Utilization of wastes from Pacific whiting surimi manufacturing: proteinases and protein hydrolysate

TitleUtilization of wastes from Pacific whiting surimi manufacturing: proteinases and protein hydrolysate
Publication TypeThesis
Year of Publication1997
AuthorsBenjakul, S
Academic DepartmentFood Science and Technology
UniversityOregon State University
CityCorvallis, OR
AbstractBoth liquid and solid wastes from Pacific whiting surimi manufacturing were characterized and value-added products were recovered. A proteinase in surimi wash water (SWW) was determined to be cathepsin L with Mr 54,200 on SDS-substrate gel. Heat treatment and acidification shifted the activity zone to M [subscript r] 39,500. No evidence of calpain, cathepsin B or H activity was found. Cathepsin L from SWW was recovered by ohmic heating (55ʻC for 3 min), ultrafiltration, and freeze-drying with overall yield of 0.83 g protein/L SWW and 78% recovery of activity. A 5.9 purification fold was achieved by these processes. The recovered enzyme had an optimum activity at pH 4.0 and showed preferable hydrolytic activity towards casein, acid-denatured hemoglobin and myofibrils. Ý-Mercaptoethanol, dithiothreitol and urea enhanced the enzyme activity. The recovered proteinase showed 18.5% residual activity after 7 wk storage at 4ʻC. Proteolytic activity in solid waste and digestive organs from Pacific whiting was investigated. Pepsin-like proteinase predominated in solid waste, while trypsin-like proteinase was predominant in viscera. Carboxypeptidase b was found in both viscera and solid waste. Protein hydrolysate was produced from Pacific whiting solid waste (PWSW) using commercial proteinase, Alcalase, under optimum hydrolysis conditions. Enzyme concentration, reaction time and waste/buffer ratio affected the hydrolysis and nitrogen recovery (NR). Correlation between the degree of hydrolysis (DH) and NR was high (R₂=0.978). Freeze-dried hydrolysate contained 79.97% protein and showed similar amino acid composition to PWSW and Pacific whiting muscle but tryptophan was reduced. With different DH (20, 30, 40, 50, 60%), surface hydrophobicity, total and surface sulfhydryl content decreased as the DH increased. The hydrolysate showed a high solubility over a wide pH range. Fat adsorption and fat binding capacity were reduced, while foam expansion was enhanced with an increased DH. Hydrolysate with DH of 30% showed highest emulsifying activity. Low emulsion stability and high foam stability were obtained in all hydrolysates tested. Hydrolysate showed antioxidant activity, but no obvious differences in activity were found with varying DH and hydrolysate concentrations.