Effect of high-pressure treatment on polyphenoloxidase activity of the Agaricus Bisporus Mushroom

High pressure treatments (100-500 Mpa/4 °C/10 min) were carried out on freshly sliced mushrooms ( Agaricus bisporus ) and on liquid extract. Pressure above 200 MPa led to respiratory activity loss, significant enzymatic browning and polyphenoloxidase (PPO) activation in treated mushrooms. Increasing pressure from 200 to 500 MPa enhanced the PPO activation (in whole tissue and in liquid extract). Stabilization of mushroom by high-pressure (HP) alone cannot be considered. A combination of HP with thermal or chemical treatments is found necessary

High pressure inactivation of Pseudomonas in black truffle - comparison with Pseudomonas fluorescens in tryptone soya broth

Pseudomonas is one of the most common genera in black Perigord truffle. Its inactivation by high pressure (100-500 MPa/10 min) applied on truffles at sub-zero or low temperatures was studied and compared with those of Pseudomonas fluorescens in tryptone soya broth. Pressurization of truffles at 300 MPa/4 °C reduced the bacterial count of Pseudomonas by 5.3 log cycles. Higher pressures of 400 or 500 MPa, at 4 °C or 20 °C, allowed us to slightly increase the level of destruction to the value of ca. 6.5 log cycles but did not permit us to completely inactivate Pseudomonas. The results showed a residual charge of about 10 CFU/g. Pressure-shift freezing of truffles, which consists in applying a pressure of 200 MPa/-18 °C for 10 min and then quickly releasing this pressure to induce freezing, reduced the population of Pseudomonas by 3.3 log cycles. The level of inactivation was higher than those obtained with conventional freezing. Endogenous Pseudomonas in truffle was shown to be more resistant to high pressure treatments than P. fluorescens used for inoculation of broths

Effect of high pressure treatment on the characteristics of a model emulsion

The aim of this study was to investigate the use of HP (high pressure) technology as a possible alternative method for decontamination of non-food medium. HP (500 MPa) did not modify significantly the physicochemical characteristics of a model non-food emulsion. A 10 min HP treatment inactivated totally Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans even if all the five microorganisms were inoculated together, regardless of the initial load. No recovery was observed until six months of storage at 25°C

Effects of high pressure on anhydrous milk fat crystallization in emulsion

Anhydrous milk fat crystallization was compared either in bulk phase or in oil in water emulsion by studying melting curves obtained by calorimetry measurements. Emulsions were submitted to a high pressure (HP) treatment (200 MPa/10 min). An aging period of 72 h was required to obtain the highest amount of crystallized fat at 4 °C. Emulsification promoted the crystallization of low melting point (LMP) triglycerides. The effect of HP on anhydrous milk fat crystallization depended on the aging time. For short aging periods (30 min and 1 h), HP treatment favored the crystallization of LMP triglycerides, thus amplifying the effect of emulsification compared with the crystallization in bulk phase. However, for a long aging time, i.e. 48 h, the amounts of crystallized matter in emulsion with or without HP treatment were comparable. This result was interpreted in terms of a different polymorphic form crystallizing under HP

Inactivation of Listeria innocua in tryptic soy broth and poultry meat samples by high pressure processing

Efficiency of high-pressure processing (HP) on the inactivation of Listeria innocua (ATTC 33090) suspensions in culture medium or inoculated into poultry samples was studied. First, the baroresistance of L. innocua in a tryptic soy broth suspension at a concentration of 108-109 Colony forming units (CFU)/ml was tested under varying cycles of pressurization in the range of 200-350 MPa (15 min total in each treatment) at 4 °C. In addition, the effect of HP on L. innocua inoculated in poultry (103 or 105/CFU/g) was examined. The results of these studies demonstrate the requisite treatment conditions and efficacy of pressure cycles in destroying L. innocua in poultry

Preservation of fatty duck liver by high pressure treatment

Fatty liver samples from duck were treated with high pressures and packaged in multilayer films. Microbiological analysis, permeability of the films to oxygen and fat loss, caused by melting, were assessed after pressure or thermal treatment. Microbiological analysis showed a noteworthy reduction in the total aerobic mesophilic flora and eradication of the coliform flora, whichever film or treatment was used. Nevertheless, a significant bacterial flora was observed during storage at 4 °C from 42 days with a polyethylene/polyamide/polyethylene film and a sample which had been treated with pressure. But, treatment at 550 MPa for 55 °C and 20 min, in combination with two low oxygen permeability films (ethylene and vinyl alcohol copolymer) gave a product with long storage life (90 days) at 4 °C and a significant reduction in the melting of lipids