论文部分内容阅读
Abstract [Objectives]This study was conducted to investigate the effect of organic nutrient solution on litchi quality.[Methods]Different concentrations of organic nutrient solutions were sprayed on litchi leaves to study their effects on amino acid contents in the fruit of litchi cultivar "Qinzhouhongli".[Results]The results showed that the organic nutrient solution could significantly promote the growth of litchi fruit at various development stages and improve fruit quality by spraying the organic nutrient solution for 3 times with a dilution concentration of 500-1 500 times during fruit development （at an interval of 15 d） of litchi. It could increase the total essential amino acid， total semiessential amino acid， lysine， phenylalanine， threonine， methionine， valine， leucine， histidine， arginine， aspartic acid， glycine， serine， proline， alanine and tyrosine contents. Spraying the organic nutrient solution with a dilution concentration of 1 000 times achieved the best effect of promoting the growth and improving quality of litchi fruit.[Conclusions]This study provides a theoretical basis for highquality production and nutritional quality evaluation of litchi and the development of functional processed litchi products.
Key words Organic nutrient solution; Litchi; Amino acids
Litchi （Litchi chinensis Sonn.） is a famous subtropical fruit tree in Litchi of sapindaceae. China is the first major producer of litchi cultivation， as well as the country with the largest planting area and the highest output in the world. In 2017， Chinaюs litchi production was 2.3 million tons， accounting for about 65% of the global production[1]. Litchi fruit is sweet and juicy， and is not only rich in sugars， proteins， organic acids， minerals and vitamins， but also contains a variety of amino acid components and other nutritive materials[2]. Amino acids are the final hydrolysate of proteins and are the basic units of protein molecules[3]. Proteins are the material basis of life phenomenon， as well as one of the essential nutrients of the human body. They play an important role in the life activities of the human body. Human bodyюs demand for proteins is actually the demand for amino acids[4]. Amino acids are also associated with some special physiological metabolic reactions. For instance， glycine can enhance plant photosynthesis and has an important impact on the improvement of crop quality[5]. Amino acids are also important biologically active ingredients in foods and beverages[6]， and are one of the important taste components. Different amino acid components and their contents directly affect the flavor quality， and most amino acids have taste properties[7]， which are mainly divided into sweetness， umami and bitterness[9]. Amino acids can also directly affect the sensory quality of processed products of fruits such as sauces and juices by participating in Maillardюs reactions[10]. In addition， essential amino acids cannot be synthesized in the body and can only be taken from food. Therefore， the type and content of amino acids are one of the important indicators for evaluating the nutritional value of food[11]. Amino acid contents and components of fruits are related to the variety， origin[6]and storage condition[12]， and are also closely related to their cultivation management techniques[13]. Fertilization management has an important impact on the quality of fruits. In recent years， there have been many studies on the application of organic nutrient solutions to fruit trees， and the spraying of different concentrations of organic nutrient solutions on leaves of pear trees can significantly improve pear quality[14-15]. Liu et al.[16]performed foliar application of organic nutrient solutions to "Okubo" peach to significantly improve the fruit quality of peach. Li et al.[11]significantly improved the quality of blueberry fruit by spraying organic selenium nutrient solution onto the leaf surface. However， few studies have been conducted on the effects of spraying organic nutrient solutions on the quality of litchi fruit， especially amino acid contents and components. In this study， with "Qinzhouhongli" as an experimental material， the effects of different concentrations of organic nutrient solution on amino acid components and contents in litchi fruit were studied at small fruit stage， with an attempt to provide a theoretical basis for highquality production， nutritional quality evaluation of litchi and the development of functional processed litchi products.
Materials and Methods
The experiment was carried out in the multipurpose specimen garden of College of Agriculture， Guangxi University. The basic soil traits of the test site were as follows： red loam soil， medium soil fertility.
