Study On The Preparation Of Antifreeze Peptide From Fish Skin And Its Cryoprotective Effects On Frozen Doughs

Antifreeze proteins(AFPs)have thermal hysteresis activity,ice recrystallization inhibition activity and could modify the ice morphology.However,there are several factors limiting the AFPs in commercial application such as low yield,high cost and poor heat stability.Antifreeze peptide is a kind of polypeptide which has same characteristics with antifreeze proteins,and it will have a promising application prospect in food industry due to its widely source,low cost and good heat stability.Therefore,the objective of this paper was devoted to prepare antifreeze peptide from salmon skin gelatin and evaluate its application in frozen dough.The results showed that the antifreeze peptide with maximal thermal hysteresis activity(THA)was obtained from gelatin hydrolysates by papain treated,and the preparation conditions were hydrolysis at pH 6.0 for 2 h at 40? with substrate concentration of 3%(w/v)and papain proportion of 3000 U/g.The antifreeze peptide with maximal THA was named as SaAFP,and the THA of Sa AFP was 0.53?.When the concentration of SaAFP was 20 mg/m L,the survival rate of Escherichia Coli was 75.10% higher than that of the control after 24 h freeze treatment.When the concentration of SaAFP was 0.5%(w/v),the survival rate of yeast cells was 27.04% higher than that of the control after 7 weeks freeze treatment.It indicated that the effect of SaAFP on the survival of microorganism was obvious.The molecular weight of SaAFP mainly distributed within the range of 3000-280.Amino acid analysis results showed that the polar amino acid content was significantly higher than the nonpolar amino acid content in SaAFP,and SaAFP was rich in alanine,glutamic acid,arginine,proline and hydroxyproline.In order to study the influence of SaAFP on frozen doughs,the effects of SaAFP on the thermal properties,rheological properties,microstructure and molecular weight distribution of frozen doughs were investigated.The results showed that SaAFP could affect the apparent specific heat,reduce the freezing temperature,melting enthalpy and the freezable water content,narrow range of melting temperature of fresh dough.During freeze-thaw treatment and freeze treatment,the hydrophilic groups in SaAFP could combine with water,lower water mobility and consequently reduce the freezable water content of frozen doughs.SaAFP could inhibit the ice recrystallization,decrease the damage of gluten network from ice,and consequently slow down the deterioration of rheological properties and microstructure of frozen doughs.SaAFP also could protect the disulfide bond,inhibit the increasement of free sulfhydryl group,and reduce the depolymerization of glutenin macropolymer(GMP)in frozen doughs during the freeze-thaw treatment and freeze treatment.For fermented dough,SaAFP could improve the fermentation ability of frozen dough by increasing the survival of yeast cells,consequently decrease the deterioration of the qualities of frozen steamed breads such as specific volume,hardness and celluar structure.In order to further explore the mechanism of the cryoprotective effects of SaAFP on frozen doughs,the effects of SaAFP on the thermal properties,rheological properties and molecular weight distribution of gluten were investigated.The results showed that the effects of SaAFP on the Capp and freeze-thawing properties of fresh hydrated gluten were consistent with that of fresh doughs.For hydrated gluten,glutenin and gliadin,SaAFP could slow down the increasement of freezable water content and the deterioration of rheological properties of frozen doughs.It can be speculated that the effects of SaAFP on apparent specific heat,freeze-thawing properties,content of freezable water and rheological properties of doughs were achieved by affecting the properties of gluten.Moreover,the addition of SaAFP could inhibit the ice recrystallization of gluten,reduce the weakening of gluten network.For gluten and glutenin,SaAFP could improve the stability of disulfide bonds at low temperature,slow down the growth of free sulfhydayl group in proteins and inhibit the depolymerization of GMP.It can be deduced that SaAFP could inhibit the ice recrystallization of gluten,improve the stability of disulfide bonds,slow down the depolymerization of GMP and the weakening of gluten network,eventually decrease the deterioration of frozen doughs during the process of freeze-thaw treatment and freeze treatment,and improve the quality of steamed breads.After purification by cation exchange column,the THA of SaAFP-P1 was 0.94?.The molecular weight of SaAFP-P1 mainly distributed within the range of 1000-250.And the polar amino acid content was significantly higher than the nonpolar amino acid content in SaAFP-P1.