Combined effects of ultrasound and pulsed-vacuum on air-drying to obtain unripe banana flour

In order to increase the water migration rate during unripe banana drying process, two pre-treatments were applied. Experiments were performed as following: 20 min of ultrasound (US) + air-drying at 50 degrees C; 20 min of US + 60 min of pulsed-vacuum (PV) + air-drying at 50 degrees C; 25 min of US + air-drying at 60 degrees C and 25 min of US + 60 min of PV + air-drying at 60 degrees C. Experimental data were adjusted to five models and the Midilli model resulted to fit best experimental data with r(2) > 0.999, RMSE < 0.0119 and x(2) < 0.00012. Increasing in water effective diffusivity, at the two falling rate periods, were observed due to the application of US, whereas the combined technique of US + PV did not improve the water migration, at both air-drying temperatures. The results revealed drying time savings of (28 and 18) % at (50 and 60) degrees C, respectively. Industrial relevance: In this work, ultrasound and ultrasound-pulsed vacuum pre-treatments prior to air-drying were applied as an alternative to produce unripe banana flour (UBF). This study indicates that the drying kinetics increased due to the application of ultrasound, preserving the resistant starch content of the final product. Hence, this technology diminishes the drying time and consequently reduces the energy costs, in comparison with to the conventional process. Therefore, the UBF rich in resistant starch content can be considered a functional ingredient that promotes dietary intake of unavailable carbohydrates, which may reduce the risks of non-communicable diseases.