High pressure processing plus technologies: Enhancing the inactivation of vegetative microorganisms

High pressure processing (HPP) is a non-thermal technology that can ensure microbial safety without compromising food quality. However, the presence of pressure-resistant sub-populations, the revival of sub-lethally injured (SLI) cells, and the resuscitation of viable but non-culturable (VBNC) cells pose challenges for its further development. The combination of HPP with other methods such as moderate temperatures, low pH, and natural antimicrobials (e.g., bacteriocins, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils) or other non-thermal processes (e.g., CO2, UV-TiO2 photocatalysis, ultrasound, pulsed electric fields, ultrafiltration) offers feasible alternatives to enhance microbial inactivation, termed as "HPP plus" technologies. These combinations can effectively eliminate pressure-resistant sub-populations, reduce SLI or VBNC cell populations, and inhibit their revival or resuscitation. This review provides an updated overview of microbial inactivation by "HPP plus" technologies and elucidates possible inactivation mechanisms.

Quality of Refrigerated Squid Mantle Cut Treated with Mint Extract Subjected to High-Pressure Processing

Squid (Loligo vulgaris) is commonly prone to spoilage, leading to a short shelf-life. High-pressure processing (HPP) can play a role in maintaining the quality and freshness of squid. Along with HPP, food preservatives from natural sources such as mint extract (ME), which are effective, safe, available, and cost-effective, are required. The present study aimed to investigate the combined effect of ME and HPP on the quality of refrigerated squid mantle cuts (SMC) over a period of 15 days. The time-kill profiles of ME and planktonic cell inactivation by HPP were assessed. ME (400 mg/L) inhibited bacterial growth, while planktonic cells treated with HPP (400 MPa) exhibited a reduction at 5 min. Physicochemical and microbial qualities of SMC treated with ME (0, 200, 400 mg/L) followed by HPP (0.1, 200, 400 MPa) for 5 min were monitored during refrigerated storage. Samples treated with ME (400 mg/L) and HPP (400 MPa) exhibited lower weight loss, cooking loss, pH changes, volatile base content, microbial counts, and higher textural properties than other samples. Based on next-generation sequencing results, Brochothrix campestris from family Listeriaceae was the predominant spoilage bacteria in treated sample after 12 days of storage. Therefore, ME and HPP combined treatments exhibited effectiveness in extending the shelf-life of refrigerated SMC.

Machine learning modeling and additive explanation techniques for glutathione production from multiple experimental growth conditions of Saccharomyces cerevisiae

Glutathione (GSH) production is of great industrial interest due to its essential properties. This study aimed to use machine learning (ML) methods to model GSHproduction under different growth conditions of Saccharomyces cerevisiae, namely cultivation time, culture volume, pressure, and magnetic field application. Different ML and regression models were evaluated for their statistics to select the most robust model. Results showed that eXtreme Gradient Boosting (XGB) was the best predictive performance model. From the best model, additive explanation techniques were used to identify the feature importance of process. According to variable analysis, the best conditions to obtain the highest GSH concentrations would be cultivation times of 72-96 h, low magnetic field intensity (3.02 mT), low pressure (0.5 kgf.cm-2), and high culture volume (3.5 L). XGB use and additive explanation techniques proved promising for determining process optimization conditions and selecting the essential process variables.

Inactivation of Salmonella, Shiga Toxin-producing E. coli, and Listeria monocytogenes in Raw Diet Pet Foods Using High-Pressure Processing

Pet food formulated with raw meat can pose health risks to pets and humans. High-pressure processing (HPP) was evaluated to achieve a 5-log reduction ofSalmonella,E. coliSTEC, andL. monocytogenesin commercial raw pet foods and maintain a 5-log reduction throughout post-HPP storage.Three formulation types that varied in the amounts of striated meat, organ meat, bone, seeds, and other ingredients (fruits, vegetables, and minor ingredients) designated as A-, S-, and R-formulations were used. Eight raw diet pet foods, consisting of three beef formulations (A-, S- and R-Beef), three chicken formulations (A-, S-, and R-Chicken), and two lamb formulations (A- and S-Lamb), were inoculated with 7 log CFU/g cocktails ofSalmonella,E. coliSTEC orL. monocytogenes, HPP at 586 MPa for 1-4 min, and stored refrigerated (4°C) or frozen (-10 to -18°C) for 21 days with microbiological analyses at various time intervals. A- formulations (20-46% meat, 42-68% organs, 0.9-1.3% seeds, and 10.7-11.1% fruits, vegetables, and minor ingredients) inoculated withSalmonellaand treated at 586 MPa for at least 2 min achieved a 5-log reduction 1 day post-HPP and maintained that inactivation level during frozen storage. A- and S-formulations inoculated withE. coliSTEC and treated at 586 MPa for at least 2 min achieved a 5-log reduction from day 6 of frozen storage. L. monocytogeneswas more HPP resistant thanSalmonellaandE. coliSTEC.S-formulations containing chicken or beef and stored frozen post-HPP had lower inactivation of L. monocytogenes compared to A-formulations containing chicken or beef. S-Lamb had higher frozen storage inactivation (5.95 ± 0.20 log CFU/g) compared to chicken (2.52 ± 0.38 log CFU/g) or beef (2.36 ± 0.48 log CFU/g). HPP coupled with frozen storage time was effective in achieving and maintaining a 5-log reduction ofSalmonellaandE. coliSTEC whileL. monocytogeneswas more resistant and requires further optimization to achieve a 5-log reduction.

