Studies On The Effect Of Different Nitrogen Levels On Rice Lipid Metabolism And Taste Quality

Lipids are one of the important nutrients,2%-3.8%content that is mostly high-quality unsaturated fatty acids and has high nutritional value in rice.Rice fat is also closely related to the cooking and eating quality of rice simultaneously.Studies have suggested that increasing rice fat content not only improves the nutritional quality of rice but also the taste quality of rice.Therefore,increasing rice fat content is one of the important methods to improve rice quality.In addition to genetic control,rice lipids are also affected by environmental factors including light,temperature,water,fertilizer,and cultivation measures.Studies has suggested that nitrogen fertilizer has a important effect on the formation of rice lipids.However,these studies mostly concentrate on the rate of nitrogen with the fat content,composition of mature stage etc.The effect of nitrogen fertilizer on lipid metabolism are rarely reported.In this study,Nanjing 9108(japonica)and IR72(indica)were used as material.Under the field cultivation conditions,four nitrogen application levels were set(N0:0 kg/hm~2,N1:90 kg/hm~2,N2:135kg/hm~2,N3:180 kg/hm~2),to investigate the effect of different nitrogen levels on lipid metabolism in rice and analyze the correlation between lipid and cooking taste quality,which provides the theoretical basis of cultivation of rice.The experiment results are as follows:1.Effect of nitrogen application rate on lipid accumulation in riceWith the grain filling process,the crude fat content of the two varieties(peaked at 25-30days after flowering)showed a trend of increasing,and then decreasing in maturation stage.Under different nitrogen application rates treatment,the crude fat content of the two varieties increased with the increase of nitrogen application rate during difference flowering period.under the same nitrogen application level,Nanjing 9108 crude fat content was higher than IR72.It indicated that the crude fat content of japonica was higher than that of indica.During the development of rice grain,the free fatty acid content of the Nanjing 9108 and IR72 showed a decreasing-increasing trend under the N0-N3 treatment.Increased nitrogen is conducive to the accumulation of free fatty acids.At maturity(35 days after flowering),Nanjing 9108 had the highest percentage of free fatty acids(25.75%)under nitrogen application at 135 kg/hm~2,IR72 was the highest under nitrogen application at 135 kg/hm~2(15.52%).The analysis result of the fatty acid components of the two varieties at maturity phase(35days after flowering)were as follows:11 kinds fatty acids were detected in Nanjing 9108 and10 kinds fatty acids were detected in IR72,that the fatty acids content of linoleic acid,palmitic acid,stearic acid and arachidic acid are the highest.the content of unsaturated fatty acids in both varieties was higher than that of saturated fatty acids.N application rate of linoleic acid and unsaturated fatty acid content had a influence of the obvious too much or too little nitrogen fertilizer is count againtst the increase of linoleic acid and unsaturated fatty acids content.Nanjing 9108 had the highest percentage of linoleic acid and unsaturated fatty acid under nitrogen application at 90 kg/hm~2,IR72 was the highest under nitrogen application at 135 kg/hm~2.2.Effects of nitrogen application rate on enzyme activity related to lipid synthesis in riceACCase,FAS,3-GPD and PPase are key enzymes in lipid synthesis.The four enzyme activity of each treatment of two varities showed a trend of increasing and then decreasing.The activity of ACCase and FAS peaked at 20d-25d after flowering,the activity of 3-GPD peaked at 30d after flowering.The PPase activity peaked at 20d-30d after flowering,indicating that the synthesis of fatty acids in rice grains was rapidly in the early stage of grain development and triglyceride and lipoid synthesis were mainly in the middle and late stage of grain development.The effect of nitrogen fertilizer on the activity of the four enzymes of two varites were increased significantly with the increase of nitrogen application rate.Howerver,the crude fat was only positively correlated with 3-GPD and PPase.3.Effects of nitrogen application rates on cooking and eating quality of riceIn this experiment,nitrogen application rate can significantly influence the physical and chemical properties and testing of rice;Among them,the amylose content of Nanjing 9108and IR72 increased with the increase of nitrogen application rate.However,The peak viscosity,disintegration value and taste value of Nanjing 9108 under nitrogen application at90-135 kg/hm~2 were highe,the subtraction value is low.The peak viscosity and disintegration value were high,the reduction value was low,the taste value was high.Correlation analysis between lipids and testing found that the free fatty acid of Nanjing 9108 was significantly positively correlated with peak viscosity and disintegration value,positively correlated with the taste value,negatively correlated with the subtraction value and peak time.The unsaturated fatty acid was significantly positively correlated with the disintegration value and significantly negatively correlated with final viscosity and peak time.The free fatty acid of IR72 was positively correlated with the taste value and significantly negatively correlated with the subtraction value.It indicated that nitrogen application rate mainly by increasing free fatty acid content in rice to increase the peak viscosity and breakdown value,reduced the peak value,shorten the peak time and improve rice taste quality.In summar,under 90-135kg/hm~2 nitrogen fertilization treament,the two varieties had better comprehensive taste with high content of free fatty acid,high content of linoleic acid and unsaturated fatty acid.In rice cultivation,we shoud not noly pay attention to the accumulation of crude fat,but also pay attention to the improvement of free fatty acid.