Experimental materials
The litchi variety tested was "Qinzhouhongli"， which was 15 years old. The row spacing was 3.0 m≠5.0 m， 660 plants/hm2. The organic nutrient solution was developed and supplied by Guangxi Benran Agricultural Technology Co.， Ltd.， with following main components： N 1.97%， P2O5 1.86%， K2O 1.61%， total humic acid （calculated as peat humic acid） 0.85%， and organic matter 0.52%.
Experimental methods
The experiment was carried out using a randomized block design， and single plant served as a plot which had three replicates. The test factors were different concentrations of organic nutrient solutions. There were four treatments in the experiment： 1 500 times dilution of the organic nutrient solution （referred to as ONS1 500≠， 1 000 times dilution of the organic nutrient solution （referred to as ONS1 000≠）， 500 times dilution of the organic nutrient solution （referred to as ONS500≠）， and water as control check （CK）. For each treatment， the foliar application was performed at the small fruit stage 20 d after flowering， once every 15 d for a total of 3 times. During each time of foliar application， the solution was sprayed on the leaves to the extent that the leaves were wet and the solution was about to drop off. Analysis methods of test indexes
At the mature stage of litchi fruit， the fruit individuals with the same maturity were selected in each plot to determine the composition and contents of free amino acids. Specifically， 20 individuals were taken from each plot， with three replicates. The instrument was a Hitachi L8900 amino acid automatic analyzer， and the method was according to GB/T5009.1242003[17].
Statistical analysis methods
The test data were statistically analyzed with SPSS18.0 software， and figures were drawn with Excel software. Variance analysis was performed using the Duncans method for multiple comparisons.
Results and Analysis
Effects of different concentrations of organic nutrient solutions on the total amino acid content in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly improve the total amino acid content in the fruit flesh， which was 4.9%-8.0% higher than the CK. The highest content was obtained when spaying 1 000 times dilution of the organic nutrient solution （Fig. 1）.
Effects of different concentrations of organic nutrient solutions on the contents of essential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly increase the total essential amino acid content （0.6%-2.5% higher than the CK） and the contents of essential amino acids such as lysine （Lys）， phenylalanine （Phe）， threonine （Thr）， methionine （Met）， valine （Val）， leucine （Leu） and isoleucine （Ile）. Among the various concentrations， the 1 500 times dilution of the organic nutrient solution most significantly improved the total essential amino acid content in the fruit flesh; the 1 000 times dilution of the organic nutrient solution most significantly improved lysine， phenylalanine， threonine and methionine contents; the 1 500 times dilution of the organic nutrient solution most significantly improved valine and isoleucine contents; and the 500 times dilution of the organic nutrient solution most significantly improved leucine content （Fig. 2 and Fig. 3）.
Effects of different concentrations of organic nutrient solutions on the contents of semiessential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi can significantly improve the total semiessential amino acid content （increased by 11.96%-15.1% compared with the CK） and the contents of histidine （His） and arginine （Arg） among the semiessential amino acids in litchi flesh. Spraying 1 000 times dilution of the organic nutrient solution achieved the best effect （Fig. 4 and Fig. 5）. Effects of different concentrations of organic nutrient solutions on the content of nonessential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly increase the contents of nonessential amino acids such as aspartic acid （Asp）， glycine （Gly）， serine （Ser）， proline （Pro）， alanine （Ala） and tyrosine （Tyr） in litchi flesh （Fig. 6）.
Effects of different concentrations of organic nutrient solutions on the proportions of various amino acids in total amino acids in litchi flesh
The contents of glutamic acid and glycine among the various amino acid components were the highest in the fruit flesh of "Qinzhouhongli"， both accounting for 15.1%-18.5% of the total amino acid content. The components ranking third and fourth were aspartic acid and tryptophan， respectively， and the contents of histidine and lysine were lower， only accounting for about 1.5%-2.0% of the total amino acid content. The essential amino acids and the semiessential amino acids in the fruit flesh of "Qinzhouhongli" accounted for 28.1%-32.3% and 5.6%-6.0% of the total amino acids， respectively. Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times for 3 times at the small fruit stage can significantly increase the proportions of various amino acids in the total amino acid content of the fruit flesh. The proportions of various amino acids in the total amino acid content were 0.2% higher than the CK. The organic nutrient solution had the greatest effect on increasing alanine content， followed by proline， and the amino acid the least affected was tyrosine （Fig. 7）.
