Quality Improvement Of Wholegrain Germinated Brown Rice By Quick-Frozen Processing

Germinated brown rice(GBR)is a brown rice product composed of young buds and endosperm with a fibrous bran layer by germinating brown rice to a certain bud length.GBR is rich in dietary,y-aminobutyric acid,y-glutamic acid,phenols and flavonoids,and other functional substances,which plays a positive role in relieving chronic diseases.However,the surface layer of GBR hinders the penetration and absorption of water,making it difficult to gelatinize the internal starch during cooking,leading to its long cooking time,poor rice taste quality and limited consumer acceptance.Therefore,in this paper heat-moisture treatment(HMT)and quick-frozen process were taken to improve the cooking and eating quality of fresh GBR,providing a practical and effective method.(1)The effects of germination time on the quality characteristics of brown rice was investigated and the correlation between physicochemical indicators and the quality of cooked rice was explored.The results showed that germination treatment reduced the content of protein and fat.With the extension of the germination time,the content of total starch and amylose continued to decrease,the content of IDF,SDF,TDF,reducing sugar and GABA gradually increased,the content of soluble protein increased first and then decreased;and the hardness decreased continuously,the elasticity gradually increased after 18 h of germination.When brown rice was soaked for 4 h,its peak viscosity,minimum viscosity,retrogradation value and final viscosity all increased significantly,and then gradually decreased with the increase of germination time.Germination treatment increased the relative content of aromatic linalool,acetoin,2-methylbutanal and esters in brown rice,but the relative content of acids decreased.The appropriate germination time(18～24 h)could maintain the content of undesirable flavor compounds at a low level,while the content of ideal flavor compounds increased.The brown rice prepared by germinating for18 h had the highest scores of eating value,appearance and taste,which were 1.35,2.83 and 1.67 times of untreated brown rice,respectively,and the gumminess and chewiness were lower,so the eating quality was effectively improved.Correlation analysis showed that the quality of cooked rice had the most significant correlation with moisture,protein,fat,IDF,regeneration value,final viscosity,and pyrazine and furan flavor substances of GBR.(2)The effects of HMT time on color,flavor,taste quality,water migration,starch properties and microstructure of GBR were investigated.The results showed that during the process of HMT,starch gelatinized,the combination of starch and water weakened the overall fluidity of water molecules,and the peak viscosity,retrogradation value and final viscosity increased first and then decreased with the extension of treatment time,the breakdown value decreased significantly with the increase of HMT time;the crystal of starch changed from A type to V type,and the crystallinity decreased from 27.51%to 17.16%.The infrared spectra showed that the absorption peak intensity reflecting the bending vibration of OH in water molecules decreased significantly after 15 min of HMT,which indicated that the hydrophilicity of GBR would be reduced after a long time of HMT.In addition,the amount of alcohols were reduced dramatically and a large amount aldehydes were produced in GBR after HMT,and pyrazines and furans also accumulated to a certain extent,the relative content of pentanal,hexanal,benzaldehyde,n-Nonanal and heptanal increased obviously.HMT for 10～15 min could bring unique fragrance and a certain roasting flavor to GBR,and at the same time lipase and polyphenol oxidase were passivated.Compared with the untreated GBR,the eating value of the GBR obtained by 10 min of HMT increased by 2.40%,and the hardness was the lowest,the chewiness was lower,so the eating quality was effectively improved,and at this time,the rice paste of GBR had a higher viscoelasticity,which was not easy to be damaged by shear force,and the gelatinization quality was better.(3)The improvement effects of quick-frozen process on cooking characteristics,edible quality,retrogradation characteristics,and nutritional quality of GBR after HMT were investigated.The results showed that compared with white rice(WR),brown rice,dried GBR and the sample that were directly quick-frozen without HMT,the cooking time of GBR treated by HMT and quick-frozen(GHQ)was the shortest,which was 30.88%shorter than WR,and the solid loss rate was the lowest,which was 59.50%lower than WR;the water absorption and volume expansion rate of GHQ were relatively high;except for WR,the hardness,gumminess and chewiness of GHQ were the lowest,which were 62.06%,56.86%and 60.91%lower than brown rice,respectively,and the elasticity and cohesiveness were the highest,the sensory score was second only to WR.Avrami retrogradation kinetic model showed that the crystallization rate k of GHQ was the lowest(except for BR),so the degree of retrogradation was the least.In addition,HMT combined with quick-frozen process had a certain effect on improving the content of GABA and flavonoids in GBR,and also favored the release of bound phenolics,resulting in an increase of total antioxidant activity.The SEM images showed that cracks occurred in the cross section and the internal network structure became loose of GBR after HMT,which made the water easily combine with starch to promote gelatinization;during quick-frozen process,the micromechanical force caused by the formation of a large number of small-sized ice crystals expanded the channels between the starch particles and the cracks reoccurred in the cross section,which further improved the water absorption performance of the GBR.Therefore,the cooking and eating qualities of GBR can be effectively improved by HMT and quick-frozen technology.