Modified refractance window drying of jamun pulp (Syzygium cumini) based on innovative infrared and microwave radiation techniques

Abstract

The present study aimed to dry jamun pulp (Syzygium cumini) by combining infrared and microwave energy in refractance window drying. The two different sets of experiments were planned using the hybrid design. The three independent parameters considered for the infrared refractance window drying (IR-RWD) included infrared lamp power (30–70% of the 1000 W lamp), pulp layer thickness (1–3 mm), and distance between the lamp and pulp layer (3.42–6.60 cm). In microwave refractance window drying (MW-RWD), the independent variables were oven-set microwave power (150–450 W), pulp layer thickness (1–3 mm), and power density (1–2.5 W g−1). The optimum conditions in IR-RWD were 40.75% infrared lamp power, 1 mm pulp layer thickness, and 3.42 cm distance between the lamp and pulp layer, resulting in dry jamun flakes with 17.93 ± 0.32 mg GAE g−1 total phenolic content, 4.37 ± 0.13 color change, 8.90 ± 0.22 mg QE g−1 total flavonoid content, and 179.05 ± 2.17 C3G mg/100g total anthocyanin content. In the case of MW-RWD, the optimum conditions were 212.4 W oven-set microwave power, 3 mm pulp layer thickness, and 2.2 W g−1 power density, resulting in 15.68 ± 0.28 mg GAE g−1 total phenolic content, 8.47 ± 0.25 color change, 8.20 ± 0.21 mg QE g−1 total flavonoid content, and 149.72 ± 1.81 C3G mg/100g total anthocyanin content. The Page model can precisely describe the jamun pulp drying behavior of IR-RWD and MW-RWD. Also, apparent moisture diffusivity was estimated in both drying methods. IR-RWD was found to be a better drying method than MW-RWD in terms of drying rates and the quality parameters of the dry jamun flakes.