Drying Characteristics and Moisture Sorption Isotherm of Batuan [Garcinia binucao (Blanco) Choisy] Fruit

Abstract

The drying characteristics and moisture sorption isotherm (MSI) of batuan, an underutilized and commonly neglected fruit that is often found in tropical climate countries like the Philippines, were investigated. Whole and sliced fruits were dried using a convection dryer set at 50°C. The constant-rate period is absent from the drying curve, and the bulk of drying happened in the falling rate period. Drying data was fitted in four drying models, namely: Newton (Lewis), Handerson and Pabis, Page, and Logarithmic. The goodness of the fit of the model was evaluated by comparing the values of coefficient of determination (R) and Root Mean Square Error (RMSE) between the observed and predicted moisture ratios. Page model provided the best fit in describing the drying behavior of both whole and sliced fruits, with highest R of 0.9867 and 0.9994 and lowest RMSE of 0.0360 and 0.0078, respectively. MSI of the dried fruits was meanwhile determined at 25°C using the static gravimetric method, and was fitted in seven different isotherm models, namely: Brunauer-Emmet-Teller (BET), Guggenheim-AndersonDeBoer (GAB), Adam and Shove, Halsey, Oswin, Henderson-Thompson, and Peleg. Fitness of models was evaluated using the values of R standard error (SE) and mean relative percentage deviation modulus (P). Among the models, Halsey showed the best fit for MSI with highest R of 0.9946, SE of 0.0185 and P of 7.0207%. Using the same model, the monolayer value of the dried batuan fruits was determined as 0.1542 g H2O/g solid, with corresponding water activity (aw) of 0.3478. 