| The oyster is the world’s largest cultivated shellfish. China has a long history in oyster culture. The oyster production of China in 2014 was 3.9488 million tons, accounting for about 32.68% of the total output of shellfish. The main content of oysters was 45~57% protein and 20~40% glycogen, which could be separated and prepared into different products respectively. The protein could also be hydrolyzed to peptides to increase the additional value of oysters. The heavy metal pollution in offshore area where the oysters live is increasing. Meanwhile, the oysters are filter feeders, which mean the pollutants are easy to accumulate in them. These lead to the heavy metal content in the oysters too high.The purpose of the thesis was to investigate the separation of the glycogen and protein in oyster, the purification of oyster glycogen and the enzymatic production of bioactive peptides from the oysters. Meanwhile, the ion exchange resin was used to reduce the content of heavy metals in the functional food prepared by oyster peptides.Firstly, organic acids were used to separate the glycogen and protein in the oysters. The optimum conditions obtained by single factor tests and orthogonal tests are as following: 0.5 mol/L acetic acid solution, the solid-liquid ratio =1:3, pH=7.0, 30 min and 60°C. 95.01% glycogen was in the supernatant, and 66.12% protein was in the precipitate. The ratio of glycogen to protein in the supernatant was 1.23:1, and that in the precipitate was 28.10:1.Secondly, glycogen in the supernatant was purified by ultrafiltration. While the operation pressure was 0.03 MPa, ultrafiltration with MWCO 10 kDa membrane was used to separate and concentrate the glycogen in the supernatant at room temperature. The rejection rate of glycogen was 89.88%, and that of protein was 10.97%. After concentration, constant volume desalination was cinducted until the conductivity of retention solution was lower than 400 μS/cm. The retention solution mainly contained 80.7% glycogen, 9.8% protein and 4.1% ash, and the desalination rate was 91.71%.Thirdly, the hydrolyzing abilities of papain, flavourzyme, mixed proteases(papain: flavourzyme=1:2) and alcalase were investigated. The result showed that the alcalase was best to produce peptides from oyster, and the protein dissolution rate was 82.82%. The optimal conditions for the production of peptides by alcalase were: pH=8.5, m: V=1:10, 55°C, E/S=911.31 U/g protein and 2 h. The degree of hydrolyzation was 18.58% and the protein dissolution rate was 88.86%. The hydrolysate, radical scavenger, was composed of peptides with 2 to 5 amino acid residue, the molecular weight(MW) of which was mainly under 2000 determined by HPLC.Finally, the effects of 732, XR601, XR605 and XR608 cation exchange resin on lead, cadmium, chromium, calcium, magnesium, zinc, iron, copper and protein in hydrolysate were compared. It was showed that the adsorption rates of 732 cation exchange resin on Pb, Cd and Cr were 79.77%, 47.89% and 61.83% respectively, and were superior to the other 3 resins. The results obtained from equilibrium adsorption studies on the 8 metal ions and protein in hydrolysate were conformed to the Langmuir and Freundlich. The adsorption was a monolayer adsorption reaction and a preferential process, and the rate controlling step of the adsorption was influenced by particle diffusion. The optimal conditions for 732 cation exchange resin to remove the heavy metals in hydrolysate were: 5 g/L resin, 30°C, 200 r/min and 2 h. After adsorption, the hydrolysate was rich in minerals and the heavy metal residues in hydrolysate didn’t exceed the limitation of national standard. |
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