Effects of Slice Thickness and Pre-Treatment Concentration on the Quality Characteristics of Solar Dried Pineapple

The overall goal of this study was to determine the quality changes (vitamin C retention, browning, rehydration ratio) that occur during solar drying of pineapple as influenced by different processing conditions (slice thickness and pre-treatment concentration). Pineapple fruits were sliced to varying thicknesses (5 and 10 mm), pre-treated at different concentrations of citric acid (2, 5, and 10 g/l), and dried for 2 days in a Hohenheim model type solar tunnel dryer until a safe moisture level about ≤15% was reached. Samples were analyzed for changes in quality characteristics using standard AOAC methods. Dried pineapple slices were found to differ significantly in terms of browning scores and vitamin C retention (p≤0.05) while no differences were observed in the rehydration ratio (p>0.05). Slice thickness and pre-treatment concentration were observed to have a significant interaction effect on the browning score/index of pineapple slices during drying (p≤0.05). Overall vitamin C concentration increased for samples during the drying process with the maximum vitamin C concentration being 36.85 mg/100 g recorded in 5mm thickness samples pre-treated with 5% citric acid solution. Maximum vitamin C retention was recorded in samples sliced to 5mm thickness and pre-treated with 5 g/l citric acid solution (15.68) while minimum vitamin C retention (2.41) was recorded in 5mm slices treated with a 10 g/l citric acid solution. Rehydration ratio ranged from 1.60 to 2.53. There was no significant difference between the rehydration ratio between the different treatments at P≤0.05. The lowest browning index was observed in samples sliced to 10 mm thickness and treated at 5 g/l while the highest browning index was observed in samples sliced to 5mm and treated at 5 g/l of citric acid. The best-optimized conditions obtained for the given criteria were 5 mm slice thickness and 2 g/l pre-treatment concentration based on a maximum desirability of 0.639. For the optimized combination of drying parameters, the vitamin C content, the rehydration ratio, and the browning were 9.14, 2.43 and 0.47, respectively.