Profiling of Flavonoid and Antioxidant Activity of Fruit Tissues from 27 Chinese Local Citrus Cultivars

Abstract

Flavonoid profile and antioxidant activity of citrus peels, pulps, and juices from 27 local citrus cultivars in China were investigated. Flavonoid composition and content were determined using UPLC-PDA. Total phenolic content (TPC) and total flavonoid content (TFC) were measured using a Folin-Ciocalteau reagent and Al(NO₃)-NaNO₂ complexometry, respectively. The antioxidant capacities of the extracts were evaluated by DPPH, ABTS and FRAP method, respectively. Citrus peel not only exhibited better antioxidant potential, but also presented more composition diversity and contained higher concentrations of flavonoids than pulp and juice. Different citrus species were characterized by their individual predominant flavonoids, contributing largely to the antioxidant activity, such as mandarin was characterized by hesperidin, nobiletin and tangeretin, while pummelo and papeda were characterized by naringin. The peel of Guihuadinanfeng (Citrus reticulata) had the highest TPC of 23.46 mg equivalent gallic acid/g DW (dry weight) and TFC of 21.37 mg equivalent rutin/g DW. Shiyueju (C. reticulata) peel showed the highest antioxidant capacity based on the antioxidant potency composite (APC) analysis. Overall, mandarin (C. reticulata) fruits peel contained more TPC and TFC, exhibiting higher antioxidant capacities than other species, and were good natural sources of flavonoids and antioxidants.

Keywords: antioxidant activity; flavonoids; local citrus cultivars; total phenolic.

Figure 1

Workflow of this study. For abbreviation of cultivars see Section 4.2. TPC: total phenolic content; TFC: total flavonoid content.

Figure 2

Characteristic UPLC-PDA chromatogram of YXWL (C. reticulata) peel, pulp, juice, and 18 flavonoid standards. Red lines and blue lines mean the chromatogram at the wavelengths of 330 nm and 283 nm, respectively. Retention time and corresponding compounds are listed as: 3.13 min, eriocitrin; 3.41 min, narirutin; 3.51 min, naringin; 3.62 min, hesperidin; 3.70 min, neohesperidin; 3.78, diosmin; 4.23 min, didymin; 5.33 min, isosinensetin; 5.48 min, sinensetin; 5.63 min, 5,7,3′,4′-tetrathoxyflavone; 5.79 min, 5,6,7,4′-tetrathoxyflavone; 5.92 min, nobiletin; 6.06 min, 3,5,6,7,8,3′,4′-hetamethoxyflavone; 6.15 min, 5,7,4′-trimethoxyflavone; 6.29 min, 5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone; 6.34 min, tangeretin. 6.46, Gardenin A; 6.71 min, Gardenin B.

Figure 3

Variations pattern of flavonoids components and contents in the peel extracts of the 27 local cultivars (eight species) analyzed in this study.

Figure 4

Flavonoids profile of different fruit parts from 27 citrus cultivars. (A) Flavonoids composition of peel. (B) PMFs of peel. (C) Flavonoids composition of pulp. (D) Flavonoids composition of juice.

Figure 5

Biplot and Pearson correlation matrix for results obtained from peels (A,D), pulps (B,E), and juices (C,F) of 27 citrus cultivars. Different colored circle represented different citrus species (A–C). Figure inside letters are listed as: a-eriocitrin, b-narirutin, c-naringin, d-hesperidin, e-neohesperidin, f-diosmin, g-didymin, h-isosinensetin, i-sinensetin, j-5,7,3′,4′-tetramethoxyflavone, k-5,6,7,4′-tetramethoxyflavone, l-Nobiletin, m-3,5,6,7,8,3′,4′-heptamethoxyflavone, n-5,7,4′-trimethoxyflavone, o-5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone, p-Tangeretin, q-gardenin A, r-gardenin B, s-ABTS, t-DPPH, u-FRAP, v-TPC, and w-TFC (D–F).