Extraction, Characterization And Applicability Of Gelatin Extracted From The Channel Catfish Skin

Galatin is one of the biomacromolecules, which represents a major source ofgood quality protein with applications in the food, pharmaceutical, cosmetics andphotographic industries. Gelatin is an abundant protein in the skins and bones ofthe mammals, and it can be obtained by acid or alkali pretreatment, then extractedby hot water. Acid-type, Alkali-type and Acid base-type gelatin are gelatin whichused acid, alkali and both respectively in the preprocessing stage. The isolatedproteins were confirmed by different physic-chemical techniques and applied tofish sausages.To establish the optimum gelatin extraction condition from channel catfishskin, response surface methodology was adopted in this study. The effects of pH（A）, water/skin ratio （v/w, B）, extraction temperature （℃，C） and extraction time（h, D） of the extraction of these three gelatins were studied. The responses wereyield （%）, gel strength （g）. Optimal conditions of Acid-type gelatin in extractiveprocess were A=5, B=1:40, C=59, and D=5, while the pretreatment condition wereH₂SO₄%=0.4%, skin/water ratio=1:15, pretreatment time=12h.Then predictedresponses were47.41%yield,622g gel strength. Optimal Alkali-type gelatinextractive process were A=6, B=1:15, C=59, and D=5, while the pretreatmentcondition were NaOH=0.05moL/L, skin/water ratio=1:15, time=12h. Thenpredicted responses were41%yield,583.2g gel strength. And Acid base-typegelatin were A=5, B=1:20, C=49, and D=5.5, while pretreatment condition wereH₂SO₄%=0.2%, time=3h, NaOH=0.05moL/L, time=3h, both skin/water ratio=1:15,then50.46%yield,513.9g gel strength. To the whole process, concentration ofH₂SO₄in Acid base-type gelatin pretreatment were less then Acid-type, and time ofpretreatment were laest. While in extraction process, skin/water ratio of Acid-typegelatin were most. Temperature of Acid base-type gelatin were lowest. But, to yield,Acid base-type gelatin is first, next, Acid-type gelatin, Alkali-type gelatin finally.But regard to gel strength, Acid-type gelatin is first, next Alkali-type gelatin, finalAcid base-type gelatin.Physical and chemical properties of gelatins in the optimal conditions were determined. The Viscosity of Acid-type, Alkali-type and Acid base-type gelatinwere6.95mPa·s,10.47mPa·s and8.68mPa·s. The denaturation temperature were113.27℃,115.68℃�'�112.43℃respectively. Acid base-type gelatin exhibitedlower gelling （16.4℃） and melting （24.1℃） points than Acid-type （17.2℃,25.2℃）and Alkali-type （17.3℃,25.2℃） gelatin. All the three gelatins had four chains, γ、β、α1and α2. α1and α2chains of gelatin were with molecular weight of120and110kDa, respectively. Γ and β had higher molecular weight. Gelatin from channelcatfish skin had glycine as the major amino acid,respectively high contents ofproline and hydroxyproline. Some essential amino-acids and semi-essential aminoacids were also observed. However, very low contents of methionine, histidine andtyrosine. The three gelatins from channel catfish skin had maximum absorptionnear220nm, with little or no absorption at280nm. The maximum absorption ofAcid-type gelatin near206nm, Alkali-type near204nm and Acid base-type near206nm. The amide A band of these three gelatins were found at3330cm^-1, whichshows that there were NH groups involved in hydrogen bonds. The amide B bandpositions were observed near3080, which shows there were CH2groups. Regionsof amides Ⅰ,Ⅱ and Ⅲ were1650cm^-1,1545cm^-1and1237cm^-1, exhibitingpeaks in some wave numbers.In application test of these three gelatins, comparing free of gelatins,containing carrageenan and these three gelatins from channel catfish skin, thesethree gelatins played roles equaling to carrageenan on gel strength, TPA and WHCof fish sausage according to those data. So we tended to believe that these threegelatins from channel catfish skin could taking place of carrageenan be applied infish sausages.