Gastric aggregation of micellar casein powders induced by high hydrostatic pressure: Effect of serum Ca2+ level

Micellar casein (MC) has a unique gastric colloidal behavior in response to Ca2+ cross-linking, and its aggregation properties are closely related to pepsin and gastric acid. In this study, MC with different levels of colloidal calcium phosphate (CCP) was obtained by high hydrostatic pressure (HHP) at different pressures, followed by spray drying to obtain the powders. Different amounts of calcium chloride (exogenous Ca2+) were added to MC powders prior to in vitro simulated digestion to investigate the effect of exogenous serum Ca2+ levels on the aggregation behavior and the structure change of curds generated in gastric tract. The results revealed that HHP induced the emergence of more Ca2+-binding sites, thus Ca2+ was more likely to bind to MC matrix with low CCP levels. Meanwhile, high serum Ca2+ level provided more opportunities to form aggregates. The Highest pressure (500 MPa) with the highest Ca2+ level (5 mM) caused the lowest solubility aggregates, which were only 30% at the end of gastric digestion (120 min), half of the control sample (0 MPa with 0.15 mM Ca2+). The results of wide-angle X-ray scattering / small-angle X-ray scattering suggested that both pepsin and gastric acid-induced aggregation via Ca2+ as a bridge. For pepsin, Ca2+ cross-linked between para-κ-casein; For gastric acid, Ca2+ recombined phosphorylation sites and caused cross-linking of casein subunits.

Ex vivo Induction of Apoptotic Mesenchymal Stem Cell by High Hydrostatic Pressure

Among promising solutions for tissue repair and wound healing, mesenchymal stem (or stromal) cells (MSCs) have been a focus of attention and have become the most clinically studied experimental cell therapy. Recent studies reported the importance of apoptosis in MSC-mediated immunomodulation, in which apoptotic MSCs (apoMSCs) were shown to be superior to living MSCs. Nowadays, high hydrostatic pressure (HHP), a physical technique that uses only fluid pressure, has been developed and applied in various bioscience fields, including biotechnology, biomaterials, and regenerative medicine, as its safe and simply operation. In the current study, we investigated the impact of HHP treatment on human bone marrow-MSC survival and proliferation. Based on the detection of executioner caspase activation, phosphatidylserine exposure, DNA fragmentation (TUNEL) and irrefutable ultrastructural morphological changes on transmission electron microscopy (TEM), our data revealed that HHP treatment induced complete apoptosis in MSCs. Notably, this technique might provide manipulated products for use in cell-based therapies as manufacturing capability expands. We hope that our findings will contribute to the improvement of MSCs or EVs in translational research development.

Time domain (TD)-NMR relaxometry as a tool to investigate the cell integrity of tomato seeds exposed to osmotic stress (OS), ultrasonication (US) and high hydrostatic pressure (HHP)

NMR relaxometry was used to investigate the proton relaxation distribution of the tomato seeds and analyze the damages of the three different processes on the cell membrane integrity of the tomato seed. Tomato seeds were subjected to osmotic stress (OS) (10, 20, 30% NaCl solutions), ultrasonication (US) (5, 10 and 20 min) and high hydrostatic pressure (HHP) (300, 400 and 500 MPa for 15 min at 20 °C). Four peaks were observed in the NMR relaxation spectra of tomato seeds due to multiexponential relation behavior of the plant cell. Each peak corresponds to different water proton compartment within the cell. According to the results, all the three treatments resulted in cell permeabilization and disruption of cellular compartmentalization. Among the treatments, HHP at 500 MPa for 15 min at 20 °C resulted in the most detrimental effect in the cell structure and OS treatment with 10% NaCl solution caused the least changes in the cell structure. In order to further analyze the extent of damage to the cell, tomato seeds exposed to OS, US and HHP were also analyzed by scanning electron microscopy (SEM). These results have demonstrated that NMR relaxometry is a useful tool to investigate the cell integrity of tomato seeds subjected to different treatments.

