Sublethal High Pressure Research Articles

A chemical study of yoghurt produced under isostatic pressure during storage

Yoghurt fermented under sub-lethal high pressure (10, 20, 30 and 40 MPa at 43 °C), and afterward placed under refrigeration (4 °C for 23 days) was studied and compared with yoghurt fermented at atmospheric pressure (0.1 MPa). For a deeper analysis, metabolite fingerprinting by nuclear magnetic resonance (NMR), sugars and organic acids assessment by high performance liquid chromatography (HPLC), total fatty acids (TFA) determination and quantification by gas chromatography with a flame ionization detector (GC-FID) were performed. Metabolomic analyses revealed that only 2,3-butanediol, acetoin, diacetyl and formate vary with the increase of pressure and probable relation with pressure influenced diacetyl reductase, acetoin reductase and acetolactate decarboxylase. Yoghurts fermented at 40 MPa had the lowest content in lactose (39.7 % of total sugar reduction) and the less content in TFA (56.1 %). Further research is of interest to understand more about fermentation processes under sub-lethal high pressure.

Effects of Sub-Lethal High Pressure Homogenization Treatment on the Adhesion Mechanisms and Stress Response Genes in Lactobacillus acidophilus 08.

Cell surface hydrophobicity (CSH) and adhesion are very important phenotypical traits for probiotics that confer them a competitive advantage for the resilience in the human gastrointestinal tract. This study was aimed to understand the effects over time of a 50 MPa hyperbaric treatment on the surface properties of Lactobacillus acidophilus 08 including CSH, autoaggregation, and in vitro adhesion (mucin layer and Caco-2 cells). Moreover, a link between the hurdle applied and the expression of genes involved in the general stress response (groEL and clpP) and adhesion processes (efTu and slpA) was evaluated. High pressure homogenization (HPH) at 50 MPa significantly increased the CSH percentage (H%), autoaggregation and in vitro adhesion on mucin of L. acidophilus 08 cells compared with the untreated cells. Moreover, the hyperbaric hurdle induced an upregulation of the stress response genes groEL and ef-TU together with a down regulation of the clpP and S-layer slpA genes. Looking at the protein profile, HPH-treatment showed an increase in the number or intensity of protein bands at high and low molecular weights.

The use of different fermentative approaches on Paracoccus denitrificans: Effect of high pressure and air availability on growth and metabolism

The performance of fermentation under sub-lethal high pressure (HP) is a strategy for stimulation of microbial growth and/or improvement of fermentation titers, rates and yields. The present work intended to study the possibility of applying HP to Paracoccus denitrificans glycerol fermentation, considering that HP-fermentation usually involves some process constrains, such as limited air volumes. Consequently, the work was divided in two main goals: i) study the effects of air availability on P. denitrificans ; ii) assess if the strain is able to grow and maintain metabolic activity under HP (10–35 MPa). Paracoccus denitrificans growth and metabolism were highly affected by air availability. Samples under higher air availability showed considerable cell growth, but no production of ethanol or organic acids. On the other hand, samples without air had lower cell growth, but active metabolic activity (with the production of ethanol and organic acids). Regarding the HP experiments, P. denitrificans was able to grow at 10, 25 and 35 MPa, but to a lower extent compared to atmospheric pressure. Application of HP promoted modifications in the production of ethanol, acetate and succinate, and the fermentative profile varied according to the pressure level. Overall, the present work demonstrated new metabolic features of P. denitrificans at atmospheric pressure and HP conditions. It also opened the way for further studies regarding P. denitrificans fermentation under HP, as well as utilization of this technology for other glycerol fermentations, in particular in the case of high requirements of air availability.