Replacing the Addition of Sulfite in Mustard Pickle Products by High-Hydrostatic-Pressure Processing to Delay Quality Deterioration during Storage

This study aimed to assess the use of the high-hydrostatic-pressure (HHP) method (200-600 MPa, 5 min) for bleaching mustard pickle products as an alternative to the conventional method of sulfite addition. The aerobic plate count (APC) and lactic acid bacteria count (LAB) of the samples decreased with the increase in pressure, and the yeast count decreased to no detectable levels. Next, compared with the control group (no high-pressure treatment) the L* (lightness), W (whiteness), ΔE (color difference), and texture (hardness and chewiness) of the HHP-processed samples, which increased significantly with increasing pressure, while the a* (redness) and b* (yellowness) values decreased slightly. This indicates that HHP processing gave the mustard pickle a harder texture and a brighter white color and appearance. Furthermore, when the mustard pickle was treated with HHP 400 and 600 MPa for 5 min and stored at 25 °C for 60 days, it was found that the APC and LAB counts in the HHP-processed group recovered rapidly and did not differ from those in the control group (the non-HHP treated group) but significantly delayed the growth of yeast, the increase in pH value, and total volatile basic nitrogen (TVBN). The high-throughput sequencing (HTS) analysis revealed that the predominant bacterial genera in the non-HHP-treated mustard pickle were Lactiplantibacillus (74%), Lactilactobacillus (12%), and Levilactobacillus (6%); after 60 days of storage, Companilactobacillus (80%) became dominant. However, after 60 days of storage, Lactiplantibacillus (92%) became dominant in the samples processed at 400 MPa, while Levilactobacillus (52%), Pediococcus (17%), and Lactiplantibacillus (17%) became dominant in the samples processed at 600 MPa. This indicated that the HHP treatment changed the lactic acid bacterial flora of the mustard pickle during the storage period. Overall, it is recommended to treat the mustard pickle with HHP above 400 MPa for 5 min to improve its texture and color and delay the deterioration of quality during storage. Therefore, HHP technology has the potential to be developed as a treatment technique to replace the addition of sulfite.

Effects of Ultra-High Pressure on Endogenous Enzyme Activities, Protein Properties, and Quality Characteristics of Shrimp (Litopenaeus vannamei) during Iced Storage

The present study aimed to explore the effects of ultra-high pressure (UHP) on the cathepsin (B, D, H, and L) activities, protein oxidation, and degradation properties as well as quality characteristics of iced shrimp (Litopenaeus vannamei). Fresh shrimps were vacuum-packed, treated with UHP (100–500 MPa for 5 min), and stored at 0 °C for 15 days. The results showed that the L* (luminance), b* (yellowness), W (whiteness), ΔE (color difference), hardness, shear force, gumminess, chewiness, and resilience of shrimp were significantly improved by UHP treatment. Moreover, the contents of surface hydrophobicity, myofibril fragmentation index (MFI), trichloroacetic acid (TCA)-soluble peptides, carbonyl, dityrosine, and free sulfhydryl of myofibrillar protein (MP) were significantly promoted by UHP treatment. In addition, UHP (above 300 MPa) treatment enhanced the mitochondrial membrane permeability but inhibited the lysosomal membrane stability, and the cathepsin (B, D, H, and L) activities. UHP treatment notably inhibited the activities of cathepsins, delayed protein oxidation and degradation, as well as texture softening of shrimp during storage. Generally, UHP treatment at 300 MPa for 5 min effectively delayed the protein and quality deterioration caused by endogenous enzymes and prolonged the shelf life of shrimp by 8 days.

Evaluating the Quality of Cheese Slices Packaged with Na-Alginate Edible Films Supplemented with Functional Lactic Acid Bacteria Cultures after High-Pressure Processing

The aim of the current study was to assess the efficacy of Na-alginate edible films as vehicles for delivering lactic acid bacteria (LAB) with functional properties to sliced cheeses, with or without high-pressure processing (HPP). A three-strain LAB cocktail (Lactococcus lactis Τ4, Leuconostoc mesenteroides Τ25 and Lacticaseibacillus paracasei Τ26) was incorporated into Na-alginate solution in a final population of 9 log CFU/mL. The cheese slices (without or with HPP treatment at 500 MPa for 2 min) were packaged in contact with the LAB edible films (LEFs), and subsequently vacuum packed and stored at 4 °C. Cheese slices without the addition of films, with or without HPP treatment, were used as controls. In all cases, microbiological, pH and sensory analyses were performed, while the presence and the relative abundance of each strain during storage was evaluated using Random Amplified Polymorphic DNA-PCR (RAPD-PCR). In addition, organic acid determination and peptide analysis were performed using high-performance liquid chromatography. The results showed that in cheeses without HPP treatment, the microbiota consisted mostly of mesophilic LAB and lactococci (>7.0 log CFU/g), while HPP caused a reduction in the indigenous microbiota population of approximately 1−1.5 log CFU/g. In the LEF samples, the populations of mesophilic LAB and lactococci were maintained at levels of >6.35 log CFU/g during storage, regardless of the HPP treatment. Sensory evaluation revealed that the LEF samples without HPP had a slightly more acidic taste compared to the control, whereas the HPP-LEF samples exhibited the best organoleptic characteristics. RAPD-PCR confirmed that the recovered strains were attributed to the three strains that had been entrapped in the films, while the strain distribution during storage was random. Overall, the results of the study are promising since the functional LAB strains were successfully delivered to the products by the edible films until the end of storage.

