Phenotypic Variation and Peel Contribution to Fruit Antioxidant Contents in European and Japanese Plums

Abstract

Herein, we studied the variation in leaf and fruit morphological traits and antioxidant contents in 43 local and foreign cultivars (cvs) grown under the same experimental conditions in the widely cultivated plum species Prunus domestica and Prunus salicina. The peel contribution of fruit bioactive compounds in a serving portion, correlations among the examined parameters, and group patterns in each plum species were also studied. The species and cvs were sufficiently separated. Compared to Japanese cvs, European cvs had less elongated leaves and smaller and sweeter fruit with less total phenol and antioxidant capacities. The Japanese cvs 'Red ace' and the widely grown 'Black Amber', together with the European 'Tuleu Dulce', 'BlueFre', and the landrace 'Asvestochoriou' make up groups with rich dietary sources of phytochemicals. The peel tissue contained higher total phenols and antioxidant capacities compared to the flesh, while the peel/flesh ratios varied widely among the cvs (6.6-fold). The variation in the antioxidant contents was lower among the cvs calculated per serving portion (3.7-fold); yet the peel tissue contribution was equal to that of the flesh (48.6%), signifying its high nutritive value. We observed increased sweetness in the fruit in the later-harvested cultivars, while cvs with more blue- and red-colored peel generally contained higher antioxidant contents mainly in the European plums. Moreover, larger fruit sizes were positively correlated with larger and more elliptic leaf shapes. In conclusion, the significant role of the genotype and the peel tissue as a source of bioactive compounds in plums were outlined with prospects of utilization in future breeding programs.

Keywords: Prunus domestica; Prunus salicina; antioxidants; fruit color; fruit fresh weight; fruit shape; leaf characters; total soluble content.

Figure 1

Mean (±SE) (a) soluble solid content (SSC, °Brix), titratable acidity (TA, mg citric acid/100 g FW), (b) maturity index (MI = SSC/TA), and ripening date (RD, Julian date) of 43 European and Japanese plums. Colored columns represent local cultivars. Least significant difference; SSC = 1.23, TA = 2.18, SSC/TA = 0.5.

Figure 2

Mean (±SE) (a) total phenol content (mg gallic acid equivalent/100 g FW), (b) total antioxidant capacity using the DPPH (TAC_DPPH), and (c) the FRAP radical (TAC_FRAP) (mg ascorbic acid equivalent/100 g FW), in fruit peel (solid bars) and flesh (rhombus) tissue of 43 European and Japanese plum cvs. Colored columns represent local cultivars. LSD: TPs–peel, 143.5; TPs–flesh, 40.5; TAC_DPPH–peel, 181.1; TAC_DPPH–flesh, 38.3; TAC_FRAP–peel, 172.4; TAC_FRAP–flesh, 15.9.

Figure 3

Mean (±SE) (a) total phenols (TPs, mg gallic acid equivalent) and total antioxidant capacity using the (b) DPPH (TAC_DPPH) and (c) FRAP radicals (TAC_FRAP) (mg ascorbic acid equivalent), expressed as per serving portion (100 g FW). The percentage (%) contributions of peel and flesh are shown as empty and hatched superimposed columns, respectively. Colored columns represent local cultivars. LSD; total phenols = 35.9, TAC_DPPH = 33.2, TAC_FRAP = 19.1.

Figure 4

(a,c) Segregation and (b,d) factor loadings, of (a,b) 19 European and (c,d) 24 Japanese plum cultivars, on the basis of fruit physical and chemical characters, determined by principal component analysis. Variable annotations are presented in Table 3.

Figure 5

Heatmap showing the clustering of fruit phenotyping traits in 19 European plum cultivars using the ClustVis software. The columns correspond to the cultivars and the rows correspond to the fruit phenotypic traits studied. Both the rows and columns were clustered using Euclidean distance and the Ward method.

Figure 6

Heatmap showing the clustering of fruit phenotyping traits in 24 Japanese plum cultivars using the ClustVis software. The columns correspond to the cultivars and the rows correspond to the fruit phenotypic traits studied. Both rows and columns were clustered using Euclidean distance and the Ward method.