Screening Of Rice Germplasm With High Resistant Starch And Its Correlation With Rice Quality,starch RVA Characteristics

As a new type of dietary fiber,resistant starch(RS)is a kind of starch with enzyme resistance,which is not absorbed by the small intestine of healthy people,but can enter the large intestine and be fermented by bacteria.RS can reduce blood lipid content,control insulin level,prevent the occurrence of diabetes,has a strong satiety,which can effectively reduce body weight,and be fermented by cell microorganism,producing short-chain fatty acids,which can reduce the risk of colon cancer morbidity.About 60% of the population in China lives on rice as their staple food,but the content of resistant starch in rice is generally low.Research shows that there is a certain positive correlation between amylose and resistant starch content,and the difference of resistant starch content will also have different effects on the main quality indexes of rice.In this study,through the improvement of the existing method for the determination of resistant starch,we established a suitable method for the determination of resistant starch content in rice.on this basis,we determined the resistant starch content of the collected and created rice germplasm resources(materials),Screened rice germplasm resources(materials)with high resistant starch content and carried out the correlation between resistant starch content and other physicochemical properties of rice to provide references for the breeding of new rice varieties with high resistant starch content.The main findings are as follows:(1)Improved the method for determination of resistant starch content in rice.The main improvement steps are as follows: a.After crushing the sample to be tested through a 100-mesh sieve,put it together with the standard sample with known RS content in a closed container to balance the moisture,determine the moisture content of the sample,the weighing range of the sample was calculated according to the moisture content of 12%.Accurately weigh the polished rice flour sample in the weighing range into a 15 ml test tube,repeat it twice;b.Do not cook before digestion,directly add 4 ml fresh prepared pancreatic a-amylase suspension,and put it into a horizontal water-bath shaker with the temperature of 37℃,the rotation speed is 100r/min for overnight digestion for 16 hours;c.When the test tube containing the sample is placed in the horizontal water-bath shaker,the direction of placement should be parallel to the direction of the shaker status;d.Using 50% alcohol for 1h wash and centrifugal purification;e.Using the pancreatic a-amylase in the Megazyme kit as the sample digestion enzyme,which is easy to store and can maintain good activity for a long time after opening,The measured resistant starch content of the sample is closer to the true value.The rice resistant starch content measured by the improved method is better,higher accurate and more reliable.(2)The highest amylose content of 1589 rice germplasm resources(materials)tested is25.86% and the lowest is 0.34%,it is mainly distributed between 8%-15%,accounting for86.22%;Among them,65 rice germplasm resources(materials)have an amylose content higher than 20%,the proportion is only 4.09%,indicating that there were few rice germplasms(materials)with high amylose content.(3)The content of resistant starch of 65 rice germplasm resources(materials)with amylose content higher than 20% was determined by the improved method,five rice germplasm resources(materials)with resistant starch content above 5% were screened,they are 9Z1682,9Z804,9Z793,9Z965,9Z307,and their resistant starch content are 5.05%,5.39%,5.32%,5.74%,7.05%,respectively.(4)The resistant starch content,rice quality and starch RVA characteristics of three types of materials with high,medium and low resistant starch content,and same growth period basically were determined.And the correlation between resistant starch content and various physical and chemical indexes of rice quality and starch RVA characteristics was analyzed.The results showed that the resistant starch content is significantly positively correlated with the brown rice percentage and chalky grain percentage,but was not significantly correlated with the other 9 physical and chemical indicators of rice quality;the content of resistant starch is significantly negatively correlated with the reduction value of starch RVA characteristics,but not significantly correlated with other physical and chemical indicators of starch RVA,indicating that varieties with high resistant starch content have poor rice appearance quality and low reduction value.