High-pressure effects on the proteolytic enzymes of sea bass (Dicentrarchus labrax L.) fillets.

High-pressure processing is a nonthermal technique ensuring food product safety and enabling a longer shelf life. The purpose of this experiment was to evaluate the effect of high pressure on the main proteolytic enzymes involved in fish muscle degradation during storage. Enzymes were extracted with sarcoplasmic proteins from Dicentrarchus labrax sea bass white muscle. Activity of cathepsins B, D, H, and L was quantified in protein extract, whereas calpain activity was evaluated after isolation from its endogenous inhibitor. High-pressure processing up to 500 MPa enhanced the activity of cathepsin B, H, and L, whereas the activity of cathepsin D increased up to 300 MPa and decreased above 300 MPa. With regard to calpain activity, high-pressure processing led to a decrease of activity, which was zero above 400 MPa. We suggest a leading explanation based on simultaneous deactivation of enzymes and an increase of liberation from lysosomes for cathepsins and on dissociation of subunits for calpains.

Effect of high pressure and salt on pork meat quality and microstructure.

The interaction of salt (0%, 1.5%, and 3% in the final product) and a high-pressure treatment (500 MPa, 20 °C, 6 min) was investigated using pork biceps femoris muscle. The Warner-Bratzler shear force and the water holding capacity (WHC) were assessed and linked to the microstructure evaluation by environmental scanning electronic microscopy (ESEM). Pressure-treated and cooked samples showed a high Warner-Bratzler shear force with a low WHC compared to control cooked samples. These negative effects could be linked to the general shrinkage of the structure as observed by ESEM. The addition of 1.5% salt was sufficient to improve the technological properties of the high-pressure-treated samples and to counteract the negative effect of high pressure on texture and WHC. This phenomenon could be linked to the breakdown in structure observed by ESEM. This study states that it is possible to produce pressurized pork products of good eating quality by adding limited salt levels.

Trends in postmortem aging in fish: understanding of proteolysis and disorganization of the myofibrillar structure.

Postmortem tenderization is caused by enzymatic degradation of key structural proteins in myofibrils as well as in extracellular matrix, and of proteins involved in intermyofibrillar linkages and linkages between myofibrils and the sarcolemma. The function of these proteins is to maintain the structural integrity of myofibrils. Current data indicate that calpains and cathepsins may be responsible for degradation of these proteins. Other phenomena occurring in cells postmortem (pH drop, sarcoplasmic Ca2+ increase, osmotic pressure rise, oxidative processes) may act in synergy with proteases. Our understanding of the underlying mechanisms of muscle degradation should be improved for an accurate evaluation of the postmortem muscle changes and consequently of the fish quality.