CAST-TAPE DRYING OF AÇAÍ PULP ASSISTED BY INFRARED RADIATION

Açaí (Euterpe oleracea Mart.) faces significant preservation challenges. Cast-tape drying (CTD) is a conductive drying process where a thin liquid layer is spread onto a flexible support, heated from below by a hot fluid, e.g. steam at atmospheric pressure. In continuous operation, the conveyor belt passes through a drying tunnel, and an exhaust system removes evaporated water, producing a dry film at the belt’s end. This study examined a continuous CTD system with simultaneous infrared (IR) heating performed with IR lamps placed above the conveyor belt (Cast-tape drying assisted by infrared, CTD-IR). A 1.5 mm tick açai pulp layer was selected to compare five drying setups: regular CTD (control); CTD-IR1 (3000 W IR lamps applied during the first 33% of drying); CTD-IR12 (IR applied during the first 66% of drying); CTD-IR123 (IR applied throughout); and CTD-IR3 (IR applied during the final 33%). Simultaneous heating by conduction and IR reduced drying time by 13% to 34% compared to the control. CTD-IR1 and CTD-IR12 achieved faster initial drying rates, indicating the benefits of early IR application. However, applying IR at the end (CTD-IR3) or throughout (IR123) increased matrix temperatures up to 135°C, causing substantial anthocyanin losses (only 13% retained in IR123), significant color fading, and longer dispersion times of the resulting powder in water. In contrast, CTD-IR1 and CTD-IR12 resulted in powders with more preserved color and easer reconstitution in water, striking a balance between drying kinetics and product quality. Results indicate that the IR use in the early stages of CTD accelerates moisture removal while minimizing thermal damage. Notably, CTD—either assisted by IR or not—shows substantial potential for drying other fruit pulps, including those that are sticky and difficult to dry without adding carrier agents.