The Effect Of Antifreeze Proteins On The Frozen Dough And Steamed Bread Quality Unber Frozen Environment

Antifreeze protein(AFPs)is a kind of protein which can reduce the freezing point of solution,and modify the ice crystal form and inhibit the recrystallization of ice crystals.It has a good application prospect in frozen food.In this study,the effects of AFPs on the quality,ferment rheology propertie,protein and water status of pre-fermented frozen dough were studied in frozen dough and steamed bread.The effect of AFPs on frozen storage and freeze-thaw stability of pre-fermented frozen dough bread was discussed,which provided the theoretical basis for the practical application of AFPs in frozen dough.The main findings are as follows:(1)The effect of AFPs on the quality of frozen dough steamed bread was studied.The results showed that with the increase of frozen storage time and the number of freeze-thaw cycles,the specific volume of frozen dough steamed bread decreased,and the hardness and chewiness increased obviously,and the elasticity and recovery were decreased,the frozen dough steamed bread quality decreased significantly under freeze-thaw cycles.This indicated that frozen storage and freeze-thaw cycles lead to the drop of frozen dough steamed bread quality.The changes of specific volume and texture characteristics of frozen dough bread added with AFPs were relatively small,which proves that antifreeze protein can slow down the decline of frozen dough steamed bread quality during frozen storage and freezing and thaw cycles.(2)Effects of AFPs on ferment rheology propertie of frozen dough by frozen storage and freeze-thaw cycles were studied by Fermentation Rheometer(F4).The results showed that the maximum dough development height,total volume of gas produced and maximum height of the gas release curve were significantly decreased after frozen storage 90 days and 5 freeze-thaw cycles.After 5 freeze-thaw cycles,the the maximum dough development height of the frozen dough was only 6.6mm.This showed that frozen storage and freeze-thaw cycles seriously affected the gassing power of yeast and gas-holdingcapacity of dough,which was related to the formation of recrystallization and large ice crystals during frozen storage and freeze-thaw cycles.The maximum dough development height of frozen dough added with AFPs was significantly larger than the control dough.The AFPs improve ferment rheology propertie of the frozen dough because of the restraining recrystallization and modifying the ice crystal morphology of AFPs.(3)Effects of AFPs in frozen dough on free thiol and disulfide bond,subunit and secondary structure properties under frozen storage and freeze-thaw cycles were studied by Ellman's reagent colorimetry,SDS-PAGE electrophoresis and Fourier transform Infrared spectroscopy.After frozen storage and freeze-thaw cycles,the content of free thiol in the frozen dough increased,and the content of disulfide bond decreased,and the protein subunit did not change significantly.The prolongation of frozen storage caused the increase of the content of the molecular ?-sheet and the decrease of ?-turns,and the freeze-thaw cycles decreased the ?-helixes structure.could The changes in protein secondary structure of frozen dough were reduced by AFPs.Therefore,in frozen storage and freeze-thaw cycles,AFPs could inhibit the rapture of disulfide bon and secondary structure change,so as to stabilize the quality of frozen dough steamed bread.(4)The effect of AFPs on the presence of water molecules in frozen dough was studied by nuclear magnetic resonance(NMR).The results showed that the water loss rate of control dough was significantly increased after frozen storage and freeze-thaw cycles,and the relaxation time T2 l gradually increased and the bound water content decreased with the prolongation of frozen storage time,indicating that the frozen storage and freeze-thaw cycles enhanced the flow of water in the dough,and the destruction of the gluten network structure weakened the water retention of the dough,which caused the water molecules migrated from the bound state to the free state.The addition of AFPs could inhibit the recrystallization of ice crystals,thus reducing the water loss of dough,slowing down the transition from the bound moisture to half bound water,and maintaining the water holding capacity of dough during frozen storage and freeze-thaw cycles.In conclusion,antifreeze proteins can improve the quality of frozen dough and steamed bread during frozen storage and freeze thawing,and can be used as a cryoprotectant in the processing and production of frozen dough steamed bread.