Conclusions and Discussion
Amino acids in fruits are one of the important nutritional components and taste components， and different amino acid compositions directly affect the nutritional and healthcare effects. The results of this study indicated that litchi fruit was rich in amino acid components， such as sweet amino acids （alanine， threonine， glycine and valine）， umami amino acids （aspartic acid and glutamic acid） and bitter amino acids （valine， leucine， isoleucine， phenylalanine and arginine）[18]， suggesting that litchi fruit has rich taste and high nutritional value.
The amino acid components and contents of different litchi varieties are different. The results of this study indicated that the main amino acids in the fruit of litchi variety "Qinzhouhongli" were glutamic acid and glycine， both of which accounted for 15.1%-18.5% of the total amino acid content. The main amino acids in the fruit of litchi variety "Lanzhu" were glutamic acid and aspartic acid[22]. The main amino acids in the juice of litchi variety " Feizixiao " were aminobutyric acid and alanine， which accounted for 26.6% and 16.9% of the total amino acid content， respectively[6]. Glutamate has the functions of preventing anemia， detoxifying and strengthening brain[5]; and alanine can reduce cholesterol in mice and is a necessity in tryptophan metabolism and glucose metabolism[23]. Fertilization management level can affect the amino acid components and contents in fruits. The results of this study showed that the application of organic nutrient solution at the small fruit stage can significantly increase the total amino acid content， essential amino acid content， semiessential amino acid content and the contents of various amino acids in litchi flesh， which accords with the result of previous studies that spaying organic nutrient solution can improve the quality of pear， peach， blueberry and other fruits[14-16]. Yao et al.[24]and other studies have also shown that the application of organic fertilizers in the soil could significantly increase the free amino acid content of the fruit of litchi variety "Baitangying". Different Nitrogen application rates also effected the amino acid components and contents in the fruit of litchi variety "Lanzhu". The litchi fruit with moderate nitrogen application rate （0.8 kg per plant） showed the highest total amino acid amount， and toohigh or toolow nitrogen application rate both reduced the accumulation of amino acids[22]. In addition， the foliar application of 1 000 times dilution of the organic nutrient solution in this study had the best effect on the improvement of the amino acid content in litchi variety "Qinzhouhongli". Because different nutrient solutions may have different formulations and different crops and varieties have different needs for various nutrients， the application performance of different organic nutrient solutions on different fruit trees may be different， and the optimal application concentration should be determined based on the various organic nutrient solutions and the performance of various fruit tree species and varieties after application. The fact that organic nutrient solutions can significantly increase the amino acid content in fruits might be because of rich and comprehensive nutrients in organic nutrient solutions[11，19-20]. In addition， organic matter in organic nutrient solutions could be decomposed to organic acids and other substances to promote the dissolution of mineral nutrients and improve the absorption of nutrients by plants[21]. Organic nutrient solutions can improve fruit quality in fruit tree production， and the application of organic fertilizers can also reduce the amount of chemical fertilizers and avoid the environmental pollution caused by chemical fertilizer abuse. The application of organic nutrient solutions should be promoted in the production and cultivation of fruit trees， so as to promote the sustainable development of agriculture.
