| Frozen technology was more and more widely used in food.Frozen products could not only keep fresh state and original nutrients,but also effectively extend shelf life.Resistant Starch?RS.?had been proved to control blood glucose in diabetic patients.When eating low glycemic index foods containing resistant starch,post-prandial insulin secretion was significantly reduced,which could effectively improve insulin sensitivity and had a significant inhibitory effect on the increase of blood glucose in diabetes.However,the frozen steamed bread had technical problems such as texture fission and insufficient fermentation.In addition,there were few studies on the freezing rules of fermented foods with low-glycemic index,and there was a lack of research on changes in freezing quality and quality control.In this study,We extracted sorghum resistant starch by enzymatic debranching and aging combined with high temperature resistant amylase hydrolysis and we studied the influence of different freezing conditions on the properties and structure of resistant starch.We explored the effect of resistant starch on frozen dough quality.We adjusted and optimized the formula of resistant starch steamed bread,and finally made frozen steamed bread with a glycemic index less than 60.?1?We prepared sorghum resistant starch by enzymatic debranching and aging combined with high temperature resistant amylase hydrolysis.The process of preparing resistant starch was mainly completed in two steps.On the one hand,we optimized the experimental conditions for debranching.Based on the results of the single factor test,a three-factor and three-level response surface optimization test was designed.The optimal debranching conditions were:Starch concentration was 25%,pullulanase concentration was 20U/g,and enzymolysis time was 14h.Secondly,the yield of resistant starch could reach 22.06%after the debranched starch was hydrolyzed by high temperature resistant?amylase.?2?The prepared resistant starch was processed by freeze-thaw cycles under different conditions,and commercial high amylose corn starch was used as a control.We determined the physical and chemical properties,structure,and stability of samples before and after freezing and thawing.The results showed:We Adjusted the water emulsion concentrations of1:1.5,1:2,and 1:2.5 and freeze-thaw cycles 0,3,and 6 times at temperatures of-35°C and-20°C,respectively and founded that compared with high amylose corn starch,resistant starch had a lower glycemic index.Resistant starch had a large solubility and water holding capacity,and the swelling potential changed significantly.As the number of freeze-thaw cycles increased,the water holding capacity of the resistant starch gradually decreased,and the solubility gradually increased.X-ray diffraction revealed that the crystal form of the resistant starch changed from A to B after freeze-thaw treatment.Scanning electron microscope?SEM?observation found that the granule appearance of the prepared resistant starch was seriously damaged,and the surface was rough and unsmooth,presenting irregular soil lumps.Moreover,freezing treatment caused cracks in the appearance of resistant starch.Through Fourier infrared scanning,it was found that more hydrogen bonds formed after the third freeze-thaw cycle.But the characteristic peaks shown in Fourier infrared spectrum were approximately the same.With the increase of freeze-thaw cycles,A1045/1022 become larger and larger,which indicated that the crystallinity of starch increases.Compared with the influence of freezing temperature and water emulsion concentration,the freeze-thaw cycle had a greater impact on starch properties.?3?We studied the effect of addition of resistant starch on dough properties.After adding resistant starch to dough,it was found that resistant starch had a good effect on gluten network of dough during freezing process.Resistant starch had less free sulfhydryl groups than the control groups,indicating that resistant starch could protect the disulfide bonds in proteins.Texture of dough with resistant starch was better.Nuclear magnetic resonance relaxation time T2 was smaller and free water was less.And by differential scanning calorimetry,it was known that the freeze-resistant water content of resistant starch dough was low,which could reduce the formation of ice crystals and had a better effect on frozen dough.?4?We ensured that the glucose index of steamed bread was less than 60 and optimized the formula of steamed bread.After optimization by single factor experiment and four factors and three levels orthogonal experiment,the results were as follows:When the addition amount of resistant starch,carrageenan,gluten and yeast in the steamed bread formula was17%,2%,5%and 1%,respectively,the sensory score of steamed bread was the highest,reaching 82.01%.At this time,the steamed bread had a smooth appearance and good taste.The bubbles in steamed bread were even and fine,which was easy to be accepted by the public. |
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