Effect of High Hydrostatic Pressure and Pulsed Electric Fields Processes on Microbial Safety and Quality of Black/Red Raspberry Juice

Black and red raspberries are fruits with a high phenolic and vitamin C content but are highly susceptible to deterioration. The effect of high hydrostatic pressure (HHP 400−600 MPa/CUT-10 min) and pulsed electric fields (PEF, frequency 100−500 Hz, pulse number 100, electric field strength from 11.3 to 23.3 kV/cm, and specific energy from 19.7 to 168.4 kJ/L) processes on black/red raspberry juice was studied. The effect on the inactivation of microorganisms and pectin methylesterase (PME) activity, physicochemical parameters (pH, acidity, total soluble solids (°Brix), and water activity (aw)), vitamin C and phenolic compounds content were also determined. Results reveal that all HHP-treatments produced the highest (p < 0.05) log-reduction of molds (log 1.85 to 3.72), and yeast (log 3.19), in comparison with PEF-treatments. Increments in pH, acidity, and TSS values attributed to compounds’ decompartmentalization were found. PME activity was partially inactivated by HHP-treatment at 600 MPa/10 min (22% of inactivation) and PEF-treatment at 200 Hz/168.4 kJ/L (19% of inactivation). Increment in vitamin C and TPC was also observed. The highest increment in TPC (79% of increment) and vitamin C (77% of increment) was observed with PEF at 200 Hz/168.4 kJ/L. The putative effect of HHP and PEF on microbial safety, enzyme inactivation, and phytochemical retention is also discussed in detail. In conclusion, HHP and PEF improve phytochemical compounds’ content, microbial safety, and quality of black/red raspberry juice.

High-pressure processing of fish and shellfish products: Safety, quality, and research prospects

Seafood products have been one of the main drivers behind the popularity of high-pressure processing (HPP) in the food industry owing to a high demand for fresh ready-to-eat seafood products and food safety. This review provides an overview of the advanced knowledge available on the use of HPP for production of wholesome and highly nutritive clean label fish and shellfish products. Out of 653 explored items, 65 articles published during 2016-2021 were used. Analysis of the literature showed that most of the earlier work evaluated the HPP effect on physicochemical and sensorial properties, and limited information is available on nutritional aspects. HPP has several applications in the seafood industry. Application of HPP (400-600 MPa) eliminates common seafood pathogens, such as Vibrio and Listeria spp., and slows the growth of spoilage microorganisms. Use of cold water as a pressure medium induces minimal changes in sensory and nutritional properties and helps in the development of clean label seafood products. This technology (200-350 MPa) is also useful to shuck oysters, lobsters, crabs, mussels, clams, and scallops to increase recovery of the edible meat. High-pressure helps to preserve organoleptic and functional properties for an extended time during refrigerated storage. Overall, HPP helps seafood manufacturers to maintain a balance between safety, quality, processing efficiency, and regulatory compliance. Further research is required to understand the mechanisms of pressure-induced modifications and clean label strategies to minimize these modifications.

High Hydrostatic Pressure to Increase the Biosynthesis and Extraction of Phenolic Compounds in Food: A Review

Phenolic compounds from fruits and vegetables have shown antioxidant, anticancer, anti-inflammatory, among other beneficial properties for human health. All these benefits have motivated multiple studies about preserving, extracting, and even increasing the concentration of these compounds in foods. A diverse group of vegetable products treated with High Hydrostatic Pressure (HHP) at different pressure and time have shown higher phenolic content than their untreated counterparts. The increments have been associated with an improvement in their extraction from cellular tissues and even with the activation of the biosynthetic pathway for their production. The application of HHP from 500 to 600 MPa, has been shown to cause cell wall disruption facilitating the release of phenolic compounds from cell compartments. HPP treatments ranging from 15 to 100 MPa during 10-20 min at room temperature have produced changes in phenolic biosynthesis with increments up to 155%. This review analyzes the use of HHP as a method to increase the phenolic content in vegetable systems. Phenolic content changes are associated with either an immediate stress response, with a consequent improvement in their extraction from cellular tissues, or a late stress response that activates the biosynthetic pathways of phenolics in plants.

Effect of Different Sterilization Methods on the Microbial and Physicochemical Changes in Prunus mume Juice during Storage

This study evaluated the pasteurization (P), ozone (O₃), ultrasonic (US), and high-hydrostatic-pressure (HHP) sterilization approaches for processing of Prunus mume regarding browning factors and microorganisms, compared with non-sterilization (control check, CK) treatment. The microorganisms (total bacterial count and fungi and yeast count) in the juice were identified after different sterilization techniques, while the quality parameter changes (degree of browning, color measurements, total phenolic content, reducing sugar, ascorbic acid, 5-hydroxymethyl furaldehyde (5-HMF), amino acid nitrogen, total soluble solids (TSS), pH value) were investigated. The results indicate that P and HHP treatment reduced non-enzymatic browning while substantially impacting the color measurements, TSS, and pH, while the sterilization effect was remarkable, with a rate exceeding 90%. Furthermore, the Prunus mume juices treated with P and HHP sterilization were used as the objects, and the CK group was used as the control group. They were placed at 4 °C, 25 °C and 37 °C, respectively, and stored in dark for 15 d. Sampling and determination were carried out on 0, 3, 6, 9, 12, and 15 d, respectively. M-&-Y (molds and yeasts) were not detected in the late storage period, and no obvious microbial growth was observed during storage, indicating that P and HHP treatments could ensure the microbial safety of Prunus mume juice. P- and HHP- treated Prunus mume juice has better quality and low temperature storage is beneficial for maintaining the quality of Prunus mume juice. Therefore, P treatment or HHP treatment combined with low temperature storage could achieve a more ideal storage effect. Overall, this study conclusively established that P and HHP methods were suitable for sterilizing Prunus mume juice. These techniques minimally affected overall product quality while better maintaining the quality parameters than the untreated juice samples and those exposed to O₃ and US treatment.

