Study On The Relationship Between Molecular Structure Basis Of Wheat Starch And Quality Of Frozen Steamed Bread

In this paper,11 different varieties of wheat were used as raw materials.Firstly,the physicochemical properties of wheat flour were studied by fermentation rheometer,mixing experiment instrument,etc.Then different varieties of wheat starch were extracted.Their molecular structure and physicochemical properties of wheat starch were analyzed by fluorescence-assisted carbohydrate electrophoresis(FACE),rapid viscosity analyzer(RVA),differential scanning calorimeter(DSC),X-ray diffractometer(XRD),etc.On this basis,these wheat flours were used as raw materials to make Chinese steamed bread(CSB).The water distribution and texture changes of CSB were measured,and the quality differences from different varieties of wheat flour CSB were analyzed during frozen storage.The changes of starch molecular structure in CSB were discussed after 60 days of frozen storage,and the effect of frozen storage on starch molecular structure was studied.Main research contents and conclusions are as follows:(1)The protein content of 11 varieties of wheat flour was 9.82%-15.70%,and the wet gluten content was 15.23%-36.45%.The total starch content was 76.63%-85.89%.It was obtained by analysis of mixed experimental instrument,Yang Nuo Mai 1 Hao had the weakest gelatinization heat stability and was the most difficult to retrogradation,while Zheng Mai 103 had the strongest gelatinization heat stability.The physicochemical properties of wheat flour were analyzed by RVA and fermentation rheometer,and the correlation between the physicochemical properties of wheat flour and the sensory quality of CSB was studied.The results showed that the protein content was significantly positively correlated with the maximum height of dough formation(Hm)and the specific volume of CSB(p<0.05).The wet gluten content had positively correlations with the total gas volume(Vt),gas retention coefficient(R),peak viscosity(PKV),breakdown value(BDV),specific volume,tissue structure,elasticity and total score of CSB(p<0.05).Vt had positively correlations with the specific volume of CSB,and R value was positively correlated with the specific volume,color,structure and appearance of CSB(p<0.05).PKV had negatively correlations with the elasticity and toughness of CSB,HPV had positively correlations with the appearance of CSB,BDV had negatively correlations with the specific volume and organizational structure,elasticity,viscosity and total score of CSB,CPV had positively correlations with the specific volume,structure,appearance,elasticity and total score of CSB(p<0.05).Therefore,protein content,wet gluten content and starch pasting properties were all important factors affecting the quality of CSB.(2)The particle size,amylose content(AC),retrogradation,freeze-thaw stability and gelatinization characteristics of starch extracted from 11 different varieties of wheat were analyzed.The fine structure of amylopectin from different varieties of wheat were studied by FACE,and the relationship were discussed between starch molecular structure and starch physicochemical properties.The results showed that the overall model of chain length distribution from 11 wheat starches were similar.The average chain length of Ai Kang 58 was the lowest(20.84),while that of Yang Nuo Mai 1 Hao was the highest(22.71).The wheat starches had a wide AC ranging from 1.75%to 28.79%.AC had negative correlations with PKV and BDV but positive correlations with HPV,CPV,and SBV(p<0.01).AC had negative correlations with thermal properties(To,Tp,Tc and ΔHgel)(p<0.01).The relative crystallinity(RC)had negative correlations with AC(p<0.01),and positive correlations with To,Tp,Tc and ΔHgel(p<0.05).The content of DP 13-24 had positive correlations with HPV,CPV and SBV,and negative correlations with BDV.The content of DP≥37 had positive correlations with PKV and BDV,and negative correlations with HPV,CPV and SBV(p<0.05).The content of DP 6-12 had negative correlations with pasting temperature,and the content of DP≥37 had positive correlations with pasting temperature.It had significant positive correlations between the content of resistant starch(RS)and DP 25-36.On this basis,the gel properties of starch were studied.The results showed that AC had the strongest correlation with the hardness of starch gel at 1 d of refrigeration,and the correlation coefficient gradually decreased with the extension of refrigeration time.The hardness of the gel had positive correlations with the content of DP 6-12(p<0.05),negative correlations with the content of DP≥37 and the average chain length,and the correlation gradually increased with the prolongation of refrigeration time.It proved that AC affected the short-term aging of starch,while the chain length distribution of amylopectin affected the long-term aging of starch.(3)CSB was made from 11 kinds of wheat flour and frozen storage.The relationship between the structure evolution of starch molecular and the quality deterioration of CSB were studied by analyzing the color,specific volume,water content,water distribution and texture of frozen CSB during frozen storage,the microstructure of frozen CSB for 60 days,the AC of starch in CSB and the chain length distribution of amylopectin.The results showed that during frozen storage,the L*value of CSB of all wheat flour varieties decreased significantly with the prolongation of frozen storage time(p<0.05),indicating that frozen storage darkened the appearance of CSB.Frozen storage would reduce the specific volume of CSB,increase the hardness and chewiness,decrease the elasticity and resilience,and reduce the moisture content.After 60 days of frozen storage,the moisture content of Wei Long 169 was the highest(39.25%),and the moisture content of Yang Nuo Mai 1 Hao was the lowest(31.52%).The microstructure of CSB after frozen storage at-18℃ for 60 days was observed by scanning electron microscopy.After 60 days of frozen storage,it was found that the distribution of protein and starch granules was dense of CSB made by Wei Long 169,showed good frozen storage stability.The relationship between the molecular structure evolution of starch and the hardness of CSB was studied by fitting the chain length distribution of amylopectin during frozen storage.βAp,i was significantly negatively correlated with the hardness of CSB after frozen storage(p<0.05).Starch was extracted from CSB after 60 days of frozen storage,and the changes of AC in CSB were analyzed after 60 days of frozen storage.It was found that AC in CSB increased after 60 days of frozen storage.Yang Nuo Mai 1 Hao,Wei Long 169 and Zheng Mai 103(AC 1.75%,25.75%and 28.79%,respectively)were used as materials,the starch chain length distribution in CSB after 60 days of frozen storage was determined.It was found that the CLD map of amylopectin was double-shouldered,and the proportion of short A-chain(DP 6-12)of Wei Long 169 and Zheng Mai 103 decreased.Compared with native starch,the content of B1(DP 13-24)and B2(DP 25-36)chains decreased after frozen storage,while the long B3 chain(DP≥37)and average chain length increased,indicating that the deterioration of CSB quality during frozen storage was accompanied by the change of starch molecular structure.The aging of amylopectin and the migration of water were the reasons for the hardening of CSB.