Advanced valorization of cocoa (Theobroma cacao L.) pod husks through 40 kHz-ultrasonic bath assisted extraction of pectins

Abstract

Theobroma cacao is an economically relevant agricultural commodity. In the Amazon region, Peru boasts 6 of the 10 genetic cacao families of the world. Cocoa pod husk (CPH), the main agro waste (67–76% of fruit), and its three constituent layers, endocarp (END), mesocarp (MSO) and epicarp (EPI) tissues, were separately evaluated, after drying and milling, as potential sources of pectin, a valuable industrial additive. A 40 kHz-ultrasonic bath (160 W; 100% amplitude) pretreatment (15 min; 50 °C) of tissue powders with citric acid solution (pH 3.0) followed by magnetic stirring (50 °C - 1400 rpm; 60 min for CPH, EPI and MSO or 345 min for END) gave the highest pectin yields, together with the 1:150 (g/mL) powder to solvent ratio for CPH and EPI pectins, and 1:75 (g/mL) for MSO and END pectins. END pectins were homogalacturonans with an 86-84 % uronic acid (UA) content, while the rest had ≈ 65 % UA, all with low degrees of methylesterification (5.26–35 %) and acetylation (9.56–30 %). Pectins exhibited high molecular weights (5.57–7.05 MDa). Phenolic compounds (216–4643 μg/g) and methylxanthines (theobromine, caffeine) were co-extracted with pectins. Mechanical spectra of 1.50 % w/v aqueous pectin with 30 mg Ca2+/g of UA revealed “weak gel” type networks, most structured for END pectin, but “dilute solution” for CPH pectin. CPH and its constituent tissues can be valorized as sources of thickening and gelling pectins.