The role of endogenous serine proteinase on disintegration of collagen fibers from grass carp (Ctenopharyngodon idellus)
Jiandong Shen, Wei Zhang, Pei Gao, Yanshun Xu, Wenshui Xia
Abstract
Softening, causing by the degradation of collagen, leads to serious quality deterioration of fish fillets during post-mortem storage. In order to study the role of endogenous enzymes in softening of fish muscle, collagen fibers from grass carp (Ctenopharyngodon idellus) were degraded by serine proteinase. The structural and biochemical changes of collagen fibers with serine proteinase digestion were investigated in terms of scanning electron microscopy, fourier transform infrared spectroscopy, electrophoresis and chemical analysis. In the present study, an endogenous proteinase (approximately 250 kDa) with gelatinolytic activity was isolated from grass carp muscle by ammonium sulfate precipitation and column chromatographies, and identified as serine proteinase. Collagen fibers were partly disaggregated into collagen fibrils after serine proteinase treatment for 48 h, coinciding with a release of hydroxyproline (5.56 ± 0.02%) and glycosaminoglycans (9.04 ± 0.03%). However, almost all gelatin and 40% of acid-soluble collagen were degraded within 1 h and 6 h, respectively. Meanwhile, serine proteinase-treated collagen fibers maintained the triple-helical structure of collagen molecule, while their thermal stability was gradually decreased with digestion time. All results indicated that disintegration of collage fibers by serine proteinase might be due to both the degradation of proteoglycans and collagen molecules during textural deterioration of chilled grass carp fillets.