| During the shrimp processing, Litopenaeus vannamei head is often discarded as waste, whose annual production reached 20 million tons at least. At present, the heads of Litopenaeus vannamei are mostly used for rough machining, such as to produce aquatic feed, less for intensive processing, which reduces its’ value of recycling utilization. The endogenous protease is abundant in Litopenaeus vannamei’s heads and its activity is very high. But after the processing of the Litopenaeus vannamei, the heads are very easy to corrupt, which not only result in the waste of resources, but also cause environmental pollution. After the processing of the Litopenaeus vannamei, the heads of them are very easy to corrupt, which may not only result in the waste of resources, but also cause environmental pollution. Because of its’ rich nutrients, the heads of Litopenaeus vannamei have high value of development and utilization. Moreover, after exposure to UV-C stress, the activities of endogenous proteases inside increase significantly.In order to make full use of endogenous protease of shrimp head(Litopenaeus vannamei) to hydrolyze protein of shrimp head for oligopeptide and increase the added value of shrimp head, this paper systematically investigated the mechanism of UV-C stress induced exogenous protease activity promotion and the the activity distribution of shrimp head, on this basis, by using UV-C stress to enhance activity of endogenous proteases, we established the autolysis kinetics model of shrimp head, then researched the release law of autolysis products based on shrimp head endogenous acid, built autolysis based on digestive protease system system by using endogenous protease from shrimp head to degrade shrimp head protein and prepare short peptide products, and explored the peptide absorption and its influencing factors by using Caco-2 cell model. The main results were as following:(1) The effects of pH, temperate, inhibitors on the endogenous protease activity of shrimp head with or without UV-C stress treatment were studied. Meanwhile the effects of specific inhibitors on the activity of endogenous alkaline protease and acid protease in shrimp head with UV-C stress treatment were studied; through the ammonium sulfate precipitation, the optimum saturation of the above two kinds of endogenous proteases in shrimp head with the treatment of UV-C stress or not were detected respectively; the above two endogenous proteases were purified through Sephacryl S-100. The results showed that the optimum temperature of alkaline protease and acid protease were 60°C and 50°C respectively; when using 50% ammonium sulfate saturation, the activity of alkaline protease and acid protease with UV-C treatment stress were higher than without the treatment. UV-C Stress had no effects on the molecular weight of endogenous proteases. Through the treatment of UV-C stress, the specific activity of protein isolate peaks of endogenous alkaline protease and acid protease of shrimp head had changed. The specific activity of partial protein peaks was increased, while the rate of inhibitors was decreased. For endogenous proteases with different molecular in shrimp head, the UV-C Stress has different effects on them. UV-C stress activated new kinds of endogenous protease in shrimp, thereby increased the overall activity.(2) The effects of pH, temperature and substrate concentrate on the autolysis rate of Litopenaeus vannamei with the treatment of UV-C stress and the change law of autolysis were investigated. After UV-C stress, the optimum condition for shrimp head degradation was determined: pH 8.5, temperature of 55°C, and substrate concentration at 1:3. The dynamic model of shrimp head autolysis after UV-C stress was established as follows: Y = 37.681e-0.173 t, which showed the dissolution of product with a tendency of exponential decay. The release amount of shrimp head protein and degradation products under 3000 Da had good linear correlation with the solid residue protein. By using the absolute temperature and rate constants, the Arrhenius equation, lnKa = 8090.2/T- 26.497, was established. The correctness of the dynamic model of autolysis degradation of shrimp head with the treatment of UV-C stress was verified.(3) The law of dissolution products of shrimp head autolysis based on endogenous acid after UV-C irradiation was studied: the autolysis based on endogenous acid after UV-C irradiation was substantially completed in 2h, ended in 5h. The release amount of shrimp head protein, the proportion of the components under 3000 Da and the degree of hydrolysis increased rapidly in 1h, then the increase trend slowed down. The proportion of the components under 3000 Da and the degree of hydrolysis were still had an obvious increasing trend after 2h. The contents of free amino acids released from degradation process were all increased, the content of eight essential amino acids increased by 2~3 times.(4) The autolysis based on digestive protease system by using endogenous protease from shrimp head to degrade shrimp head protein and prepare oligopeptides products was studied. The results showed that after UV-C stress, by using shrimp head endogenous digestive protease to autolysis to prepare oligopeptides, the process was designed to autolysis based on endogenous acid protease 1.5h, then transferred to autolysis based on endogenous alkaline protease 1.5~5h. The release amount of shrimp head protein, the degree of hydrolysis and the proportion of the components under 3000 Da in the hydrolysate all showed twice significant increase. During autolysis based on endogenous digestive protease to prepare oligopeptides, the molecular weight of most of resulted product was distributed in 2000 ~ 3000 Da after 1.5h of autolysis of shrimp head protein. While 4~5h later, the content of under 3000 Da increased by 51.3%, and most of them were about 1000 Da.(5) The features, amino acid composition and transport situation in Caco-2 cells of oligopeptides which prepared were studied. The results showed that oligopeptides had a good solubility, and NSI value of oligopeptides increased with increasing temperature range from 35°C to 50°C, the NSI value of oligopeptides reached 97.9% at 50°C and pH had little influence on peptide solubility. The amino acid composition and content of 0~1000Da and 1000~3000Da oligopeptides were almost consistent and the total amount of essential amino acids account for more than 36% in total amino acids. Their transport belonged to a concentration-dependent manner in Caco-2 cells, and most were passive transport. 1 mg/m L of short peptide was added and transported 2h, the transport rate of 0~1000Da oligopeptides across the Caco-2 cell membrane was 14.2% and the transport rate of 1000~3000Da oligopeptides was 12.9%... |
PDF Full Text Request