Effect of Drying Conditions on the Drying Kinetics and Colour Changes of Plantain (Musa X Paradisiaca) Slices using Combined Heated Air and Infrared Dryers

Abstract

Most agricultural crops with high moisture content are difficult to preserve. The most common method of preservation is drying. Thus, drying operation where a combination of two or more modes is used, could speed-up drying process. However, the scalability of combined heated air and infrared drying (CHAID) for rural consumers have not been investigated. This study was conducted to examine the effect of drying conditions (temperature and infrared intensity) on the drying kinetics and total colour changes (∆E) of plantain slices using a CHAID dryer. Matured unripe plantain samples were sourced from a market, peeled, washed in running water and then sliced into 4 × 20 × 20 mm dimension. Initial moisture content (MC_i) determined using oven drying method. 2.0 g of the sliced sample were weighed and dried in a combined heated air and infrared dryer (IR) operated at 800 W/m² alone till the mass (bone dry mass) did not vary after repeated weighing. Also, samples ∆E was monitored using colorimeter within the drying period. The same procedure was repeated using heated air-drying mode (HAD) operated at 65 ± 2 °C; IR-800 W/m² plus HAD at 65 ± 2 °C, and IR-1000 W/m² plus HAD at 65 ± 2 °C.  The moisture content (MC) and drying rate were computed from duplicate data using Microsoft Excel programme. The variation of % MC with drying time, drying rate against MC and ∆E versus drying time were made and ∆E compared using Tukey Honest Significant Difference. Results showed that the samples’ MC_i by oven dried method was 55.84%wb whereas those dried using IR-800 W/m² alone, HAD (65 ± 2 °C) alone, IR-800 W/m² plus HAD (65 ± 2 °C) and IR-1000 W/m² plus HAD (65 ± 2 °C) modes were 57.43, 52.13, 57.41 and 57.03% wb, respectively, and their corresponding critical or equilibrium moisture content were 5.62, 5.03, 12.45 and 5.95%wb, respectively. Similarly, a shortest drying time (30 mins) and minimal total colour changes (ΔE = 12.42) were found when IR (1000 W/m²) plus HAD (65 ± 2 °C) was used. It also observed that, plantain slices dried using HAD (65 ± 2 °C) mode showed statistically significant mean difference in ΔE when compared with other three drying modes within 10 to 30 minutes drying time. Since, IR (1000 W/m²) plus HAD (65 ± 2 °C) mode gave shortest drying time and minimal ΔE, it is recommended for use in drying plantain slices by restaurant, hotels operators and food processors.