Study On The Relationship Between Structure And Function Of Yiyang Rice Starch And Its Effect On The Nutrition And Digestibility Of Rice Cake

Yiyang rice is a special product in Yiyang county of Jiangxi province.The Yiyang rice cake manufactured by Yiyang rice cake is known for its flexibility and smoothness,which is a national geographical indication product of China.The relationships between structure and function of Yiyang rice and its starch were studied to provide the basis for determining the application direction of rice in food industry.At the same time,the changes of quality and starch hydrolysis of Yiyang rice cake during mechanical processing were investigated,which provided theories and data reference for the optimization of processing technology of Yiyang rice cake and local characteristic rice products in the future.In order to meet the needs of different consumers,the effect of adding fermentable carbohydrate on the quality and starch hydrolysis of Yiyang rice cake was studied,which provided a reference for the development of new products of Yiyang rice cake and other functional high moisture food.Main conclusions are as follows:1.The basic components and functional characteristics of 10 varieties of Yiyang rices(Makeda No.2,Nongke Baiguoda,Zhongtian Fanda,Nongju No.1,Nongju No.2,Nongju No.3,Nong No.1,Nong No.2,Qigongda No.1,Qigongda No.2),a kind of indica rice(Jiuxiangnian)and a kind of japonica rice(Jihong No.6)were compared.The results showed that the amylose content of Yiyang rices was between 15.55%and26.30%,and they had lower rice yield rate but had similar amino acid composition.In terms of gelatinization and rheological properties,the peak viscosity and breakdown values of Yiyang rices were lower,but the pasting temperature and setback values were higher,and they had strong resistance to heat and mechanical force.2.Starches were extracted from Jihong No.6,Makeda No.2 and Jiuxiangnian to understand the reason why some Jiangxi rice cultivars are directly consumed and some are further processed into rice based products from the perspective of starch molecular structure and function.The amylose content of starches from Jihong No.6(JH-6),Makeda No.2(MKD)and Jiuxiangnian(JXN)was 19.32%,16.90%and 14.72%,respectively.JH-6 had the highest amylose content,better gelatinization and freeze-thaw stability,and the highest gel strength and hardness.These are characteristics making JH-6 suitable for consumption as day-to-day edible rice in its non-processed form.JXN exhibited the lowest freezing-thawing stability.The long chain component of its amylopectin and the degree of crystalline order in JXN was,however,high and JXN had better thermal stability and lower retrogradation characteristics.In view of these characteristics as well as its soft gelling behaviour,JXN is suitable for further processing into softer rice based food.MKD had the largest granule size,the highest solubility and swelling power,the highest freezing-thawing stability and the highest resistant starch content(while the other indicators are at a relatively medium level)which makes it not suitable for direct consumption like that of JH-6.Its stronger gelling properties(relative to JXN)makes it suitable for further processing into harder rice based products such as for making rice cakes.3.The quality of Yiyang rice cake changed obviously in the process of production and processing.The gelatinized starch of the rice cake swelled and the starch chains were entangled with each other,while the starch hydrolysis rate was significantly increased and the C_?increased to 60.73%.After extrusion molding,the cooking loss of rice cake decreased from 10.83%to 0.73%,its hardness,springiness and chewines increased significantly,and its taste improved significantly.The spin-spin relaxation time(T₂)increased from 8.39 ms to 9.52 ms and the relative crystallinity of starch decreased to 4.41%after high temperature sterilization.After 2 months of storage,the hardness,gumminess and the order degree of starch of the rice cake increased significantly but the sensory evaluation decreased,meanwhile the C_?value increased.The changes of quality and in vitro digestibility of Yiyang rice cake during processing provided theoretical reference for the production process optimization of rice products.4.The effects of the addition of resistant starch(RS),inulin(IN)and xylo-oligosaccharide(XOS)on the cooking properties,texture properties,ordered structure of starch,water mobility and in vitro digestion of Yiyang rice cake were investigated.XOS can significantly reduce the cooking loss of rice cakes.The hardness,viscosity and chewiness in rice cakes were improved with the addition of these fermentable carbohydrates(4%,8%,12%,based on dough).The rice cake gradually became smooth with the increase of the amount of the carbohydrates.RS and XOS promoted the retrogradation and the free movement of water oin the rice cakes,and increased the ordered structure formed by the correlation between starch chains;while IN had no significant effect on the retrogradation.The addition of RS or XOS reduced the C_?of rice cake.