Bromelain Kinetics and Mechanism on Myofibril from Golden Pomfret (Trachinotus blochii)

Bromelain was used to tenderize golden pomfrets (Trachinotus blochii). The enzyme kinetic model was x=2.447xln[1+(1332.21xE0S0-1.74)t]=0.33em, which indicated that the degree of hydrolysis (DH, x) was dependent on hydrolysis time (t), the initial concentration of myofibril (S-0) and bromelain (E-0). The relationship between the overall hydrolysis rate (v), S-0, E-0, and t is demonstrated as: v=(16.50(E0S0)-1.33)S0=0.33em exp {-2.447ln[1+(1332.21E0S0-1.74)t2]}. Sample of 0.40% E-0/S-0 was further used to study the effects of hydrolysis time on the changes of proteins, peptides, free amino acids (FAA), and protein nanostructure. SDS-PAGE result showed that myosin heavy chain was degraded dramatically from 22.88% before treatment to 12.03% after 2 min bromelain treatment. Meanwhile, bromelain did not exhibit activity towards actin, trypomyosin, myosin light chain, and troponin C. A general increase of amino acids indicated the increased DH and the preferential cleavage sites of bromelain in the descending order of lysine, glutamic acid, glycine, ornithine, methionine sulfoxide, and alanine. Atomic force microscope images showed that the strip-like structure of myofibril was considerably degraded by bromelain, and the granulation of protein after 20 min indicated possible self-assembling of protein hydrolysate. Confocal laser scanning microscopy further confirmed the degradation of myofibril proteins and formation of protein aggregates. Practical ApplicationMeat of golden pomfrets is tough, thus not idea for fish balls or fish cakes. Tenderization is essential to achieve desired texture and consumer acceptance, especially for this fish meat with intrinsic hard texture. Bromelain can be extracted from pineapple processing waste. Enzymatic kinetics was studied to instruct industry to control the tenderness of the processed fish meat. The microstructural and mechanism study elucidate the process, thus could be applied to improve the quality of the seafood products correspondingly.