A microbiological, physicochemical, and texture study during storage of yoghurt produced under isostatic pressure

This work aimed to study refrigeration storage (4 °C for 23 days) of yoghurt produced at 43 °C under sub-lethal high pressure, at 10, 20, 30 and 40 MPa, in comparison with the fermentation process at atmospheric pressure (0.1 MPa). Lactic acid bacteria (S. thermophilus and L. bulgaricus, LAB) and quality parameters like pH, titratable acidity, syneresis and colour were evaluated, along with textural analyses to infer how pressure would impact the obtained yoghurt along storage. Higher fermentation pressures resulted in slightly lower LAB loads (a maximum of 1.01 Log (CFU/mL)) and increased the fermentation time (a maximum of 3 h 25 min), syneresis (a maximum of 44%), all for 40 MPa and firmness (a maximum of 2.5-fold) for 30 MPa. Under refrigeration, LAB were more active during the first 15 days of storage in yoghurts fermented under pressure (increasing loads up to 0.54 Log (CFU/mL)). Colour, pH and titratable acidity were not affected by pressure or storage. Further research is of interest to ascertain the biotechnological potential of fermentation processes under sub-lethal high pressure in general and in particular for yoghurt production.

Utilization of glycerol during consecutive cycles of Lactobacillus reuteri fermentation under pressure: The impact on cell growth and fermentation profile

Abstract Exposure of bacterial cells to sub-lethal high pressure (HP) during growth and fermentation may promote development of new adaptive features, with potential biotechnological interest. The present work evaluated the effect of consecutive fermentation cycles under HP on Lactobacillus reuteri growth and glycerol/glucose co-fermentation. At all conditions tested (0.1, 10 and 25 MPa), 1,3-propanediol production from glycerol was enhanced over the cycles. The highest titers, yields and productivities were achieved at 10 MPa. In addition, the HP-cycles promoted shifts in by-product formation (ethanol, acetate and lactate), with different profiles according to the pressure. Ratios between 1,3-propanediol:by-products increased throughout the cycles, especially at 10 MPa, indicating shifts in metabolic selectivity. Data regarding the effects of HP-cycles on protein and nucleic acid leakage suggested that, in some cases, L. reuteri changed membrane permeability as a possible adaptation to HP. Overall, this work confirms that HP may be an useful tool to stimulate production of 1,3-propanediol, as well as other biocompounds.

Potential of high pressure homogenisation on probiotic Caciotta cheese quality and functionality

The probiotic Lactobacillus paracasei A13, treated at 50 MPa sub-lethal high pressure homogenisation (HPH), was used as adjunct for producing Caciotta cheese. The cell HPH treatment was used because it has been proven to increase the in vitro strain functionality. The starters and Lb. paracasei A13 viability, the cheese hydrolytic patterns and organoleptic profiles were monitored. After cheesemaking and during ripening, the Lb. paracasei A13 gastric acid resistance in cheese and the ability of the cheese, containing HPH-treated or untreated cells, to modulate the gut mucosal immune system in mice were evaluated. Traditional Caciotta was used as controls. The HPH-treated probiotic strain maintained high viability for 14 days whilst the physico-chemical analyses on Caciotta cheese containing HPH-treated cells showed a faster ripening, compared to other cheeses. For functional properties, the 50 MPa treatment increased the Lb. paracasei gastric resistance in Caciotta, maintaining high strain viability, but IL-10 producing capacity was lost by HPH-treatment whilst IgA production was not modified.

Pressure-Dependent Gene Activation in Yeast Cells.

Hydrostatic pressure is one of the physical factors affecting cellular physiology. Hydrostatic pressure of a few tens MPa decreases the growth rate and a few hundred MPa decreases the cellular viability. To find clues to understand how such pressure effects on living cells relating to damages on protein molecules, we employed yeast DNA microarrays and analyzed genome-wide gene-expression levels in yeast cells which have been exposed to different levels of hydrostatic pressure. These include the cells temporarily adapted to a high pressure (from 0.1 to 30MPa) and to a low pressure (from 30 to 0.1MPa). These conditions cause yeast cells decreases of growth rate. We also analyzed gene expression profiles from the cells recovering after the sublethal pressure treatment at 180MPa at 4°C for 0min and at 40MPa at 4°C for 16h. These conditions cause yeast cells decreases of cellular viability. The activated genes by the temporary adaptations to both of the high pressure and the low pressure suggest that proteins related to membrane biosynthesis and cell wall biosynthesis can be crucial targets of pressure-induced damages, whereas the activated genes under recovering conditions after exposure to the sublethal high pressure suggest that proteasome activity and proteins localized in endoplasmic reticulum can be the crucial targets or the essential factors to survive.

