Escherichia coli in phosphate-buffered saline was treated with high hydrostatic pressures (HHPs) of 400, 500, and 600 MPa at 25 degrees C for 10 min. The cell suspension was then plated on nonselective agar and incubated at 20, 25, 30, 35, 37, and 40 degrees C to study the effect of the incubation temperatures on the detection of HHP-injured populations. The number of detected cells was maximum when incubated at 25 degrees C for 72 h. Cold storage at 4 degrees C for 7 d after HHP-treatment improved the detection efficacies of incubations at 30-40 degrees C, implicating increased tolerance of HHP-injured cells against the mild heat. Combined incubation at 25 degrees C for more than 6 h with subsequent incubation at 35 degrees C shortened total incubation period from 72 h to 24 h while achieving the maximized colony number obtained by the incubation at 25 degrees C for 72 h.

Carrot was impregnated with pigment solution by vacuum heat sealing (VS) and/or high hydrostatic pressure treatment (HHP; 100-600 MPa, 25 degrees C, 5 min). Impregnation efficacy was evaluated as impregnation ratio (%) by image analysis, while damages of cell membrane and texture were quantified by electrical impedance spectroscopy and texture analysis, respectively. Combinations of VS and HHP exclusively achieved 100% impregnation. Meanwhile, the damages were comparable between the samples after VS and VS + 100 MPa treatment and aggravated by elevated levels of HHP. As for the texture, breaking stress (hardness) decreased after VS and VS + HHP (100-600 MPa) comparably. Meanwhile, breaking strain (deformability) significantly increased after VS + HHP (200-600 MPa), indicating further damage of strain texture as compared with that after VS and VS + 100 MPa treatments. It was indicated that impregnation of carrot was fully achieved by a combination of VS and 100 MPa treatment, while minimizing the cell membrane and texture damages. Difference in the impregnation efficacy between carrot and apple was discussed based on their image data.

Raw salad vegetables are evaluated for the consumer’s perceptions on taking ready to eat fresh cut-vegetables and the effectiveness of some non-chlorine disinfectants [peracetic acid (PAA), shell powder (SP) and hydrogen peroxide (H2O2)] in improving the microbial safety, quality and shelf life of ready to eat fresh-cut vegetables (lettuce, carrot and cucumber) at ambient and refrigeration temperature. Consumer’s perception study results identified three clusters of consumers, whose preferences are related to purchasing styles and socio-demographic variables.The overall positive attitude of consumers was evident towards convenience, taste and appearance, but safety and health benefit attributes get importance while buying the ready to eat fresh-cut vegetables.The microbiological and visual observation result demonstrated that, all the non-chlorine sanitizers used were able to decrease the bacterial population in fresh-cut vegetables initially; however, microbial population increases or remain constant or decrease depending on the types of vegetables, storage temperature and duration. In addition, among the wash-sanitizers, PAA and H2O2 showed better microbial reduction for fresh-cut lettuce, and cucumber, and SP showed better microbial reduction for fresh-cut carrot. Irrespective of sanitizer treatment refrigerated storage showed better visual quality, microbial safety and shelf life of fresh-cut produce. Therefore, this study results suggested that washing fresh-cut vegetables with produce specific sanitizer and stored at refrigerated temperature keep the quality of fresh-cut produce better compared to ambient storage. Bangladesh J Microbiol, Volume 38, Number 2, December 2021, pp 51-62

In food processing, high hydrostatic pressure (HHP) can inactivate microbes, and the inactivation is either lethal or sublethal, depending on the intensity of HHP-induced stress. Inactivation of bacteria is a key to ensure food safety by HHP food processing. This manuscript reviews HHP-induced injury of bacteria such as Escherichia coli, Listeria monocytogenes, and (vegetative) Bacillus subtilis. The stress in the sublethal inactivation depends on HHP level, holding time, bacterial species/strain, and other environmental factors. The sublethal inactivation induces injury of bacteria, and the injured bacteria may recover under suitable conditions. The recovery behavior depends on nutrients surrounding the bacteria and the storage temperature. In the detection of HHP-injured bacteria, detection media and incubation temperature play important roles. Mechanisms involved in HHP-injured bacteria can be discussed from several viewpoints including membrane damage, reactive oxygen species, HHP resistance, ribosomes, metabolome, and colony-forming behavior. HHP-induced injury of molds, yeasts, parasites, and viruses has not been sufficiently studied.

