Study On The Effect Of High-amylose Corn Flour On Dough Characteristics And Quality Of Chinese Steamed Bread

High-amylose corn has a high amylose content and is a good source of resistant starch（RS）,which can significantly reduce the glycemic index（GI）of food and improve the glucolipid metabolism of diabetic patients in the long term.The use of high-amylose corn flour（HACF）to replace wheat flour（WF）in the preparation of Chinese steamed bread（CSB）is an important way to extend the high-amylose corn industry chain,and can also provide an important development direction for China’s corn staple food strategy.Most studies so far have focused on the effect of high-amylose corn starch（HACS）on the quality of bakery products,and less research has been conducted on the application and impact mechanism of HACF in CSB and other bakery staples.Therefore,in this thesis,HACF with an amylose content of55 g/100g starch is used as raw material to study its effects on the physicochemical properties of WF dough,edible quality and digestive properties of CSB and the related influence mechanism,so as to develop CSB with both organoleptic quality and certain anti-digestive properties and provide theoretical guidance for the application of HACF in pasta staple foods.The main contents of the thesis are as follows:Firstly,the basic physicochemical properties of HACF,WF and composite flour with different HACF ratios were analyzed.As the ratio of HACF increased,the water absorption increased from 129.59%for WF to 161.33%for 50%HACF,while the solubility of 50%HACF increased by 9.56%and the swelling power decreased by up to 8.73 g/g compared to WF at the simulated steaming temperature（100°C）;the relative crystallinity of the composite flour decreased from 28.39%for WF to 12.77%for 50%HACF;with the increase in the ratio of HACF substitution,the gelatinization process of the composite flour was hindered and its peak viscosity and breakdown value decreased significantly,and the regeneration value decreased by 456.5 m Pa·s for 50%HACF compared to WF,indicating that the addition of HACF could slow down the ageing rate of the pasta products to a certain extent.Secondly,the effects of different HACF substitution ratios on the physicochemical properties of the doughs were investigated by means of Mixolab,fermentation rheometer,dynamic rheometer and low-field NMR.The thermomechanical properties of the composite flour showed that the addition of HACF increased the water absorption of the dough.Compared with the control sample,the stabilisation time of the dough prepared with 50%HACF decreased from 7.35 min to 5.40 min,and the C2 value（protein weakness）decreased from 0.48 Nm to0.42 Nm,indicating that HACF competed with the alcoholic protein and wheat gluten in WF for water absorption,resulting in difficulties for both to absorb water to form a stable protein network structure.The rheological characteristics of the dough fermentation showed that the addition of 50%HACF reduced the fermentation height（H_m）from 39.85 mm to 15.15 mm and the total dough gas yield decreased by 161 m L,which prevented the dough from rising and expanding.At the same time,the addition of HACF significantly reduced the content of bound water,increased the content of semi-bound water and free water,and increased the overall water movement;the elastic and viscous moduli of the dough increased significantly,and the creep strain and recovery strain of the dough prepared with 50%HACF decreased by 80.27%and78.53%respectively compared to the control sample,indicating that the dough tended to have some of the characteristics of an elastic solid.Thirdly,the effect of different HACF substitution ratios on the edible quality of the composite CSB was investigated by measuring the specific volume,textural characteristics,stomatal distribution and quality changes during storage.The results showed that the specific volume of CSB decreased by 61.79%and the elasticity decreased by 14.43%when the HACF ratio was increased to 50%,and the hardness and viscosity increased by a factor of four,indicating that the sensory quality of CSB deteriorated.In addition,the stomatal distribution of CSB showed that the addition of HACF led to a decrease in the stomatal consistency from455.95 stomata/cm² in WF-CSB to 53.55 stomata/cm² in 40%HACF-CSB,while the stomatal surface fraction increased from 24.08%to 34.13%,indicating that the stomatal stability of CSB was enhanced.The addition of HACF caused the overall sensory evaluation of CSB to be lower than that of the WF-CSB,and the sensory evaluation score decreased by up to 28.3 points as the ratio of HACF increased to 50%.During storage（0-72 h）,the relaxation times T₂₁,T₂₂ and T₂₃ decreased and the water molecules became less mobile,resulting in a faster ageing rate and increased hardness of CSB;the hardness of CSB increased with different HACF substitution ratios,with the 30%substitution ratio having the slowest hardening rate,consistent with the results of the ageing enthalpy tests.Finally,the starch digestibility of composite CSB with different HACF substitution ratios was investigated,and the potential mechanisms affecting the starch digestibility of CSB after partial WF substitution by HACF were briefly analyzed from the perspectives of starch inhibition on enzymes and starch-protein binding mode.In-vitro digestion of starch in CSB showed that HACF could effectively regulate the digestibility of starch,the content of rapidly digestible starch（RDS）and slowly digestible starch（SDS）in CSB decreased,while the RS content of 50%HACF-CSB increased by 16.48 g/100g starch compared to WF-CSB,and the hydrolysis rate at all time points of digestion was also lower in HACF-CSB than in WF-CSB;The GI value also decreased from 94.39 in WF-CSB to 57.55 in the 50%HACF-CSB,meeting the medium GI requirement.Combining the results of sensory quality and digestive characteristics,it was found that when the HACF substitution ratio was 30%,CSB was able to maintain some resistance to digestibility without causing excessive deterioration to sensory quality and the GI value was reduced.Afterα-amylase action,the reducing sugars produced by HACF-CSB were significantly lower than those of WF-CSB,and the enzyme inhibition ability gradually increased with the increase of the HACF substitution ratio;the addition of HACF led to an increase in the short-range ordering of starch in CSB,which showed stronger resistance to enzymatic digestion,while the X-ray diffraction results showed that the relative crystallinity of starch granules in CSB first decreased and then increased,but all were lower than those of the WF-CSB,corresponding to the results of short-range orderliness,and the amorphous structure of the starch decreased,thus affecting the quality and nutritional functional properties of CSB.The scanning electron microscopy（SEM）results showed that the gluten network continuity decreased and tended to be fragmented after HACF addition;with the increase in the ratio of HACF substitution,the more orderedα-helix andβ-turn angle in the gluten protein shifted to the disorderedβ-fold,the skeletal structure of the protein network was disrupted and the spatial aggregation orderliness decreased,which was consistent with the SEM results:the addition of HACF diluted the gluten network and thus led to a decrease in the air-holding properties of the dough,which in turn affected the quality of CSB.