The Influence of Convective, Microwave Vacuum and Microwave-Assisted Drying on Blueberry Pomace Physicochemical Properties

The effect of hot air convective drying (HACD), microwave-vacuum drying (MWVD) and combined drying (HACD + MWVD) on the drying kinetics, bioactive compounds and color of blueberry pomace was evaluated. Drying time of blueberry pomace ranged from 0.6 to 6.7 h and moisture diffusion coefficients ranged from 7.94 x 10(-8) to 1.83 x 10(-7) m(2)/s. Drying caused degradation of total polyphenolics (TP) (39-76%), monomeric anthocyanins (21-77%) and antioxidant capacity values (24-76%). Drying time was shortened even by 91%, when MWVD was used instead of HACD. MWVD of blueberry pomace resulted in the smallest, while HACD at 60 degrees C in the greatest loss of bioactive compounds and antioxidant capacity. HACD at 60 degrees C + MWVD allowed to obtain a product with a higher content of TP, monomeric anthocyanins and a stronger antioxidant capacity than HACD at 90 degrees C + MWVD. Combination of HACD at 60 degrees C with MWVD allowed for the shortening of HACD time by 75% as well as for hapering the chemical changes as compared to HACD at 60 degrees C. Even when the combination of HACD at 90 degrees C with MWVD shortened the drying time by 68%, it did not improve the retention of TP, monomeric anthocyanins and antioxidant capacity when compared to HACD at 90 degrees C.