Preparation Of Aquatic Flavoring And Investigation Of Physiological Activity Of Protein Hydrolysate From Samll Yellow Croaker Scraps

The cultivation area in coastal beach of Wenzhou in Zhejiang exceeds 65,000 hectares. The vast cultivation area has made the aquatic products processing enterprises springing up, which produces lots of fish scraps at the same time. These waste fish scraps not only pollutes environment but also makes direct economic loss. With the larger demands of fish protein sources, the full use of these scraps can rise the added value of fish, and achieve excellent economic effect and social effect. The small yellow croaker is one of the typical low value fish. Therefore, there is a practical significance to study the preparation of aquatic flavoring and investigation of the physiolagical activity from small yellow croaker scraps.In this study, small yellow croaker scraps were chosen as the raw material to prepare aquatic flavoring by enzymolysis and thermal reaction. The characteristic flavor compounds of small yellow croaker scraps were used as the main evaluation indicators to track the change of amino acids as well as characteristic flavor types and contents in the flavor processing scheme. On the other hand, physiological activity (including the antioxidant and the anticoagulation activity) of protein hydrolysate from small yellow croaker scraps by enzymolysis and ultrafiltration were preliminary studied. Our detailed works are mainly concentrated on the following aspects:1) Volatile aroma compounds of small yellow croaker scraps were extracted by the simultaneous distillation extraction method and solid phase micro-extraction method. The extracts were isolated and identified by gas chromatograph mass spectrometry, and the contents of aroma compounds were determined via internal standard method by gas chromatography. Fifty seven kinds of small yellow croaker scraps flavor compounds were isolated and identified successfully. The result showed that alcohol and ketone compounds were the major flavor compounds, aldehyde and alkene compounds came second. Among these flavor compounds, ten kinds of flavor compounds which mainly contributed to the characteristic flavor of small yellow croaker scraps were regarded as evaluating indictors.2) The taste compounds and flavor precursors were extracted after enzymolysis of small yellow croaker scraps. The optimum hydrolysis conditions of alcalase and falvorzyme were determined respectively by single factor experiments and response surface analysis. The results showed that, the optimum enzymatic hydrolysis condition was material-water ratio 1/7, Alcalase enzyme dosage 2.5%, Flavourzyme enzyme dosage 3.0%, temperature 55℃, initial pH 8.0, and hydrolysis time 6.5 h. Under this condition, the degree of hydrolysis (DH) was 40.11 %, the concentration of free amino acids in the hydrolysate was 40.03 g/100g, the concentration of the essential amino acids was 15.20 g/100g, and the concentration of flavor acids was 44.44%. The amino acid content in the products increased significantly as compared with that before enzymolysis. The concentration of the total free acid increased by 39.77%, the essential amino acids increased by 51.85%, and the flavor acids increased by 49.75%. The products had a unique flavor of small yellow croaker. And the umami taste was significantly strengenthed by enzymatic hydrolysis and the products had an enjoyable complex, mostly umami, including salty, sweet and bitter taste.3) To study thermal reaction of enzymatic hydrolysate to prepare aquatic flavoring, the effect of reaction temperature, reaction time, pH value, exogenous amino acids, and exogenous sugar were investigated. The uniform designs and fuzzy matrix were used to compare the products' taste. The optimum thermal reaction condition was as follows: enzymatic hydrolyzate 40 g, the initial pH 9.0, the reaction time 25 min, the reaction temperature 110℃, glucose 6.00 g, Glu 3.00 g, Gly 0.80 g, Met 0.70 g, Pro 0.70 g, Ala 3.00 g, Arg 0.20 g, and Cys 1.78 g. To further optimize the thermal reaction product flavor, the effect of Vc, garlic powder and citric acid were investigated. The results showed that the suitable additional quantity of Vc, garlic powder, and citric acid was 0.1%,0.1% and 1.5% respectively. The result of amion acids analysis indicated that the concentration of free amino acids in the aquatic flavoring was 40.29 g/100g, and that of the essential amino acids was 10.44 g/100g. After thermal reaction, the content of Cys was reduced by 20.00%, and that of the flavor acids of Glu, Gly and Ala were increased by 16.43%,33.91%,33.10%, respectively.4) In order to analysis the change of flavor compounds in the processing of small yellow croaker scraps, the flavor compounds of raw mateials, enzymolysis product and the thermal reaction product were investigated. The results showed that compared with the raw materials, the thermal reaction product was better in the aroma intensity and tastiness intensity, and easily accepted. The contribution to flavor of alkenes, acids compounds and ester compounds were little, the contribution of aldehyde compounds and sulfur-containing compounds with low aroma threshold were obvious. Besides, the stink odour compounds were significantly reduced. 5) In addition to analysis of the processing applicability and the flavor of enzymolysate, the physiological activity of enzymolysate was also discussed. The effect of DPPH·scavenging activity, O2-·scavenging activity, HO·scavenging activity and anticoagulation activity of the enzymolysates with different hydrolysis time were investigated. The results showed that, the different components separated from the Master Flex ultrafiltration system had a different degree of suppression on DPPH·, O2-·, OH·, and had some effect on the clotting time prolongation. Among the measured concentration range, the DPPH·scavenging capacity of each component was up to half inhibitory concentration, the O2-·scavenging capacity of each component partly reached half-inhibitory concentration, but each components almost had no inhibitory effect on the OH·. What's more, they had anti-clotting ability in a certain extent. Although the antioxidant activity and the anticoagulant activity was not high, but we enhanced the product's nutritional value by giving the functionality of products as a re-use waste of resources.