High drying temperatures preserve the phenolic compounds and antioxidant, antihyperglycemic and antibacterial activities in avocado peel (Persea americana)

Freeze-drying and heat-drying (60–120 °C) experiments were performed with avocado peels, and changes in the phenolic profile of the peels were examined in relation to various activities, including antioxidant (ABTS and DPPH) activity; antibacterial activity against S. aureus, E. coli and P. aeruginosa; and inhibitory activity against α-glucosidase. Twenty-nine metabolites were identified as caffeoylquinic acid derivatives, procyanidins types A and B, and flavonoids. Freeze-drying preserved the highest levels of caffeoylquinic acid derivatives, procyanidins, total phenolic (TP) and total flavonoid (TF) contents; antioxidant and antibacterial activities; and inhibitory activity against α-glucosidase. Drying at 120 and 80 °C resulted in similar TP and TF contents, antioxidant activities and inhibitory activities against E. coli and P. aeruginosa, but these parameters were greater to those exhibited by samples dried at 100 and 60 °C. Nevertheless, more caffeoylquinic acid derivatives, procyanidins, and flavonoids were extracted from the samples dried at 120 °C, and a better inhibitory activity for S. aureus and α-glucosidase were obtained; the inhibition of S. aureus was comparable to that observed for freeze-dried peels. Therefore, compared to the other temperatures, drying at 120 °C was more effective in preserving the phenolic compounds and biological activities of avocado peels.