Preparation Of Low Oils Content Quick-frozen Non-fermented Pancakes And Its Quality Change During Frozen Storage

Along with the development of frozen flour products industry,frozen pancakes gradually appear in the vision of public and occupy the frozen market.One of the advantages of quick-frozen non-fermented pancakes is popular because of its easy circulation,storage and convenience.However,there are a series of problems in the actual production of quick-frozen non-fermented pancakes: excessive intake of saturated fatty acids in quick-frozen non-fermented pancakes can lead to atherosclerosis and increase the risk of coronary heart disease;the formation of ice crystals and recrystallization can lead to deterioration in the quality of quick-frozen non-fermented pancakes during the frozen storage process.The subject is to develop quick-frozen non-fermented pancakes with low oils content by screening the types and additions of oils,to investigate the quality changes during freeze-thawed cycles(FTs),and to provide process strategies for the quality improvement of quick-frozen non-fermented pancakes;the deterioration mechanism of quick-frozen non-fermented pancakes was analyzed by analyzing the physicochemical properties of gluten protein,starch and fat in quick-frozen non-fermented pancakes in terms of characteristic components and key structures.First,the effects of oil types and additions on the quality of quick-frozen non-fermented pancakes were investigated.The results showed that after 10 FTs,the tanδ of quick-frozen non-fermented raw pancakes reached the minimum and the gluten network structure of raw pancakes was the most stable when the addition amounts of rapeseed oils,sunflower oils and soybean oils were 8%,12% and 12%,respectively.The rate of change of texture properties of quick-frozen non-fermented raw pancakes was the smallest and the freezing resistance was better when rapeseed oils,sunflower oils and soybean oils were added at 8%,16% and10%,respectively.The rate of change of ΔE for rapeseed oils,sunflower oils and soybean oils was the smallest at 16%,10% and 10%,respectively.From the TPA test,it was obtained that the hardness and chewiness of quick-frozen non-fermented cooked pancakes reached the minimum at 10%,12% and 14% additions of rapeseed oils,sunflower oils and soybean oils,respectively;the differences of elasticity,cohesiveness and recovery were less.The puncture test showed that the hardness of the quick-frozen non-fermented cooked pancakes was minimized at 10%,12% and 16% additions of rapeseed oils,sunflower oils and soybean oils,respectively,and there was no significant difference in crispness.The highest total sensory scores of quick-frozen non-fermented cooked pancakes were obtained at 10%,12% and 12%for rapeseed oils,sunflower oils and soybean oils,respectively,and 12% sunflower oils had the highest score.In conclusion,the 12% sunflower oils quick-frozen non-fermented pancakes had the best quality.Secondly,the changes of the quality of sunflower oils quick-frozen non-fermented pancakes were investigated during frozen storage.The results showed that the hardness and chewiness of the quick-frozen non-fermented cooked pancakes showed an increasing trend with the times of FTs,and the elasticity,cohesiveness and reversibility gradually decreased;the hardness of the puncture test also gradually decreases;at 8FTs~10FTs,the total sensory evaluation score decreased sharply,and the quality deteriorated seriously.0FTs~10FTs,the hardness,cohesiveness and chewiness of the quick-frozen non-fermented raw pancakes decreased significantly,the magnitude of elasticity change was not obvious,and the reversibility decreased significantly at 2FTs,and the change trend tended to stabilize after2FTs;the brightness gradually decreased,the redness and yellowness gradually increased;both G′ and G″ decreased with the extension of FTs,and the viscoelasticity of raw pancakes significantly decreased after 10FTs;the value of |G*| gradually decreased,and the structural strength of dough decreased;in addition,the deformation resistance and recovery ability of quick-frozen non-fermented raw pancakes weakened with FTs increased;the structure of raw pancakes became worse.Again,the changes of structural properties,functional properties and microstructure of gluten proteins in sunflower oils quick-frozen non-fermented raw pancakes were investigated during FTs.The results showed that with the increase of FTs,GMP underwent different degrees of depolymerization and the content of polymeric and monomeric proteins increased;the content of free sulfhydryl groups tended to increase and the content of disulfide bonds decreased;the more ordered α-helical structure was transformed intoβ-turned and irregularly curled structures;the surface hydrophobicity increased;after 10 FTs,the network of gluten proteins was severely damaged,a large part of it was broken and the structure became loose.As the number of FTs increased,more hydrophobic groups were exposed in gluten proteins,leading to a significant decrease in water-holding power and an increase in oils-holding power;the Td of gluten proteins in quick-frozen non-fermented raw pancakes showed a trend of gradual decrease,and the resistance of gluten proteins to thermal denaturation was reduced;the z value showed a trend of fluctuating increase with the increase of FTs,and the value of K showed a trend of gradual decrease,and the dependence of gluten proteins on frequency increased,and the stability and structural strength decreased.As a result,the viscoelasticity and hardness of the quick-frozen non-fermented raw pancakes were reduced,the hardness of the cooked pancakes increased,the internal structure deteriorated,the texture was harder and the taste became worse.Then,the changes of structural and physicochemical properties of starches in sunflower oils quick-frozen non-fermented raw pancakes were investigated during FTs.The results showed that: with the increase of FTs,the damage of ice crystals on starch granules gradually increased,starch broke or degraded into more small and medium-sized molecules,and the molecular weight decreased;straight-chain starch dissolved;solubility and swelling potential showed a trend of first increasing and then decreasing,and reached the maximum at 8FTs.The granule size of starch increased significantly at 2FTs,and gradually decreased at 4FTs~10FTs;after 10 FTs,the crystallinity of starch increased by 6.66%;the values of R1047/1022 and R995/1022 increased by 6.46% and 1.91%,respectively,and the starch formed a more ordered molecular structure;the pasting temperature of starch showed a fluctuating increasing trend,and the pasting enthalpy increased from(7.39±0.05)J/g to(9.02±0.28)J/g;the peak viscosity,trough viscosity,disintegration viscosity,final viscosity and regenerative viscosity reached the maximum at 4FTs,respectively,and then gradually decreased;the surface of starch at 0FTs was complete and smooth without cracks,and the surface of starch granules became rough with the increase of FTs,and large depressions and folds appeared.The changes of starch fraction increased the hardness of quick-frozen non-fermented cooked pancakes and decreased the smoothness and fineness of cooked pancakes.Finally,the changes of oils quality in sunflower oils quick-frozen non-fermented raw pancakes were investigated during FTs.The results showed that during FTs,unsaturated fatty acids were oxidized and decomposed into diglycerides,monoacylglycerols,free fatty acids,glycerol,etc.and formed volatile compounds including aldehydes,alcohols,ketones and other small molecules,resulting in higher saturated fatty acids content and lower unsaturated fatty acids content;with the increase of FTs,the value of acids,peroxide,anisidine and thiobarbituric acid in sunflower oils quick-frozen non-fermented pancakes gradually increased and the oxidation induction times gradually decreased,indicating that after 10 FTs,the oxidative stability of sunflower oils significantly deteriorated and the storability of quick-frozen non-fermented pancakes decreased,which reduced the flavor and taste of quick-frozen non-fermented pancakes.In summary,the quality of quick-frozen non-fermented pancakes prepared with 12%sunflower oils was optimal,it laid the foundation for the development of healthy low oils content quick-frozen non-fermented pancakes;the deterioration mechanism of quick-frozen non-fermented pancakes were analyzed from the characteristic components(gluten proteins,starches and oils)and their key structures,which provided a theoretical basis for the quality improvement of frozen foods.