Nicolas Chapleau

Pressure Shift Freezing of Pork Muscle: Effect on Color, Drip Loss, Texture, and Protein Stability

Cylindrical specimens (50 mm diameter and 160 mm length) of fresh pork muscle (boneless rib portions) packed in plastic bags were frozen by pressure shift freezing (PSF) at 100, 150, and 200 MPa, air blast freezing (ABF), and liquid immersion freezing (LIF). Temperature and phase transformations of the muscle tissue were monitored during the freezing process at three locations: center, midway between the center and the surface, and near the surface. Pork muscle quality changes [color, drip loss (both thawing and cooking), texture (shear force), and protein stability (DSC thermal profiles)] were evaluated after thawing the frozen samples at room temperature (20 °C). Employing pressures above 150 MPa caused very significant ( P < 0.01) color changes in pork muscle during the PSF process. The PSF process reduced thawing drip loss of pork muscle but did not cause obvious changes in total drip loss following thawing and subsequent cooking. PSF at 150 and 200 MPa resulted in considerable denaturation of myofibrillar proteins of pork muscle. The PSF process also caused an increase in the pork muscle toughness as compared with that of unfrozen, ABF, and LIF samples.

Effects of High Pressure, Subzero Temperature, and pH on Survival of Listeria monocytogenes in Buffer and Smoked Salmon

High pressure processing is a novel food preservation technology, applied for over 15 years in the food industry to inactivate spoilage and pathogenic microorganisms. Many studies have shown the differential resistance of bacterial cells to high pressure. Listeria monocytogenes is a bacterium able to grow at refrigerated temperature and to survive for a long time in minimally processed foods such as raw smoked fish. The freezing process does not cause significant decline of L. monocytogenes. The phase diagram of water under pressure permits a pressure treatment under subzero temperature, without the disadvantages of freezing for food quality. The aim of this study was to estimate if combined effects of pressure and subzero temperature could increase the destruction of L. monocytogenes in buffer and in smoked salmon. We investigated effects of high pressure processing (100, 150, and 200 MPa) combined with subzero temperatures (-10, -14, and -18 degrees C) and pH (7.0 and 4.5). Results showed that the most effective high-pressure treatment to inactivate L. monocytogenes was 200 MPa, -18 degrees C, and pH 4.5. The relevance of pressure holding time and the synergistic effect of pressure coupled with the subzero temperature to inactivate bacteria are highlighted. Modifications of physical properties (color and texture) were a lightening of color and an increase of toughness, which might be accepted by consumers, since safety is increased.

High pressure effects on myofibrillar proteins

Abstract Myofibrillar proteins were extracted from post rigor bovine meat with a potassium phosphate/potassium chloride buffer. Viscoelastic properties of myofibrillar properties were studied in a 0.6MKCl buffer, at pH = 6, used in an oscillating mode. Enthalpy patterns were determined with a differential scanning calorimeter. SDS PAGE was performed. Results show that high pressure processing denatures myofibrillar proteins, which result in a decrease of myofibrillar protein extractability. Moreover, the viscoelastic properties of myofibrillar extracts are modified by a preliminary high-pressure treatment of meat. The storage modulus (G′) versus temperature graph presents an intermediate peak; the height of this peak and the final value (90°C) are dependant on the level of pressure. Finally, enthalpy and electrophoresis patterns allow us to understand myofibrillar protein modifications induced by high hydrostatic pressure processing of meat.

High Pressure Effect on Meat and Lupin Protein Digestibility

High pressure treatment is a mild treatment concerning the nutritional characteristics: for instance vitamins content is very few affected by high-pressure treatment. But the impact of high-pressure on protein digestibility remains poorly understood. This work presents effect of high-pressure treatment on in vitro digestibility of meat and lupin proteins. Two high-pressure conditions (200 and 500 MPa 10 min.) and a heat treatment of 95 °C, 30 min were studied. In vitro digestibility was evaluated with a pepsin reaction. Results show than for both type of proteins, samples pressurised at 500 MPa were the most hydrolysed. Meat proteins were less hydrolysed than control either after heat or 200 MPa treatment. Lupin proteins where more hydrolysed than control after heat or 200 MPa treatment. Thus we revealed that high-pressure treatment presents an effect on the in vitro digestibility of proteins, opening a new perspective of investigations.

Effect of high pressure on food enzyme activities: Behavior of cathepsin D

Abstract During the ageing (acquisition of beef meat tenderness) several enzymatic systems are involved. Among them, the lysosomal enzymes, i.e. cathepsins and specially the cathepsin D, are responsible for the myofibrillar proteins alterations. Previous results have shown, after high pressure treatment of post rigor beef meat, an important increase of the toughness of meat, in spite of an increase of the cathepsin D activity was also observed. The aim of this work was to determine if the application of a high pressure treatment modified the reaction between cathepsin D and its natural substrate (myofibrils) The pressurization of cathepsin D does not modify its active site as the electrophoretic patterns and the amount of myofibrillar solubilised proteins were similar to the control. The HP treatment does not perturb the recognition between the enzyme and its natural substrate.

High pressure processing of chicken meat: change in total aerobic counts after pressure treatment and during chilled storage.

ABSTRACT Aims: To investigate the effect of pressure, pressurization time, pressurization temperatureand their interaction on inactivation and recovery of Listeria innocua inoculated in mincedchicken meat.Study Design: Effect of the parameters of high pressure processing (HPP) on theinactivation of L. innocua were studied by response surface methodology using Box-Behnken design.Place and Duration of Study: Study conducted during an 11 months postdoctoral study atAgriculture, Agronomy and Food Sciences Department at LUNAM Universite, Oniris,Nantes, France.Methodology: Minced chicken meat inoculated with Listeria innocua strain ATCC 33090 togive a total aerobic count (TAC) of 10 8 cfu/g and samples were subjected to high pressuresof 200, 300, 400 MPa, temperatures of 0oC, 20oC, 40oC and holding times of 5, 10 and 15minutes. Survival of L. innocua was determined by TAC immediately after pressuretreatment and during 35 days of storage at 3oC.Original Research Article

Effect of high pressure on the reaction between bovine myofibrils and cathepsin D

This study deals with the effect of high pressure [50-500 MPa] and time of treatment [20-900 s] on the reaction between myofibrils and cathepsin D from bovine post mortem meat, using Surface Response Methodology. We shown that every high pressure treatment enhanced activity of cathepsin D as evaluated on haemoglobin as a substrate or on control meat myofibrils. We also put in evidence that cathepsin D could carry out the hydrolysis of high pressure treated myofibrils. At last we studied the action of pressurised cathepsin D on pressurised myofibrils, and proved that the hydrolysis was increasing up to 170 MPa and then decreased; above 300 MPa the activity was lower than with control cathepsin D and control myofibrils. Thus above 300 MPa recognition of natural substrate is affected by high pressure induced modifications. These results may help to explain why high pressure treatment of post rigor meat is not able to increase tenderness.