References
[1]HUANG Y. 2018 China litchi summit conference[J]. World Tropical Agriculture Information， 2018（5）： 34. （in Chinese）
[2]SHEN J， LI C， WANG SY. Hyoon storage impact on litchiюs amino acid and other qualities[C]. 2010（9）： 62-65. （in Chinese）
[3]AUTORENKOLLEKTIV VE. Food Chemistry and Nutrition[M]. Beijing： Peopleюs Medical Publishing House，1985 ：60-61. （in Chinese）
[4]HE SS， ZHOU ZQ. Evaluation of amino acid composition and nutritional quality of different kinds of citrus fruits[J]. South China Fruits，2018，47（3）：18-29. （in Chinese）
[5]ZHAO QL， JIN J， SHA YC， et al. Composition and content of amino acid of Phyllanthus emblica L. fruit from different sources[J]. Chinese Agricultural Science Bulletin，2017，33（36）：78-84. （in Chinese）
[6]CUI SS， HU ZY， YU K， et al. Amino acid composition of Feizixiao litchi juice from different geographic origins[J]. Food Science，2011，32（12）：269-272. （in Chinese）
[7]YVON M， RIJNEN L. Cheese flavour formation by amino acid catabolism[J]. International Dairy Journal， 2001， 11（4/7）： 185-201. [8]WU YW， OUYANG J. The taste effect of amino acids and peptides in food[J]. China Condiment，2001，1：21-24. （in Chinese）
[9]JIANG Y， XU Y， ZHU KB. Human taste and amino acid taste[J]. Amino Acids and Biotic Resources，2002，24（4）：1-3. （in Chinese）
[10]SILVA BM， CASAL S， ANDRADE PB， et al. Free amino acid composition of quince （Cydonia oblonga Miller） fruit （pulp and peel） and jam[J]. Journal of Agricultural and Food Chemistry， 2004， 52（5）：1201-1206.
[11]LI CX， LIU W， CHEN LY， et al. Effect of organic selenium solution on the nutrition quality and antioxidant function of blueberry[J]. Food and Fermentation Industries， 2018（3）： 179-185. （in Chinese）
[12]CHEN ZH， HU ZY， LYU EL， et al. Changes in amino acid contents of Shuangjianyuhebao litchi during different storage conditions[J]. Modern Food Science & Technology，2013，29（8）：1955-1960. （in Chinese）
[13]DAI LZ， LIN CX， LIU LY， et al. Effects of the levels of nitrogen application on the amino acid contents and flower sex of Lanzhu litchi[J]. Journal of Fujian Agriculture and Forestry University，1998（4）：36-39. （in Chinese）
[14]ZHAO M， GAO Y， TIAN SF， et al. Probe into effects of spraying organic nutrient solution to leaf and fruit of pear on fruit quality[J]. Journal of Zhejiang Agricultural Sciences2008（3）： 274-275.（in Chinese）
[15]GENG J， CUI NN， ZHANG J， et al. Effect of aromatic plantderived nutrient solution on the growth， fruit quality and disease prevention of pear trees[J]. Acta Ecologica Sinica， 2011（5）： 1285-1294.（in Chinese）
[16] LIU XL， LIU ZW， LI JH. Effect of application of organic nutrient liquid on peach[J]. Hebei Fruits， 2006（2）： 7-8.（in Chinese）
[17]GB/T5009.1242003. Determination of amino acid content in food[S]. Beijing： China Standards Press， 2003.（in Chinese）
[18]HE J， MO RF， LIAO J， et al. Principal component analysis of free amino acids in Passiflora edulis Sims[J]， Guangxi Journal of Light Industry，2018（11）：5-7.（in Chinese）
[19]DAI ML， LI ST， HAN ZH， et al. Effects of plantderived nutrient solutions on the growth and fruit quality of ‘Xueqing’ pear[J]. Journal of China Agricultural University，2008（05）：19-23.（in Chinese）
[20]DENG YY， PAN JC， ZHENG X， et al. Effects of applying cassava starch anaerobic liquid on the traits and quality of banana fruit[J]. South China Fruits，2013，42（3）：62-64.（in Chinese）
[21] ZHANG JH， MA LL， LI JM. Effects of allorganic nutrient solution and water coupling on quality， yield and water use efficiency of tomato[J]. Scientia Agricultura Sinica， 2018，51（14）：2788-2798.（in Chinese）
[22]DAI LZ， LIN CX， LIU LR， et al. Effects of the levels of nitrogen application on the amino acid contents and flower sex of Lanzhu litchi[J]. Journal of Fujian Agriculture and Forestry University，1998，27（4）： 419-422.（in Chinese）
[23]BELITZ HD， GROSCH W， SCHIEBERLE P. Food Chemistry[M]. Berlin， Germany： SpringerVerlag， 2009.
