed, which provided digital guidance for protein aggregation regulation.

Regulation of the Ice Ⅰ to Ice III high pressure phase transition meta-stability in milk and its bactericidal effects

This study was focused on a novel approach of creating perturbations under high pressure (HP) meta-stable Ice Ⅰ to Ice Ⅲ phase transition and its bactericidal effects. Experiments were carried out under subzero high pressure processing conditions using Escherichia coli suspended in milk, and the microbial inactivation before and after the meta-stable state regulation was compared. The phase transition position of unperturbed milk was 302 MPa/–37.5 °C. The volume change resulting from the phase transition was employed as the perturbation mechanism. Glucose (5 %, 20 %) and sodium chloride solutions (5 %, 20 %) were used as regulatory sources. Glucose solutions accelerated the phase change of the milk better than the sodium chloride solution and resulted in an optimum phase transition position of milk at 243 MPa/–30.6 °C. The induced perturbations accelerated meta-stable transformation and enhanced the microbial destruction. At 330 MPa/3s, compared to the unfrozen samples, the lethality of E. coli in the frozen-regulated samples significantly increased by 1.79 log. The relationship between the E. coli inactivation within the phase change pressure range and the pressure was not continuous, but a segmented one, both before and after meta-stable state regulation. A higher level of E. coli destruction was accomplished by a 5 min pressure-holding of frozen samples at 220 MPa and 280 MPa as compared to the one-pulse and two-pulses treatments without holding time. The maximum lethality of 6.73 log was achieved at 280 MPa/5 min in the frozen-regulated application.

A Quality Assessment of Strawberry Nectar Stabilized by Thermal and High-Pressure Processing Conditions

This study is aimed at evaluating the quality of strawberry nectar following high-pressure processing (HPP) at different pressure levels (400, 500, and 600 MPa for 3 minutes) and thermal pasteurization (TT) at 75°C for 15 s. Key parameters include total colour difference ( Δ E ∗ ), aparent viscosity, colour analysis via CIELAB coordinates, and pH. Additionally, residual enzymatic activity (RA%) of polyphenol oxidase (PPO) and peroxidase (POD) was measured. Strawberry nectar (12°Brix) was prepared and subjected to processing, with thermal treatment in 50 mL tubes and HPP in 40 mL polyethylene bags. Samples were stored under refrigeration during 21 days, with microbial analysis conducted to assess microbiological stability during storage. TT exhibited a more pronounced reduction in total aerobic microbial count (TAMC) compared to HPP, which showed no detectable yeast and mould. Apparent viscosity varied among samples, with HPP at 600 MPa displaying a significant increase of 52.1% compared to the control. The pseudoplastic behavior, characterized by n values lower than 1, was consistent across all treatments. TT led to a reduction in L ∗ brightness value during storage, whereas HPP-treated samples underwent colour changes over time with Δ E ∗ of 3.1 for 400 MPa, 3 minutes, at 21 days. For PPO and POD, the 600 MPa treatment exhibited the highest inhibition (44% and 4% RA, respectively). This comprehensive study provides insights into how different HPP processing conditions affect the quality attributes, enzymatic activity, and microbiological stability of strawberry nectar during production and refrigerated storage. The research’s significance lies in its holistic comparison of HPP with traditional thermal pasteurization, offering valuable information for both industry and consumers.

Modelling and Evaluation of the Effect of Pulsed Electric Fields and High Pressure Processing Conditions on the Quality Parameters of Osmotically Dehydrated Tomatoes

