Effects of High-Pressure Processing (HPP) on Bacterial Spores: An Overview

High-pressure-induced viable but non-culturable lactic acid bacteria inhibit its post-acidification

Inhibiting post-acidification while preserving viable probiotics in lactic acid bacteria (LAB) fermentation is pivotal to preserving quality and probiotic benefits. In this study, following high-pressure processing (HPP) at 400 and 500 MPa for 600 s, Lactiplantibacillus plantarum entered the viable but non-culturable (VBNC) state. Resuscitation curves, pH levels, acid generation, and glucose metabolism were monitored at 4 °C. VBNC L. plantarum began resuscitation on Day 6 and reached stationary phase by Days 24-27. Glucose metabolism decreased significantly, with no detectable pH drop or acid production, indicating post-acidification was delayed by at least 24 days. Mechanistic insights revealed that post-acidification inhibition was due to HPP-disrupted riboflavin metabolism, related to the cellular respiratory chain and downgraded ATP-depended biosynthesis of NADH, a key coenzyme for lactic acid production. Ultimately, HPP-induced VBNC L. plantarum effectively prevented post-acidification and preserved alive L. plantarum in fermented tomato sauce, verified its ability in real foods.

High pressure processing at different hydration levels as a tool to enhance rice bran stability and techno-functionality

High-pressure processing (HPP) enhances food safety and shelf life by inactivating microorganisms and preserving food quality, yet its effectiveness in low-humidity environments has not been evaluated. This study investigated the effects of HPP at 500 MPa for 15 min across varying hydration levels (15, 30, 60, 77 %) on rice bran (RB), aiming to identify microbial effectiveness, besides techno-functional and physicochemical properties. HPP effectively reduced mesophilic bacteria, molds and yeast of RB at > 15 % hydration level, achieving reductions of up to 4 logarithmic cycles in the latter, nearing the detection limit of the method. However, it did not significantly impact spore inactivation. HPP treatment of ≥ 30 % hydrated RB induced particles aggregation and a honeycomb formation. The interaction between hydration and HPP treatment significantly affected the distribution of total dietary fibers, with an increase in soluble dietary fiber from 8.73 g/100 g to 11.03 g/100 g after HPP treatment at 15 % hydration level. Protein solubility was enhanced by hydration (15, 30 and 60 %), and peroxide values decreased after HPP treatment at low hydration (≤30 %) but increased when applied to high hydrated (>30 %) RB. Emulsifying activity decreased upon HPP treatment of highly hydrated RB (≥60 %), but more stable emulsions were achieved after HPP, regardless of the hydration level. Therefore, this study highlights the potential of HPP as a sustainable approach to enhance the utilization of rice bran in food applications, addressing existing knowledge gaps regarding its processing under different moisture conditions.

Characterization and Genome Study of a Newly Isolated Temperate Phage Belonging to a New Genus Targeting Alicyclobacillus acidoterrestris

The spoilage of juices by Alicyclobacillus spp. remains a serious problem in industry and leads to economic losses. Compounds such as guaiacol and halophenols, which are produced by Alicyclobacillus, create undesirable flavors and odors and, thus, decrease the quality of juices. The inactivation of Alicyclobacillus spp. constitutes a challenge because it is resistant to environmental factors, such as high temperatures, and active acidity. However, the use of bacteriophages seems to be a promising approach. In this study, we aimed to isolate and comprehensively characterize a novel bacteriophage targeting Alicyclobacillus spp. The Alicyclobacillus phage strain KKP 3916 was isolated from orchard soil against the Alicyclobacillus acidoterrestris strain KKP 3133. The bacterial host's range and the effect of phage addition at different rates of multiplicity of infections (MOIs) on the host's growth kinetics were determined using a Bioscreen C Pro growth analyzer. The Alicyclobacillus phage strain KKP 3916, retained its activity in a wide range of temperatures (from 4 °C to 30 °C) and active acidity values (pH from 3 to 11). At 70 °C, the activity of the phage decreased by 99.9%. In turn, at 80 °C, no activity against the bacterial host was observed. Thirty minutes of exposure to UV reduced the activity of the phages by almost 99.99%. Based on transmission-electron microscopy (TEM) and whole-genome sequencing (WGS) analyses, the Alicyclobacillus phage strain KKP 3916 was classified as a tailed bacteriophage. The genomic sequencing revealed that the newly isolated phage had linear double-stranded DNA (dsDNA) with sizes of 120 bp and 131 bp and 40.3% G+C content. Of the 204 predicted proteins, 134 were of unknown function, while the remainder were annotated as structural, replication, and lysis proteins. No genes associated with antibiotic resistance were found in the genome of the newly isolated phage. However, several regions, including four associated with integration into the bacterial host genome and excisionase, were identified, which indicates the temperate (lysogenic) life cycle of the bacteriophage. Due to the risk of its potential involvement in horizontal gene transfer, this phage is not an appropriate candidate for further research on its use in food biocontrol. To the best of our knowledge, this is the first article on the isolation and whole-genome analysis of the Alicyclobacillus-specific phage.

