Effect Of Pigskin Gelatin On Frozen Dough And Its Bread Quality And Mechanistic Study

Frozen dough market is in constant evolution owing to its facilitation of the centralization of dough production and the extension of distribution area.Frozen dough technology can effectively solve many problems such as short shelf life,inconvenient transportation,and unreliable quality of products.However,the ice growth and recrystallization during frozen storage cause the detrimental changes including reduced bread volume,increased crumb firmness,longer proof time,less aroma,and decreased consumer acceptance.Therefore,it's of great importance to control the ice growth and recrystallization on ice crystals for maintaining the quality of frozen dough.It has been reported that pigskin gelatin showed a significant ice crystal inhibitory activity in ice cream.In this study,the effect of pigskin gelatin and its hydrolysates on overall changes that frozen dough underwent during storage was investigated.Furthermore,the interaction of pig skin gelatin with the gluten network of frozen dough during freezing was clarified and bread staling was studied in terms of rheological properties of dough,starch retrogradation and water migration.The main research contents and conclusions were as follows:1.Pigskin gelatin contributed to delaying the quality deterioration of frozen dough bread.Bread specific volume,TPA,internal texture structure and bread color were applied as indicators.The influence of different gelatin addition levels(0%,0.5%,1.0% and 1.5%)and different hydrolysis degrees of gelatin(Gelatin hydrolysates,GHY;Unhydrolyzed gelatin,UHG)on the baking characteristics of frozen dough bread were explored during long-term frozen storage(0,30 and 60 days).The specific volume of gelatin-rich group was larger than that of the control samples regardless of hydrolysis degree.The specific volume of bread showed an increasing trend with the gelatin addition increased.TPA analysis indicated gelatin resulted in lower hardness of the crumb.The internal texture structure displayed pigskin gelatin caused less changes of crumb porosity and cell density.Bread colors showed the incorporation of gelatin(GHY or UHG)contributed to reducing the increments in L*,a* and b* values of the crust,thus preserving the baking color.There was a significant difference between 1.0% and 1.5% gelatin on the quality of frozen dough bread(p<0.05).Nevertheless,the effect of pigskin gelatin on qualities of frozen dough was independent on its hydrolysis degree.2.Pigskin gelatin reduced the degree of glutenin macropolymer(GMP)depolymerization during 60-day frozen storage.A more flexible and dense gluten network was formed through non-covalent bonds to reduce the damage of gluten network caused by the growth and the recrystallization of ice crystals.UHG showed a stronger protective effect than GHY.SDSpolyacrylamide gel electrophoresis(SDS-PAGE),size exclusion chromatography(SE-HPLC),GMP analysis,free thiol content analysis,Fourier transform infrared spectroscopy(FT-IR),thermogravimetric analysis(TGA)were measured.The interaction between 1.0% pigskin gelatin(GHY and UHG)and gluten network during long-term frozen storage(60 days)was investigated.SDS-PAGE analysis showed that both GHY and UHG led to an increase in band intensity,but the numbers of bands remained.SE-HPLC analysis indicated that pig skin gelatin caused an increase in content of SDS-soluble protein.GMP analysis found the GMP depolymerization degree of the GHY group(32.36%)and the UHG group(24.55%)were lower than that of the control group(36.94%)after 60-day frozen storage.Analysis of free thiol content showed compared with the control group,GHY and UHG significantly reduced the SH content by 9.76% and 4.18%,respectively.FT-IR results found that there were no statistical differences between the control group and the gelatin group concerning the content of the ?-helices,?-sheets,?-turns and random coils.Nevertheless,pigskin gelatin significantly increased the proportion of glutamine side chain(p<0.05).Thermogravimetric analysis(TGA)displayed that the pyrolysis temperature of the gelatin group was higher than the control group regardless of freezing treatment,however,the differences in degradation temperature were not obvious.3.Pigskin gelatin retarded the staling process of bread,which was related to starch retrogradation and water migration.Staling rate,farinograph,extensograph,viscoelasticity,Xray diffraction(XRD),differential scanning calorimetry(DSC),moisture content,water activity,low field nuclear magnetic resonance(LF-NMR)were applied to study the effect of pigskin gelatin on the rheological properties of dough and bread staling.Farinograph and extensograph indicated that pigskin gelatin partly weakened the gluten.Viscoelasticity measured that the G' and G'' of the gelatin-containing dough were higher than those of the control group,and the tan ? value decreased with the increase of the gelatin addition amount.Compared with the control samples,7-day staling rate of bread containing 0.5% and 1.0% gelatin decreased by 6.56% and 20.83%,respectively.XRD analysis showed that as the addition amount of gelatin increased,the relative crystallinity decreased from 15.12%,11.60% to 10.75%.DSC analysis found that pigskin gelatin reduced the enthalpy values.Moisture content and water activity analysis demonstrated that pigskin gelatin led to a decrease in the rate of water loss.LF-NMR analysis indicated gelatin reduced the water mobility of the bread during storage,preventing the dehydration of gluten.In conclusion,pigskin gelatin can significantly delay the deterioration of the quality of frozen dough and extend the shelf life of bread.Thereby,the improvement may contribute to reducing food waste and improving economic efficiency.