This study explores the osmotic dehydration (OD) of fresh-cut cherry tomatoes through the application of Pulsed Electric Fields (PEF) and High-Pressure (HP) pre-treatments. Untreated, PEF-treated (1.8 kV/cm, 0–300 pulses), and HP-treated (0–600 MPa, 5 min) tomatoes were subjected to osmotic dehydration at 35 °C for up to 3 h. The results reveal that a 100-pulse PEF treatment and HP treatment at 600 MPa yielded optimal outcomes in terms of both OD enhancement (with effective moisture diffusion coefficients of 7.91 · 10−10 m2/s for PEF and 7.40 · 10−10 m2/s for HP-treated tomatoes compared to 5.17 · 10−10 m2/s for untreated samples) and product acceptability (achieving overall acceptance scores between 7 and 8). Applying PEF (100 pulses) and HP (600 MPa) pre-treatments reduced the water activity (aw) to 0.887 and 0.760, respectively, after 3 h of OD, compared to aw = 0.923 for untreated OD samples. The selection of these pre-treatment conditions enabled effective dehydration and quality retention, extending the shelf life by up to 40 days under chilled storage.

Comparison between the use of hydrocolloids (xanthan gum) and high-pressure processing to obtain a texture-modified puree for dysphagia

Enriched lentil protein vegetable purees (10% zucchini, 10% carrots, 2.5% extra virgin olive oil and 21.8% lentil protein concentrate) suitable for people with dysphagia were developed with 0.8% xanthan gum (XG) or 600 MPa/5 min high pressure processing (HPP) treatment with the aim of comparing their rheological and textural properties. Selection of the appropriate XG % and HPP conditions was made by performing initial pilot trials. Purees showed a good nutritional profile (12% protein, 3.4% fiber, 100 Kcal/100 g), being adequate for people with dysphagia. Microbiological testing of HPP treated purees indicated that it has a good shelf-life under refrigerated conditions 14 days). Both types of purees showed a gel-like character (tan delta 0.161–0.222) and higher firmness, consistency and cohesiveness than control samples. Comparing XG and HPP samples at time 0, HPP treated purees showed the highest stiffness ( G′), the lowest deformability capacity (yield strainLVR) and the lowest structural stability (yield stressLVR). With storage, HPP treatment samples showed significant increases in all rheological and textural parameters. These results confirm the suitability of HPP as an alternative technology to hydrocolloids for the obtained dysphagia dishes.

High-Pressure Effects on Selected Properties of Pea and Soy Protein Isolates

The use of vegetable proteins has been the focus of research efforts to develop new products and/or to replace other sources of protein. Ergo, there is a need to assess the effects of new processing technologies on this type of protein. This work evaluated the influence of high-pressure processing (HPP) (pressure: 200, 400 and 600 MPa; holding time: 5, 10 and 15 min) on selected properties of pea (PPI) and soy (SPI) protein isolates at three pH values (6, 7 and 8). SPI presented a higher percentage of soluble proteins than PPI, still, HPP increased protein solubility of both isolates. This effect was more pronounced on SPI, particularly at pH 7 and 8, where the percentage of soluble proteins almost tripled under some HPP conditions. Similarly, the surface hydrophobicity also increased with HPP for proteins from both sources, increasing, in general, with increasing pressure and holding time. On the contrary, the content of free sulfhydryl groups generally decreased with HPP for proteins from both sources, suggesting a complex balance between protein unfolding and further aggregation under certain conditions. The effects of HPP on the emulsifying properties of the protein isolates were dependent on pH, pressure, holding time and whether the soluble or total fraction of the protein isolates were used.

Recent Progress in the Synergistic Bactericidal Effect of High Pressure and Temperature Processing in Fruits and Vegetables and Related Kinetics.

Traditional thermal processing is a widely used method to ensure food safety. However, thermal processing leads to a significant decline in food quality, especially in the case of fruits and vegetables. To overcome this drawback, researchers are extensively exploring alternative non-thermal High-Pressure Processing (HPP) technology to ensure microbial safety and retaining the sensory and nutritional quality of food. However, HPP is unable to inactivate the spores of some pathogenic bacteria; thus, HPP in conjunction with moderate- and low-temperature is employed for inactivating the spores of harmful microorganisms. Scope and approach: In this paper, the inactivation effect of high-pressure and high-pressure thermal processing (HPTP) on harmful microorganisms in different food systems, along with the bactericidal kinetics model followed by HPP in certain food samples, have been reviewed. In addition, the effects of different factors such as microorganism species and growth stage, process parameters and pressurization mode, and food composition on microbial inactivation under the combined high-pressure and moderate/low-temperature treatment were discussed. The establishment of a reliable bactericidal kinetic model and accurate prediction of microbial inactivation will be helpful for industrial design, development, and optimization of safe HPP and HPTP treatment conditions.

