May the superfruit red guava and its processing waste be a potential ingredient in functional foods?

Guava (Psidium guajava L.), a popular fruit in tropical countries, can be consumed in natura or transformed into many products. Guava's processing waste (seed, peel, and pulp leftovers) can represent up to 30% of the fruit's volume. Evidence indicates that this fraction still holds a significant amount of antioxidant substances, such as phenolic compounds. Therefore, the objective of this study was to investigate the phytochemical composition (total phenolics, flavonoids, flavonols, and condensed tannins), phenolic profile, and antioxidant activity (DPPH, modified DPPH, ABTS, and FRAP) of guava's pulp and waste extracts (GPE and GWE) obtained from guava's pulp and waste powders (GPP and GWP). The extraction was performed using a probe-type ultrasound for 2 min at 25 °C, using ethanol:water (30:70, v/v) as the solvent (15 mL for 1 g of sample). The phenolic profile of guava's powders and extracts was performed by LC-ESI-MS/MS analysis. GPE showed the highest concentration of total phenolics (2348.3 mg GAE 100 g^-1 by Folin-Ciocalteu and 518.00 mg GAE 100 g^-1 by Prussian Blue), and the greater in vitro antioxidant activity among all the assays tested. On the other hand, GWE was found to hold a higher amount of flavonoids (1006.08 mg QE 100 g^-1), flavonols (352.59 mg QE 100 g^-1), and condensed tannins (1466.9 mg g^-1). Overall, 37 phenolic compounds were identified among all the samples, with 14 compounds being reported for the first time for red guava. Ellagic acid was the major phenolic present in all samples. The results showed that guava's pulp and waste are a rich source of phenolics compounds and may be used as an ingredient for the development of functional foods.