ABSTRACT

Single-layer drying kinetics of UG I and UG II whole and split (peeled and unpeeled) treatments, for Unblanched and Blanched at 50℃ for 3, 6, and 9 minutes respectively, were investigated using solar and cabinet drying methods.There was an initial high moisture removal (constant rate period) followed by slow moisture removal in the latter stages (falling rate period) of drying.The effect of blanching on drying characteristics of UG I and UG II samples of whole peeled, whole unpeeled, split peeled, and split unpeeled treatments during solar and cabinet drying, indicates that blanching increases the drying rate. There was a significant difference between the drying curves for blanched and unblanched samples for whole and split UG I and UG II samples. This difference becomes minimum at whole peeled, split peeled, and split unpeeled treatments. This might be because, during blanching, the samples were partially cooked, and some cells or tissues of split peeled, split unpeeled, and whole peeled UG I and UG II samples might be disrupted or loosened. As a result, moisture diffusion was higher, and hence the drying rate was higher. The moisture content of the whole unpeeled UG I and UG II samples remained almost constant during the drying period, and this is true for either blanched whole unpeeled UG I and UG II samples and unblanched whole unpeeled UG I and UG II samples. This shows that the thick skin of the entire unpeeled UG I and UG II samples prevents moisture diffusion through the skin.While the drying process started with the short constant rate period, the drying bulk took place in the falling rate period. It concluded with the equilibrium moisture content threshold (EMC) being reached.The initial moisture content of 71.12% and 72.47% was reduced to the final moisture content of 6.09% and 6.94% for UG I and UG II, respectively.The drying data (MR) were fitted into ten thin-layer drying models and validated with the coefficients of determination on (R2), root means square error (RMSE), and reduced chi-square (χ2) parameters to estimate the drying behavior during the water removal stage.According to the results, the model found to explain the single layer best drying kinetics of UG I and UG II varies at different blanched treatments and unblanched compared to the other models over different experimental conditions for solar drying and cabinet drying, respectively. The results proved that the various models are efficient thin-layer models used in dryer designing and processing of UG I and UG II unblanched and blanched treatments. The data obtained were used to develop empirical equations for predicting the single-layer drying kinetics of UG I and UG II unblanched and blanched treatments for solar drying and cabinet drying methods.Proximate composition of UG I and UG II dried and milled samples with various treatments show that higher values in percentage for Unblanched UG I and UG II indicate high moisture content, ash content, crude fibre, crude protein, fat, and carbohydrate. Blanched treatment for UG I and UG II shows a reduction in percentage moisture content, ash content, crude fibre, crude protein, fat, and carbohydrate.The phytochemical analysis of UG I and UG II dried and milled samples with various treatments indicate terpenoids, flavonoids, and polyphenol. It was noted that the colour variation of flavonoids was yellow, terpenoids were brown, and that of polyphenol was blue for both UG I and UG II.