Quality Improvement in Mackerel Fillets Caused by Brine Salting Combined with High-Pressure Processing.

Simple SummaryHigh-pressure processing enhanced the pasteurization effect of mackerel fillets that had undergone brine salting and improved the effect of texture hardening and fish discolouration observed after the high-pressure treatment alone. Our findings provide seafood processors as an alternative option to improve the safety of salt-brined mackerel fillets.The purpose of the study is to investigate the effects of brine salting and high-pressure processing (HPP) on the microbial inactivation and quality parameters of mackerel fillets. Mackerel fillets were immersed in 3% and 9% sodium chloride brine for 90 min at refrigerator temperature, and then treated at 300, 400, 500, and 600 MPa pressure for 5 min. The microbial counts and physicochemical qualities of the fish were examined. In comparison with fish fillets treated with brine or high pressure alone, those treated with the combination of brine salting and HPP showed significantly reduced aerobic plate count (APC) and psychrotrophic bacteria count (PBC). The hardness and chewiness of salt-brined fillets were obviously lower than those of the unsalted fillets under the same pressure condition. Thus, brine salting imparted mackerel fillets a softer texture, which compensated for the HPP-induced increased hardness and chewiness of the fillets. The L* (lightness) and ΔE (colour difference) values of the fillets increased with increasing pressure, with or without brine salting. Conversely, a* (redness) values decreased with increasing pressure. The samples treated with 3% brine in combination with 300 or 400 MPa pressure had a* values similar to those of the samples processed under similar HPP conditions alone but showed lower ΔE values than the other groups. Therefore, as a very high pressure would adversely affect the texture and colour of the fish fillets, this study suggests that immersion in an appropriate brine concentration (3%) and treatment with HPP at 400 MPa for 5 min improved or maintained the colour and texture relatively well and produced a synergistic bactericidal effect.

The efficacy and safety of high-pressure processing of food.

High‐pressure processing (HPP) is a non‐thermal treatment in which, for microbial inactivation, foods are subjected to isostatic pressures (P) of 400–600 MPa with common holding times (t) from 1.5 to 6 min. The main factors that influence the efficacy (log10 reduction of vegetative microorganisms) of HPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) and microorganism‐related (type, taxonomic unit, strain and physiological state). It was concluded that HPP of food will not present any additional microbial or chemical food safety concerns when compared to other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrum caused by the current HPP conditions applied by the industry are lower than those achieved by the legal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations) could be identified to achieve specific log10 reductions of relevant hazards based on performance criteria (PC) proposed by international standard agencies (5–8 log10 reductions). The most stringent HPP conditions used industrially (600 MPa, 6 min) would achieve the above‐mentioned PC, except for Staphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows’ milk, is relatively pressure resistant and its use would be limited to that of an overprocessing indicator. Current data are not robust enough to support the proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditions applied by the industry. Minimum HPP requirements to reduce Listeria monocytogenes levels by specific log10 reductions could be identified when HPP is applied to ready‐to‐eat (RTE) cooked meat products, but not for other types of RTE foods. These identified minimum requirements would result in the inactivation of other relevant pathogens (Salmonella and Escherichia coli) in these RTE foods to a similar or higher extent.

