Thin layer drying kinetics of Banana var. Monthan (ABB): Influence of convective drying on nutritional quality, microstructure, thermal properties, color, and sensory characteristics

Abstract

Banana with a good amount of resistant starch (RS) offers greater benefit to human health. Studying the dehydration mechanism of the raw banana slice is very important for subsequent processes and the quality of the product. Thus the study aimed to investigate the influence of varying temperatures viz., 45, 55, and 65°C in a convective dryer on thin layer drying kinetics and to infer their influence on the rheological properties coupled thermal and sensory quality. Time for reducing the moisture content from the initial 71.2 ± 0.2% to a final 4.66–6.13% was found to be 270, 210, and 150 min for the drying temperatures 45, 55, and 65°C, respectively. The moisture ratio decreased exponentially with an increase in drying time. Page and logarithmic models obtained the highest r2, lowest chi-square values and least root mean square error, and better-reflected drying mechanism of banana slices. Improved rehydration ratio (1:2.4) and RS content (36.26%) were observed with the drying temperature of 55°C. Higher water absorption capacity (WAC) was observed at 55°C (4.86%). The swelling power of the flour was maintained at 4–6% till 70°C but it reached 22% with the increase in temperature to 90°C. The thermal properties and microstructure of flour differed significantly with the temperatures. The lower value for the whiteness index with low-temperature drying reflected better drying than at higher temperatures. Dehydration at 55°C was superior with nutrients like ascorbic acid. The banana flour had rod-shaped starch granules and traces of protein on its surface as evidenced. Irregular spherical shape, surface dents, and shrinkages were observed in powders dehydrated with high temperatures (>65°C). Equilibrium relative humidity (ERH) studies revealed that 13.27 and 15.23% were the danger and critical points, respectively, for the banana flour. Descriptive sensory scores of the banana flour endorsed that dehydration at 65°C was found superior to other temperatures.