| As one of the most important centers of origin for the genus Citrus L., China is rich in wild mandarin germplasms. Phenolic compounds are a large group of secondary metabolites, which exhibit important physiological properties. In recent years, increasing attention has been paid by nutritionist and pharmacological researches to the phenolic compounds of citrus fruits. In this study, the content and composition of phenolic compounds in the wild mandarin genotypes native to China were determined and their antioxidant capacities were evaluated. The results obtained were compared with those of Satsuma and Ponkan, the most commonly cultivated mandarin fruits types, to provide useful information for the utilization of citrus genetic resources. And also provide theoretical basis and practical value for the future study of the nutrition, medicine and health promotion applications of citrus fruits. The main results were presented as follows:1. This study had developed a high-performance liquid chromatograph (HPLC) method for the determination of different kinds of flavonoids, namely, eriocitrin, taxifolin, narirutin, naringin, hesperidin, neohesperidin, rhoifolin, quercitrin, eridictyol, didymin, poncirin, naringenin, luteolin, kaempferol, diosmetin, sinensetin, nobiletin, and tangeretin in citrus fruits. Results showed that18flavonoids were separated within42min. Chromatographic separation was performed using a reverse phase column (ZORABX SB-C18,250mm×4.6mm internal diameter). The mobile phase was composed of (A)0.1%formic acid (aqueous) and (B) methanol. Gradient elution was performed as follows:from0—20min,37%—50%B; from20—35min,50—80%B; from35—40min,80—100B; from40—50min,100%B; from50—60min,37%—50%B. The column temperature was maintained at25℃, and the flow rate was0.7mL/min. The method exhibited a linear range of62.4—960mg/L (r=0.9996—1.0000), and limits of quantification (LOQ) ranging from0.05—0.133μg/mL. The average recovery rates of this method were88.70%—104.76%, with a relative standard derivation range of0.33%—3.05%(n=6). This method is simple, rapid, accurate, and can be used for the determination of flavonoids in citrus fruits.2.14wild mandarin genotypes and2cultivars native to China were investigated mainly on the content and composition of total phenolic, total flavonoid, flavonoids and phenolic acids using by Folin-Ciocalteu, Sodium nitrite-aluminum nitrate, and HPLC methods respectively. The result showed that total phenolic, total flavonoid, individual flavonoid and phenolic acid content were higher in the peel than in the pulp for all citrus fruits analyzed. The content and composition of phenolic compounds differed significantly (p<0.05) among the genotypes studied. Among the14wild mandarins tested, the highest total phenolic content was detected in the peels and pulps of the Nieduyeju (51.14±0.26mg/g DW and22.26±0.64mg/g DW, respectively).Hesperidin, which was the dominant flavonoid in the fruits studied, was observed to be both the highest in the peels and pulps of Guangxihongpisuanju. Ferulic acid was the most abundant phenolic acid analyzed. Both of the peels and pulps of the Nieduyeju had ferulic acid contents in the soluble phenolic acid, while Guangxihongpisuan had the highest ferulic acid in the bound phenolic acid.3. The antioxidant capacities of the extracts of14wild genotypes and2cultivars were evaluated by DPPH, FRAP, ABTS, and ORAC methods. Results showed that the antioxidant capacities of peels were significantly higher than those of pulps. Antioxidant potency composite indices showed the peels of Nieduyeju, Cupigoushigan, Dakengyeju, Daoxianyeju, Guangxihongpisuan, Banyeshengjuzi No.2, and Xipigoushigan were found to exhibit higher antioxidant capacities than that of the cultivars studied. Whereas the pulps of Nieduyeju, Xichuanzhoupigan, and Guangxihongpisuan had higher antioxidant capacities than that of the cultivars studied.4. The relevance between the contents of total phenolic and total flavonoids and the antioxidant capacities measured by DPPH, FRAP, ABTS and ORAC was investigated. The results indicated that there was a close positive correlation between the total phenolic contents and antioxidant capacities measured by four methods in the peels of fruits tested (p<0.05). A high correlation was observed between total phenolic contents and antioxidant capacities determined by DPPH, FRAP and ABTS in the pulps of fruits tested (p<0.05). While the total flavonoid contents had a lower or even negative relationship with antioxidant activity, which indicated that total phenolic was one of the major contributors to antioxidant capacity of the wild mandarin genotypes. |
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