Study On Resistant Starch In Sorghum

Sorghum [Sorghum bicolor (L.) Moench], is the world’s fifth-largest crop afterwheat, rice, maize and barley. Because of its salinity, drought, strong resistance andother excellent characteristics, it can be grown in the arid and poor geographicalconditions, that’s why they widely planted in the world. In our country sorghum notonly planted widely, but also used in many areas because the excellent hybridvarieties were cultivate these resent years.In this paper, made sorghum as the research object, we collected34high-qualityhybrid sorghum varieties across the country, and use wet milling extracted starch fromsorghum. The main factors which influenced the yield of starch were three: soakingtime, alkaline soaking time and grinding time. According to the single factor experimentof each factor to design Box-Behnken experiment. Design-Expert8.0software wasused get the extract condition: soaking time18h, alkaline soaking time8.97min,grinding time3.33min, under this condition, the weight of the starch can up to42.1037g. Considered the actual conditions of the experiment, we selected the soakingtime18h, alkaline soaking time9min, and high speed grinding time3min20s forstarch extraction.We used the measured in vitro: McCleary et al’s method (AOAC2002.02) tomeasure the content of resistant starch in34sorghum cultivars. Pancreatic α-amylaseand Glucoamylase were hydrolysis the starch samples of sorghum, and the content ofsugar was measured by DNS method, the content of resistant starch were calculatedby it. The results showed that the resistant starch content of sorghum have a higherlevel than corn, wheat, rice and other crops. Jiza No.131had the highest content ofresistant starch with22.21g/100g, and Xinuo No.1had the least content of resistantstarch which hard to detected resistant starch.Select five sorghum cultivars from34sorghum varieties for the further research,including water holding capacity, SEM, XRD and DSC. Five sorghum resistant starchwith lower water holding capacity and it increased by the content of resistant starchreduced, resistant starch had higher water holding capacity than native starch, but ithad the lowest water holding capacity in dietary fiber. SEM results showed that thesize of sorghum starch molecules were between5~20nm in different shapes andsizes. After the enzymatic hydrolysis, the granules morphology of starch were changed, Jiza No.131had the strongest resistance to hydrolysis, and it surface ofresistant starch was porous, but still keep the original shape. JIza No.101, which caneasily digested by enzymes, the shape of particle was not exist, the particles werelargely hydrolysis by enzymes.The crystal type of sorghum native starch and resistant starch were both type A.resistant starch has a lower crystallinity degree than native starch, and it reduced bythe ability of resistance to hydrolysis became lower. DSC results show that resistantstarch gelatinization temperature was lower than native starch from the beginning, andit reduced by the content of resistant starch decreased. Resistant starch had a longgelatinization temperature range, about twice time than the native starch, and needhigher gelatinization enthalpy.