| Tilapia is a major aquaculture product in China,with delicious meat,high protein content,and abundant essential amino acids required by the human body.Fish scale,a high-quality source of collagen and gelatin,is one of the by-products of tilapia.Fishderived gelatin can not only solve the safety problem of gelatin source,but also comprehensively utilize fish by-products,reduce the pollution to the ecological environment and dispel the concerns of religious believers.Therefore,they are used as the main raw materials in this paper.Fish scales are decolorized before extracting gelatin to explore the influence of decolorizing agent on its physical and chemical properties.Subsequently,they were pretreated with acid or alkali to extract gelatin and then hydrolyzed at different degrees by biological enzymatic hydrolysis technology.The effects of pretreatment,enzymes and hydrolysis time on its physical and chemical structure and functional characteristics were investigated.At the same time,the hydrolysates were dried by different drying methods,as well as the effects of enzyme types and drying methods on the hydrolysis physicochemical properties and water distribution of fish scale gelatin were analyzed.Finally,the fish scale gelatin hydrolysates were compounded with other additives to obtain a functional composite beverage.The technological formula,stability and sterilization technology of compound beverage was also explored.The research results were as follows:2% and 5% hydrogen peroxide(HP),sodiumsulfite(SS),and sodium hypochlorite(SH)were used to pretreat fish scales before extracting gelatin.The results of SDSPAGE and FT-IR showed that decolorizing agents promoted a degradation of triple helix structure in fish scale gelatin,resulted a decrease in the β-folded content and an increase in the random coil content,as well as a decrease in molecular weight.Compared with untreated fish scale gelatin,HP and SS significantly increased the yield of fish scale gelatin(P<0.05),and the extraction rate increased with the increase of decolorizing agent concentration,while SH had the opposite effects.Results of carbonyl and amino group content showed that decolorized treatment could cause oxidation of fish scale gelatin,and the degree of oxidation was positively correlated with the concentration of the bleaching agent.Gel strength results showed that the gel strength of fish scale gelatin decreased as the concentration of decolorizing agent increased.Notably,the gel strength of fish scale gelatin after SH treatment was significantly lower than that treated by HP and SS.In addition,decolorizing treatment significantly improved the emulsifying,foaming,and chromaticity properties of fish scale gelatin,but had no significant effect on its rheological properties,gelation temperature,and melting temperature.Compared with acid pretreatment,alkali pretreatment can inhibit degree of hydrolysates(DH)and decrease TCA soluble peptide content of fish scale gelatin hydrolysates(FSGHs).At the same time,it can also change the amino acid composition(the contents of Val,Leu and Ile decreased,while the contents of Met and Ala increased),and improve emulsification,emulsion stability as well as antioxidant capacity.Under the same pretreatment,the hydrolysate of alkaline protease obtained the highest DH,which was contrary to the results of emulsify-ability and emulsion stability.When DH of FSGHs increased,its β-folding decreased significantly,but ahelix and β-rotation angle raised slightly.Tricine SDS-PAGE showed that the molecular weight of acid protease hydrolysates were the largest(﹥27 k Da),followed by neutral protease hydrolysates(10-27 k Da)and alkaline protease hydrolysates were the smallest(﹤18 k Da).The broken degree of peptide chain in FSGHs hydrolyzed by alkaline protease and dried via freezing were the highest,the particle size,surface hydrophobicity and emulsification were the lowest.These results of acidic protease hydrolysates were just the opposite.However,the particle size of alkaline protease hydrolysate with spray drying was increased due to the re-aggregation of small molecular peptides in solution.FSGHs dried by freezing had slightly higher DPPH radical scavenging ability and OH radical scavenging ability.The results of LF-NMR showed that there were only two types of water components in all samples: bound water and immobilized water,even the conversion rate of immobilized water into bound water was higher than that of free water into immobilized water.Meanwhile,the spray-dried FSGHs had faster relaxation time and higher bound water content.It could release more fixed water,convert into bound water further,and show higher hygroscopicity.In addition,the drying method has the most obvious effects on acid protease hydrolysates(FAPH and SAPH).The optimum technological formula of cranberry compound beverage from fish scale gelatin hydrolysates were determined through single factor analysis and orthogonal analysis combined with sensory evaluation. |
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