Inactivation of microbial loads and retardation of quality loss in Asian hard clam (Meretrix lusoria) using high-hydrostatic-pressure processing during refrigerated storage

The effects of high pressure processing (HPP) at 200, 300, 400, 500, and 600 MPa for 3 min on physicochemical quality and inactivation of microbial loads of Asian hard clam (Meretrix lusoria) were evaluated. In addition, the retardation effects in microbial growth and quality loss of pressurized hard clams stored at 4 °C were investigated. Results showed that the expanding rate, moisture content, shucking ratio, pH, L* (lightness), and W (whiteness) of clam meat increased significantly with the increase in pressure, but a* (redness) and b* (yellowness) values decreased. With the increase in pressure, the levels of aerobic plate count (APC), psychrotrophic bacteria count (PBC), coliform, and Vibrio parahaemolyticus in clam meat significantly decreased. Furthermore, HPP with a pressure of >400 MPa on clam samples significantly delayed the increase in APC (by 6–9 days within Taiwan's regulation standard limit) and PBC during storage at 4 °C. However, the samples pressurized more than 300 MPa had significantly lower levels of total volatile basic nitrogen (TVBN) than control samples during storage. Overall, the results indicated that pressurization at least 400 MPa for 3 min on Asian hard clam were able to reach the highest expanding rate and moisture content, and 100 % shucking, while it can reduce the coliform, and V. parahaemolyticus to a non-detectable level. In addition, HPP conditions of ≥400 MPa for 3 min significantly extended the shelf-life of hard clam during refrigerated storage. Therefore, HPP is a useful technique to preserve Asian hard clam meats due to its ability to reduce bacterial load and retard TVBN production.

Effects of high-hydrostatic-pressure processing on the chemical and microbiological quality of raw ready-to-eat hard clam marinated in soy sauce during cold storage

The aim of this study was to determine whether high-pressure processing (HPP) shucking method can replace the conventional frozen shucking method for the preparation of soy sauce-marinated Asian hard clams products, while also inactivating microorganisms. The chemical and microbiological quality of samples marinated in soy sauce and HPP treatments at 300, 400, and 500 MPa for 3 min (marinated HPP clam), and frozen and marinated in soy sauce (frozen marinated clam) were evaluated during storage at 4 °C for 15 days. Surface area, moisture content, aerobic plate count (APC), psychrotrophic bacteria count (PBC), and coliform counts of marinated HPP clams were significantly lower than those of frozen marinated clams. During storage at 4 °C, the APC and PBC of frozen marinated clams increased rapidly, reaching 8.3 log CFU/g and 8.4 log CFU/g at day 15, while the pH of frozen marinated clams decreased rapidly, reaching 3.4 at day 15. In contrast, high-pressure treatment could delay the increase of APC and PBC loads, and the drop of pH. Therefore, the results indicated that HPP conditions of ≥300 MPa for 3 min significantly extended the shelf life of marinated clam during cold storage.

Effect of high hydrostatic pressure on microbial inactivation and quality changes in carrot-orange juice blends at varying pH

This study investigates the effect of high hydrostatic pressure, also known as high pressure processing (HPP), on microbial inactivation and changes in physicochemical characteristics of carrot-orange juice blends at different pH values. HPP conditions (200–400 MPa, up to 5 m) were evaluated to reach at least 5-log inactivation of L. innocua (ATCC 51742) in each blend. HPP at 300 MPa for 2 m, 400 MPa for 1 m, and 400 MPa for 3 m achieved more than 6-log reduction of L. innocua in pH 4, pH 5, and pH 6 blends, respectively. Ascorbic acid (16–45 mg/100g), total carotenoid (66–241 mg/L), and total phenolic (30–44 mg/L) contents did not significantly change after HPP compared to the corresponding untreated blends. The natural microbiota (i.e. aerobic mesophilic bacteria) was kept below 2-log CFU/mL for 28 d of storage. pH and total soluble solids remarkably changed for untreated blends in 10 d while HPP-treated blends were more stable during 28 d. Color attributes (L*, a*, b*) were retained after HPP and during storage. This study identified less intense high pressure processes for carrot-orange juice blends compared to commercially applied pressure levels (i.e. 600 MPa) to produce microbiologically stable blends with preserved quality attributes depending on pH and blend proportion.

