Abstract
This study investigated the flavonoid compounds in Actinidia chinensis and Actinidia arguta fruits. A total of 125 flavonoids, including 9 anthocyanins, 12 catechins, 17 flavanones, 48 flavones (including 14 flavone C-glycosides), 29 flavonols, 6 isoflavones, and 4 proanthocyanidins, were identified in “Hongyang” kiwifruit (red flesh), “Jintao” kiwifruit, “Mini Amethyst” kiwiberry (purple flesh), and “Kuilv” kiwiberry. Thirty-nine metabolites showed significantly different contents between “Hongyang” and “Jintao,” and 38 of them showed higher content in “Hongyang,” whereas 39 metabolites showed significantly different contents between “Mini Amethyst” and “Kuilv,” and 31 of them showed higher content in “Mini Amethyst.” This result indicates the superior nutritional value of the pigmented kiwi cultivars in terms of flavonoids. Multivariate statistical analysis indicates that the variation in flavonoid profiles contributes to the pigmentation phenotypes of “Hongyang” and “Mini Amethyst.” Further comparative transcriptomic analysis revealed that structural genes in the anthocyanin synthesis pathway (AcF3H, AcF3′H, AcDFR, AcUFGT) and transcription factors (AcMYB10, AcbHLH5) may be involved in the pigmentation of the red-fleshed A. chinensis, whereas AaF3H, AaF3GT, and AaMYB110 may play important roles in the pigmentation of the purple-fleshed A. arguta. This study provides broader insight into the variation in flavonoid profiles among kiwifruit/berry, evaluates the flavonoid nutrition of the four cultivars, and provides additional evidence for the correlation between the genes and metabolites involved in flavonoid synthesis.
Highlights
Kiwifruit (Actinidia chinensis) is a high-value fruit crop that is recognized for its nutrient content and attractive appearance (Li et al 2007)
A total of 125 flavonoids, including 9 anthocyanins, 12 catechins, 17 flavanones, 48 flavones, 29 flavonols, 6 isoflavones, and 4 proanthocyanidins, were identified in the fruits of the four cultivars (Fig. 1b; Table S1); this represents the broadest characterization of the flavonoids in kiwi species to our knowledge
Between AcG and A. arguta “Kuilv” (AaG), 37 metabolites (1 anthocyanin, 3 catechins, 5 flavanones, 12 flavones, 2 flavones C-glycosides, 11 flavonols, and 3 isoflavones) showed significantly differential content, among which 13 showed higher and 24 showed lower content in AcG (Table S1). These results indicate a great difference in flavonoid composition in pigmented kiwifruit/kiwiberry and unpigmented kiwifruit/kiwiberry, suggesting the distinct flavonoid synthesis and regulation mechanism of A. chinensis and A. arguta
Summary
Kiwifruit (Actinidia chinensis) is a high-value fruit crop that is recognized for its nutrient content and attractive appearance (Li et al 2007). Most kiwifruit and kiwiberry varieties have green or pale-yellow flesh and are rich in vitamin C, dietary fiber, and flavonoids that can contribute to human diet (Richardson et al 2018). Arguta, have exhibited great commercial potentials in recent years due to their gorgeous color and antioxidant function provided by accumulated anthocyanins (Jaeger and Harker 2005). These qualities all share at least a partial basis in the flavonoid pathway, which gives rise to fruit colors, flavors, and healthful compounds (Winkel-Shirley 2001). Large-scale evaluation of anthocyanin-related flavonoid compounds has seldom been reported despite colorless/pale-color or yellow flavonoids predominating among the total flavonoids of kiwi species, influencing fruit pigmentation and supporting health functions as well
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