Analysis of Polyphenol Profiles in Fractional Extracts of Passion Fruit Peels and Screening of Their Antioxidant Active Substances

To investigate the extraction efficiency of polyphenols from passion fruit (Passiflora edulis Sims) peel by using different solvents and to identify the characteristic polyphenols with high contribution to antioxidant activity, ethanolic crude extract (CE) was sequentially extracted with petroleum ether (PE), ethyl acetate (EE), n-butanol (BE) and water (WE). The total content of phenolics and flavonoids was then measured by using spectrophotometry. Phenolic compounds in the extracts were profiled by using ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS), and differential metabolites were screened and quantified by using an untargeted metabolomics approach. Antioxidant activities in vitro were assessed through DPPH free radical scavenging, ABTS⁺ free radical scavenging and FRAP methods. Furthermore, the phenolic markers of antioxidant activity in the peels were explored through pearson correlation analysis. The results indicated obvious variations in the total phenolic and flavonoid content among the extracts (P<0.05), ranked in descending order as follows: EE>BE>CE>WE>PE. A total of 33 phenolic compounds were identified from both CE and each fractional extract, while CE, EE, and BE exhibited a greater variety and quantity of phenolic compounds. Principal component analysis (PCA) distinguished the metabolites of extracts, while orthogonal partial least squares discriminant analysis (OPLS-DA) identified p-hydroxybenzoic acid, protocatechuic acid, isoquercitrin and iso-orientin as differential compounds. EE exhibited the highest levels of p-hydroxybenzoic acid (653.44 μg/g), isoquercitrin (2420.64 μg/g) and iso-orientin (113.23 μg/g), while CE showed the highest content of proto-catechuic acid (152.40 μg/g). The in vitro antioxidant activity of passion fruit peel varied significantly among extracts, with EE showing the strongest capacity, suggesting its potential as a premium antioxidant agent. The correlation analysis revealed that the total phenols and flavonoids formed the basis of antioxidant active substances, while iso-orientin and isoquercitrin were the antioxidant active phenolic markers. The finding provided fundamental data for establishing quality control standards of antioxidant products derived from passion fruit peels, as well as for the precise development and utilization of phenolic compounds in the peels.