Investigation of the Drying Kinetics of Pre-treated and Untreated Sweet Potato to Prevent the Growth of the Fungi Rhizopus oryzae

Sweet potatoes are susceptible to the fungi Rhizopus oryzae, which causes rapid spoilage upon delivery due to the moisture content, which can develop a fungus that produces a foul odor and a cottony white color. The reduction in moisture content can extend the sweet potato's shelf life. This problem can be addressed by a drying process using a hot-air tray dryer. The drying kinetics of pre-treated and untreated sweet potatoes was investigated to produce dried sweet potatoes without the growth of the fungi. Sweet potatoes were peeled and cut into 5x5x30 mm uniformly. For the pre-treatment, the sliced sweet potato strips were soaked in 2%(w/v) Potassium Metabisulfite (KMS) solution at 50 C for 15 minutes and were drained under standard conditions. The pre-treated and untreated sweet potato strips were dried in separate trays at 40 C, 50 C and 60 C using a hot-air dryer until the constant weight of the batch was obtained. Numerical simulation using the Laplace Transform Model, Non-Linear Decomposition Model, and Page Model were compared to determine the best fit model for the drying of the pre-treated and untreated sweet potato strips. Based on the data gathered, the Page Model was found to be the most suitable model to describe the drying characteristics of pre-treated and untreated sweet potato strips. The optimum drying temperature was 60 C and predicted a drying time of 46.01 minutes using the Lagrange interpolation to achieve 10% moisture that inhibit the growth of Rhizopus oryzae. The air-dried pre-treated samples showed a good sensory quality parameter such as color and texture compared to air-dried untreated sample. The pre-treated sweet potato strips avoid the undesirable changes such as the natural color, texture and odor of sweet potatoes after air-drying.