Study On Storage Characteristics And Enzymatic Hydrolysis Of Razor Clam (Sinonovaculla Constricta)

Preliminary studies on the chemical properties of razor clam ( Sinonovaculla Constricta) during storage at different temperatures and with the addition of complex biological preservatives were conducted using sensory, chemical, microbiological methods. The optimum hydrolytic conditions of razor clam with the addition of proteases were determined so as to provide some theoretical references for the preservation and advanced processing of razor clam.The total volatile basic nitrogen (TVB-N) and free fatty acids (FFA) of razor clam increased with the rise of temperature during storage at ambient temperature, +5#, and -18#, with the slowest speed at -18#, the fastest at ambient temperature The extractable protein nitrogen (EPN) change was opposite to the change of TVB-N and FFA, the EPN of razor clam decreased with the rise of temperature during storage at ambient temperature, +5癈, and -18#, with the slowest speed at -18#, the fastest at ambient temperature. The EPN change was closely associated with the denaturation of proteins, and also with the freshness of razor clam. Different storage temperatures showed a significant impact on the chemical properties of razor clam.The TVB-N and total bacterial counts of razor clam with the addition of complex biological preservatives consisting of lysozyme and / or nisin increased more slowly during storage than ; hat. of the control ,group. It was indicated from thesensory evaluation that the color, springiness, odor, and stickiness of the groups with the addition of complex biological preservatives were also much better than those of the control group. The complex biological preservatives consisting of lysozyme and / or nisin possessed a good preserving effect on razor clam, with the combination of lysozyme and nisin better than the individual one, possibly because the condition of their application and anti-bacterial spectrum can supplement each other as to increase their anti-bacterial spectrum.Razor clam was hydrolyzed with four kinds of proteases including subtilisin (neutral protease), flavourzyme(flavored protease), bromelain and acid protease. By adopting single-factor and orthogonal tests, the optimum hydrolytic conditions of razor clam such as enzyme concentration, hydrolysis temperature, reaction time, substrate concentration and pH value wore determined with the degree of hydrolysis (DH) as the main index. Some experiments on combinations of two kinds of proteases were also conducted. Taking degree of hydrolysis, extraction rate of total nitrogen, color and clearness of the hydrolysate into consideration, the optimum individual proteases for hydrolysis were neutral protease and acid protease, and the optimum combination of two kinds of proteases was that of neutral protease and flavourzyme. The optimum hydrolytic conditions of razor clam for neutral protease were : enzyme concentration 2.4%, hydrolysis temperature 50癈, substrate concentration 1:3, pH 7 and reaction time 6 hrs with the degree of hydrolysis and extraction rate of total nitrogen 42.46% and 83.04% respectively; and foracid protease they were: en/yme concentration 6.0%, hydrolysis temperature 50癈, substrate concentration 1:4, pH3.5 and reaction time 5 hrs with the degree of hydrolysis and extraction rate of total nitrogen 46.37% and 87.94% respectively, the hydrolysate being clear light yellow. For the combination of two kinds of proteases they were: first hydrolyzing with 2.6% f 1 avouryme for 3 hrs, then hydrolyzing with 2.4% neutral protease for 3 hrs with the degree of hydrolysis and extraction rtiie of total nitrogen 4-1.57% and 86.95% respectively. The hydrolysate may be formulated into compound ami no acid condiments, nutritious oral liquids and functional oligopeptides after removing bitter and fishy smell with activated charcoal, 3 -eyeLodextrin and yeast.