| Rice is the most important staple food and mainly consumed in white rice.However,white rice characterizes with rapid digestion rate and high postprandial blood glucose This may affect the health of Chinese residents.Parboiled rice,with slow digestion,is obtained by soaking,steaming and drying treatment,then,dehusked and milled.The soaking and steaming during parboiling can be understood as hydrothermal treatment.During hydrothermal treatment,the physichemical properties and starch structure of parboiled rice may change which affected its sensory quality and digestion.However,the mechanism of its affection has been still rarely reported.In this study,the relationship amone physiochemical properties-sensory quality,multi-scale structure-digestibility in parboiled rice after different moisture,heating temperature and heating time processing was elaborated.Meanwhile,the effect on glucose tolerance after intaking different glycemic index(GI)parboiled rice as the main dietary carbs in high-fat diet induced mice was also compared.The main conclusions were as follows:(1)The effect of hydrothermal treatment on physiochemical properties of parboiled riceThe moisture was controlled at 45%,55%,65%,70%and 75%by changing the soaking condition,and then,heated at different temperatures(100,110,120°C)and different time(5,10,20 min).The results suggested that parboiled rice showed as amber color and became deeper and deeper with the increasing of heating temperature and heating time.The hydrothermal treatment did not significantly affect the basic nutrition content(starch,protein,fat,etc.)and cooking property,but increased the free and bound phenolic acids(p<0.05).Compared with white rice,the amylose leaching and swelling power of parboiled rice significantly decreased from 30.77%,16.77%to 23.24～14.53%,9.91～6.29%,respectively.The elasticity and network structure formation capability of parboiled rice gel was also reduced by hydrothermal treatment.The hardness and chewiness of parboiled rice significantly increased due to the starch gelatinization and aging during hydrothermal treatment.(2)The effect of hydrothermal treatment on sensory quality and volatile substances of parboiled riceThe results of sensory experiments and rice taste meter suggested that the sensory quality of parboiled rice significantly decreased with the increase of heating temperature and heating time(p<0.05).The sensory quality reduction of parboiled rice mainly due to the decreasing of appearance and odor sensory.The GC-MS results showed that hydrothermal treatment eliminated two important volatile substances(OAV>1,(E)-2-heptenal and indole)from parboiled rice,which reduced its fruity aroma.Compared with white rice,21 type of volatile substances were newly detected in parboiled rice.Among them,8 type of volatile substances were important flavor substances,which increased the fatty and waxy odor.Correlation analysis showed that the odor sensory score of parboiled rice was positively correlated with the relative concentration of pentylfuran(R~2=0.77).The sensory scores of palatability,tasting and cold rice texture were positively correlated with amylose leaching and swelling power(0.61<R~2<0.89).And the sensory appearance score was significantly positively correlated with the L*value(R~2=0.87).(3)The effect of hydrothermal treatment on multi-scale structure and digestibility of parboiled rice starchThe side chain length distribution of parboiled rice amylopectin starch did not significantly change.The original starch structure was destroyed by hydrothermal treatment.And the starch molecules rearranged,resulting in that that the double helices content decreased from 63.14%to 59.97～61.68%.And the single helices content significantly increased from 1.30%to 2.30～7.43%.Besides,hydrothermal treatment blurred the boundary of the crystalline and amorphous region in parboiled rice starch granule,which caused the reduction ofαvalue.The helical structure may mainly from microcrystals in starch granules.This led to a result that the relative crystallinity of parboiled rice starch significantly reduced from 30.45%to 20.08～6.18%(p<0.05).The hydrothermal treatment promoted the formation of V-type crystal.And the relative crystallinity of V-type crystals significantly increased from 0.57%to 1.20～5.40%(p<0.05)along with heating temperature and heating time.According to the results of scanning electron microscope,the internal structure of parboiled rice also became more compact,especially after 120°C heating treatment.The in vitro and in vivo digestion suggested that the initial digestion rate of parboiled rice was significantly slowed down by the homogeneous starch granule structure and compact internal structure.This reduced the parboiled rice GI value.Especially,after 75%-110℃,5min,45%-120℃,20min,and 65%-120℃,10min hydrothermal treatment,the GI value of parboiled rice decreased to 63.16,63.15 and 61.19,respectively.Correlation analysis showed that the GI value of parboiled rice was positively correlated with C chains proportion,double helices content,degree of double helices,stack density and relative crystallinity.(4)The improvement of glucose tolerance for parboiled rice in mice induced by high-fat dietThe different degree starch structure changes of parboiled rice resulted in different GI value which may affect the glucose tolerance.In this chapter,the effects on glucose tolerance after intaking different GI parboiled rice(83.78,61.19)as the main carbs in high-fat diet induced mice were investigated.The results showed that only medium GI parboiled rice significantly slowed down the weight increase rate and decreased the food intake of high-fat diet induced mice.The glucose tolerance was also significantly improved by medium parboiled(p<0.05).The parboiled rice had no impact on the insulin resistance,blood lipid levels and short-chain fatty acids content.Meanwhile,parboiled rice not only reduced the infiltration and accumulation of fat in liver tissue,but reduce the size of fat cells.This was enhanced with the reduction of parboiled rice GI value.The liver metabolomics suggested that parboiled rice may promote the utilization of liver and controversion of pyruvate,especially for medium GI parboiled rice.This may be achieved by changing the composition and relative abundance of gut microbiota in high-fat diet induced mice after parboiled rice intervention.Sequencing results showed that parboiled rice increased the relative abundance of Dubosiella,Ligilactobacillus、Mucispirillum,Romboutsia,Anaerotruncus,etc.These results suggested that parboiled rice may enhance glucose tolerance by promoting the relative abundance of specific bacterial species.This may increase the utilization of fat and glycolytic processes in liver tissues which may increase the glucose tolerance in high-fat diet induced mice.Generally,the lighter amber appearance,better gelatinization ability and strong fat odor made parboiled rice retain good sensory quality.The hydrothermal treatment prometed the rearrangement of starch molecules,which increased the degree of double helice and homogeneous starch structure of parboiled rice starch.This enhanced the resistance of starch-digesting enzymes degradation,which made parboiled rice became into medium GI food.Long-term consumption of medium GI parboiled rice as the main carbs may reverse the imbalance of intestinal flora in high-fat diet mice.This may improve glucose tolerance by promoting the utilization of fat and glycolysis in liver tissues. |
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