Abstract:In order to improve the comprehensive utilization rate of the by-products of guava (Psidium guajava), the biological activities and phenolic constituents of extracts from 4 cultivars (‘Zhenzhu’, ‘Shuimi’, ‘Hongbaoshi’, ‘Xigua’) of guava were studied. The contents of total phenols and flavonoids were determined, then the correlations between the contents of phenols and flavonoids with biological activities were analyzed, including the scavenging abilities on DPPH·, ABTS+, HO· free radicals, and the α-glucosidase inhibitory activity. Furthermore, the phenolic constituents of extracts were identified by ultra-high performance liquid chromatography and the triple-quadrupole tandem mass spectrometry (UPLC-MS/MS). The results showed that the contents of total phenols and flavonoids, the free radicals scavenging abilities and α-glucosidase inhibitory activity in leaves of 4 cultivars were significantly higher than those in young fruits, ‘Zhenzhu’ leaf had the highest content of total phenols as well as the most potent free radicals scavenging abilities and α-glucosidase inhibitory activity. Correlation analysis revealed that the contents of phenols and flavonoids were significantly positively correlated with the scavenging abilities towards DPPH·, ABTS+, HO· free radicals (P<0.01), as well as the α-glucosidase inhibitory activity (P<0.05). UPLC-MS/MS analysis showed that the contents of quercetin-3-O-glucoside, hyperoside, ellagic acid and myricitrin in leaves of 4 cultivars were high, and most of the constituents found in leaves except ellagic acid also existed in the young fruits, and the contents in leaves were higher than those in young fruits. Therefore, ‘Zhenzhu’ guava leaf could be a good resource for developing natural antioxidant and α-glucosidase inhibitor among 4 cultivars.