Study On Preparation Of Tilapia Skin Collagen By Solid-state Fermentation And Antioxidant Activity Of Its Hydrolysates

Tilapia is an important cultured fish in China.However,by-products during production such as fish scales and skins are usually discarded or made into cheap feed.It has become the key issue facing breeding and processing industry of tilapia about how to realize high value utilization of these resources.Tilapia skin is rich with collagen,so it is possible to use it as the raw material for industrial production in a large scale.Considering the quality of the product,the level of production cost,and whether it is environmentally friendly,there are many limitations of the current methods for extracting collagen.In this study,taking the tilapia skin as the research object,the solid-state fermentation method(SSF)was used to extract fish skin collagen and the production process was optimized as well.The structure and physicochemical properties of collagen in fish skin were analyzed.The production technology of producing collagenase by solid-state fermentation with Bacillus subtilis was optimized to obtain the optimum culture conditions,and the antioxidant activity of the obtained fermentation products was investigated.(1)The production technology of extracting collagen from tilapia skin by solid-state fermentation with Bacillus subtilis was studied.The extraction rate of collagen was selected as evaluation index,the fermentation conditions were optimized by single factor test and response surface methodology,the effect of five factors on the extraction rate of collagen was studied including cell age,water addition,inoculum size,fermentation temperature,and fermentation time.The results showed that the optimum fermentation process parameters were cell age 20 h,water addition 11.7 m L,inoculum size 5.8%,fermentation temperature 34 °C,and fermentation time 48 h.Under such conditions,the extraction rate of SSF collagen was 65.03%.(2)The extraction rate,characteristic structure,and physicochemical properties of SSF collagen extracted by solid-state fermentation and acid-soluble collagen(ASC)extracted by acid extraction method was compared with each other.The results of sodium dodecyl sulfate poly acrylamide gel electrophoresis(SDS-PAGE),fourier transform infrared spectra,ultraviolet spectra,amino acid composition,thermal stability and solubility showed the extraction rate of SSF collagen(65.03%)was higher than that of ASC(57.26%)and these two kinds of collagen were collagen type I retaining the complete triple-helix structure.SSF collagen has a higher content of sub-amino acids and hydrophobic amino acids,as well as better heat resistance and solubility than that of ASC.(3)The activity of collagenase was selected as evaluation index,the effect of five factors on the production of collagenase from tilapia skin by solid-state fermentation with Bacillus subtilis was studied including initial p H,cell age,water addition,fermentation temperature and fermentation time.To optimize the culture conditions,the orthogonal test was designed based on the results of single factor test.The results showed that the optimum conditions for production of collagenase were initial p H7,cell age 14 h,water addition 10 m L,fermentation temperature 35 °C,and fermentation time 24 h.Under such conditions,the activity of collagenase was 90.05 U/m L with an increase by 40.1%.(4)The collagen hydrolysates was obtained from tilapia skin by solid-state fermentation with Bacillus subtilis.The antioxidant activity of tilapia skin hydrolysates with different molecular weight were assayed.The results showed that the three different molecular weight peptide of tilapia skin hydrolysates isolated by two ultrafiltration membranes(MW 5 and 10 k Da)presented different antioxidant activity and the hydrolysates presented the highest antioxidative activity which molecular weight was below 5 k Da(TSCP-c).