Study On The Clean Co-production Of Crayfish Shell Enzymatic Hydrolysate Of Protein And Astaxanthin

Crayfish is the main export of aquatic products in China. The national aquaculture production amounted to 486319 t in 2011, the aquaculture production occupied 231119 t in HuBei province. Meanwhile, the export of crayfish processed product topped 120 million dollars in HuBei province. Most of the crayfish processed product are shrimps, as the shrimps take up 20-30% of weight, hence, it would generate abundant crayfish by-product after processing. The crayfish by-product have high value of protien, fat, minerals, chitin and et al. The acid-alkali method was used to treat crayfish by-product for the time being in industry. It not only caused environmental pollution,but also brought many difficulties to recover protein in by-product. In the present work, crayfish by-product head and shell after processed was the object of study. By observing the effect of pretreatments, enzymolysis method on nitrogen recovery and degree of hydrolysis (DH) of shell-protein hydrolysate,and the effect of parameters on astaxanthin extraction, the clean co-production of crayfish shell protein enzymolysis and astaxanthin was established. Meanwhile,the characteristics of the hydrolysis and astaxanthin stability was also studied, laying a foundation to efficient utilization of crayfish by-product.The results are as followed:1. Studied on the effects of hydrolysis process parameters on crayfish shell-protein. The conditions of hydrolysis temperature、initial pH、percent enzyme、 hydrolysis time、water-to-substrate ratio and pretreatments have significant effect on nitrogen recovery and DH of shell-protein hydrolysate. The optimal step-by-step hydrolysis condition was investigated using L9(43) experimental design, results showed that the optimal hydrolysis process was based on preheated frozen material at 50℃, firstly alkaline protease was added at the dose of 2000U/ml (protein) for 2.4h and then Flavourzyme was added at the dose of 3000U/g (protein) for 3.6 h at 50℃ and initial pH 8.0 with 1:4 solid/liquid ratio. On this condition, the nitrogen recovery attained to 66.52% and DH was 29.89%.2. The properties of crayfish shell-protein hydrolysate was investigated. The nitrogen recovery declined to 32.78% after using TCA solution. The molecular weight distribution was detected by the means of Refractive Index method, it showed that there were two protein peptide in hydrolysate,they were 3.591 X 106Da,4.703×102Da,and they accounted for 0.1%,88.6%,respectively. Through the analysis of free amino acid, the hydrophobic amino acids was higher 1 time than others. As for the volatile components, the raw material, hydrolysate and its shell was detected 51,50,75 volatile components respectively. The highest content of volatile components was aldehyde compound in hydrolysate, it accounted of 58.37%. Nevertheless, the aldehyde and ketone were highest in raw material. Aldehyde and alcohol were highes in hydrolysated shell. Pyrazine, Furan, dimethyl sulphide and et al was newly detected in sample of hydrolysate3. The extraction conditions of astaxanthin was investigated. The condition of hydrolysis、organic solvent type、temperature、pH、ultrasonication and time have significant effect on astaxanthin extraction in de-protein crayfish shell. The extraction content was increasing with hydrolysis temperature, the extraction content was highest on both at initial pH 7.5 and 6h hydrolysis time.Absolute ethyl alcohol was better than ethyl acetate, acetone, petroleum ether and dichloromethane in extracting astaxanthin. The highest extracting content was under the conditions of using Ultrasonic pretreatment, initial pH 8.0 with 1:6 solid/liquid ratio for 120min at 40℃.4. The properties, stability and protective measures of astaxanthin was investigated. It indicated that the isomerization of astaxanthin, therefore, leading to the color more darker during extraction at 70-100℃. From the comparation of HLPC of astaxanthin standard, the astaxanthin extraction solubility was 3.3575mg/100ml. By the analysis of thin-layer chromatography,it could separate the free astaxanthin, astaxanthin one ester and astaxanthin two ester. Temperature, light, H2O2, antioxidant and metal ions could affect the stability of astaxanthin in anhydrous ethanol. High temperature and light faded the color of astaxanthin, hence it should be kept in the dark and low temperature condition; H2O2 led it fading fast, so it should be kept away from oxidizing material; the adding of Vc、BHA might cause isomerization of astaxanthin, turnning red to more darker with the adding dose, however, the lower dose of BHT at 0.01g/100g can stable astaxanthin; Cu2+, Fe2+ sped up the astaxanthin fade, it should be kept away from these during producted. During the hydrolysis, BHT could significantly enhance the extraction content, for the sake of cost, the dose of BHT was appropriate at 6g/100ml; filling N2 during hydrolysis significantly increased the extraction content than non-protective condition; the crayfish shell after hydrolysis was dried, the extraction content was about 5 times higher than wet shell.