High hydrostatic pressure (HHP) process as a nonthermal technology can be used to inactivate microbes while minimizing chemical reactions in food. Food industry applies HHP level of 100 MPa (986.9 atm/1019.7 kgf/cm2) and more to process foods. Thermal processes often damage food components relating to color, flavor, and nutritional value via enhancing undesired chemical reactions, whereas HHP process minimizes the damages and inactivates microbes toward high quality safe foods. The first commercial HHP-processed foods were launched in 1990 for fruit products such as jams, and then some other products have been commercialized in the world to inactivate microbes for shelf life extension and enhance water impregnation: cooked hams and sausages (shelf life extension), soy sauce with minimized salt (short-time fermentation owing to enhanced enzymatic reactions), and beverages (shelf life extension). The characteristics of HHP food processing are reviewed from viewpoints of nonthermal process, history, research and development, physical and biochemical changes, and processing equipment.

Escherichia coli cells were suspended in phosphate-buffered saline solutions (pH 7.4) at physiological (0.9 %) and hyperosmotic (3.5, 5.0, and 10.0 %) concentrations of sodium chloride (NaCl) and stored at 5, 10, 15, 20, and 25 °C up to 48 d. During storage at 5 and 10 °C, viable cell counts decreased approximately from 9 log CFU/ml to 6-7 log CFU/ml, and NaCl showed slight protective effect on the decrease. When stored at 15, 20, and 25 °C, the counts decreased with increases in NaCl concentration and/or storage temperature. The cells in 10.0 % NaCl suspension became nondetectable after storage at 25 °C for 28 d. Under some storage conditions (NaCl ≤ 5 %, 20 and 25 °C), the counts approached constant values, indicating possible adaptation to NaCl. Injured cells were observed at 5.0 and 10.0 % NaCl. However, recovery was observed only at 5.0 % NaCl during storage at 20 °C. In addition, more cells were detected on nonselective medium when incubated at 37 °C than at 25 °C. Higher hyperosmotic NaCl solutions at higher storage temperatures reduced more viable cells of E. coli.

食品高圧加工について，その特徴を解説しつつ，基礎および応用に関する取り組みについて概説した．基礎的視点からは，系統的理解が進んでいなかった澱粉の圧力糊化について，糊化および老化の有無を明確に示す状態図を作成し，その理解を進めた．また，微生物の高圧不活性化，とくに細菌不活性化に及ぼす高圧処理の影響を調べ，高圧殺菌の効用と限界とについての知見を拡げた．さらに，不十分な圧力での高圧処理後に残存しうる損傷菌について，保存中の回復挙動を保存温度の視点から精査し，損傷菌の検出時には，培養温度，培地組成に注意すべきことを提示した．応用的視点からは，ものづくりに役立つ技術として，中高圧処理を活用したかぶら寿しの促成製造法ならびに脱気中温中高圧処理による高圧加工果実コンポート製造法を提示した．

The increasing world population requires a sufficient production of crops and animals for food use, and the production needs to be environmentally and socially sustainable. Meat analogues made from plant, fungal, and insect proteins are expected to serve as a substitute for animal meats. Plant-derived proteins (plant proteins), which are attracting great attention, are focused on in this review as meat and dairy substitutes, since plant proteins may help mankind as a substitute for animal proteins to achieve a secure supply of proteins worldwide while also responding to the demand for plant-derived products by vegetarians and vegans. Aspects discussed in this review also include the role of soybeans as one of the key plant protein sources; its recent production in the world has been increasing due to the extended harvest area of genetically modified soybean varieties. Plant proteins can be processed by extrusion to give meat-like textures. In addition, plant proteins from soybean, wheat, and other plants have traditionally been utilized via fermentation in Japan and other Asian countries. It is expected that the fermentation methods used for those traditional plant protein foods as well as other processing technologies could be applied to produce novel foods based on plant proteins.

