Drying kinetics and mathematical modeling of coconut meat slices: Insight into pretreatment and drying synergic effect

Abstract

Coconut consumption provides nutritional and health benefits to humans. Yet, poor postharvest and preservation methods result in the loss of coconut fruit bunches yearly. Investigations into achieving drying techniques that result in optimum drying rates coupled with consumer's desired end products that are both commercially and nutritionally viable remain paramount in the food industry. Consequently, osmotic dehydration is commendable for its low-cost pretreatment merit. Therefore, the study examined the drying-kinetics, energy consumption, effective moisture diffusivity (Deff), vitamin C retention, color, and rehydration behavior of coconut cultivars (Sri Lanka Green Dwarf × Vanuatu Tall (SGD × VTT), Catigan (CAT), and Tacunan Green Dwarf (TGD)) meat slices. Samples were osmotically pretreated with sucrose solution (30 %/30 min) and subjected to oven drying (80, 90, 100, and 110 °C (air velocity of 2 m/s) and lyophilization (−45 ± 2 °C) methods. A mathematical model was employed to predict the effect of osmotic pretreatment on drying dynamics and the assessment of utilized energy, vitamin C content, color, and rehydration of coconut meat slices at different drying conditions. The oven-dried sample's color changed (p < 0.05) compared to lyophilized samples. Drying-kinetics models were validated using determination coefficient (R2) and root mean square error (RMSE). The Asymptotic model satisfactorily suited the samples' drying data goodness fitting based on R2≥0.90−0.99 and low RMSE ≤0.01−0.12 compared to other models for both drying methods. Deff ranged between 1.10 × 10−07 m2s−1 and 7.90 × 10−08 m2s−1 for all the drying methods. CAT sample retained high vitamin C content compared to SGD × VTT and TGD samples. Rehydration ratio values were significant at lower temperatures among oven-dried experimental samples whereas TGD samples exhibited a significant rehydration values compared to SGD × VTT and CAT lyophilized samples. Among the drying methods, oven drying exhibited low energy consumption with shorter drying time and optimum Deff per adopted temperature ranges compared to lyophilization. The study revealed that temperature, time, the sucrose solution, and the thickness of the coconut slices strongly influenced the drying kinetics of the osmotically pre-treated coconut meat slice's drying features.