[24]YAO LX， ZHOU CM， WANG XH， et al. Effect of application of organic fertilizers on litchi[J]. Soil and Fertilizer Sciences in China， 2017， （5）： 87-93. （in Chinese）
Key words Organic nutrient solution; Litchi; Amino acids
Litchi （Litchi chinensis Sonn.） is a famous subtropical fruit tree in Litchi of sapindaceae. China is the first major producer of litchi cultivation， as well as the country with the largest planting area and the highest output in the world. In 2017， Chinaюs litchi production was 2.3 million tons， accounting for about 65% of the global production[1]. Litchi fruit is sweet and juicy， and is not only rich in sugars， proteins， organic acids， minerals and vitamins， but also contains a variety of amino acid components and other nutritive materials[2]. Amino acids are the final hydrolysate of proteins and are the basic units of protein molecules[3]. Proteins are the material basis of life phenomenon， as well as one of the essential nutrients of the human body. They play an important role in the life activities of the human body. Human bodyюs demand for proteins is actually the demand for amino acids[4]. Amino acids are also associated with some special physiological metabolic reactions. For instance， glycine can enhance plant photosynthesis and has an important impact on the improvement of crop quality[5]. Amino acids are also important biologically active ingredients in foods and beverages[6]， and are one of the important taste components. Different amino acid components and their contents directly affect the flavor quality， and most amino acids have taste properties[7]， which are mainly divided into sweetness， umami and bitterness[9]. Amino acids can also directly affect the sensory quality of processed products of fruits such as sauces and juices by participating in Maillardюs reactions[10]. In addition， essential amino acids cannot be synthesized in the body and can only be taken from food. Therefore， the type and content of amino acids are one of the important indicators for evaluating the nutritional value of food[11]. Amino acid contents and components of fruits are related to the variety， origin[6]and storage condition[12]， and are also closely related to their cultivation management techniques[13]. Fertilization management has an important impact on the quality of fruits. In recent years， there have been many studies on the application of organic nutrient solutions to fruit trees， and the spraying of different concentrations of organic nutrient solutions on leaves of pear trees can significantly improve pear quality[14-15]. Liu et al.[16]performed foliar application of organic nutrient solutions to "Okubo" peach to significantly improve the fruit quality of peach. Li et al.[11]significantly improved the quality of blueberry fruit by spraying organic selenium nutrient solution onto the leaf surface. However， few studies have been conducted on the effects of spraying organic nutrient solutions on the quality of litchi fruit， especially amino acid contents and components. In this study， with "Qinzhouhongli" as an experimental material， the effects of different concentrations of organic nutrient solution on amino acid components and contents in litchi fruit were studied at small fruit stage， with an attempt to provide a theoretical basis for highquality production， nutritional quality evaluation of litchi and the development of functional processed litchi products.
Materials and Methods
The experiment was carried out in the multipurpose specimen garden of College of Agriculture， Guangxi University. The basic soil traits of the test site were as follows： red loam soil， medium soil fertility.
Experimental materials
The litchi variety tested was "Qinzhouhongli"， which was 15 years old. The row spacing was 3.0 m≠5.0 m， 660 plants/hm2. The organic nutrient solution was developed and supplied by Guangxi Benran Agricultural Technology Co.， Ltd.， with following main components： N 1.97%， P2O5 1.86%， K2O 1.61%， total humic acid （calculated as peat humic acid） 0.85%， and organic matter 0.52%.
