Conventional drying of cassava peel from starch industry waste

Abstract

Cassava peels from starch industry waste are highly perishable. The drying process is an alternative way to provide a safe storage, free from the development of microorganisms, for the production of flour destined to human consumption. This study aimed at evaluating the kinetics and modeling of the cassava peels drying process, with the aid of a central composite rotational experimental design. Eleven tests were performed with different temperatures (53°C, 55°C, 60°C, 65°C and 67°C) and air flow rates (0.0159 m³ kg^-1 s^-1, 0.0166 m³ kg^-1 s^-1, 0.0183 m³ kg^-1 s^-1, 0.0199 m³ kg^-1 s^-1 and 0.0206 m³ kg^-1 s^-1). The drying process was carried out in a conventional dryer tray and the drying times, instrumental color parameters (lightness - L*; a* and b* coordinates), titratable acidity and pH of the flour samples obtained after grinding the dehydrated cassava peels from each drying test were evaluated. The temperature increase resulted in a tendency to bleach the material, and a slight variation was observed for titratable acidity and pH in the samples. Temperature and air flow speed affected the drying kinetics, since their increase reduced the time for drying the cassava peels. The minimum drying time (420 min.) was reached when the dryer temperature was set to 67°C and the air flow to 0.0183 m³ kg^-1 s^-1. This was considered the ideal setting, because it minimized the processing time, without altering the product features. The Crank model for plane geometry fitted well the experimental data obtained from the cassava peel drying process.