High‐pressure processing applied for enhancing the antioxidant content of minimally processed peaches

SummaryIn addition to the capacity of high‐pressure processing (HPP) to preserve fruits, recent studies highlight the ability of this technology to increase the content of antioxidants. The aim of this work was to find the HPP conditions able to maximise the increase in antioxidants in minimally processed peaches without affecting the overall quality, complemented by a microstructural study to better understand the observed effects. Therefore, minimally processed peaches were subjected to HPP treatment with different pressure levels (100, 300 and 500 MPa) and holding times (1,5 min). Results showed that 300 and 500 MPa induced a significant increase in the antioxidant content, which can be partially linked to the increase in the extractability of these compounds brought about by the changes in the microstructure. It can be concluded that a treatment at 300 MPa for 1 min is enough to induce a significant increase in antioxidants, without causing deterioration of the product.

Effect of high pressure processing (HPP) on spore preparation of probiotic Bacillus coagulans LBSC [DSM 17654

Abstract High pressure processing (HPP) has become a mainstream technology for modern age food processing. HPP conditions are detrimental to inherent microbial flora, including food pathogens. A probiotic intended for supplementation in a high-pressured processed food should therefore be stable to processing and subsequent storage conditions. The present study reports the viability of Bacillus coagulans LBSC [DSM 17654] spores at high hydrostatic pressures (HHP, 450 and 550 MPa) processing. B. coagulans LBSC spores were viable under both pressure condition at pH 2.60, 5.00, 7.00, and 8.25. Similar HPP conditions completely inactivated a reference strain Escherichia coli ATCC 25922. The HPP treated B. coagulans LBSC spore preparation showed no reduction in the viability on room temperature storage for a duration of six months. Results demonstrated the resilience of probiotic B. coagulans LBSC spores under HPP treatment, suggesting its potential incorporation in a range of functional foods and beverages.

Novel Colour-Based, Prototype Indicator for Use in High-Pressure Processing (HPP)

The preparation and testing of a colour-based prototype indicator for high-pressure processing (HPP) are described. The indicator is a layered structure comprising a pressed disc of a mixture of silica gel, which has been previously loaded with a set wt% of acidified water, and polytetrafluoroethylene, PTFE, powders, a water-permeable barrier layer, and a Congo-Red-based pH indicator layer, all vacuum-sealed in a water impermeable plastic film. The value of the wt% is calculated from the ratio of the mass of acidified water added to the mass of originally dry silica gel. The high pressures associated with HPP drive the release of the acidified water from the silica gel and its subsequent transport through the water-permeable barrier layer to the pH indicator, thereby producing a striking red-to-blue colour change. The response of the HPP indicator can be tuned to different HPP conditions by varying the wt% of acidified water used to load the silica gel powder. Indicators, with 61, 63, and 65 wt% acidified water loaded silica gel, are prepared and found to require, respectively, the application of at least, 600, 400, and 300 MPa pressure for 3 min to effect a change colour. To our knowledge, this is the first reported example of a prototype HPP indicator that can be tuned to respond to the very different pressure and time conditions used in HPP to sterilise such very different products as milk, apple and orange juice, and aloe vera gel.

High-Pressure Processing for the Production of Added-Value Claw Meat from Edible Crab (Cancer pagurus).

