DRYING BEHAVIOUR OF CASSAVA (Manihot esculenta) CHIPS

Abstract: Interest in exporting dried chips form Trinidad and Tobago for use in the production of extruded snacks led to the investigation of the drying of the popular local variety MMEX 59. Drying of cassava (Manihot esculenta Crantz) chips of two sizes (3 x 2 x 1cm and 0.8 x 0.6 x 0.4 cm) was carried out in a natural convection (<0.5 m/s) cabinet type dryer at 60°C. Samples were dried until constant weight was achieved. Analyses included determination of moisture content (% wet basis), pH, crude protein (%), crude fibre, fat (%), ash (%) and HCN (mg/kg). Drying data was used to generate rate and Moisture Ratio (MR) curves and thin layer models applied to the MR data. The moisture content of chips was reduced from 1.57 g H2O/g DM (61.06 % wb) to 0.02 g H2O/g DM (2.12 % wb) and the rate of decline in moisture was significantly affected by piece size. Equilibrium moisture values were attained after 18h for the larger chips and 14h for the smaller chips. Drying to a safe moisture content of 13% (wb) was achieved after 7h for the larger chips and 3h for the smaller chips. Drying of all samples occurred in the falling rate period only and drying was described through the drying rate constant (k1). The cyanide content of the dried chips was well below the maximum acceptable limit. While size did not affect overall appearance and quality of the dried product, the smaller chip size (0.8 x 0.6 x 0.4 cm) would be recommended for cassava export based on the rapid drying rate. Curve fitting of the moisture ratio (MR) data resulted in the application of mathematical models which successfully predicted the extent of drying with respect to drying time as well as the moisture content of the cassava chips. It is hoped that this can form the basis of further studies which will look at the prediction of moisture content changes in dried cassava chips at a range of drying temperatures and cassava chip sizes.