EFFECT OF FERMENTATION ON DRYING CHARACTERISTICS OF TRIFOLIATE YAM VARIETIES (WHITE, YELLOW AND DEEP-YELLOW TRIFOLIATE YAM)

This study determined the effect of fermentation on drying characteristics of trifoliate yam varieties (white, yellow and deep-yellow trifoliate yam). Thin layer drying method was adopted using oven dry method at constant drying temperature of 70ºC with air velocity of 2.35 m s-1 and relative humidity 35%. The unfermented samples shoed lower values of drying constant than the fermented samples. The drying constant of unfermented samples of Trifoliate Yam A, B and C ( A= Deep-Yellow, B= White, C= Yellow) were -0.729, 1.3972 and 0.2787, respectively. While, the drying constant of fermented samples of Trifoliate Yam D, E and F (D= Deep-Yellow, E= White, F= Yellow) were -0.776,-0.763 and 1.5815, respectively. The drying rate of the samples solely dependent on the magnitude of drying constants sequel to this, fermented samples with larger magnitude of drying constant will dry faster than the unfermented samples with lower drying constant. Best fit equations and relationship between moisture content and drying time were developed with correlation coefficient (R2) higher than 0.94. The sample A, B, C, D, E and F reached a constant moisture ratio of 0.021, 0.015, 0.021, 0.015, 0.014 and 0.016 at drying time of 540, 600, 600, 480, 540 and 540 minutes, respectively. Sample B and C had highest drying time followed by sample A, E and F while sample D had the lowest value of drying time. The fermentation had significant effect on the drying characteristics of trifoliate yam slices and drying of trifoliate yam samples occurred solely in the falling rate period which showed that internal moisture diffusion phenomenon is dominant and controlled the drying process.