Study On Quality Change And Retrogradation Of Cooked Black Rice With High Pressure Treatment During Storage

Black rice?BR?,as the treasure of rice since ancient times,is considered as a whole grain due to its pericarp,seed coat and germ containing abundant physiologically important components and possessing many health functional properties.However,the compact arrangement of surface cellulose of BR will hinder the absorption of water and the transfer of heat in the cooking process,resulting in poor palatability,low digestibility and undesirable cooking properties,thus it is difficult to be accepted by most consumers as a staple food.High hydrostatic pressure?HHP?is a typical non-thermal processing technology,which can better retain the color,flavor and nutrition of food.Moreover,studies have found that HHP treatment can improve the quality of rice.Therefore,this study introduced high hydrostatic pressure technology to improve the palatability of BR,and obtained the optimal production process of cooked BR with HHP by response surface analysis method,and studied the influence of HHP on nutrition composition,digestibility,flavor and retrogradation properties of cooked BR during storage.The main results were as follows:?1?The results showed that the hardness and adhesiveness of the texture parameters could be used as the evaluation indexes of cooked BR by the investigation of the texture parameters,sensory evaluation and correlation analysis of cooked BR with HHP treatments stored for 21 days.The optimal preparation conditions by response surface analysis were:pressure 413 MPa,ratio of water to rice 1.4:1,cooking time 16 min.?2?During the storage period,the value of L^*in the HHP-treated group was slightly higher than that in the control with no significant difference and the redness value a^*and yellowness value b^*fluctuated.Under 4?storage,the content of total phenol,flavonoids,anthocyanins and DPPH radical scavenging ability gradually reduced with the extension of storage period and the antioxidant compounds content in the samples treated at 400 and 500 MPa was higher than other samples.The overall trend of antioxidants content in samples stored at 37?was similar to that at 4?,but showed a greater decline.The content of rapidly digestible starch?RDS?and slowly digestible starch?SDS?in cooked BR increased with the increasing pressure,while the level of resistant starch?RS?decreased.After storage for 7 days,no significant difference was observed in flavor compounds between different treatments,except the difference in content.Compared with the control?0.1 MPa?,the content of flavor compounds in the HHP-treated group increased,indicating that HHP treatment was beneficial to improve the flavor of cooked BR.?3?HHP treatment obviously decreased the leached amylose of cooked BR.The gelatinization curves of BR showed that the value of peak viscosity,tough viscosity,final viscosity,breakdown and setback decreased in comparison with the control group,while there were no significant difference in pasting temperature,peak time and peak temperature.The hardness of cooked BR increased with storage time extended,the adhesiveness and springiness gradually decreased,and the trend of increasing or decreasing in the HHP-treated group was lower than that of the control one.The thermal characteristics of cooked BR were analyzed by differential scanning calorimeter.The results showed that compared with control,the values of ?H and retrogradation degree of the HHP treatment group were significantly lower.The X-ray diffractograms of cooked BR during storage suggested that the starch crystal changed from type A to type B+V,and the crystal peak intensity and relative crystallinity decreased significantly with the increase of pressure,especially when the pressure reached 500 MPa.The T₂ spectrum of cooked BR after storage for 7 days was measured by low-field NMR instrument,and it was found that HHP treatment changed the water distribution,the bound water and macromolecules were more closely combined,and part of the bound water was converted into immobilized water and free water.