| As we known, oyster is a perfect food which rich in protein and low in fat. The production of oyster is large in China. Most of the oysters are main fresh consuming and dried oysters, while less oyster processing products, resulting in low value-added oyster products. After hydrolysis, oyster enzymatic hydrolysates contain lots of peptides and amino acids. The oyster enzymatic hydrolysates can be used to produce oral solution, seafood seasoning and separate antioxidant peptides, which can significantly improve oyster products value. Therefore, this thesis will pay more attention on the further research of oyster. As raw material, oysters were hydrolyzed by several kinds of proteases to prepare oyster enzymatic hydrolysates firstly, then deodorized oyster enzymatic hydrolysates which can mask unpleasant smell efficiently, evaluated antioxidant activity of oyster enzymatic hydrolysates at last. The specific tasks and conclusions of this research are as follows:1. Study on preparation of oyster enzymatic hydrolysates by ficinOysters were hydrolyzed by ficin. Investigated by single-factor and orthogonal tests, the optimal hydrolysis conditions were protease dosage 5.5%, hydrolysis temperature 50?, pH6.0, hydrolysis time 3.5 h. Under such conditions, amino acid-nitrogen content of oyster enzymatic hydrolysates reached 0.181g/100mL, DPPH radical scavenging activity was 71.80%.2. Study on selecting proteases and hydrolysis methodOysters were hydrolyzed with six proteases, respectively. Results indicated that ficus and flavourzyme were relatively preferable to prepare oyster antioxidant enzymatic hydrolysates. Inactivation protease was not beneficial to enzymatic hydrolysis. The study found that ficin and flavourzyme hydrolyzed oysters at the same time was better than ficin and flavourzyme hydrolyzed oysters step by step. The content of amino acid-nitrogen of oyster enzymatic hydrolysates prepared by ficin and flavourzyme at the same time reached 0.181g/100mL, DPPH radical scavenging activity was 71.80%.3. Study on the preparation technology of oyster enzymatic hydrolysates hydrolyzed by ficin and flavourzymeSingle-factor and orthogonal tests were used to gain the optimal parameter of processing. The optimal hydrolysis conditions were protease dosage 12%, pH6.5, hydrolysis time 3h, and proportion of ficin and flavourzyme were 3:1. Under such conditions, amino acid-nitrogen content of oyster enzymatic hydrolysates up to 0.212g/100mL, DPPH radical scavenging activity reached 89.74%.4. Determination the content of metal and amino acid on oysters and hydrolysates.The inductively coupled plasma mass spectrometry (ICP-MS) was used to determined metal content in oysters and its hydrolysates. The content of lead, cadmium, mercury, arsenic and chromium in oysters and its hydrolysates were in line with the national food safety standards. Amino acid compositions in oysters and its hydrolysates were detected by HPLC. It was found that there were 17 amino acids both in oysters and its hydrolysates. Essential amino acids were accounted for 35.84% of total amino acids in oysters, histidine (143.83 mg/g) and glutamic acid (110.12 mg/g) were rich in oysters, while the highest threonine was 118.27mg/g and the essential amino acid accounted for 45.71% of total amino acids in the hydrolysates. Using gel permeation chromatography (GPC) to determinate the number average molecular weight of hydrolysates and the number average molecular weight was 10134Da,324 Da and 109 Da.5. Study on the deodorization process of oyster enzymatic hydrolysatesPerlite, ?-cyclodextrin and yeast were the good agent for deodorization. Using three agents to deodorize oyster enzymatic hydrolysates. It was found that the combination of perlite and yeast was the better way to deodorize. The orthogonal tests were used to optimize deodorization process. According to the results, The optimal deodorization conditions were 1% yeast to deodorize at 40? for 45min, and then 100% perlite to deodorize oyster enzymatic hydrolysates at 50? for 30min.With all these treatment, the hydrolysates had little fishy smell. The volatile components content in hydrolysates and hydrolysates after deodorization were analyzed by GC-MS. The result showed that the content of aldehydes, amines and acids were significantly reduced, especially for aldehydes, which decreased from 31.48% to 13.21%.6. Evaluation of antioxidant activity of oyster enzymatic hydrolysatesThe antioxidant activity of oyster enzymatic hydrolysates was measured by the phosphomolybdate method, DPPH method, ABTS method, hydroxyl radical method, reducing power method, pyrogallol autoxidation method and ferric thiocyanate method. The results indicated that hydrolysates had a higher antioxidant activity. |
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