High-pressure effects on lysosome integrity and lysosomal enzyme activity in bovine muscle

Changes in immunoelectron microscopic localization of cathepsin D in muscle induced by conditioning or high-pressure treatment

Changes in the localization of cathepsin D in postmortem and pressurized rabbit muscles were investigated by immunoelectron microscopy. The anti-cathepsin D monoclonal antibody strongly labeled a large vesicle in a subsarcolemmal part of the cell , which strongly suggests that this is the primary lysosome. The liberation of the cathepsin D entrapped in the lysosomes in the muscle prepared immediately after death proceeded with the progress of the conditioning. The release of almost all cathepsin D from the lysosomes and its absorption on the myofibrils were observed in the muscle conditioned for 14 days. The accumulation of lysosomes having various volumes and shapes accompanied with the disruption of myofibrillar structure was also observed. The liberation of cathepsin D from the lysosomes can be attributed to the modification of membranes permeability of the lysosomes during conditioning. When the muscle was pressurized at 100 MPa, the modification of the round shape of the lysosome was observed. With the increase of the pressure applied to the muscle, the release of cathepsin D from the lysosome due to the disruption of membrane was accelerated, and absorption of the released cathepsin D on the myofibrils was observed. From the results obtained, it was clear that the changes in the localization of cathepsin D accompanied with the modification of lysosomes induced by the brief exposure to high pressure were drastic in comparison with that in the muscle during conditioning.

Inactivation of Escherichia coli O157:H7 in ground beef by single-cycle and multiple-cycle high-pressure treatments

The effect of single- and multiple-cycle high-pressure treatments on the survival of Escherichia coli CECT 4972, a strain belonging to the O157:H7 serotype, in ground beef was investigated. Beef patties were inoculated with 10(7) CFU/g E. coli O157:H7, and held at 4 degrees C for 20 h before high-pressure treatments. Reduction of the E. coli O157:H7 population by single-cycle treatments at 400 MPa and 12 degrees C ranged from 0.82 log CFU/g for a 1-min cycle to 4.39 log CFU/g for a 20-min cycle. Multiple-cycle treatments were very effective, with four 1-min cycles at 400 MPa and 12 degrees C reducing the E. coli O157:H7 population by 4.38 log CFU/g, and three 5-min cycles by 4.96 log CFU/g. The color parameter L* increased significantly with high-pressure treatments in the interior and the exterior of beef patties, whereas a* decreased in the interior, and b* increased in the exterior-changes that might diminish consumer acceptance of the product. Kramer shear force and energy were generally higher in pressurized than in control ground beef. Maximum values for these texture parameters, which corresponded to tougher patties, were reached after one 10-min cycle in the case of single-cycle treatments or two 5-min cycles in the case of multiple-cycle treatments. High-pressure treatments had no significant effect on Warner-Bratzler shear force.

Aminogenesis control in fermented sausages manufactured with pressurized meat batter and starter culture

The application of high hydrostatic pressure (200MPa) to meat batter just before sausage fermentation and the inoculation of starter culture were studied to improve the safety and quality of traditional Spanish fermented sausages (fuet and chorizo). Higher amounts of biogenic amines were formed in chorizo than in fuet. Without interfering with the ripening performance in terms of acidification, drying and proteolysis, hydrostatic pressure prevented enterobacteria growth but did not affect Gram-positive bacteria significantly. Subsequently, a strong inhibition of diamine (putrescine and cadaverine) accumulation was observed, but that of tyramine was not affected. The inoculated decarboxylase-negative strains, selected from indigenous bacteria of traditional sausages, were resistant to the HHP treatment, being able to lead the fermentation process, prevent enterococci development and significantly reduce enterobacteria counts. In sausages manufactured with either non-pressurized or pressurized meat batter, starter culture was the most protective measure against the accumulation of tyramine and both diamines.

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.