| Citrus fruits and their processed products are important agricultural products in international trade.They have high nutritional value and health effects on human health.So citrus is a kind of fruit both used for food and medicine.Amino acid is the basic unit of the protein molecules that constitute the organism,and has a close relationship with the life activities of the organism.It is the essential nutrient for the organism.Modern nutrition theory believes that the amino acids that make up the proteins of various tissues of the body follow a certain proportion,and the various amino acids provided by the proteins in the daily diet also need to be roughly consistent with the ratio so that the human body can effectively synthesize the body proteins.The closer the amino acid composition of a protein in a food is to human proteins,the higher the human body’s utilization of the protein and the higher its nutritional value.Citrus fruits contain a variety of amino acids that have important nutritional and health benefits.In this study,the citrus edible parts of different species,different varieties of the same species,different production areas of the same variety were used as the materials,and the optimized pre-column derivatized with phenyl isothiocyanate(PITC)by reversed-phase high-performance liquid chromatography(RP-HPLC)method and external standard method were used for the determination of amino acid content and composition analysis of different types of citrus fruits.The essential amino acid(EAA)daily estimated average requirement(EAR)recommended by WHO/FAO was used as the evaluation standard and the “three degree” evaluation method was applied to systematically evaluate the nutritional value of different types of citrus fruits from the aspects of degree of diversity(DD),degree of match(DM),and degree of balance(DB).The main findings are as follows:(1)A standard curve for the determination of 17 kinds of amino acids in citrus was established by studying the conditions of the sample-acid ratio,the hydrolysis time and the hydrolysis temperature,the elution procedure,the mobile phase flow rate,and thecolumn temperature.The correlation coefficient ranged from 0.9908 to 0.9998;the detection limit was 0.36-4.87 mg/L;the standard addition recovery was from 86.9% to107.6%,and the relative standard deviation(RSD)was from 0.47% to 3.84%.The results showed that the method had better accuracy and higher sensitivity and could meet the quantitative analysis of amino acids in citrus fruits.(2)For different species of citrus fruits: 17 kinds of amino acids were detected,and the types were complete.Among them,the total amount of amino acids(TAA)in kumquat was the highest(352.05 ± 16.73 mg/100 g FW).From the amino acid balance point of view to inspect its DD,DM and DI,it was known that the comprehensive evaluation index deviation index(DI)value of loose-skin mandarin was the lowest,i.e.,loose-skin mandarin had a relatively high nutritional value.(3)For different varieties of citrus fruits: As could be seen from the results of the "three degree" evaluation method,Shatangju and Liangping pummelo had the highest nutritional value(the lowest DI value).17 kinds of amino acids were also detected,among which,TAA was the highest in Satsuma orange(206.55 ± 27.32 mg/100 g FW)and Shatian pummelo(reaching 344.44 ± 10.45 mg/100 g FW),but E/T and E/N of Shatangju and Liangping pummelo were higher than those of the other citrus fruits of the same species.(4)For citrus of different production areas of the same variety: Judging from the DD,DM,and DB of amino acids,the lowest DI values were found in Anyue lemon,Suichuan kumquat,and Ganzhou navel orange.That’s to say,they had the highest nutritional value.17 kinds of amino acids were detected in different production areas of‘Eureka’ lemon,‘Huapi’ kumquat and ‘Newhall’ navel orange.Among them,Tongnan lemon,Suichuan kumquat and Zigui navel orange had the highest levels of TAA content reaching 423.60 ± 30.16 mg/100 g FW,370.16 ± 20.37 mg/100 g FW and 267.90 ±34.61 mg/100 g FW,respectively.Asp(aspartic acid),Pro(proline)and Glu(glutamic acid)were all abundant in the edible parts of citrus from different production areas.In this study,an optimized method was used to systematically determine the amino acids in different types of citrus fruits,and the “three-degree” evaluation method was used for the first time to evaluate the nutritional value of different types of citrus fruits in a systematic,comprehensive and standardized way from the aspects of DD,DM,and DB so as to further study their internal quality,guide people to a reasonable diet,and provide scientific basis for further development of citrus fruits in flavorings,food additives,nutritional supplements,preservatives,and pharmaceuticals. |
