The dynamic changes in pigment metabolites provide a new understanding of the colouration of Pyracantha fortuneana at maturity

The type, content and accumulation characteristics of pigments are the material basis for fruit colour and the evaluation basis of the fruit maturity and nutritional value of P. fortuneana. However, little information is available on the changes in carotenoids, anthocyanins, procyanidins and major flavones during the ripening process of P. fortuneana fruits. Thus, this study investigated the colour conversion characteristics, the main changes in the above four metabolites and the association landscape with those metabolites. The results showed that thirty-nine kinds of carotenoids and derivatives, eighteen anthocyanins, five procyanidins and five flavone compounds were identified in the fruits of P. fortuneana. The total content and contents of most individual carotenoids, anthocyanins, procyanidins and flavones reached the highest values at the TS2, TS4, TS1 and TS1 stages, respectively. Among the variations, the contents of β-carotene and lutein increased first and then decreased, cyanidin-3-galactoside and cyanidin-3-glucoside accumulated, the concentrations of procyanidin C1 and procyanidin B2 decreased, and the contents of rutin and quercetin-3-O-glucoside also decreased; these changers were responsible for the main changes in carotenoids, anthocyanidin, procyanidins and flavones, respectively. For the correlation analysis results, there might be two modes of action that together affected the colour conversion of P. fortuneana fruits during ripening, i.e., (E/Z)-phytoene communicated with the carotenoid metabolic pathway that might promote the accumulated ABA content, which might cause the increased anthocyanidin (primarily through cyanidin-3-(6-malonyl-beta-d-glucoside) (C3MG)) at the final stage; most of the decreased flavone and procyanidin metabolites produced by the flavonoid metabolic pathway were another important factor affecting the accumulation of C3MG.