Effects of Thermal and High-Pressure Processing on Quality Features and the Volatile Profiles of Cloudy Juices Obtained from Golden Delicious, Pinova, and Red Delicious Apple Cultivars

In this study, juices extracted from three apple cultivars (Golden Delicious, Pinova, and Red Delicious) were stabilized by means of thermal treatment (TT) and high-pressure processing (HPP, 600 MPa 3 min); pH, total titratable acidity, total soluble solids content, color, and viscosity, as well as volatile profile, were investigated. Qualitative characteristics (pH, titratable acidity, colorimetric parameters, viscosity, and volatile profile) results were significantly influenced by both cultivars and treatments; for example, juice viscosity greatly increased after HPP treatment for Golden Delicious, and after both TT and HPP for Pinova, while no influence of stabilization treatment was registered for Red Delicious juices. Regarding the volatile profile, for Golden Delicious cultivar, HPP treatment determined an increase in volatile compounds for most of the classes considered, leading to a supposed quality implementation. For the other two cultivars, the stabilization treatment that better preserved the volatile profile was the HPP one, even if the results were quite similar to the thermal treatment. Further studies are needed to evaluate different time/pressure combinations that could give better results, depending on the specific apple cultivar.

Volatile compounds in high-pressure-treated dry-cured ham: A review

The use of high pressure processing (HPP) for the treatment of dry-cured ham and other meat products has considerably increased worldwide. Its well-documented lethal effect on pathogenic and spoilage bacteria ensures the microbial safety of dry-cured ham and extends its shelf life. However, the effects of HPP on the volatile compounds, odor and aroma of dry-cured ham are less known. In the present review, the effects of HPP on the enzymes and microorganisms responsible for the generation of volatile compounds in dry-cured ham and the changes in the levels of the main groups of volatile compounds resulting from different HPP treatments are discussed. Particular attention is devoted to the fate of odor-active compounds after HPP treatments and throughout further commercial storage. The use of efficient sensory techniques yielding odor and aroma outputs closer to those perceived by consumers is encouraged. Needs for future research on the volatile compounds, odor and aroma of HPP-treated dry-cured ham are highlighted.

A comparative study on the textural and nutritional profile of high pressure and minimally processed pineapple

High pressure processing of pineapple has potential implication in food industry. The impact of high pressure (HP) processing and minimal processing, on quality parameters of pineapple was analysed. Changes in the pineapple quality in terms of texture, colour, total flavonoids, total polyphenols, vitamin C and sensory properties were investigated within the domain of 100-300 MPa and 5-20 min. Quality changes induced by HP processing was compared with the minimally processed pineapple. High pressure processing significantly (p < 0.0001) affect the firmness, total flavonoids, total polyphenols, vitamin C and colour values and were significantly increased in HP processed samples, while in minimal processed samples, these quality attributes exhibited a major degradation. On the basis of quality analysis, microbial quality and sensory assessment, high pressure treatment at 300 MPa for 10 min was found to be suitable for preserving the quality of pineapple up to 16^th day in refrigeration condition.

Structure and adsorption behavior of high hydrostatic pressure-treated β-lactoglobulin

HYPOTHESIS

High hydrostatic pressure treatment causes structural changes in interfacial-active β-lactoglobulin (β-lg). We hypothesized that the pressure-induced structural changes affect the intra- and intermolecular interactions which determine the interfacial activity of β-lg. The conducted experimental and numerical investigations could contribute to the mechanistic understanding of the adsorption behavior of proteins in food-related emulsions.

EXPERIMENTS

We treated β-lg in water at pH 7 with high hydrostatic pressures up to 600 MPa for 10 min at 20 °C. The secondary structure was characterized with Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD), the surface hydrophobicity and charge with fluorescence-spectroscopy and ζ-potential, and the quaternary structure with membrane-osmometry, analytical ultracentrifugation (AUC) and mass spectrometry (MS). Experimental analyses were supported through molecular dynamic (MD) simulations. The adsorption behavior was investigated with pendant drop analysis.

FINDINGS

MD simulation revealed a pressure-induced molten globule state of β-lg, confirmed by an unfolding of β-sheets with FTIR, a stabilization of α-helices with CD and loss in tertiary structure induced by an increase in surface hydrophobicity. Membrane-osmometry, AUC and MS indicated the formation of non-covalently linked dimers that migrated slower through the water phase, adsorbed more quickly due to hydrophobic interactions with the oil, and lowered the interfacial tension more strongly than reference β-lg.

Effect of High-Pressure Processing on Physico-Chemical, Microbiological and Sensory Traits in Fresh Fish Fillets (Salmo salar and Pleuronectes platessa)

High-pressure (HP) treatment could lead to several advantages when applied to fish and seafood since it would affect the extension of the shelf life of this highly perishable food. In this regard, this study aimed to evaluate the effect of high-pressure treatment (500 MPa for 2 min at a temperature of 4 °C) on changes in quality on two different kinds of fresh fish fillets (Salmo salar and Pleuronectes platessa). Specifically, physico-chemical (VOCs, untargeted metabolomics spectra, pH and color), microbiological (Enterobacteriaceae, Pseudomonas spp., mesophilic and psychrotrophic bacteria) and sensory traits were evaluated at different days of refrigerated storage. From the results obtained, it is possible to state that the high pressure significantly (p ≤ 0.05) reduced microbial growth for each investigated microorganism. Regarding the colorimetric coordinates, no remarkable effects on a* and b* indices were found, while a significant effect (p = 0.01) was observed on the colorimetric index L*, making the HP-treated samples lighter than their respective controls. The sensory analysis showed that for the odor attribute, the HP treatment seems to have had a stabilizing action during shelf-life. Moreover, the treated samples obtained a better score than the respective controls (p ≤ 0.05). With regards to texture and appearance attributes, the treatment seems to have had a significant (p ≤ 0.05) effect, making the treated samples more compact and opaque than controls, therefore resulting in the loss of the characteristics of raw fish for the treated samples. Moreover, from a chemical point of view, HP treatment prevents the development of volatile sulfides and delays the formation of histamine (p ≤ 0.05). Very interestingly, the metabolomic approach revealed novel dipeptide markers for the HP procedure.

Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety

The last two decades saw a steady increase of high hydrostatic pressure (HHP) used for treatment of foods. Although the science of biomaterials exposed to high pressure started more than a century ago, there still seem to be a number of unanswered questions regarding safety of foods processed using HHP. This review gives an overview on historical development and fundamental aspects of HHP, as well as on potential risks associated with HHP food applications based on available literature. Beside the combination of pressure and temperature, as major factors impacting inactivation of vegetative bacterial cells, bacterial endospores, viruses, and parasites, factors, such as food matrix, water content, presence of dissolved substances, and pH value, also have significant influence on their inactivation by pressure. As a result, pressure treatment of foods should be considered for specific food groups and in accordance with their specific chemical and physical properties. The pressure necessary for inactivation of viruses is in many instances slightly lower than that for vegetative bacterial cells; however, data for food relevant human virus types are missing due to the lack of methods for determining their infectivity. Parasites can be inactivated by comparatively lower pressure than vegetative bacterial cells. The degrees to which chemical reactions progress under pressure treatments are different to those of conventional thermal processes, for example, HHP leads to lower amounts of acrylamide and furan. Additionally, the formation of new unknown or unexpected substances has not yet been observed. To date, no safety-relevant chemical changes have been described for foods treated by HHP. Based on existing sensitization to non-HHP-treated food, the allergenic potential of HHP-treated food is more likely to be equivalent to untreated food. Initial findings on changes in packaging materials under HHP have not yet been adequately supported by scientific data.

Unravelling the Molecular Mechanisms Underlying the Protective Effect of Lactate on the High-Pressure Resistance of Listeria monocytogenes

Formulations with lactate as an antimicrobial and high-pressure processing (HPP) as a lethal treatment are combined strategies used to control L. monocytogenes in cooked meat products. Previous studies have shown that when HPP is applied in products with lactate, the inactivation of L. monocytogenes is lower than that without lactate. The purpose of the present work was to identify the molecular mechanisms underlying the piezo-protection effect of lactate. Two L. monocytogenes strains (CTC1034 and EGDe) were independently inoculated in a cooked ham model medium without and with 2.8% potassium lactate. Samples were pressurized at 400 MPa for 10 min at 10 °C. Samples were subjected to RNA extraction, and a shotgun transcriptome sequencing was performed. The short exposure of L. monocytogenes cells to lactate through its inoculation in a cooked ham model with lactate 1h before HPP promoted a shift in the pathogen’s central metabolism, favoring the metabolism of propanediol and ethanolamine together with the synthesis of the B12 cofactor. Moreover, the results suggest an activated methyl cycle that would promote modifications in membrane properties resulting in an enhanced resistance of the pathogen to HPP. This study provides insights on the mechanisms developed by L. monocytogenes in response to lactate and/or HPP and sheds light on the understanding of the piezo-protective effect of lactate.

Analysis of temporal gene regulation of Listeria monocytogenes revealed distinct regulatory response modes after exposure to high pressure processing

BACKGROUND

The pathogen Listeria (L.) monocytogenes is known to survive heat, cold, high pressure, and other extreme conditions. Although the response of this pathogen to pH, osmotic, temperature, and oxidative stress has been studied extensively, its reaction to the stress produced by high pressure processing HPP (which is a preservation method in the food industry), and the activated gene regulatory network (GRN) in response to this stress is still largely unknown.

RESULTS

We used RNA sequencing transcriptome data of L. monocytogenes (ScottA) treated at 400 MPa and 8∘C, for 8 min and combined it with current information in the literature to create a transcriptional regulation database, depicting the relationship between transcription factors (TFs) and their target genes (TGs) in L. monocytogenes. We then applied network component analysis (NCA), a matrix decomposition method, to reconstruct the activities of the TFs over time. According to our findings, L. monocytogenes responded to the stress applied during HPP by three statistically different gene regulation modes: survival mode during the first 10 min post-treatment, repair mode during 1 h post-treatment, and re-growth mode beyond 6 h after HPP. We identified the TFs and their TGs that were responsible for each of the modes. We developed a plausible model that could explain the regulatory mechanism that L. monocytogenes activated through the well-studied CIRCE operon via the regulator HrcA during the survival mode.

CONCLUSIONS

Our findings suggest that the timely activation of TFs associated with an immediate stress response, followed by the expression of genes for repair purposes, and then re-growth and metabolism, could be a strategy of L. monocytogenes to survive and recover extreme HPP conditions. We believe that our results give a better understanding of L. monocytogenes behavior after exposure to high pressure that may lead to the design of a specific knock-out process to target the genes or mechanisms. The results can help the food industry select appropriate HPP conditions to prevent L. monocytogenes recovery during food storage.

