| Oyster is a kind of high-protein and low-fat seafood shellfish which has perfect amino acid composition.Besides, it has essential amino acids whose abundance extent and quality proportions are better than that of milk and human milk. Oyster protein hydrolyzate obtained by zymohydrolysing oyster with lots of physiological functions, such as enhancing immunity, reducing blood sugar and blood lipid, relieving physical fatigue, lowering blood pressure, protecting liver and so on. Oyster protein beverage is a new functional drink developed from oyster protein zymohydrolysis by adding seasonings, sterilizating and other processes.The study found that serious browning took place in oyster protein beverage in the processing(zymohydrolysis, sterilization and storage), which had affected the appearance and quality of beverage. Therefore, controlling the color change is one of the key processing technologies for the beverage. The study used fresh ostrea rivularis as experimental material and tested the changes of browning index, chromatism value, free amino acids and reducing sugar of the beverage to preliminarily study the main reason of color formation for oyster protein beverage in the processing. According to the color formation mechanism, corresponding measures were adopted to optimize the color. Based on the above study, an oyster protein beverage with white color and special seafood flavors has been developed.The mainly contents and results of this study are as follows:1,Preliminary study on mechanism of color formation of oyster protein zymohydrolysis.The results showed that the Browning index increased 104.7% along with the prolonging of reation time during the zymohydrolysis process of oyster protein. During this period, total free amino acids raised from 1.73 mg/mL to 2.45 mg/mL and reducing sugar from 0.17mg/mL to 0.7mg/mL. Large number of free amino acids and reducing sugars and mild zymohydrolysis temperatures (53℃) provide sufficient conditions for Maillard reaction to take place in the oyster protein hydrolysate. These results inferred that Maillard reaction may be relevant with color formation during zymohydrolysis process of oyster protein. On the other hand, the content of Browning substanceses increased during the proteolytic process and correlation coefficient between Browning index and it is 0.9885. Browning indicators has the largest RP-HPLC chromatography absorption peak in 284nm and its corresponding time is 18.4 min. While 5-HMF, Maillard reaction indicator, has the largest absorption peaks in the same wavelength with its time at 17.5 min. LC-MS tests showed that the molecular weight of Browning indicators was 116 more than that of 5-HMF.2,The study on mechanism of color formation of oyster protein beverage in the step of sterilization and during storage. Mechanism of color formation was preliminarily discussed by determining browning index, pH value, free amino acids, total sugar and reducing sugar content under two pH conditions (pH 4.9 and pH 6.7) and three storage temperature conditions (4℃, 20℃and37℃). The results showed the browning index in pH 6.7 groups was higher than that of pH 4.9 groups in both of the sterilization and storage step, in addition, temperature promoted the browning action as a whole. Composition analysis showed that both groups of beverage were similar in change of compositions, but the pH 6.7 group was violent compared with that of pH 4.9 group. The kinds of amino acids and their contents became fluctuant during storage, in which some amino acids such as aspartic acid increased remarkably, while some amino acids such as threonine, serine, cystein, tyrosine and arginine decreased evidently. Besides, the contents of total sugar and reducing sugar decreased obviously during storage. These results implied that amino acids such as threonine, serine, cystein, tyrosine, arginine and reducing sugar are the main factors involved in the Maillard reaction,which caused the beverage color brown during processing and storage.In addition ,both pH value and storage temperature were significant conditions for Maillard reaction.3,Based on the decolorization rate and protein recovery, activated carbon decolorization was used to optimize the color of oyster protein zymohydrolysis. The optimum technological conditions are studied by single-factor test and orthogonal test. The optimal technological parameters are as follows: dosage of activated carbon 1.5%, adsorption time 50min, heating temperature 45℃.Decolorization rate and protein recovery rate were 40.9% and 86.2% respectively under such conditions. Composite browning inhibitors were added to control browning of oyster protein beverage in the process of sterilization and storage. The results showed that inhibitory effect of beverage browning was better under low storage temperature (4℃). Under higher storage temperature (37℃),composite browning inhibitors had more significant inhibitory effect for browning index with browning degree 49.4%,which is far lower than that of the control group(108.6%).The chromatism test showed that inhibition effect of the inhibitor for b value is the most significant( inhibition rates 21.0% at 4℃a nd 24.3% at 37℃).Besides, the inhibitor also had good effect for a value under higher storage temperature (inhibition rate 23.3% at 37℃), It was invalid for L value,however.4,Development of oyster protein beverage. Based on the clear oyster protein zymohydrolysis, a few accessories and stabilizer were added.The beverage has special seafood flavor and pleasant color and taste. Besides, oyster protein beverage is nutrient-rich whose contents of protein, fat, oligopeptide, amino acid, ash, and total sugar are 2.99g/100mL, 0.78g/100mL,1.55g/100mL, 1.27g/100mL, 0.31g/100mL and7.54g/100 mL, respectively. Its amino acid composition is perfect and is rich in taurine. In addition, the oyster protein beverage is rich in calcium, iron, zinc and micronutrients. After storing for 4 weeks under 4℃,texture, color, flavor and taste of the beverage did not change significantly and microbiological index is up to the state standard GB 16322-2003... |
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