High-pressure processing (HPP) in a large-scale industrial unit was explored as a means for producing added-value claw meat products from edible crab (Cancer pagurus). Quality attributes were comparatively evaluated on the meat extracted from pressurized (300 MPa/2 min, 300 MPa/4 min, 500 MPa/2 min) or cooked (92 °C/15 min) chelipeds (i.e., the limb bearing the claw), before and after a thermal in-pack pasteurization (F9010 = 10). Satisfactory meat detachment from the shell was achieved due to HPP-induced cold protein denaturation. Compared to cooked or cooked–pasteurized counterparts, pressurized claws showed significantly higher yield (p < 0.05), which was possibly related to higher intra-myofibrillar water as evidenced by relaxometry data, together with lower volatile nitrogen levels. The polyunsaturated fatty acids content was unaffected, whereas the inactivation of total viable psychrotrophic and mesophilic bacteria increased with treatment pressure and time (1.1–1.9 log10 CFU g−1). Notably, pressurization at 300 MPa for 4 min resulted in meat with no discolorations and, after pasteurization, with high color similarity (ΔE* = 1.2–1.9) to conventionally thermally processed samples. Following further investigations into eating quality and microbiological stability, these HPP conditions could be exploited for producing uncooked ready-to-heat or pasteurized ready-to-eat claw meat products from edible crab.

Suitability Assessment of PLA Bottles for High-Pressure Processing of Apple Juice.

The aim of the present study is to assess the use of polylactic acid (PLA) bottles as an alternative to polyethylene terephthalate (PET) ones for high-pressure processing (HPP) of apple juice. The treatment of PLA bottles at 600 MPa for 3 min did not cause alterations in the packaging shape and content, confirming the suitability of PLA bottles to withstand HPP conditions as well as PET bottles. Quantification of total mesophilic bacterial and fungal load suggested HPP treatment can be effectively applied as an alternative to pasteurization for apple juice packed in PLA bottles since it guarantees microbial stability during at least 28 days of refrigerated storage. The headspace gas level did not change significantly during 28 days of refrigerated storage, irrespective of the bottle material. Color parameters (L*, a*, and b*) of the HPP-treated juice were similar to those of the fresh juice. Irrespective of the packaging type, the total color variation significantly changed during storage, showing an exponential increase in the first 14 days, followed by a steady state until the end of observations. Overall, PLA bottles proved to offer comparable performances to PET both in terms of mechanical resistance and quality maintenance.

Assessing the pressure resistance of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica to high pressure processing (HPP) in citric acid model solutions for process validation

Despite the commercial success of high pressure processing (HPP) in the juice industry, some regulatory agencies still require process validation. However, there is a lack of consensus on various aspects regarding validation protocols, including the selection of representative strains to be used in challenge tests. This study characterized the variable response of Escherichia coli O157:H7 (34 strains), Listeria monocytogenes (44 strains) and Salmonella enterica (45 strains) to HPP, and identified potential candidates to use in process validation. Stationary phase cells were submitted to 500 MPa for 1 min at 10 °C in model solutions consisting of tryptic soy broth + 0.6% yeast extract (TSBYE) adjusted to pH 4.5 and 6.0 with citric acid. At pH 6.0, pressure resistance widely varied between species and within strains of the same species. E. coli O157:H7 and L. monocytogenes were the most pressure resistant and showed high variability at strain level, as the total count range given by minimum and maximum counts spread between 2.0 and 6.5 log10 CFU/ml. S. enterica was the least resistant pathogen with more than 82% of the isolates displaying non-detectable counts after HPP. Recovery through storage at 12 °C was also variable for all pathogens, but eventually most strains recovered with median counts on day 14 between 8.3 and 8.9 log10 CFU/ml. For pH 4.5 solutions, 26 E. coli O157:H7 strains displayed survivors after HPP but did not adapt, registering non-detectable counts in the next sampling dates. None of the L. monocytogenes and S. enterica strains survived HPP or incubation at pH 4.5 (<2.0 log10 CFU/ml), suggesting that citric acid at 4.16 g/l is a safe barrier for pathogen control under moderate HPP conditions. Principal component and cluster analyses served to propose strain cocktails for each species based on their pressure resistant and adaptation phenotypes. Additionally, S. enterica was identified as less pressure resistant and less prone to recover following HPP than E. coli O157:H7 and L. monocytogenes, so its relevance in process validation for juices should be questioned. Future work will validate the proposed strain cocktails on real food systems.