Lactic acid bacteria (Leuconostoc mesenteroides, Enterococcus faecalis, and Lactobacillus fermentum) were subjected to high hydrostatic pressures (HHPs) of 400 and 600MPa at 25 degrees C for 10min in phosphate-buffered saline. Differential plating methods were applied to evaluate HHP-treated cell populations, assuming that healthy and injured cells during plate incubation survived maximum and minimal stress, respectively. The stress was altered by using several selective media in combination with aerobic or anaerobic incubation at 25 degrees C or 30 degrees C. E.faecalis was detectable after 600MPa treatment while L.mesenteroides and L.fermentum were nondetectable. Specific combinations of incubation conditions were suggested to determine maximum and minimum viable counts of L.mesenteroides and E.faecalis. The difference between the maximum and minimum counts can be used to evaluate HHP-injured population with reduced risks to overestimate healthy and/or underestimate HHP-injured cells.

Spores of Bacillus subtilis suspended in water or aqueous solution of NaCl, CaCl2, sodium lactate, or calcium lactate at pH 4 - 7 was subjected to spore inactivation by simultaneous combination of medium high hydrostatic pressure (MHHP; 100 MPa) treatment for germination and medium high temperature (MHT; 65℃) treatment for pasteurization of germinated vegetative cells. The spores at pH 4 in NaCl solution and those at pH 5 and 6 in Na lactate solutions were less killed than in water by MHHP+MHT treatment. Spore inactivation was promoted by calcium ion in NaCl solution at pH 4 and in Na lactate solutions at pH 5 and pH 6, while it was more suppressed at pH 5 and pH 6 in Na lactate solutions than at pH 4 in NaCl solution. The spores treated by MHHP+MHT in NaCl or Na lactate solution at pH 4 were further killed by subsequent MHT treatment.

Mass, volume, electrical and mechanical properties of four apple cultivars after high hydrostatic pressure (HHP) treatment were investigated. Volume changes were greater than those of mass after HHP treatment. Electric properties were measured by electrical impedance spectroscopy, and their frequency dependences were analyzed using the Cole-Cole plot and cell-based electrical circuit model (modified Hayden model). The analyzed electric parameters showed differences among the cultivars, indicating cell membrane damage after HHP treatment. HHP treatment also affected the mechanical properties such as breaking stress and strain, indicating changes in cell structure. However, the mechanical properties after HHP treatment of 'Shinanogold' and 'Fuji' fruit were retained to a greater extent than those of 'Jonathan' and 'Jonagold' despite cell membrane destruction. This study is the first to reveal cultivar differences in the physical property changes after HHP treatment and their tolerances to treatment.

Cells of Listeria monocytogenes suspended in phosphate-buffered saline (PBS) were treated by high hydrostatic pressure (HHP; 500MPa, 25 degrees C, 10min), diluted by ten folds using trypticase soy broth (TSB) or PBS, and stored at cold temperatures of 0-15 degrees C. Viable cell count in TSB increased logarithmically close to the initial count at each storage temperature, while that in PBS increased temporarily and subsequently decreased to almost nondetectable level except the case at 15 degrees C, where it showed logarithmic increase thereafter. Based on proliferation experiments where their healthy cells were inoculated to TSB or to PBS containing their heat-killed dead cells, it was suggested that increase in the viable count of HHP-treated cells in TSB and PBS could be ascribed to the recovery of colony forming ability and/or proliferation depending on the cold storage temperature.

