| In recent years, the shrimp farming industry was developing rapidly in China, which is a major shrimp producer in the world’s market now, but at the same time, caused500,000tons/year of discards, such as shrimp head. The head of Penaeus vannamei is rich in chitin,protein, carotenoids, minerals and amino acids. At present, only a small quantity of these discards were utilized, leaves large quantities of them wasted and results in the loss of valuable components and environmental pollution. In this study, shrimp heads have been fermented with Streptococcus thermophilus, which was a lactic acid bacterium and widely used for manufacturing yogurt and cheese. Then, the ingredient changes in shrimp head fermentation with Streptococcus thermophilus were investigated to analyze their function. In addition, the technology of extraction and purification of astaxanthin has been studied. The results and conclusions are as follows:The fermentation conditions were optimized by response surface methodology. The highest deproteinization rate of94.15%was obtained under the condition of10%shrimp head,5%glucose,1.2%(v/v) inoculum size, and64h of incubation time at42℃and an initial pH of5.00with RSM optimization. At the same time, the changes of enzyme activity, deproteination (DP), amino nitrogen content, as well as the PH value of the shrimp biowaste during the fermentation process were investigated. At the same time, the relations between each parameter were analyzed. The observed DP%at the initial stage of fermentation (more than35%), when low Streptococcus thermophilus growth, might be explained by the presence of digestive enzymes in the hepatopancreas. Protein hydrolysis refered to any process in which protein was broken down by protein-digesting enzymes. As the fermentation progresses, the pH decreased, the deviation from the enzyme optimum pH, enzyme activity decreased. Fermentation resulted in83.27%decalcification,94.15%of deproteination and3.29mg/ml amino nitrogen content at the end of64h of fermentation. Study on the technological conditions of the extraction and the saponification of astaxanthin esters isolated from shrimp head into free astaxanthin. The optimized extraction technique is ethanol and waste (with a ratio of6:1) used in the maceration procedure, at the temperature of15℃for60min. The extraction amount reached21.6μg/g shrimp head. The results showed that astaxanthin esters were completely turned into free astaxanthin by40mol/L NaOH-methanol, at the temperature of10℃for12h. Centrifugal thin layer chromatography was used to purify the astaxanthin and the optimum was n-hexane, methylene dichloride and acetone (5:2:2). Effects of temperature, light, cations and reducing agents on the stability of astaxanthin were studied. The results indicated the content of astaxanthin decreased when temperatures were higher than40℃. Mg2+,Na+, Ca2+shows minor effects on astaxanthin, while the other cations such as Zn2+, Cu2+, Fe2+and Fe3+could seriously damage astaxanthin. Reducing agents such as Ve, Vc and Na2SO2can protect astaxanthin from oxidation. VE shows better protection effects than Na2SO3and Vc.The amino acids contents analysis in supernate before and after fermentation shows:the amino acid content after fermentation (796.98mg/L) is higher than that (690mg/L) before fermentation, especially for the eight essential amino acids and the γ-aminobutyric acid. The comparison of FTIR spectra and XRD pattern among commercial chitin (CTa), chitin prepared by the Streptococcus thermophilus fermentation (CTb) and chitin prepared by chemical treatments (CTc) indicated that CTb demonstrated the highest degree of deacetylation, whch is critical to the preparation of chitosan under moderate condition. Antioxidants with high bioactivity were dramatically found in a large amount in the supernatant fluid from the fermentation process. At the end of the fermentation process, the DPPH radical scavenging ability of the culture supernatant reached98.70%. |
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