Effect of sub-lethal high pressure homogenization treatments on the in vitro functional and biological properties of lactic acid bacteria

The aim of this work was to assess if a sub-lethal high pressure homogenization (HPH) treatment could modulate in vitro functional and biological properties of probiotic bacteria. Lactobacillus paracasei A13, Lactobacillus acidophilus 08 and Dru, Lactobacillus delbrueckii subsp. lactis 200 and bile-resistant derivatives L. acidophilus Dru+ and L. delbrueckii subsp. lactis 200+ were suspended in phosphate buffered saline solution and treated at 50 MPa. Data obtained showed that HPH can modulate hydrophobicity and auto-aggregation without modification of viability and decarboxylase activity. Resistance to simulated gastric conditions resulted strain-dependent. High resistance was observed for treated L. paracasei A13, L. acidophilus Dru and 08 and L. delbrueckii subsp. lactis 200. The HPH-treatment reduced the resistance to simulated stomach duodenum-passage of L. acidophilus Dru while increased it for L. paracasei A13.Strain viability and resistance to simulated gastric conditions were evaluated treating at 50 MPa cells suspended in acidified buttermilk (pH 4.6) and stored at 4 °C for 30 days. The highest cell viability loss, after 30 d of refrigerated storage, was observed for L. acidophilus Dru, independently of the application of HPH. However, after 30 days of storage, the resistance of L. paracasei A13 to simulated gastric digestion significantly increased in HPH treated cells.

The role of proteasome in yeast Saccharomyces cerevisiae response to sub-lethal high pressure treatment

Hydrostatic pressure is a physical factor that can induce stress in organisms. This stress leads to growth inhibition, cellular arrest, and cellular death, and these effects depend on the degree of pressure, temperature, and sensitivity of the organisms to hydrostatic pressure. Genomics studies of yeast cells under conditions recovering from high pressure-induced cellular damage showed evidence that multiprotein complexes or membrane proteins, and not soluble proteins, are the critical targets. We performed a metabolomic analysis. The metabolomics results suggested that membrane-spanning proteins broke down after high pressure treatment and recovery conditions. We also found 13 genes that were common to essential and pressure-induced gene groups. Among these 13 genes, more than 10 were associated with proteasome structure and functions. This suggests that proteasome structure or functions can be the critical target or a highly important factor. This hypothesis is supported by the fact that yeast cells are sensitive to the proteasome inhibitor MG132 after high pressure treatment.

Characterisation of a Piezotolerant Mutant of Lactobacillus sanfranciscensis

Incubation under sublethal high pressure (50 MPa) allowed the isolation of a piezotolerant mutant of Lactobacillus sanfranciscensis. Compared to the wild type this strain showed faster growth at 50 MPa and an altered temperature-dependent growth at ambient pressure. Additionally, an altered antibiotic resistance pattern was detected. To address the molecular basis of the mutation the genotypic characterisation was focused on alterations of ribosomal components. Northern analysis using ssrA (transfer mRNA) as probe revealed a constitutive overexpression in the mutant. A 2.2 fold induction after pressure shock and increased pressure sensitivity of a ssrA-insertional mutant of L. sanfranciscensis indicate the tmRNA as genetic determinant of a piezotolerance response in the wild type. Thus, we propose trans-translation and peptide tagging, processes that promote recycling of stalled ribosomes and prevent accumulation of abortively synthesised polypeptides to be involved in combating high-pressure damage and conferring moderate piezotolerance.