| Flounder(Pleuronichthys cornutus)is a deep sea fish,which is one of the main economic fish species in the northern area of China.What's more,it is also the important component of seawater cultured fish species.Because of its delicious meat,unique taste,rich nutrition and other characteristics,has been deeply favored by people as a high-grade fish.Since the deep processing technology is scare,the skin of flounder is the main by-products with a large yield produced in the processing of flounders,and the highest content of fish skin collagen can be accounted for 80%of the total amount of protein,so flounder skin is a good raw materials for the production of collagen.In the paper,to make more effective use of underutilized resources,physiochemical characteristics and functional properties of acid-soluble collagen from different parts of the skins of flounder {Pleuronichthys cornutus)were studied,and the effects of extraction methods on physicochemical and functional properties of collagen from flounder skins were also comparatively analyzed.The main research conclusions are as follows:1.Flounder skins are an excellent source of protein,and protein content of black and white skins of flounder are 83.95%and 81.58%,respectively(dry basis),So they are an ideal raw material to extract collagen.Fresh flounder was used as the raw materials in this study,the acid-soluble collagens were respectively extracted from black and white skins of flounder,and comparative analysis of the difference on physical and chemical properties of black and white skins ASC.From the naked eye,the black and white skins ASC presented milky white,soft texture,flocculent hierarchical state.The yields of black and white skins ASC were 36.35%and 40.08%,respectively,based on dry skin weight,and the color of white skin ASC was slightly higher than that of black skin ASC,however,the gel strength of white skin ASC was slightly lower than that of black skin.Ultraviolet spectrum scanning revealed that black and white skins ASC had strong absorption peaks at 230 and 230.5 nm respectively,but didn't have strong absorption peaks at 280 nm,suggesting that these proteins were in accordance with the characteristics of collagen.Fourier transform infrared spectra showed that the black and white skins ASC were similar and some bands vibration indicated their structural integrity in the secondary structures.In different NaCl concentrations and pH two systems,the black skin ASC had a better solubility than white skin ASC.The results of isoelectric point showed that the isoelectric point of black and white skins ASC solutions were 7.5 and 6.5 respectively,suggesting that both isoelectric point were in neutral range.The results of scanning electron microscopy indicated that black and white skins ASC looked like disorder fiber porous beam.SDS-polyacrylamide gel electrophoresis showed that black and white skins ASC should be most likely classified as type ? collagen,but there were some differences in the proportion of? and ? components.The results of DSC indicated that the thermal denaturation temperature of black and white skins ASC were 70.5? and 78.6? respectively.The results of particle size distribution showed that both ASC presented uniform and normal distribution,and particle size distribution was not significantly different.2.In different concentrations conditions,G' and G" of black and white skins ASC were increased with increasing shear frequency and collagen solution concentrations,and G,,of both was greater than their respective G' with increasing collagen solution concentrations.In different temperatures conditions,G' and G" of both ASC were also increased with increasing shear frequency,but G' and G" of both ASC were decreased with increasing temperatures.The hygroscopic and moisture retention curves of black and white skins ASC showed a similar trend with increasing times,suggesting the trend of a gradual increase in moisture absorption rate with the increasing times,however,the trend of a gradual decrease in moisture retention with the increasing times.Water absorption capacity(WAC)and oil absorption capacity(OAC)indicated that both ASC had a certain WAC and OAC,suggesting that the WAC and OAC of black skin ASC were higher than that of white skin ASC.The results of foaming capacity and its stability of both ASC showed that both foaming capacity and its stability of white skin ASC were higher than that of black skin ASC,suggesting that molecular weight of white skin ASC was higher than that of black skin ASC.With the extension of time,the aggregation kinetics curves of both ASC showed a S trend,and the aggregation ability of black skin ASC was higher than that of white skin ASC in the whole process.Emulsifying activity(EAI)and emulsifying stability(ESI)indicated that the EAI of white skin ASC was significantly higher than that of black skin ASC(p<0.05).However,the ESI of white skin ASC was significantly lower than that of black skin ASC(p<0.05).3.Fresh flounder black skins were used as the raw materials in this study,ASC and PSC were respectively extracted from the black skins of flounder,of which structure characteristics and physicochemical properties were compared and studied.The results of yields of ASC and PSC showed that the yield of PSC was significantly higher than that of ASC(p<0.05)were 49.39%and 36.35%(on a dry weight basis),respectively.The colors and gel strength of ASC and PSC revealed that colors and gel strength of ASC significantly were higher than that of PSC(P<0.05).UV absorption showed strong absorption peaks at 230 nm,but almost no absorption in the 260 to 280 nm region for ASC as expect for collagen but a little for PSC,suggesting an impurity.Fourier transform infrared spectra showed that ASC and PSC existed Amide A,Amide B,Amide ?,Amide ?,Amidelll,revealing that the protein secondary structures of ASC and PSC were similar.In different NaCl concentrations and pH two systems,PSC had a better solubility than ASC.SDS-PAGE confirmed that ASC and PSC contained ?1 and ?2 chains in a ratio of approximately 2:1,and the estimated molecular weight of ?1 and ?2 chains was approximately 116.0 Ku,which was consistent with type ? collagen.Moreover,the proportion of ? and ? components in PSC was lower than that in ASC,but the intensity of a chains PSC was higher than that in ASC.4.In the same concentrations conditions,G' and G" of ASC and PSC were increased with increasing shear frequency,and G" of ASC and PSC were greater than their respective G' with increasing collagen solution concentrations.In the same temperatures conditions,G' and G"of ASC and PSC were also increased with increasing shear frequency,and G' and G" of PSC were greater than that of ASC with increasing temperatures,but G' and G" of ASC and PSC were decreased in the change process of the temperatures.Hygroscopicity and moisture retention indicated that moisture absorption rate of PSC was significantly higher than ASC(p<0.05).However,there was not significant difference for ASC and PSC in moisture-retention ability(p>0.05).WAC and OAC indicated that both ASC and PSC had a certain WAC and OAC,suggesting that the WAC and OAC of PSC were higher than that of ASC.The results of foaming capacity and its stability of ASC and PSC showed that both ASC and PSC had a certain foaming capacity and its stability,and the foaming capacity of ASC and PSC were greater than their respective foaming stability,what's more,the foaming capacity and its stability of PSC were higher than that of ASC.EAI and ESI indicated that the EAI of PSC was significantly lower than that of ASC(p<0.05),However,the ESI of ASC and PSC were not significantly different(p>0.05). |
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