Loquat Flowers Exceed Leaves: A Less Explored Phenolic Source with Functional Potential

<b>Background/Objectives</b>: Loquat (<i>Eriobotrya japonica</i>) is widely cultivated for its fruit, while its aerial by-products remain largely underexploited despite increasing interest in plant-derived bioactive compounds and sustainable food systems. This study comprehensively investigates and compares the phenolic composition and in vitro bioactivities of loquat leaves and flowers to support their potential valorisation as functional ingredients. <b>Methods</b>: Extractable and non-extractable polyphenolic fractions were obtained and quantified, and the extractable fraction was further characterised using HPLC-ESI-QTOF-MS. In vitro bioactivity assessment included antioxidant capacity (FRAP and ABTS), glucose dialysis retardation index, and α-glucosidase inhibition. <b>Results</b>: Flowers contained significantly higher levels of both extractable and non-extractable polyphenols than leaves. Qualitative and semi-quantitative phenolic profiling, including multivariate analysis, revealed clear compositional differences between the two organs. Flowers showed a higher relative abundance of phenolic acids, as well as the presence of several compounds absent in leaves, such as kaempferol, naringenin-3-<i>O</i>-glucoside, and three glycosilated anthocyanins. Flower-derived fractions exhibited consistently higher antioxidant activity across all phenolic fractions than leaf-derived fractions, in agreement with their greater polyphenol content. Regarding antidiabetic activity, leaf samples showed a modest capacity to delay glucose diffusion, whereas this effect was not observed in flowers. In contrast, flower extracts displayed a strong inhibitory effect against α-glucosidase, exceeding that of the reference inhibitor acarbose, while this activity was not detectable in leaf extracts under the experimental conditions. <b>Conclusions</b>: These findings support the revalorisation of loquat by-products, particularly flowers, as sustainable sources of bioactive compounds with potential applications in functional foods and health-related products.