| Abalone is an important marine economic shellfish widely cultured in East Asia. During processing, the viscera, which account for 20% of the total weight of abalone, is discharged or became feed. To reduce the burden on environment, enhance the added value, effective utilization methods of the wastes are required. The enzyme-assisted aqueous method has been used to recycle useful substances such as protein (peptide) and lipid from by-product of fish. In this paper, abalone (Haliotis discus hannai Ino) gonad was processed by the enzyme-assisted aqueous method. The distributions of the main nutrients in cream (fat), aqueous and solid phases were measured. The study provided the theoretical basis for the application of enzyme-assisted aqueous method on utilization of the by-products of shellfish.Abalone gonad was treated with neutral protease (Nep) and alcalase (Ale) respectively. Homogeneous hydrolysates were collected at 0,5,10,20,30,40,60,120,180, and 240 min. Following centrifugation, the hydrolysates were separated into cream, aqueous, and solid phases. The masses of dry matter in the three phases were weighed. The contents of protein, sugar and oil of the dry matters in the three phases were measured. The molecular weight (MW) distribution and amino acid composition of protein in the aqueous phase were determined. Through alcohol precipitation, the protein and polysaccharide samples were obtained from the aqueous phase. The dry matter and nutritional substances of the samples were measured.Results showed that the nutritional substances moved from solid phase to the cream and aqueous phases along with hydrolysis. Before hydrolysis, the dry matter of cream, aqueous, and solid phases were 3.28%,14.68% and 82.05% percent by mass; the protein of cream, aqueous, and solid phases were 1.21%,9.67% and 89.12% percent by mass; the sugar of cream, aqueous, and solid phases were 0.45%,38.90% and 60.65% percent by mass; the lipid of cream, aqueous, and solid phases were 0.14%,3.14% and 96.73% by mass. During the initial 5 min of hydrolysis, the degree of hydrolysis (DH) increased clearly, and the nutritional substances moved from solid phase to the cream and aqueous phases ripidly. For abalone gonad treated with Nep protease at 5 min, the dry matter of cream, aqueous, and solid phases were6.87%,23.23% and 69.90% percent by mass; the protein of cream, aqueous, and solid phases were 7.72%,20.77% and 71.52% percent by mass; the sugar of cream, aqueous, and solid phases were 1.95%,48.09% and 49.96% percent by mass; the lipid of cream, aqueous, and solid phases were 8.27%,4.20% and 87.53%. For abalone gonad treated with Alc at 5 min, the dry matter of cream, aqueous, and solid phases were 8.59%,23.15% and 68.26% percent by mass; the protein of cream, aqueous, and solid phases were 5.19%,24.71% and 70.11% percent by mass; the sugar of cream, aqueous, and solid phases were 3.45%,50.28% and 46.28% percent by mass; the lipid of cream, aqueous, and solid phases were 11.57%, 5.46% and 82.97% by mass. After that, the degree of hydrolysis (DH) increased slowly, and the nutritional substances moved from solid phase to the cream and aqueous phases slowly, too. For abalone gonad treated with Nep at 240 min, the dry matter of cream, aqueous, and solid phases were 15.13%,28.60% and 56.28% percent by mass; the protein of cream, aqueous, and solid phases were 18.94%,25.59% and 55.47% percent by mass; the sugar of cream, aqueous, and solid phases were 15.02%,53.34% and 31.64% percent by mass; the lipid of cream, aqueous, and solid phases were 21.04%,5.00% and 73.96% by mass. For abalone gonad treated with Alc at 240 min, the dry matter of cream, aqueous, and solid phases were 11.02%,31.38% and 57.60% percent by mass; the protein of cream, aqueous, and solid phases were 11.39%,37.79% and 50.82% percent by mass; the sugar of cream, aqueous, and solid phases were 5.68%,58.06% and 36.25% percent by mass; the lipid of cream, aqueous, and solid phases were 19.37%,6.77% and 73.86%. Through hydrolysis, some insoluble structural proteins decomposed into soluble parts and the polysaccharides and lipid attached to structural proteins were released, which maybe account for the changes of aqueous phase.Through alcohol precipitation, the protein and polysaccharide samples were obtained from the aqueous phase, respectively. The recorvery of protein for the protein samples derived from aqueous phases-of Nep- and Alc-hydrolyzed abalone gonad were 18.72% and 20.15%, respectively. The contents of protein for the protein samples derived from aqueous phases of Nep- and Alc-hydrolyzed abalone gonad were were 67.14% and 63.35%, respectively. The substrate was not hydrolyzed completely, and the release of protein from solid phase to aqueous was not fully, which account for the low protein yield. The recorvery of sugar for the polysaccharide samples derived from aqueous phases of Nep- and Alc-hydrolyzed abalone gonad were 44.08% and 44.58% respectively. The contents of sugar for the polysaccharide samples derived from aqueous phases of Nep-and Alc-hydrolyzed abalone gonad were 25.74% and 27.60%, respectively. As the incomplete hydrolysis, the polysaccharides from abalone gonad probably exist in the form of glycoproteins, contributing to the low sugar purity of the polysaccharide sample. |
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