Development And Quality Study Of Stabilized Black Rice And Its Solid-state Fermentated Product

Black rice has attracted wide attention in recent years due to its high nutritional value and many physiological functions.However,its difficult cooking,short shelf life,and poor palatability have led to low acceptance by consumers in their daily lives.Superheated steam,far infrared radiation and microwave are common emerging stabilization technologies for inactivated peroxidase in grains,which can effectively improve the storage stability of grains.However,there are few reports on the stabilization of black rice using these technologies and the quality changes of black rice after stabilization.In addition,solid state fermentation technology is widely used in grains,which can effectively improve their edible quality and nutritional value.Therefore,this paper used superheated steam(SS),far infrared radiation(FIR),microwave(Mw)three techniques to stabilize black rice,and compared the effects of these stabilization treatments on the edible and nutritional quality of black rice.At the same time,a comparative study was conducted on the structural characteristics and in vitro digestibility of stabilized black rice after cooking.On this basis,solid-state fermentation technology was combined to further improve the edible and nutritional quality of black rice.The main research results were as follows:(1)The black rice was stabilized by SS,FIR and Mw,respectively,and the effects of stabilization treatments on the cooking property and polyphenols of black rice were investigated.The results showed that the shortest inactivation time of SS,FIR and MW for peroxidase in black rice was 960 s,480 s and 480 s,respectively.In FIR stabilized black rice(SBR-FIR)and Mw stabilized black rice(SBR-Mw),the pasting viscosities and pasting enthalpies were significantly reduced due to starch pasting and even starch molecular degradation.But SS stabilized black rice(SBR-SS)had most of the increased pasting viscosity and almost no change in pasting enthalpy,while having similar cooking quality,color and microstructure to the original black rice.In addition,the total phenol,total flavonoid,anthocyanin contents and antioxidant properties of SBR-SS and SBR-FIR were higher than those of SBR-Mw.Therefore,SS stabilization treatment prolonged the shelf life of black rice with minimal damage to its cooking property and polyphenols,while Mw stabilization treatment caused more damage to it.(2)Three types of stabilized black rice were cooked into rice,and investigated the structural characteristics and in vitro digestibility of different cooked stabilized black rice.The results showed that cooked SS stabilized black rice(CSBR-SS)had the highest relative crystallinity of starch,the lowest porosity and the most complete protein network structure,while the structural characteristics of cooked FIR stabilized black rice(CSBR-FIR)and cooked Mw stabilized black rice(CSBR-Mw)were more different from the cooked black rice(CBR)structure.In addition,CSBR-SS had the lowest rapidly digestible starch content and the highest resistant starch content,and its equilibrium hydrolysis rate,kinetic constant and expected glycemic index of starch after in vitro digestion were the lowest,while CSBR-SS and CSBR-FIR became medium GI foods,but CSBR-Mw became high GI foods.The release of polyphenols and antioxidant properties of all black rice after intestinal digestion was higher than that of gastric digestion,indicating that more phenolic compounds were released after intestinal digestion,and the bioavailability of polyphenols and antioxidant properties of CSBR-SS and CSBR-FIR was significantly higher than that of CSBR-Mw.In conclusion,the nutritional quality and physiological functions of black rice were lost more by using Mw stabilization treatment.(3)Based on the results of previous studies,stabilized black rice by SS and FFIR were selected and combined with solid-state fermentation technology to prepare fermented stabilized black rice,in order to further improve the quality of black rice.The results showed that fermented SS stabilized black rice(FSS)and fermented FFIR stabilized black rice(FFIR)produced higher hydrolase activity,and the changes in soluble protein and polysaccharide content were more significant.The starch of FSS and FFIR was more easily pasted,and the crystal structure and microstructure changed greatly,which was more conducive to improving the cooking quality of black rice than fermented black rice(FBR),and the cooking time was significantly reduced from 31.58 min to 18.52 min and 15.38 min(p<0.05),respectively.The contents of total phenols,total flavonoids and antioxidant properties in FSS and FFIR were significantly increased,and the fatty acid value and peroxide value were lower after 50 days of accelerated storage at 37 °C,which could effectively improve the nutritional value and storage stability of black rice compared with FBR.In addition,the content of pungent flavor substances such as acetic acid,guaiacol,carvacrol,eugenol and indole in cooked fermented stabilized black rice were significantly reduced,while the content of sweet,floral,fruity and caramel substances such as 2,3-butanediol,phenethyl ethanol,phenylacetaldehyde and 2-pentylfuran increased,which made the black rice flavor milder.Therefore,fermented stabilized black rice improved edible quality and nutritional characteristics of black rice.