Encapsulation of Nutraceuticals in Yoghurt and Beverage Products Using the Ultrasound and High-Pressure Processing Technologies

Dairy and beverage products are considered highly nutritious. The increase demand for added nutritional benefits within the food systems consumed by the consumers paves the pathway towards fortifying nutraceuticals into these products. However, nutraceuticals are highly unstable towards harsh processing conditions. In addition, the safety of dairy and beverage products plays a very important role. Therefore, various heat treatments are in practice. As the heat-treated dairy and beverage products tends to illustrate several alterations in their organoleptic characteristics and nutritional properties, the demand for alternative non-thermal processing technologies has increased extensively within the food industry. Ultrasound and high-pressure processing technologies are desirable for this purpose as well as a safe and non-destructive technology towards encapsulation of nutraceuticals into food systems. There are benefits in implementing these two technologies in the production of dairy and beverage products with encapsulants, such as manufacturing high-quality products with improved nutritional value while simultaneously enhancing the sensory characteristics such as flavour, taste, texture, and colour and attaining the microbial quality. The primary objective of this review is to provide detailed information on the encapsulation of nutraceuticals and mechanisms involved with using US and HPP technologies on producing encapsulated yoghurt and beverage products.

Selective Survival of Protective Cultures during High-Pressure Processing by Leveraging Freeze-Drying and Encapsulation

High-Pressure Processing’s (HPP) non-thermal inactivation of cells has been largely incompatible with food products in which the activity of selected cultures is intended (e.g., bio-preservation). This work aims to overcome this limitation using a cocoa butter encapsulation system for freeze-dried cultures that can be integrated with HPP technology with minimal detrimental effects on cell viability or activity capabilities. Using commercially available freeze-dried protective cultures, the desiccated cells survived HPP (600 MPa, 5 °C, 3 min) and subsequently experienced a 0.66-log increase in cell counts during 2 h of incubation. When the same culture was rehydrated prior to HPP, it underwent a >6.07-log decrease. Phosphate-buffered saline or skim milk inoculated with cocoa butter-encapsulated culture up to 24 h before HPP displayed robust cell counts after HPP and subsequent plating (8.37−9.16 CFU/mL). In addition to assessing viability following HPP, the study sought to test the applicability in a product in which post-HPP fermentation is desired While HPP-treated encapsulated cultures initially exhibited significantly delayed fermentative processes compared to the positive controls, by 48 h following inoculation, the HPP samples’ pH values bore no significant difference from those of the positive controls (encapsulated samples: pH 3.83 to 3.92; positive controls: pH 3.81 to 3.85). The HPP encapsulated cultures also maintained high cell counts throughout the fermentation (≥8.95 log CFU/mL).

