Effects Of Different Pretreatments On Cooking Quality And Nutritional Properties Of Black Rice

Black rice is a special variety of rice that is rich in nutritional value.The rice bran layer contains a lot of crude fiber and pectin,which leads to the problems of long cooking time,poor taste,poor digestion and absorption,etc.It is difficult to be accepted by most consumers as a staple food,which limits the development and utilization of black rice and affects its production and consumption value.In this paper,three pretreatment methods including plant compound hydrolase enzymolysis,microwave treatment and addition of soluble soybean polysaccharide(Soluble soybean polysaccharide SSPS soaking)were used to improve the cooking and eating quality of black rice.Firstly,with hardness/viscosity and sensory score as indicators,the three pretreatment methods were optimized to obtain the best treatment conditions.The effects of different pretreatment methods on the cooking and eating quality,gelatinization characteristics,nutritional quality and digestive characteristics of black rice were further discussed.The main findings are as follows:(1)The optimal treatment conditions of three different pretreatment methods(plant complex hydrolase enzymatic hydrolysis,microwave treatment,and SSPS soaking)were optimized by single factor and response surface methodology.The single factor experiment examined the effects of enzyme addition,enzymolysis solution pH,enzymolysis temperature and enzymolysis time on the hardness,viscosity and sensory score of black rice.The response surface method was used to optimize the enzyme treatment conditions,and the enzyme treatment conditions and hardness/viscosity were established.And the model between the sensory score and the sensory score was analyzed,and the optimal treatment conditions were as follows:the enzyme addition amount was 20 U/g,the pH of the enzymatic hydrolysis solution was 5,the enzymatic hydrolysis temperature was 46℃,and the enzymatic hydrolysis time was 2.7 h.Under these conditions,the hardness of black rice was The/viscosity ratio was 25.077,and the sensory score was 41.667.Single factor experiments were conducted to examine the effects of microwave treatment power and microwave treatment time on the hardness,viscosity and sensory score of black rice.The response surface method was used to optimize the microwave treatment conditions.Under this condition,the hardness/viscosity of black rice is 45.213,and the sensory score is 38.5.Single factor experiments were conducted to examine the effects of SSPS concentration,soaking time and soaking temperature on the hardness,viscosity and sensory score of black rice.The response surface methodology was used to optimize the conditions of soaking black rice with SSPS.The optimal treatment conditions were SSPS concentration 0.4%,soaking temperature 40%℃ and soaking time of 41 min,the hardness/viscosity of black rice is 60.981,and the sensory score is 36.83.At the same time,the correlation analysis between the texture properties of black rice and the sensory score showed that the smaller the hardness of the black rice,the higher the viscosity,and the smaller the hardness/viscosity,the sensory quality of the rice was the best.(2)Effects of three pretreatment methods on cooking and eating quality,gelatinization characteristics and structural characteristics of black rice.The enzymatic treatment significantly reduced the cooking time,hardness/viscosity of black rice by degrading the rice bran layer,and significantly increased the sensory score,cooking water absorption rate and volume expansion rate.The microwave treatment shortened the cooking time,and improved the water absorption rate and volume expansion rate of the cooking.SSPS soaking treatment can form a film on the surface of black rice,which increases the cooking water absorption rate and volume expansion rate of black rice,thereby shortening the cooking time.Among them,the plant compound hydrolase treatment has the best effect.All three pretreatment methods increased the gelatinization temperature of black rice,decreased the gelatinization enthalpy,and increased the gelatinization viscosity;FTIR and SEM showed that after the three pretreatments,no new functional groups were formed in the black rice,and more Most are changes in the surface microstructure.(3)Effects of different pretreatments on the nutritional properties of black rice.The analysis of the nutritional components of black rice after different pretreatment showed that the basic components of black rice after soaking in SSPS did not change significantly compared with the control group.After enzyme treatment and microwave treatment,the starch content of black rice increased by 2.81%and 0.94%,the protein content increased by 0.26%and 0.24%,the fat content increased by 0.11%and 0.24%,and the ash content decreased by 0.33%and 0.21%,respectively.,dietary fiber content was significantly increased.It can be seen that these three pretreatment methods basically retain the nutrients of black rice.Three different pretreatments caused a certain loss of free phenol and total phenol content in black rice,among which microwave treatment had the least loss,followed by SSPS soaking treatment and enzyme treatment group,while the content of bound phenol increased significantly.At the same time,the antioxidant activity of free phenol decreased and the antioxidant activity of combined phenol increased after the three pretreatment methods.The three pretreatment methods still retained the antioxidant capacity of black rice to the greatest extent.In vitro simulated digestion results showed that the three pretreatments increased the content of rapidly digestible starch(RDS)and slowly digestible starch(SDS),and decreased the content of resistant starch(RS)in black rice.At the same time,the starch digestibility and protein digestibility of black rice were improved.