| The application of native starch is limited by insolubility in cold water,weak structure and function,easy retrogradation,and loss of viscosity during processing,etc.Therefore,in order to meet the technical requirements of the industry,especially in the food field,various methods including chemical,physical or enzymatic treatment are used to improve the properties to meet specific applications.In recent decades,enzyme treatment has been safer and moderater to achieve the functional characteristics required for food industry production.However,the price of commercial amylase and enzyme-modified starch is very high.So,the industrial production is greatly restricted.Barley malt mainly containsα-amylase,β-amylase and limited dextrinase,and it has been widely used in beer fermentation production.However,there are few reports about improving the physicochemical properties of starch derivatives with fresh malt crude enzyme solution.In this study,endogenous enzymes（α-amylase,β-amylase,limit dextrinase,etc.）in fresh wort were directly added to the reaction system to prepare modified starch with excellent performance.Firstly,the effects of the enzymatic activity and enzymatic hydrolysis time of malt endogenous enzymes on the physicochemical properties of raw starch granules were studied.Secondly,the characteristics of resistant starches prepared by with commercial enzymes combined with pullulanase and barley endogenous enzymes combined with pullulanase were studied and compared.Finally,the effects of resistant starches on sensory quality,in vitro digestion characteristics and texture characteristics of steamed bread were studied.The results were as follows:（1）The endogenous amylase activity of barley cultured on the third day was the highest（103.3U/g）.Compared with native corn starch,higher malt endogenous enzymes activity significantly damaged the integrity of starch granules,resulting in the reduction inpeak strength ratio of 1047cm-1/1022cm-1（1.042 to 0.838）and relative crystallinity of starch granules（35.30%to 28.76%）.While gelatinization temperature increased by about5℃.The gelatinization viscosity of enzyme-treated starch showed the increase of peak,breakdown,final and setback viscosity;（2）Compared with native starch,short chains（DP 6-12）of enzymatically hydrolyzed starches increased at hydrolysis time（≤12 h）and decreased at hydrolysis time（>12 h）.The B chain（DP>13）decreased when hydrolysis time was less than 12 h,and increased when the hydrolysis time was more than 12 h.Furthermore,the relative crystallinity decreased from 25.63%to 21.38%and the IR peak intensity ratio of1047cm-1/1022cm-1 decreased from 1.042 to 0.942 during hydrolysis time（0 to 72 h）.The thermal degradation temperature decreased from 323.19 to 295.94°C,while the gelatinization temperature slightly increased;（3）The V-type diffraction peak intensity of the modified starch prepared by malt endogenous enzyme combined with pullulanase was higher than that of other modified starches.Compared with other modified starches,apparent amylose content（45.56%）,resistant starch content（53.93%）and thermal stability（302°C）of starch modified by a combination with malt endogenous enzyme and pullulanase increased,but the solubility index and glycemic index（GI=46）decreased;（4）With the increasing proportion of resistant starch,the volume and specific volume of steamed bread decreased gradually,and the quality of steamed bread become worse,but the digestive resistance gradually increased,and it had higher hardness and chewiness.When the addition amount of resistant starch is 5%,the gluten of the dough is stronger.And the steamed bread samples containing resistant starch exhibited significantly slower glucose release during the first 40 min of in vitro digestion.This study will provide an important theoretical and application basis for promoting the production of low-cost,high-quality green starch and resistant starch. |
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