Peanut Butter Food Safety Concerns-Prevalence, Mitigation and Control of Salmonella spp., and Aflatoxins in Peanut Butter

Peanut butter has a very large and continuously increasing global market. The food safety risks associated with its consumption are also likely to have impacts on a correspondingly large global population. In terms of prevalence and potential magnitude of impact, contamination by Salmonella spp., and aflatoxins, are the major food safety risks associated with peanut butter consumption. The inherent nature of the Salmonella spp., coupled with the unique chemical composition and structure of peanut butter, present serious technical challenges when inactivating Salmonella spp. in contaminated peanut butter. Thermal treatment, microwave, radiofrequency, irradiation, and high-pressure processing all are of limited efficacy in inactivating Salmonella spp. in contaminated peanut butter. The removal of aflatoxins in contaminated peanut butter is equally problematic and for all practical purposes almost impossible at the moment. Adopting good manufacturing hygiene practices from farm to table and avoiding the processing of contaminated peanuts are probably some of the few practically viable strategies for minimising these peanut butter food safety risks. The purpose of this review is to highlight the nature of food safety risks associated with peanut butter and to discuss the effectiveness of the initiatives that are aimed at minimising these risks.

Role of Pascalization in Milk Processing and Preservation: A Potential Alternative towards Sustainable Food Processing

Renewed technology has created a demand for foods which are natural in taste, minimally processed, and safe for consumption. Although thermal processing, such as pasteurization and sterilization, effectively limits pathogenic bacteria, it alters the aroma, flavor, and structural properties of milk and milk products. Nonthermal technologies have been used as an alternative to traditional thermal processing technology and have the ability to provide safe and healthy dairy products without affecting their nutritional composition and organoleptic properties. Other than nonthermal technologies, infrared spectroscopy is a nondestructive technique and may also be used for predicting the shelf life and microbial loads in milk. This review explains the role of pascalization or nonthermal techniques such as high-pressure processing (HPP), pulsed electric field (PEF), ultrasound (US), ultraviolet (UV), cold plasma treatment, membrane filtration, micro fluidization, and infrared spectroscopy in milk processing and preservation.

Bacillus spore germination at moderate high pressure: A review on underlying mechanisms, influencing factors, and its comparison with nutrient germination

Spore-forming bacteria are resistant to stress conditions owing to their ability to form highly resistant dormant spores. These spores can survive adverse environmental conditions in nature, as well as decontamination processes in the food and related industries. Bacterial spores may return to their vegetative state through a process called germination. As spore germination is critical for the loss of resistance, outgrowth, and development of pathogenicity and spoilage potential, the germination pathway has piqued the interest of the scientific community. The inhibition and induction of germination have critical applications in the food industry. Targeted germination can aid in decreasing the resistance of spores and allow the application of milder inactivation procedures. This germination-inactivation strategy allows better maintenance of important food quality attributes. Different stimuli are reported to trigger germination. Among those, isostatic high pressure (HP) has gained increasing attention due to its potential applications in industrial processes. However, pressure-mediated spore germination is extremely heterogeneous as some spores germinate rapidly, while others exhibit slow germination or do not undergo germination at all. The successful and safe implementation of the germination-inactivation strategy, however, depends on the germination of all spores. Therefore, there is a need to elucidate the mechanisms of HP-mediated germination. This work aimed to critically review the current state of knowledge on Bacillus spore germination at a moderate HP of 50-300 MPa. In this review, the germination mechanism, heterogeneity, and influencing factors have been outlined along with knowledge gaps.

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.

Effect of production process and high-pressure processing on viability of Listeria innocua in traditional Italian dry-cured coppa

In this study the effect of the application of High Pressure Treatment (HPP) combined with four different manufacturing processes on the inactivation of Listeria innocua, used as a surrogate for L. monocytogenes, in artificially contaminated coppa samples was evaluated in order to verify the most suitable strategy to meet the Listeria inactivation requirements needed for the exportation of dry-cured meat in the U.S. Fresh anatomical cuts intended for coppa production were supplied by four different delicatessen factories located in Northern Italy. Raw meat underwent experimental contamination with Listeria innocua using a mixture of 5 strains. Surface contamination of the fresh anatomical cuts was carried out by immersion into inoculum containing Listeria spp. The conditions of the HPP treatment were: pressure 593 MPa, time 290 seconds, water treatment temperature 14°C. Listeria innocua was enumerated on surface and deep samples post contamination, resting, ripening and HPP treatment. The results of this study show how the reduction of the microbial load on coppa during the production process did not vary among three companies (P>0.05) ranging from 3.73 to 4.30 log CFU/g, while it was significantly different (P<0.01) for the fourth company (0.92 log CFU/g). HPP treatment resulted in a significant (P<0.01) deep decrease of L.innocua count with values ranging between 1.63-3.54 log CFU/g with no significant differences between companies. Regarding superficial contamination, HPP treatment resulted significant (P<0.01) only in Coppa produced by two companies. The results highlight that there were processes less effective to inhibit the pathogen; in particular for company D an increase of L. innocua count was shown during processing and HPP alone cannot be able to in reaching the Listeria inactivation requirements needed for exportation of dry-cured meat in the U.S. According to the data reported in this paper, HPP treatment increases the ability of the manufacturing process of coppa in reducing Listeria count with the objective of a lethality treatment.

