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Starch gelatinization corresponds to a melting phase transition in aqueous medium. Such a transition involves important mass transfer of water. Using a high-pressure bomb including optical ports, the volume variation of starch granules in suspension was related to gelatinization during a high-pressure treatment up to 420 MPa. Microscopic observations of wheat and potato starch granules were compared with macroscopic measurements of compressibility up to 600 MPa and gelatinization intensity using differential scanning calorimetry on treated suspensions. Wheat starch gelatinization started below 300 MPa and was completely achieved at 600 MPa. Potato starch was not altered under 600 MPa. The behavior of the volume variation of starch granules under pressure compared with starch suspensions compressibility could be explained by simultaneous compression and hydration mechanisms. Keywords: Starch gelatinization; high hydrostatic pressure; image analysis

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This work studied the viabilities of five types of cells (two yeast cells, Saccharomyces cerevisiae CBS 1171 and Candida utilis; two bacterial strains, Escherichia coli and Lactobacillus plantarum; and one human leukemia K562 cell) as a function of cooling rate during freezing. The range of investigated cooling rates extended from 5 to 30,000°C/min. Cell viability was classified into three ranges: (i) high viability for low cooling rates (5 to 180°C/min), which allow cell water outflow to occur completely and do not allow any intracellular crystallization; (ii) low viability for rapid cooling rates (180 to 5,000°C/min), which allow the heat flow to prevail over water outflow (in this case, cell water crystallization would occur as water was flowing out of the cell); (iii) high viability for very high cooling rates (>5,000°C/min), which allow the heat flow to be very rapid and induce intracellular crystallization and/or vitrification before any water outflow from the cell. Finally, an assumption relating cell death to the cell water crystallization as water is flowing out of the cell is made. In addition, this general cell behavior is different for each type of cell and seems to be moderated by the cell size, the water permeability properties, and the presence of a cell wall.The freeze-thawing process remains the principal method of cell preservation to date, and the high survival rates achieved by this method are of interest from both the biophysical and practical points of view. This is to ensure that the recovery of entire cell populations is free from the risk of possible subsequent alteration of its genetic composition.Cell cryopreservation, which is commonly used in the food and pharmaceutical industries, requires optimization for each type of microorganism. Moreover, each type of cell has its own protocol for freezing. Numerous researchers have attempted to develop methods that permit 100% preservation of freezethawing of diverse cellular specimens (3, 6), but some microorganisms cannot yet be preserved by freezing.For a better cell preservation some cryoprotectants such as glycerol or dimethyl sulfoxide can be used (8). These molecules improve the cell preservation by minimizing the cell water content (6) and/or supporting the vitrification occurrence (1) and finally by protecting the cell's constitutive macromolecules (2, 5).The freeze-thawing process constitutes a double stress for the cell, i.e., thermal and hyperosmotic stresses, which act simultaneously during cooling (15, 16). The scenario of cell evolution during slow freezing is well known (13). The water surrounding the cell freezes before the cell contents, because the cytoplasm is more concentrated than the growth medium, and because thermodynamically, the component with the largest volume will nucleate first (6, 16). This freezing increases the osmotic pressure of the medium, and the extracellular solutes become concentrated in the remaining liquid extracellular water. Consecutive osmosis will then dehydrate cells as water diffuses from the cy...

Wheat starch suspensions of 5% dry matter were treated at 86 °C, 15 min, or with pressure at 600 MPa, 25 °C, 15 min. Both treatments were found to induce no further melting peak when differential scanning calorimetry was used. Under these previous conditions, starch suspensions subjected to pressure gave original products in terms of swelling index (water binding), amylose release and specific gravity. Pressure induced starch gelatinization with preservation of the granular structure. As a consequence, peculiar properties were expected for pressure-induced gels of 30% dry matter obtained at 600 MPa, 25 °C, 15 min. By using Young modulus measurements, calorimetry, X-ray diffraction, and drying kinetics experiments, results showed a limited retrogradation for gels obtained under pressure. Keywords: Starch gelatinization; gel; high pressure; specific gravity; retrogradation

The aim of this study was to evaluate the efficiency of pulsed light on the destruction of dried microorganisms on fluidized glass beads and to determine treatment parameters (energy level, water activity, final product quality) for process optimization. The applied drying method allowed microorganisms to remain viable on glass beads or dried powdered products with viability yields approaching 100%. The pulsed UV light system enabled an efficient fluidization of food powders, even for granular products (up to 5 mm diameter) and avoided shadowed areas. For Saccharomyces cerevisiae decontamination, the dose effect of UV rays was preponderant with glass beads and quartz plate, and in this case, 58 J/cm2 were required to decrease the microbial population by 7 log. For colored food powders (black pepper and wheat flour), the thermal effect of pulsed light dominated the UV effect.

In Bacillus subtilis, several phenolic acids specifically induce expression of padC, encoding a phenolic acid decarboxylase that converts these antimicrobial compounds into vinyl derivatives. padC forms an operon with a putative coding sequence of unknown function, yveFG, and this coding sequence does not appear to be involved in the phenolic acid stress response (PASR). To identify putative regulators involved in the PASR, random transposon mutagenesis, combined with two different screens, was performed. PadR, a negative transcriptional regulator of padC expression, was identified. padR is not located in the vicinity of padC, and the expression of padR is low and appears constitutive. This is

In this study, we investigated the kinetic and the magnitude of dehydrations on yeast plasma membrane (PM) modifications because this parameter is crucial to cell survival. Functional (permeability) and structural (morphology, ultrastructure, and distribution of the protein Sur7-GFP contained in sterol-rich membrane microdomains) PM modifications were investigated by confocal and electron microscopy after progressive (non-lethal) and rapid (lethal) hyperosmotic perturbations. Rapid cell dehydration induced the formation of many PM invaginations followed by membrane internalization of low sterol content PM regions with time. Permeabilization of the plasma membrane occurred during the rehydration stage because of inadequacies in the membrane surface and led to cell death. Progressive dehydration conducted to the formation of some big PM pleats without membrane internalization. It also led to the modification of the distribution of the Sur7-GFP microdomains, suggesting that a lateral rearrangement of membrane components occurred. This event is a function of time and is involved in the particular deformations of the PM during a progressive perturbation. The maintenance of the repartition of the microdomains during rapid perturbations consolidates this assumption. These findings highlight that the perturbation kinetic influences the evolution of the PM organization and indicate the crucial role of PM lateral reorganization in cell survival to hydric perturbations.