Vegetative cells of Bacillus subtilis can recover from injury after high-hydrostatic-pressure (HHP) treatment at 250 MPa. DNA microarray analysis revealed that substantial numbers of ribosomal genes and translation-related genes (e.g., translation initiation factors) were upregulated during the growth arrest phase after HHP treatment. The transcript levels of cold shock-responsive genes, whose products play key roles in efficient translation, and heat shock-responsive genes, whose products mediate correct protein folding or degrade misfolded proteins, were also upregulated. In contrast, the transcript level of hpf, whose product (Hpf) is involved in ribosome inactivation through the dimerization of 70S ribosomes, was downregulated during the growth arrest phase. Sucrose density gradient sedimentation analysis revealed that ribosomes were dissociated in a pressure-dependent manner and then reconstructed. We also found that cell growth after HHP-induced injury was apparently inhibited by the addition of Mn2+ or Zn2+ to the recovery medium. Ribosome reconstruction in the HHP-injured cells was also significantly delayed in the presence of Mn2+ or Zn2+. Moreover, Zn2+, but not Mn2+, promoted dimer formation of 70S ribosomes in the HHP-injured cells. Disruption of the hpf gene suppressed the Zn2+-dependent accumulation of ribosome dimers, partially relieving the inhibitory effect of Zn2+ on the growth recovery of HHP-treated cells. In contrast, it was likely that Mn2+ prevented ribosome reconstruction without stimulating ribosome dimerization. Our results suggested that both Mn2+ and Zn2+ can prevent ribosome reconstruction, thereby delaying the growth recovery of HHP-injured B. subtilis cells. IMPORTANCE HHP treatment is used as a nonthermal processing technology in the food industry to inactivate bacteria while retaining high quality of foods under suppressed chemical reactions. However, some populations of bacterial cells may survive the inactivation. Although the survivors are in a transient nongrowing state due to HHP-induced injury, they can recover from the injury and then start growing, depending on the postprocessing conditions. The recovery process in terms of cellular components after the injury remains unclear. Transcriptome analysis using vegetative cells of Bacillus subtilis revealed that the translational machinery can preferentially be reconstructed after HHP treatment. We found that both Mn2+ and Zn2+ prolonged the growth-arrested stage of HHP-injured cells by delaying ribosome reconstruction. It is likely that ribosome reconstruction is crucial for the recovery of growth ability in HHP-injured cells. This study provides further understanding of the recovery process in HHP-injured B. subtilis cells.

Escherichia coli cells suspended in phosphate-buffered saline (PBS) were treated by high hydrostatic pressure (HHP; 400 - 600 MPa) at 25 ℃ for 10 min and then stored at 5 - 25 ℃ . When treated at 600 MPa, the cells were inactivated lethally. Treatment at 400 and 500 MPa reduced viable cell counts by approximately 7 and 8 log, respectively. Viable counts of cells treated at 400 or 500 MPa increased obviously during storage at 15 and 25 ℃ , whereas they did not increase at 5 and 10 ℃ . Meanwhile, healthy E. coli cells inoculated to a heat-killed dead cell suspension in PBS showed drastic growth during storage at 15 and 25 ℃ , but no growth at 5 and 10 ℃ . Therefore, the obvious increase in viable counts of HHP-treated cells might be attributed to their cannibalism of the dead cells.

Greeneye (Chlorophthalmus albatrossis) in soaking liquids such as tap water, salty water (SW), vinegar water, salty vinegar water, and salty vinegar broth (SVB) was processed by medium high hydrostatic pressure at medium high temperature (MHHP+MHT; 100 MPa, 65 65 degrees C, 30 min) or high hydrostatic pressure at low temperature (HHP+LT; 600 MPa, 10 degrees C, 5 min). Both treatments sufficiently inactivated endogenous fish microflora, however MHHP+MHT treatment partly degraded the fish. The suitability of HHP+LT treatment to extend shelf life under refrigeration was further studied since this process preserved the fish shape. The fish with or without head and viscera was immersed in SW or SVB and treated by HHP+LT. Greeneye without head and viscera in SVB was processed by HHP+LT and stored for 3 months, and its suitability for deep-frying was evaluated as high in terms of microbial safety, shape, and palatability.