Effects of high hydrostatic pressure on the microbial inactivation and extraction of bioactive compounds from açaí (Euterpe oleracea Martius) pulp

The aim of this study was to investigate the effects of high hydrostatic pressure (HHP) on the inactivation of Lactobacillus fructivorans, on the inactivation of Alicyclobacillus acidoterrestris spores and on the extraction of anthocyanins and total phenolics from açaí pulp. The tested conditions comprised pressures of 400-600 MPa, treatment times of 5-15 min, and temperatures of 25 °C and 65 °C. Results were compared to those of conventional thermal treatments (85 °C/1 min). Regarding A. acidoterrestris spores, applying HHP for 13.5 min, resulted in a value of four-decimal reduction. L. fructivorans presented considerable sensitivity to HHP treatment, achieving inactivation rates above 6.7 log cycles at process conditions at 600 MPa and 65 °C for 5 min. All samples of açaí pulp processed showed absence of thermotolerant coliforms during the 28 days of refrigerated storage (shelf life study). The açaí pulps processed by HHP (600 MPa/5 min/25 °C) had anthocyanin extraction increased by 37% on average. In contrast, conventional thermal treatment reduced anthocyanin content by 16.3%. For phenolic compounds, the process at 600 MPa/5 min/65 °C increases extraction by 10.25%. A combination of HHP treatment and moderate heat (65 °C) was shown to be an alternative to thermal pasteurization, leading to microbiologically safe products while preserving functional compounds.

Inactivation of Microorganisms in Foods by Ohmic Heating: A Review

Ohmic heating (OH) is an alternative food processing technology for effectively inactivating microorganisms that depends on the heat that has been generated when electrical current passes directly through food material. The advantages of OH for microbial inactivation include shorter heating time, more uniform heat distribution inside food, reduced nutrition losses, and higher energy efficiency. This review presents some published information regarding the inactivation of microorganisms by OH, including the major factors that influence the inactivation effectiveness of OH, the inactivation of vegetative cells and spores in foods by OH, the inactivation mechanisms of OH, and the challenges and prospects of OH for food processing. This information will improve the understanding of OH for inactivation of microorganisms and promote the application of OH in the food industry.

Main Groups of Microorganisms of Relevance for Food Safety and Stability

Microbiology is important to food safety, production, processing, preservation, and storage. Microbes such as bacteria, molds, and yeasts are employed for the foods production and food ingredients such as production of wine, beer, bakery, and dairy products. On the other hand, the growth and contamination of spoilage and pathogenic microorganisms is considered as one of the main causes to loss of foodstuff nowadays. Although technology, hygienic strategies, and traceability are important factors to prevent and delay microbial growth and contamination, food remains susceptible to spoilage and activity of pathogen microorganisms. Food loss by either spoilage or contaminated food affects food industry and consumers leading to economic losses and increased hospitalization costs. This chapter focuses on general aspects, characteristics, and importance of main microorganisms (bacteria, yeasts, molds, virus, and parasites) involved in food spoilage or contamination: known and recently discovered species; defects and alterations in foodstuff; most common food associated with each foodborne disease; resistance to thermal processing; occurrence in different countries; outbreaks; and associated symptoms.

