| Rice,a major source of staple food in human daily life,is the second most productive crop in the world.With the improvement of life,the bioactive composition of rice has attracted interest because of its antioxidant activity and its ability to reduce the risk of chronic diseases for people.However,current research on the bioactive composition of rice is not systematically combining pre-harvest factors and post-harvest processing due to different subject areas.Therefore,this study combined pre-harvest factors and post-harvest processing from the perspectives of agriculture and food,hoping to conduct a systematic study from field planting to food processing and then to human absorption and utilization to explore the changing rules of composition in rice,so as to provide a theoretical basis for actual agricultural production.It also provides information on japonica rice with high nutritional value for food manufacturers.In this paper,we investigated the effects of pre-harvesting factors on two types of active components,namely polyphenols and phytosterols,and the antioxidant activity of rice with different varieties of japonica rice,different fertilizer treatment patterns,different amounts of nitrogen fertilizer and different amounts of phosphorus fertilizer.The effects of pre-harvesting factors on the antioxidant activity of japonica rice were evaluated comprehensively using typical correlation analysis and multiple linear regression analysis,and a preliminary linear regression equation between the integrated antioxidant capacity and bioactive components was established.The pre-harvesting factors(nitrogen level)with greater influence were screened by antioxidant capacity,and the effect of nitrogen level on the biosynthetic regulation mechanism of two major active components in brown rice,polyphenols as well as phytosterols,was further investigated at the molecular level using combined transcriptomic and metabolomic analyses.At the same time,the effects of three cooking methods on the bioactive components and antioxidant activity of brown rice at different nitrogen rates were investigated,as well as the bioaccessibility and antioxidant capacity of brown rice after in vitro simulated oralgastrointestinal digestion.The following main results were obtained:(1)A comprehensive analysis of phenolic and phytosterol composition and antioxidant activity of nine main rice cultivars from saline areas of Liaoning Province.The results showed that the total phenol and flavonoid contents of the nine varieties of brown rice and white rice ranged from 241.98-296.76 and 133.08-215.06 GAE mg/100 g and 225.30-276.80 and 119.81-211.03 RE mg/100 g,respectively,with the highest content of brown rice Yanfeng 47.The proportion of bound phenols and free flavonoid contributing to the total polyphenols and flavonoids was higher than 50%.The proportions of different phytosterols in the nine varieties were: β-sitosterol > stigmasterol > campesterol > ergosterol> fucosterol,where the proportion of total sterols accounted for β-sitosterol was higher than 50%.In addition,the content of phenolic compounds in brown and white rice was linearly correlated with the antioxidant capacity.The antioxidant activity was related to β-sitosterol and p-hydroxybenzoic acid and was influenced by their appearance and color characteristics.The weight ratios of the four antioxidant activities were calculated by the independent weighting method to comprehensively evaluate the antioxidant levels of the nine varieties,and the results showed that the combined antioxidant capacity of Yanfeng 47 was the highest in brown rice and the second in white rice.(2)The phenolic and phytosterol composition and antioxidant activity of rice under five different fertilization patterns were comprehensively analyzed using the Yanfeng 47 variety as the study target.Compared with no fertilization,the FP model had higher total phenol and total flavonoid contents,which were 30-50% higher than the other models,respectively.The strawfertilization pattern was higher than the non-straw-fertilization pattern in terms of total phenol and phytosterol contents.(3)The composition and antioxidant activity of phenols and phytosterols under different nitrogen and phosphorus application rates were analyzed comprehensively.According to the antioxidant activity index,N260 in brown rice and N210 in white rice had the best comprehensive antioxidant capacity,and both brown rice and milled rice had the best antioxidant capacity under P90 condition.In addition,multiple linear regression analysis was used to establish a multivariate correction model for antioxidant.The linear equation is Y=1.9557X1 + 0.2593X4-1.86479X7 + 0.7635X8 + 1.8192X9 + 0.3193X10 + 1.4554X11 +7.8782X12 + 2.3109X13-1.1194X14-1.4586X15 + 0.0714X16-4.5411X17.According to the linear equation,the antioxidant capacity of nitrogen fertilizer was higher than that of phosphorus fertilizer,and the coefficient of variation of the effect of nitrogen fertilizer on active substances in brown rice was higher than that of phosphorus fertilizer.(4)Based on transcriptomic and non-targeted metabolomics,the N2 group had 2495 DEGs with 119 differential metabolites compared to the N0 group,while the N6 group had3970 DEGs with 191 differential metabolites.Based on bioinformatics analysis it was revealed that the intracellular ribosomal structure and molecular activity of brown rice had a positive and positive effect on increasing nitrogen levels.The b HLH and MYB,transcription factors mainly involved in defense responses,influenced the shikimic acid and mevalonate(MVA)pathways,contributing to the metabolites phytosterols and phenolics that could be synthesized in large quantities.Brown rice stimulated by nitrogen levels stimulates the pentose phosphate pathway,the amino acid metabolic pathway,promotes the biosynthesis of flavonoids,and acts as an antioxidant.Increased nitrogen level in rice application enhanced photosynthesis,promoted plant sugar metabolism,providing energy through the process of glycolysis and tricarboxylic acid cycle,induced gene transcription,which accelerated carbon metabolism,promoted the synthesis of shikimic acid,phenylalanine as well as tyrosine,and provided carbon skeleton and precursors for secondary metabolites such as caffeic acid,ferulic acid and erucic acid.It also regulates the gene expression of SOD,PAL,CAT enzymes during the metabolic pathway of phenylpropane and promotes the synthesis of phenolic substances.(5)The three cooking methods(steaming,boiling and microwave treatment)resulted in different levels of loss of phenolic and phytosterol contents in brown rice at different nitrogen levels.Compared to unprocessed,the total phenolic and total flavonoid contents of steamed and microwave treated were reduced by more than 40%,and the contents of ferulic acid,phydroxybenzoic acid,syringic acid,and p-coumaric acid were reduced by 21.07-22.11%,9.73-10.76%,8.44-11.04% and 14.92-22.84% after steaming,while the contents of microwave treated were reduced by 14.03-14.66%,5.44-9.36%,6.79-13.66% and 8.16-14.01%.The phenolic acid content after cooking was higher under N210-260 conditions.At the same level of nitrogen application,microwave treatment showed less loss of phenolic content than steaming.The content of stigmasterol and β-sitosterol in brown rice increased after cooking,while the loss of fucosterol,ergosterol and campesterol content were above 30%.The antioxidant activity indices of brown rice at different levels of nitrogen application were in descending order: unprocessed > microwave treatment > steamed > boiled.(6)In vitro simulated oral-gastrointestinal digestion of unprocessed,steamed and microwave-treated brown rice showed release rates of 34.34-42.50%,61.90-76.42%,and86.53-92.37%,respectively,compared to undigested samples.The total phenol content of brown rice at different nitrogen levels was released more mainly in the stomach,with higher total phenol content in the digest at N210-260.The bioaccessibility and antioxidant activity of microwave-treated brown rice after in vitro digestion were higher by factor analysis.The combined scores of steamed and microwave-treated brown rice were higher at N160-260. |
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