The protective effect of food matrices on Listeria lytic bacteriophage P100 application towards high pressure processing

The application of lytic phages as biocontrol agents is emerging as a promising strategy towards elimination or reduction of foodborne pathogens in a variety of food products. This technology is particularly advantageous for minimally processed and ready-to-eat (RTE) foods. In this study, the potential use of Listex™ P100 combined with high hydrostatic pressure (HPP), to enhance the control of Listeria monocytogenes in food was evaluated. For that, the effect of three pressures (200, 300 or 400 MPa; 5 min, 10 °C) on phage P100 stability was tested when inoculated in six different matrices: phosphate buffered saline (PBS, pH 7.4); apple juice (pH 3.41); orange/carrot nectar (pH 3.54); UHT whole milk (pH 6.73); and, two traditional Portuguese fermented products, "Serra da Estrela" cheese (pH 5.66) and "Alheira", a meat sausage (pH 6.07). The results showed that treatment at 400 MPa reduced phage titres to below the detection level in all matrices, whereas at milder pressures the survival of the phage was matrix dependent. "Alheira", "Serra da Estrela" cheese and UHT whole milk were shown to be baroprotective matrices that support phage P100 application in HHP up to 300 MPa; however, an accentuated phage inactivation was observed in apple and orange/carrot nectar, which may be related to the acidic pH values of these matrices. The initial phage load did not affect the inactivation rate during HHP processing (300 MPa, 5 min, 10 °C) in PBS, cheese, sausage or milk matrices, and the phage titres were stable in these matrices during storage at 4 °C for 28 days for milk and 60 days for "Alheira" and "Serra da Estrela" cheese. In addition, a baroprotective effect on phage stability was observed when PBS was supplemented with reducing sugars, dextrin, casein, and tween 80. In conclusion, at mild HHP treatment, phage P100 remained active in specific matrices and seems to present potential to be added in non-thermal inactivation of L. monocytogenes.

Characterization of amorphous granular starches prepared by high hydrostatic pressure (HHP)

Amorphous granular starches (AGS) and non-granular amorphous starches (non-AGS) of corn, tapioca and rice were prepared using high hydrostatic pressure (HHP) treatment with ethanol and water washing, respectively and their physicochemical properties were investigated. Water holding capacity and apparent viscosity of AGS and non-AGS were higher than those of native one in all starches. In RVA pasting properties, AGS and non-AGS showed higher pasting temperature and lower peak viscosity than those of native one. Furthermore, non-AGS showed distinctively lower peak viscosity compared to that of AGS possibly due to its non-granular structure. Apparent viscosity of non-AGS revealed relatively lower than commercial pre-gelatinized starch because of heat and pressure-induced gelatinization. Maintaining granular structure in HHP treated pre-gelatinized starch provide a distinctive physicochemical characteristics compared to native starch and preparation of gelatinized starch with different gelatinization and washing methods could cause big differences in their physicochemical properties.

Antibodies under pressure: A Small-Angle X-ray Scattering study of Immunoglobulin G under high hydrostatic pressure

In the present work two subclasses of the human antibody Immunoglobulin G (IgG) have been investigated by Small-Angle X-ray Scattering under high hydrostatic pressures up to 5kbar. It is shown that IgG adopts a symmetric T-shape in solution which differs significantly from available crystal structures. Moreover, high-pressure experiments verify the high stability of the IgG molecule. It is not unfolded by hydrostatic pressures of up to 5kbar but a slight increase of the radius of gyration was observed at elevated pressures.

High hydrostatic pressure effects on Listeria monocytogenes and L. innocua: Evidence for variability in inactivation behaviour and in resistance to pediocin bacHA-6111-2

The effect of high hydrostatic pressure (HHP) on the survival of 14 strains of Listeria monocytogenes from food or clinical origins, selected to represent different pheno and genotypes, was evaluated. Stationary phase cells were submitted to 300, 400 and 500 MPa at 10 °C, for 5 min. A high variability in the resistance of L. monocytogenes to pressure was observed, and particularly two strains isolated from food were significantly more baroresistant than the rest. Strains of L. monocytogenes resistant to one or more antibiotics exhibited significantly higher levels of survival after the high pressure treatment at 400 MPa. No correlation was found between strains' origin or thermal tolerance and resistance to HHP. The suitability of two strains of L. innocua as surrogates of L. monocytogenes, was also investigated. These exhibited significantly higher sensitivities to HHP than observed for some L. monocytogenes. The antimicrobial effect of the antilisterial bacteriocin (bacHA-6111-2) increased after L. monocytogenes cells had been exposed to pressure. The data obtained underlines the importance of strain selection for studies aiming to evaluate HHP efficacy to ensure safety of HHP-treated foods.