Experimental methods
The experiment was carried out using a randomized block design， and single plant served as a plot which had three replicates. The test factors were different concentrations of organic nutrient solutions. There were four treatments in the experiment： 1 500 times dilution of the organic nutrient solution （referred to as ONS1 500≠， 1 000 times dilution of the organic nutrient solution （referred to as ONS1 000≠）， 500 times dilution of the organic nutrient solution （referred to as ONS500≠）， and water as control check （CK）. For each treatment， the foliar application was performed at the small fruit stage 20 d after flowering， once every 15 d for a total of 3 times. During each time of foliar application， the solution was sprayed on the leaves to the extent that the leaves were wet and the solution was about to drop off. Analysis methods of test indexes
At the mature stage of litchi fruit， the fruit individuals with the same maturity were selected in each plot to determine the composition and contents of free amino acids. Specifically， 20 individuals were taken from each plot， with three replicates. The instrument was a Hitachi L8900 amino acid automatic analyzer， and the method was according to GB/T5009.1242003[17].
Statistical analysis methods
The test data were statistically analyzed with SPSS18.0 software， and figures were drawn with Excel software. Variance analysis was performed using the Duncans method for multiple comparisons.
Results and Analysis
Effects of different concentrations of organic nutrient solutions on the total amino acid content in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly improve the total amino acid content in the fruit flesh， which was 4.9%-8.0% higher than the CK. The highest content was obtained when spaying 1 000 times dilution of the organic nutrient solution （Fig. 1）.
Effects of different concentrations of organic nutrient solutions on the contents of essential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly increase the total essential amino acid content （0.6%-2.5% higher than the CK） and the contents of essential amino acids such as lysine （Lys）， phenylalanine （Phe）， threonine （Thr）， methionine （Met）， valine （Val）， leucine （Leu） and isoleucine （Ile）. Among the various concentrations， the 1 500 times dilution of the organic nutrient solution most significantly improved the total essential amino acid content in the fruit flesh; the 1 000 times dilution of the organic nutrient solution most significantly improved lysine， phenylalanine， threonine and methionine contents; the 1 500 times dilution of the organic nutrient solution most significantly improved valine and isoleucine contents; and the 500 times dilution of the organic nutrient solution most significantly improved leucine content （Fig. 2 and Fig. 3）.
Effects of different concentrations of organic nutrient solutions on the contents of semiessential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi can significantly improve the total semiessential amino acid content （increased by 11.96%-15.1% compared with the CK） and the contents of histidine （His） and arginine （Arg） among the semiessential amino acids in litchi flesh. Spraying 1 000 times dilution of the organic nutrient solution achieved the best effect （Fig. 4 and Fig. 5）. Effects of different concentrations of organic nutrient solutions on the content of nonessential amino acids in litchi flesh
Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times at the small fruit stage of litchi for 3 times can significantly increase the contents of nonessential amino acids such as aspartic acid （Asp）， glycine （Gly）， serine （Ser）， proline （Pro）， alanine （Ala） and tyrosine （Tyr） in litchi flesh （Fig. 6）.
Effects of different concentrations of organic nutrient solutions on the proportions of various amino acids in total amino acids in litchi flesh
The contents of glutamic acid and glycine among the various amino acid components were the highest in the fruit flesh of "Qinzhouhongli"， both accounting for 15.1%-18.5% of the total amino acid content. The components ranking third and fourth were aspartic acid and tryptophan， respectively， and the contents of histidine and lysine were lower， only accounting for about 1.5%-2.0% of the total amino acid content. The essential amino acids and the semiessential amino acids in the fruit flesh of "Qinzhouhongli" accounted for 28.1%-32.3% and 5.6%-6.0% of the total amino acids， respectively. Spraying the organic nutrient solution with a dilution concentration of 500-1 500 times for 3 times at the small fruit stage can significantly increase the proportions of various amino acids in the total amino acid content of the fruit flesh. The proportions of various amino acids in the total amino acid content were 0.2% higher than the CK. The organic nutrient solution had the greatest effect on increasing alanine content， followed by proline， and the amino acid the least affected was tyrosine （Fig. 7）.
