Evaluation of selected drying models of white sapote (Casimiroa edulisL.) slices as affected by drying methods and pre-drying treatments

This investigation was performed on the drying modelling of white sapote slices that were influenced by drying methods and pre-drying treatments. The experimentation was performed by two factors: drying techniques and pre-drying treatments. The drying techniques included oven-, solar- and open sun-driers, whereas the pre-drying pretreatments were blanching, sodium metabisulfite, sodium-chloride and control. Behaviours of the drying were plotted with the moisture ratio vs time of drying, moisture content (% db) vs time of drying, and drying rate (g of water/100 g dm/hr) versus drying time (t). At the commencement of the drying progression, the drying rate was increased steadily and reduced through the advancement of drying model parameters a and n (empirical constants) and k (drying rate constant) were determined. Their combinations were optimised to suit the requirements of the minimal value of the sum of square deviation on the expected data values (model values). The models were evaluated with the regression coefficient (R2) and chi-square (χ2), resulting in values of 0.95-0.99 and 0.000132 to 0.00511, respectively. Henderson and Pabis's model demonstrated the highest coefficient R2 values (0.99) for oven-dried drying techniques. Also, the Page model gave the highest R2 value (0.99) for sodium metabisulphite pretreatments. It can be concluded that the Henderson and Pabis model is best suited for oven drying among the drying techniques. In contrast, the Page model best fits sodium metabisulphite among the pre-drying treatments. Hence, Henderson and Pabis, and Page models might describe the drying characteristics of the white sapote fruit slices based on respective drying methods and pre-drying treatments.

Study of water absorption in Raffia vinifera fibres from Bandjoun, Cameroon

The study is focused on the water diffusion phenomenon through the Raffia vinifera fibre from the stem. The knowledge on the behavior of those fibres in presence of liquid during the realization of biocomposite, is necessary. The parameters like percentage of water gain at the point of saturation, modelling of the kinetic of water absorption, and the effective diffusion coefficient were the main objectives. Along a stem of raffia, twelve zones of sampling were defined. From Fick's 2nd law of diffusion, a new model was proposed and evaluated compared to four other models at a constant temperature of 23°C. From the proposed model, the effective diffusion coefficient was deduced. The percentage of water gain was in the range of 303–662%. The proposed model fitted better to the experimental data. The estimated diffusion coefficient was evaluated during the initial phase and at the final phase. In any cross section located along the stem of Raffia vinifera, it was found that the effective diffusion coefficient increases from the periphery to the centre during the initial and final phases.