The coconut (Cocos nucifera L.) husk is basically composed by fiber and pith material and remained under-utilized. This is an important source of phenolic compounds that could be used as functional ingredients. The aim of this study was to determine the effect of: ovendrying (OD) and microwave drying (MD), on the water activity, color, phenolic compound content and antioxidant activity of coconut husk. The OD was performed at 60°C for 12 h and MD was performed at 900 W for 10 min. The total phenolic content (TPC) in fresh coconut husk was 64.2 mg GAE/g dry wt and significant higher than observed after OD and MD of 35.8 and 45.5 mg GAE/ g dry wt, respectively. Ten phenols were identified in fresh and dehydrated coconut husks. The husk MD showed an increase in the content of gallic, 4-hydroxybenzoic, ferulic and syringic acids and epicatechin compared with the fresh; while coconut husk OD and MD, showed a decrease in the content of vanillic acid, vanillin, catequin and kaempferol. The antioxidant activity decreased after both OD and MD. However, MD resulted in a better antioxidant activity in husk than OD. MD of husk resulted into better retention of preserved color, TPC and TFC than OD.

Xoconostle, the acidic cactus pear fruit of Opuntia joconostle of the Cactaceae family, is the source of several phytochemicals, such as betalain pigments and numerous phenolic compounds. The aim of the present study was to analyze the effect of four cooking procedures (i.e., boiling, grilling, steaming and microwaving) on the total phenolic content (TPC) and antioxidant activity (measured by ABTS, DPPH, reducing power, and BCBA) of xoconostle. In addition, HPLC-DAD analyses were performed to identify and quantify individual phenolic compounds. After microwaving and steaming xoconostle, the TPC remained the same that in fresh samples, whereas both grilling and boiling produced a significant, 20% reduction (p ≤ 0.05). Total flavonoids remained unchanged in boiled and grilled xoconostle, but steaming and microwaving increased the flavonoid content by 13 and 20%, respectively. Steaming and microwaving did not produce significant changes in the antioxidant activity of xoconostle, whereas boiling and grilling result in significant decreases. The phenolic acids identified in xoconostle fruits were gallic, vanillic, 4-hydroxybenzoic, syringic, ferulic and protocatechuic acids; the flavonoids identified were epicatechin, catechin, rutin, quercitrin, quercetin and kaempferol. Based on the results, steaming and microwaving are the most suitable methods for retaining the highest level of phenolic compounds and flavonoids in xoconostle.