The effect of structural change on the digestibility of sarcoplasmic proteins in Nanjing dry-cured duck during processing.

To evaluate the effect of structural change on the digestibility of sarcoplasmic proteins in Nanjing dry-cured duck during processing, carbonyl content, sulfhydryl (SH) group, disulfide (S-S) group, surface hydrophobicity, particle size, secondary structures, and in vitro digestibility were determined. During processing, carbonyl content increased; SH groups turned into S-S groups; α-helix turned into ß-sheet. From marinating to early dry-ripening stage, surface hydrophobicity increased but particle size decreased, whereas these had opposite tendencies at the late dry-ripening stage. The in vitro digestibility of pepsin decreased at drying-curing and drying-ripening stages, whereas the one of pancreatic proteases kept stable until late drying-ripening stage. We concluded that salting, drying, and protein oxidation caused the denaturation and aggregation during processing. The oxidation and aggregation of sarcoplasmic proteins of Nanjing dry-cured duck resulted in a loss of nutritional quality during drying-ripening stage.

The effect of dry-cured salt contents on accumulation of non-volatile compounds during dry-cured goose processing.

Twenty-four Eastern Zhejiang White Geese were slaughtered, dry-cured by 2 different kinds of salt contents (12 geese with 4% low salt level [LS]; 12 geese with 8% high salt level [HS]) for one d, marinated in brine for one d, and air dry-ripened at 16 °C for 7 d. The effect of dry-curing salt contents on the changes in myofibril proteins, potential proteolysis activities, and total free amino acid (TFAA) in dry-cured goose was investigated. Compared to the raw, cathepsin B+L and calpains activities decreased at the end of dry-curing and the third d of dry-ripening. At the final products, the activities of cathepsin B+L and calpains were about half of those in raw meat. There was no difference in proteolysis activities except for the end of dry-curing (P < 0.05) and the 3 d of dry-ripening (P < 0.05) for cathepsin B+L, and the end of dry-curing (P < 0.05) for calpains (P < 0.05) between groups. Myosin light chain (MLC) and troponin-I were cleaved. Compared to the raw, TFAA increased by 36.64 and 31.82% in the final products for HS (P < 0.001) and LS (P < 0.01), respectively. The increase of TFAA could be attributed to the proteolysis of myofibril proteins and retained proteolysis activities. No significant difference on TFAA and MLC and troponin-I bands was observed between groups in final products. This means that different proteolysis activities during processing did not cause the difference in quality of final products between groups, and that 4% low salt can be used in future applications.

Activation of caspase-3 and its correlation with shear force in bovine skeletal muscles during postmortem conditioning.

The study was aimed at exploring the mechanism of tenderization by establishing a correlation between caspase-3 activity and shear force, verifying the activation occurring by analyzing active caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP) fragments, and understanding the pathways involved in activation of caspase-3 by evaluating its correlation with caspase-8 and -9 activities in LM, semitendinosus (STN), and psoas minor (PM) muscles. The results indicated that shear force decreased at 48 h in PM (P < 0.01), LM (P < 0.01), and STN (P < 0.05). We detected p22, p23, p20, and p18 caspase fragments as well as distinctive PARP fragments of 24 kDa by caspase-3 and 36 kDa by µ-calpain. Caspase-3 activity correlated with shear force negatively at 24 and 48 h in STN (P < 0.01 at 24 h; P < 0.01 at 48 h), PM (P < 0.001 at 24 h; P < 0.01 at 48 h), and LM muscles (P < 0.05 at 24 h; P < 0.01 at 48 h). The greatest activities of caspase-8 (P < 0.001 in PM and STN; P < 0.01 in LM) and caspase-9 (P < 0.001 in muscles) appeared at 4 h whereas that of caspase-3 was at 24 h (P < 0.001 in muscles). Caspase-9 activity correlated positively with caspase-3 at 4, 24, and 48 h in STN (P < 0.01 at 4 h; P < 0.05 at 24 h; P < 0.001 at 48 h) and at 4 and 96 h in PM (P < 0.001 at 4 h; P < 0.05 at 96 h) and LM muscles (P < 0.001 at 4 h; P < 0.001 at 96 h). The caspase-8 activity correlated with caspase-3 at 4, 48, and 96 h in STN (P < 0.05 at 4 h; P < 0.001 at 48 h; P < 0.05 at 96 h), at 4 and 24 h in PM (P < 0.001 at 4 h; P < 0.05 at 24 h), and at 4 and 96 h in LM (P < 0.001 at 4 h; P < 0.01 at 96 h). We concluded that caspase-3 was associated with the decline of shear force; the activation of caspase-3 was mediated by caspases -8 and -9 in muscles. However, more detailed studies are needed to define the precise mechanism for the cleavage of pro-caspases -8 and -9 during conditioning.