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 × 10–8 to 1.83 × 10–7 m2/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°C in the greatest loss of bioactive compounds and antioxidant capacity. HACD at 60°C + MWVD allowed to obtain a product with a higher content of TP, monomeric anthocyanins and a stronger antioxidant capacity than HACD at 90°C + MWVD. Combination of HACD at 60°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°C. Even when the combination of HACD at 90°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°C.

Epiphyton Biomass is Related to Lake Trophic Status, Depth, and Macrophyte Architecture

The relationship between epiphyton biomass and water column total phosphorus concentration (TP) was studied in macrophyte beds in 11 lakes covering a wide range of trophic status (TP = 5.8–72.8 μg∙L−1). Phosphorus concentration was a poor predictor of epiphyton biomass when considered alone. Our data do not agree with previous studies that found that epiphyton biomass increased continuously with TP. Instead, we found a very weak, nonlinear relationship between TP and epiphyton biomass, where epiphyton biomass increased up to TP≈39 μg∙L−1, and decreased at higher TP. Season and sampling depth accounted for significantly more variation in epiphyton biomass than did TP. Epiphyton biomass increased with depth in oligotrophic lakes but decreased with depth in eutrophic lakes. Seven common species of macrophytes of differing architecture developed significantly different epiphyton biomass. Macrophytes with flexible, ribbon-like leaves supported lower epiphyton biomass than species of broad-leaved or whorled architecture. The effect of host type on epiphyton algae biomass was not, however, as great as the influence of environmental variables.