Introduction: Guava (Psidium guajava) is a nutritious fruit containing various bioactive compounds that are beneficial to human health. In this study, we investigated the total phenolic content, total flavonoid content, level of vitamin C, antioxidant activity, and anticancer activity of three guava cultivars (Kimju, Paen Sitong, and Paen Saidang) that are commonly cultivated and consumed in Thailand. These properties were compared among the different cultivars and between different parts of the fruit.

Methods: In this study, we evaluated the phytochemical contents (total phenolic, total flavonoid contents and vitamin C) and antioxidant activity (DPPH, ABTS, FRAP) using spectrophotometry. Anticancer activity was examined by XTT assay.

Results: The results showed that guava fruit extracts possess antioxidant activity, which is correlated with the amounts of phytochemicals. They also exhibited a significant cytotoxic effect on leukaemia cells (U937). The extract of guava fruit peel exhibited higher phytochemical contents, antioxidant activities, and anticancer activity than the pulp extract. Among guava cultivars, the highest anticancer activity was obtained from Paen Saidang, whereas the highest antioxidant activity was obtained from Kimju.

Conclusion: The results of the present study suggest that Thai guava fruits possess potential antioxidant and anticancer activity due to the presence of different phytochemicals. Guava peel must be eaten with the pulp to maximize the health benefits of guava fruits.