Effects of microwaves, hot air and freeze-drying on the phenolic compounds, antioxidant capacity, enzyme activity and microstructure of cacao pod husks (Theobroma cacao L.)

The cacao pod husk (CPH) is the primary waste byproduct of the chocolate industry. One ton of cacao beans generate approximately ten times that amount of fresh CPH. The husk is rich in phenolic compounds. The aim of this study is to determine the effects of microwaves, hot air and freeze-drying on the phenolic compound content, antioxidant capacity, enzyme activity and microstructure of CPH. The results showed that fresh CPH contain 323.7 ± 26.5 mg gallic acid equivalents (GAE)/100 g dry mass (d.m.) of total phenolic compounds, and dehydration had a positive effect on the CPH phenolic content and antioxidant capacity. Catechin, quercetin, and (−)-epicatechin and gallic, coumaric and protocatechuic acids were identified in fresh and dried CPH. Drying the material using a microwave and freeze-drying preserved the husk microstructure. The results showed that microwave drying was a better drying method than hot air and as good as freeze-drying. Industrial relevance The food industry is currently searching for new sources of natural antioxidants. The cacao pod husk (CPH) is a good source of phenolic compounds that can function as antioxidants and could be used as ingredients in functional foods. However, due to their high water content, fresh CPH are perishable products, and for this reason, the first step would be dry the pod husk to improve its shelf life. The findings of this study showed that the use of microwaves to dry CPH may release polyphenols, thereby enhancing the antioxidant capacity and decreasing the polyphenol oxidase (PPO) activity while maintaining the microstructure. Thus, microwave drying could be of interest as a method for enhancing the extractability of phenolic compounds from CPH.