Identification of Microorganisms in Duck Meat Products Available in Korea and the Effect of High Hydrostatic Pressure

The objective of this study was to investigate the microbial count of duck meat and duck meat products commercially available in Korea. High hydrostatic pressure (HHP) treatment was applied at 0.1, 300, 400, and 500 MPa for 5 min to enhance the microbiological safety of duck meats. The levels of total aerobic bacteria were in the ranges of 3.53-6.19 and 3.62-6.85 Log CFU/g in raw and smoked duck products, respectively. By DNA sequence analysis, we identified microorganisms responsible for spoilage, with the most common species in the raw and smoked duck products being Aeromonas spp. or Pseudomonas spp. and Leuconostoc mesenteroides, respectively. HHP treatment significantly reduced the levels of total aerobic bacteria in raw and smoked duck products. This study demonstrates that HHP treatment may be used to effectively improve the safety of raw and smoked duck meat products.

Combined effects of high pressure processing and addition of soy sauce and olive oil on safety and quality characteristics of chicken breast meat

This study was conducted to evaluate the combined effect of high pressure (HP) with the addition of soy sauce and/or olive oil on the quality and safety of chicken breast meats. Samples were cut into 100 g pieces and 10% (w/w) of soy sauce (SS), 10% (w/w) of olive oil (OO), and a mixture of both 5% of soy sauce and 5% olive oil (w/w) (SO) were pressurized into meat with high pressure at 300 or 600 MPa. Cooking loss was lower in OO samples than SS samples. With increased pressure to 600 MPa, the oleic acid content of OO samples increased. The total unsaturated fatty acids were the highest in SO and OO 600 MPa samples. Lipid oxidation was retarded by addition of olive oil combined with HP. The addition of olive oil and soy sauce followed by HP decreased the amount of volatile basic nitrogen during storage and reduced the population of pathogens. Sensory evaluation indicated that the addition of olive oil enhanced the overall acceptance and willingness to buy. In conclusion, the combination of HP with the addition of soy sauce and/or olive oil is an effective technology that can improve chemical, health, sensory qualities and safety of chicken breast.

Effect of high-pressure processing on reduction of Listeria monocytogenes in packaged Queso Fresco

The effect of high-hydrostatic-pressure processing (HPP) on the survival of a 5-strain rifampicin-resistant cocktail of Listeria monocytogenes in Queso Fresco (QF) was evaluated as a postpackaging intervention. Queso Fresco was made using pasteurized, homogenized milk, and was starter-free and not pressed. In phase 1, QF slices (12.7 × 7.6 × 1 cm), weighing from 52 to 66 g, were surface inoculated with L. monocytogenes (ca. 5.0 log10 cfu/g) and individually double vacuum packaged. The slices were then warmed to either 20 or 40°C and HPP treated at 200, 400, and 600 MPa for hold times of 5, 10, 15, or 20 min. Treatment at 600 MPa was most effective in reducing L. monocytogenes to below the detection level of 0.91 log10 cfu/g at all hold times and temperatures. High-hydrostatic-pressure processing at 40°C, 400 MPa, and hold time ≥ 15 min was effective but resulted in wheying-off and textural changes. In phase 2, L. monocytogenes was inoculated either on the slices (ca. 5.0 log10 cfu/g; ON) or in the curds (ca. 7.0 log10 cfu/g; IN) before the cheese block was formed and sliced. The slices were treated at 20°C and 600 MPa at hold times of 3, 10, and 20 min, and then stored at 4 and 10°C for 60 d. For both treatments, L. monocytogenes became less resistant to pressure as hold time increased, with greater percentages of injured cells at 3 and 10 min than at 20 min, at which the lethality of the process increased. For the IN treatment, with hold times of 3 and 10 min, growth of L. monocytogenes increased the first week of storage, but was delayed for 1 wk, with a hold time of 20 min. Longer lag times in growth of L. monocytogenes during storage at 4°C were observed for the ON treatment at hold times of 10 and 20 min, indicating that the IN treatment may have provided a more protective environment with less injury to the cells than the ON treatment. Similarly, HPP treatment for 10 min followed by storage at 4°C was the best method for suppressing the growth of the endogenous microflora with bacterial counts remaining below the level of detection for 2 out of the 3 QF samples for up to 84 d. Lag times in growth were not observed during storage of QF at 10°C. Although HPP reduced L. monocytogenes immediately after processing, a second preservation technique is necessary to control growth of L. monocytogenes during cold storage. However, the results also showed that HPP would be effective for slowing the growth of microorganisms that can shorten the shelf life of QF.