Conclusions and Discussion
Amino acids in fruits are one of the important nutritional components and taste components， and different amino acid compositions directly affect the nutritional and healthcare effects. The results of this study indicated that litchi fruit was rich in amino acid components， such as sweet amino acids （alanine， threonine， glycine and valine）， umami amino acids （aspartic acid and glutamic acid） and bitter amino acids （valine， leucine， isoleucine， phenylalanine and arginine）[18]， suggesting that litchi fruit has rich taste and high nutritional value.
The amino acid components and contents of different litchi varieties are different. The results of this study indicated that the main amino acids in the fruit of litchi variety "Qinzhouhongli" were glutamic acid and glycine， both of which accounted for 15.1%-18.5% of the total amino acid content. The main amino acids in the fruit of litchi variety "Lanzhu" were glutamic acid and aspartic acid[22]. The main amino acids in the juice of litchi variety " Feizixiao " were aminobutyric acid and alanine， which accounted for 26.6% and 16.9% of the total amino acid content， respectively[6]. Glutamate has the functions of preventing anemia， detoxifying and strengthening brain[5]; and alanine can reduce cholesterol in mice and is a necessity in tryptophan metabolism and glucose metabolism[23]. Fertilization management level can affect the amino acid components and contents in fruits. The results of this study showed that the application of organic nutrient solution at the small fruit stage can significantly increase the total amino acid content， essential amino acid content， semiessential amino acid content and the contents of various amino acids in litchi flesh， which accords with the result of previous studies that spaying organic nutrient solution can improve the quality of pear， peach， blueberry and other fruits[14-16]. Yao et al.[24]and other studies have also shown that the application of organic fertilizers in the soil could significantly increase the free amino acid content of the fruit of litchi variety "Baitangying". Different Nitrogen application rates also effected the amino acid components and contents in the fruit of litchi variety "Lanzhu". The litchi fruit with moderate nitrogen application rate （0.8 kg per plant） showed the highest total amino acid amount， and toohigh or toolow nitrogen application rate both reduced the accumulation of amino acids[22]. In addition， the foliar application of 1 000 times dilution of the organic nutrient solution in this study had the best effect on the improvement of the amino acid content in litchi variety "Qinzhouhongli". Because different nutrient solutions may have different formulations and different crops and varieties have different needs for various nutrients， the application performance of different organic nutrient solutions on different fruit trees may be different， and the optimal application concentration should be determined based on the various organic nutrient solutions and the performance of various fruit tree species and varieties after application. The fact that organic nutrient solutions can significantly increase the amino acid content in fruits might be because of rich and comprehensive nutrients in organic nutrient solutions[11，19-20]. In addition， organic matter in organic nutrient solutions could be decomposed to organic acids and other substances to promote the dissolution of mineral nutrients and improve the absorption of nutrients by plants[21]. Organic nutrient solutions can improve fruit quality in fruit tree production， and the application of organic fertilizers can also reduce the amount of chemical fertilizers and avoid the environmental pollution caused by chemical fertilizer abuse. The application of organic nutrient solutions should be promoted in the production and cultivation of fruit trees， so as to promote the sustainable development of agriculture.
References
[1]HUANG Y. 2018 China litchi summit conference[J]. World Tropical Agriculture Information， 2018（5）： 34. （in Chinese）
[2]SHEN J， LI C， WANG SY. Hyoon storage impact on litchiюs amino acid and other qualities[C]. 2010（9）： 62-65. （in Chinese）
[3]AUTORENKOLLEKTIV VE. Food Chemistry and Nutrition[M]. Beijing： Peopleюs Medical Publishing House，1985 ：60-61. （in Chinese）
[4]HE SS， ZHOU ZQ. Evaluation of amino acid composition and nutritional quality of different kinds of citrus fruits[J]. South China Fruits，2018，47（3）：18-29. （in Chinese）
[5]ZHAO QL， JIN J， SHA YC， et al. Composition and content of amino acid of Phyllanthus emblica L. fruit from different sources[J]. Chinese Agricultural Science Bulletin，2017，33（36）：78-84. （in Chinese）
[6]CUI SS， HU ZY， YU K， et al. Amino acid composition of Feizixiao litchi juice from different geographic origins[J]. Food Science，2011，32（12）：269-272. （in Chinese）
[7]YVON M， RIJNEN L. Cheese flavour formation by amino acid catabolism[J]. International Dairy Journal， 2001， 11（4/7）： 185-201. [8]WU YW， OUYANG J. The taste effect of amino acids and peptides in food[J]. China Condiment，2001，1：21-24. （in Chinese）
[9]JIANG Y， XU Y， ZHU KB. Human taste and amino acid taste[J]. Amino Acids and Biotic Resources，2002，24（4）：1-3. （in Chinese）
[10]SILVA BM， CASAL S， ANDRADE PB， et al. Free amino acid composition of quince （Cydonia oblonga Miller） fruit （pulp and peel） and jam[J]. Journal of Agricultural and Food Chemistry， 2004， 52（5）：1201-1206.