High pressure processing combined with selected hurdles: Enhancement in the inactivation of vegetative microorganisms

High pressure processing (HPP) as a nonthermal processing (NTP) technology can ensure microbial safety to some extent without compromising food quality. However, for vegetative microorganisms, the existence of pressure-resistant subpopulations, the revival of sublethal injury (SLI) state cells, and the resuscitation of viable but nonculturable (VBNC) state cells may constitute potential food safety risks and pose challenges for the further development of HPP application. HPP combined with selected hurdles, such as moderately elevated or low temperature, low pH, natural antimicrobials (bacteriocin, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils), or other NTP (CO₂ , UV-TiO₂ photocatalysis, ultrasound, pulsed electric field, ultrafiltration), have been highlighted as feasible alternatives to enhance microbial inactivation (synergistic or additive effect). These combinations can effectively eliminate the pressure-resistant subpopulation, reduce the population of SLI or VBNC state cells and inhibit their revival or resuscitation. This review provides an updated overview of the microbial inactivation by the combination of HPP and selected hurdles and restructures the possible inactivation mechanisms.

The effect of isostatic pressing on the quality indicators of plant products (the example of Lonicera Caerulea L.)

The results of studying quality indicators (organoleptic, physicochemical, microbiological) puree from the fruits of Lonicera caerulea L. (blue honeysuckle) before and after pressure treatment are presented. It was found that organoleptic and microbiological indicators meet the requirements established by the standard for these products. The content of organic acids in the puree during processing increases due to an increase in the level of lactic acid as a result of the destruction of sugars. The amount of vitamin C and sugars is reduced slightly. The content of anthocyanins undergoes the greatest changes, the amount of which decreases to a greater extent compared with other studied substances.

Matrix- and Technology-Dependent Stability and Bioaccessibility of Strawberry Anthocyanins during Storage

Anthocyanins are often associated with health benefits. They readily degrade during processing and storage but are also dependent on the matrix conditions. This study investigated how strawberry anthocyanins are affected by preservation technologies and a relatively protein-rich kale juice addition during storage. A strawberry–kale mix was compared to a strawberry–water mix (1:2 wt; pH 4), untreated, thermally, pulsed electric fields (PEF) and high-pressure processing (HPP) treated, and evaluated for anthocyanin stability and bioaccessibility during refrigerated storage. The degradation of strawberry anthocyanins during storage followed first-order kinetics and was dependent on the juice system, preservation technology and anthocyanin structure. Generally, the degradation rate was higher for the strawberry–kale mix compared to the strawberry–water mix. The untreated sample showed the highest degradation rate, followed by HPP, PEF and, then thermal. The relative anthocyanin bioaccessibility after gastric digestion was 10% higher for the thermally and PEF treated samples. Anthocyanin bioaccessibility after intestinal digestion was low due to instability at a neutral pH, especially for the strawberry–kale mix, and after thermal treatment. The storage period did not influence the relative bioaccessibility; yet, the absolute content of bioaccessible anthocyanins was decreased after storage. This research further presents that processing and formulation strongly affect the stability and bioaccessibility of anthocyanins during storage.

Use of UHPH to Obtain Juices With Better Nutritional Quality and Healthier Wines With Low Levels of SO2

Ultra-high pressure homogenization (UHPH) is a high pressure technique in which a fluid is pressurized by pumping at higher than 200 MPa and instantaneously depressurized at atmospheric pressure across a special valve. The full process takes <0.2 s and the in-valve time is <0.02 s. In the valve, extremely intense impacts and shear forces produce the nanofragmentation of biological tissue at a range of 100-300 nm. The antimicrobial effect is highly effective, reaching easily inactivation levels higher than 6-log cycles even at low in-valve temperatures. At in-valve temperatures of 140-150°C (0.02 s) the destruction of thermoresistant spores is possible. Even when the temperature in-valve can be elevated (70-150°C), it can be considered a gentle technology because of the tremendously short processing time. It is easy to get outlet temperatures after valve of 20-25°C by the expansion and assisted by heat exchangers. Thermal markers as hydroxymethylfurfural (HMF) are not formed, nor are deleterious effects observed in sensitive compounds as terpenes or anthocyanins, probably because of the low effect in covalent bonds of small molecules of the high-pressure techniques compared with thermal technologies. Additionally, intense inactivation of oxidative enzymes is observed, therefore protecting the sensory and nutritional quality of fruit juices and avoiding or reducing the use of antioxidants as sulphites. UHPH can be consider a powerful and highly effective continuous and sterilizing technology without thermal repercussions, able to keep fresh juices with most of their initial sensory and nutritional quality and allowing high-quality and natural fermented derivatives as wine.

Non-thermal technologies: Solution for hazardous pesticides reduction in fruits and vegetables

Pesticide residues in the food above the maximum permissible residual limit (MRL) for safe consumption are a severe concern today. Though unit operations employed in domestic and industrial-scale processing of foods such as high-temperature decontamination and chemical washings degrade the agrochemicals and reduce toxicity, eliminating pesticides from the fresh and raw fruits and vegetables with the retainment of nutritional and organoleptic attributes demand appropriate non-thermal technologies. In this review, the potential of novel technologies like the pulsed electric field, high-pressure processing, irradiation, ozone, ultrasonication, and cold plasma for the reduction of pesticides in fruits and vegetables have been discussed in terms of their mechanism of action, playing around factors, advantages, and limitations. All the reviewed non-thermal technologies exhibited promising effects on pesticide degradation with their unique mechanism of action. Also, these techniques' potential to reduce the pesticides below MRLs and yield nontoxic metabolites in fruits and vegetables were analyzed. However, investigating the impact of the technologies on the nutritional and organoleptic quality profile of the commodities at the processing conditions causing noticeable pesticide reduction and the pathways of degradation reactions of various pesticides with each emerging technology should be studied to enhance the applicability.

