Psidium guajava L. for COVID-19

Guava (Psidium guajava L.) is a highly nutritious and economically important fruit. Although fruit peel is generally regarded as a waste, researchers believe that the peel of the guava is rich in bioactive constituents, even higher than the fruit's flesh. The present study aimed to estimate phenolic content (total phenolic and total flavonoid) and assess antioxidant properties of guava fruit peel (pink variety, cv Arka kiran) by 2,2-di (4-tert-octylphenyl)-1-picryl-hydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and Ferric Reducing Antioxidant Potential (FRAP) assays at five different ripening stages (stage 1 to 5). The TPC and TFC assays were performed by Folin-Ciocalteu and aluminium chloride (AlCl3) methods, respectively. The molecular docking experiment between the major phenolic of guava peel, Catechin and the spike protein of SARS-CoV-2 was performed by the Dockthor online server. Results showed that the peel had high phenolic (highest TPC and TFC, 7307.3 mg gallic acid equivalent/g dry weight [DW] and 433.9 mg quercetin equivalent/g DW, respectively) and antioxidant values (highest DPPH, ABTS and FRAP values 4784.8, 206.6 and 2451 mg ascorbic acid equivalent/g DW, respectively) throughout all stages, although there was a gradual decline in the activity at the later stages. Furthermore, it was found that catechin had a strong binding affinity (-7.591 kcal mol-1) with the spike protein, in silico when compared with the control drug ceftazidime (-7.250 kcal mol-1). The overall outcome of our experiemnts revealed that guava peel could be explored for future pharmacological applications through in vivo studies, and the ‘green mixed with the yellow’ stage of ripening is optimum for such studies.