[11]LI CX， LIU W， CHEN LY， et al. Effect of organic selenium solution on the nutrition quality and antioxidant function of blueberry[J]. Food and Fermentation Industries， 2018（3）： 179-185. （in Chinese）
[12]CHEN ZH， HU ZY， LYU EL， et al. Changes in amino acid contents of Shuangjianyuhebao litchi during different storage conditions[J]. Modern Food Science & Technology，2013，29（8）：1955-1960. （in Chinese）
[13]DAI LZ， LIN CX， LIU LY， et al. Effects of the levels of nitrogen application on the amino acid contents and flower sex of Lanzhu litchi[J]. Journal of Fujian Agriculture and Forestry University，1998（4）：36-39. （in Chinese）
[14]ZHAO M， GAO Y， TIAN SF， et al. Probe into effects of spraying organic nutrient solution to leaf and fruit of pear on fruit quality[J]. Journal of Zhejiang Agricultural Sciences2008（3）： 274-275.（in Chinese）
[15]GENG J， CUI NN， ZHANG J， et al. Effect of aromatic plantderived nutrient solution on the growth， fruit quality and disease prevention of pear trees[J]. Acta Ecologica Sinica， 2011（5）： 1285-1294.（in Chinese）
[16] LIU XL， LIU ZW， LI JH. Effect of application of organic nutrient liquid on peach[J]. Hebei Fruits， 2006（2）： 7-8.（in Chinese）
[17]GB/T5009.1242003. Determination of amino acid content in food[S]. Beijing： China Standards Press， 2003.（in Chinese）
[18]HE J， MO RF， LIAO J， et al. Principal component analysis of free amino acids in Passiflora edulis Sims[J]， Guangxi Journal of Light Industry，2018（11）：5-7.（in Chinese）
[19]DAI ML， LI ST， HAN ZH， et al. Effects of plantderived nutrient solutions on the growth and fruit quality of ‘Xueqing’ pear[J]. Journal of China Agricultural University，2008（05）：19-23.（in Chinese）
[20]DENG YY， PAN JC， ZHENG X， et al. Effects of applying cassava starch anaerobic liquid on the traits and quality of banana fruit[J]. South China Fruits，2013，42（3）：62-64.（in Chinese）
[21] ZHANG JH， MA LL， LI JM. Effects of allorganic nutrient solution and water coupling on quality， yield and water use efficiency of tomato[J]. Scientia Agricultura Sinica， 2018，51（14）：2788-2798.（in Chinese）
[22]DAI LZ， LIN CX， LIU LR， et al. Effects of the levels of nitrogen application on the amino acid contents and flower sex of Lanzhu litchi[J]. Journal of Fujian Agriculture and Forestry University，1998，27（4）： 419-422.（in Chinese）
[23]BELITZ HD， GROSCH W， SCHIEBERLE P. Food Chemistry[M]. Berlin， Germany： SpringerVerlag， 2009.
[24]YAO LX， ZHOU CM， WANG XH， et al. Effect of application of organic fertilizers on litchi[J]. Soil and Fertilizer Sciences in China， 2017， （5）： 87-93. （in Chinese）