High-pressure processing of meat: Molecular impacts and industrial applications

High-pressure processing (HPP) has been the most adopted nonthermal processing technology in the food industry with a current ever-growing implementation, and meat products represent about a quarter of the HPP foods. The intensive research conducted in the last decades has described the molecular impacts of HPP on microorganisms and endogenous meat components such as structural proteins, enzyme activities, myoglobin and meat color chemistry, and lipids, resulting in the characterization of the mechanisms responsible for most of the texture, color, and oxidative changes observed when meat is submitted to HPP. These molecular mechanisms with major effect on the safety and quality of muscle foods are comprehensively reviewed. The understanding of the high pressure-induced molecular impacts has permitted a directed use of the HPP technology, and nowadays, HPP is applied as a cold pasteurization method to inactive vegetative spoilage and pathogenic microorganisms in ready-to-eat cold cuts and to extend shelf life, allowing the reduction of food waste and the gain of market boundaries in a globalized economy. Yet, other applications of HPP have been explored in detail, namely, its use for meat tenderization and for structure formation in the manufacturing of processed meats, though these two practices have scarcely been taken up by industry. This review condenses the most pertinent-related knowledge that can unlock the utilization of these two mainstream transformation processes of meat and facilitate the development of healthier clean label processed meats and a rapid method for achieving sous vide tenderness. Finally, scientific and technological challenges still to be overcome are discussed in order to leverage the development of innovative applications using HPP technology for the future meat industry.

Effect of high-pressure processing and chemical composition on lipid oxidation, aminopeptidase activity and free amino acids of Serrano dry-cured ham

Lipid oxidation and proteolysis are essential processes in Serrano dry-cured ham quality. The influence of high pressure processing (HPP) at 600 MPa for 6 min on lipid oxidation, aminopeptidase (AP) activities and free amino acids (FAA) in ripened Serrano hams of different chemical composition after 5 months at 4 °C were studied. HPP increased lipid peroxidation indexes. Composition influenced both indexes, with higher levels in hams of medium or high intramuscular fat (IMF) content and in hams of low or medium salt content or salt-in-lean ratio. HPP lowered AP activities by more than 50%. Composition also affected AP activities, with lower levels in hams of low a_w, high IMF content, low salt content or low salt-in-lean ratio. At the end of refrigerated storage, HPP only affected Arg and Tyr levels. Many of the individual FAA reached higher levels in hams of low a_w, medium or high IMF content, low or medium salt content, or low or medium salt-in-lean ratio.

Unconventional Methods of Preserving Meat Products and Their Impact on Health and the Environment

A dual objective of food storage is to retain nutritional value and safe consumption over time. As supply chains have globalized, food protection and preservation methods have advanced. However, increasing demands to cater for larger volumes and for more effective food storage call for new technologies. This paper examines promising meat preservation methods, including high pressure process, ultrasounds, pulsating electric and magnetic field, pulsed light and cold plasma. These methods not only make it possible to obtain meat and meat products with a longer shelf life, safer for health and without preservatives, but also are more environment-friendly in comparison with traditional methods. With the use of alternative methods, it is possible to obtain meat products that are microbiologically safer, whilst also high quality and free from chemical additives. Moreover, these new technologies are also more ecological, do not require large quantities of energy or water, and generate less waste.

Optimization of high pressure processing for microbial load reduction in Diospyros kaki 'Fuyu' pulp using response surface methodology

Diospyros kaki L., cv. Fuyu is a non-astringent seasonally available persimmon variety from New Zealand having short shelf life. Most of the current preservation techniques like pasteurization, spray drying etc. use high temperature for microbial inactivation, which results in quality reduction. In the present study, response surface methodology having Box-Behnken design used to explore the consequence of pressure (200-600 MPa), time (5-15 min) and temperature (20-45 °C) for controlling microbial load in fruit pulp. A mathematical model created to envision the responses, and the R² value indicated that the established model proved highly accurate in the prediction of response. The optimization process advocated non-thermal minimal processing of persimmon pulp by high pressure processing at low temperature 20 °C, 400 MPa pressure for 5 min holding time for reducing total plate count and yeast mould count.

High-pressure homogenization and high hydrostatic pressure processing of human milk: Preservation of immunological components for human milk banks

Human milk (HM) constitutes the first immunological barrier and the main source of nutrients and bioactive components for newborns. Immune factors comprise up to 10% of the protein content in HM, where antibodies are the major components (mainly IgA, IgG, and IgM). In addition, antibacterial enzymes such as lysozyme and immunoregulatory factors such as soluble cluster of differentiation 14 (sCD14) and transforming growth factor β2 (TGF-β2) are also present and play important roles in the protection of the infant's health. Donor milk processed in HM banks by Holder pasteurization (HoP; 62.5°C, 30 min) is a safe and valuable resource for preterm newborns that are hospitalized, but is reduced in major immunological components due to thermal inactivation. We hypothesized that high hydrostatic pressure (HHP) and high-pressure homogenization (HPH) are 2 processes that can be used on HM to reduce total bacteria counts while retaining immunological components. We studied the effects of HHP (400, 450, and 500 MPa for 5 min applied at 20°C) and HPH (200, 250, and 300 MPa, milk inlet temperature of 20°C) applied to mature HM, on microbiological and immunological markers (IgA, IgG, IgM, sCD14, and TGF-β2), and compared them with those of traditional HoP in HM samples from healthy donors. The HHP processing between 400 and 500 MPa at 20°C reduced counts of coliform and total aerobic bacteria to undetectable levels (<1.0 log cfu/mL) while achieving approximately 100% of immunological component retention. In particular, comparing median percentages of retention of immunological components for 450 MPa versus HoP, we found 101.5 versus 50.5% for IgA, 89.5 versus 26.0% for IgM, 104.5 versus 75.5% for IgG, 125.0 versus 72.5% for lysozyme, 50.6 versus 0.1% for sCD14, and 88.5 versus 61.1% for TGF-β2, respectively. Regarding HPH processing, at a pressure of 250 MPa and inlet temperature of 20°C, the process showed good potential to reduce coliforms to undetectable levels and total aerobic bacteria to levels slightly above those obtained by HoP. The median percentages of retention of immunological markers for HPH versus HoP were 71.5 versus 52.0%, 71.0 versus 27.0%, 104.0 versus 66.5%, and 30.9 versus 0.2%, for IgA, IgM, IgG, and sCD14, respectively; results did not significantly differ for lysozyme and TGF-β2. The HPH at 300 MPa produced higher inactivation of immunological components, similar to values achieved with HoP.

Endospore Inactivation by Emerging Technologies: A Review of Target Structures and Inactivation Mechanisms

Recent developments in preservation technologies allow for the delivery of food with nutritional value and superior taste. Of special interest are low-acid, shelf-stable foods in which the complete control or inactivation of bacterial endospores is the crucial step to ensure consumer safety. Relevant preservation methods can be classified into physicochemical or physical hurdles, and the latter can be subclassified into thermal and nonthermal processes. The underlying inactivation mechanisms for each of these physicochemical or physical processes impact different morphological or molecular structures essential for spore germination and integrity in the dormant state. This review provides an overview of distinct endospore defense mechanisms that affect emerging physical hurdles as well as which technologies address these mechanisms. The physical spore-inactivation technologies considered include thermal, dynamic, and isostatic high pressure and electromagnetic technologies, such as pulsed electric fields, UV light, cold atmospheric pressure plasma, and high- or low-energy electron beam.

Emerging strategies for the development of food industries

Undoubtedly, the food industry is undergoing a dynamic process of transformation in its continual development in order to meet the requirements and solve the great problems represented by a constantly growing global population and food claimant in both quantity and quality. In this sense, it is necessary to evaluate the technological trends and advances that will change the landscape of the food processing industry, highlighting the latest requirements for equipment functionality. In particular, it is crucial to evaluate the influence of sustainable green biotechnology-based technologies to consolidate the food industry of the future, today, and it must be done by analyzing the mega-consumption trends that shape the future of industry, which range from local sourcing to on-the-go food, to an increase in organic foods and clean labels (understanding ingredients on food labels). While these things may seem alien to food manufacturing, they have a considerable influence on the way products are manufactured. This paper reviews in detail the conditions of the food industry, and particularly analyzes the application of emerging technologies in food preservation, extraction of bioactive compounds, bioengineering tools and other bio-based strategies for the development of the food industry.

Modifying the Functional Properties of Egg Proteins Using Novel Processing Techniques: A Review

Egg proteins can be used in a wide range of food products, owing to their excellent foaming, emulsifying, and gelling properties. Another important functional property is the susceptibility of egg proteins to enzymatic hydrolysis, as protein digestion is closely related to its nutritional value. These functional properties of egg proteins are likely to be changed during food processing. Conventional thermal processing can easily induce protein denaturation and aggregation and consequently reduce the functionality of egg proteins due to the presence of heat-labile proteins. Accordingly, there is interest from the food industry in seeking novel nonthermal or low-thermal techniques that sustain protein functionality. To understand how novel processing techniques, including high hydrostatic pressure, pulsed electric fields, ionizing radiation, ultraviolet light, pulsed light, ultrasound, ozone, and high pressure homogenization, affect protein functionality, this review introduces the mechanisms involved in protein structure modification and describes the structure-functionality relationships. Novel techniques differ in their mechanisms of protein structure modification and some have been shown to improve protein functionality for particular treatment conditions and product forms. Although there is considerable industrial potential for the use of novel techniques, further studies are required to make them a practical reality, as the processing of egg proteins often involves other influencing factors, such as different pH and the presence of other food additives (for example, salts, sugar, and polysaccharides).

Effects of Killing Methods on Lipid Oxidation, Colour and Microbial Load of Black Soldier Fly (Hermetia illucens) Larvae

Black soldier fly (BSF) larvae represent a promising alternative ingredient for animal feed. Post-production processing can, however, affect their quality. This project aimed to optimize larval killing by comparing the effects on the nutritional and microbiological quality of 10 methods, i.e., blanching (B = 40 s), desiccation (D = 60 °C, 30 min), freezing (F20 = -20 °C, 1 h; F40 = -40 °C, 1 h; N = liquid nitrogen, 40 s), high hydrostatic pressure (HHP = 3 min, 600 MPa), grinding (G = 2 min) and asphyxiation (CO2 = 120 h; N2 = 144 h; vacuum conditioning, V = 120 h). Some methods affected the pH (B, asphyxiation), total moisture (B, asphyxiation and D) and ash contents (B, p < 0.001). The lipid content (asphyxiation) and their oxidation levels (B, asphyxiation and D) were also affected (p < 0.001). Killing methods altered the larvae colour during freeze-drying and in the final product. Blanching appears to be the most appropriate strategy since it minimizes lipid oxidation (primary = 4.6 ± 0.7 mg cumen hydroperoxide (CHP) equivalents/kg; secondary = 1.0 ± 0.1 mg malondialdehyde/kg), reduces microbial contamination and initiates dehydration (water content = 78.1 ± 1.0%). We propose herein, an optimized protocol to kill BSF that meet the Canadian regulatory requirements of the insect production and processing industry.