Solar drying kinetics and bioactive compounds of blackberry (Rubus fruticosus)

In this article, the effect of direct solar drying, indirect solar drying, and freeze drying on the phenolic compound contents and antioxidant capacities of blackberry fruits was investigated. The solar drying kinetics were determined and fitted to six thin layer different mathematical models. The total phenolic, anthocyanin, and flavonoid contents as well as the antioxidant capacity based on ABTS, DPPH, and OH^• assays were determined for the dried blackberry samples. The results show that the Midilli–Kuçuk model provides the best fit to the experimental data of solar drying in both methods tested. Greater antioxidant capacities were observed in the samples dried by using direct solar drying method in all experiments, that is, the ABTS, DPPH, and OH^• activities were 36,757 ± 1.27; 21.120 ± 1.33, and 47 ± 7.31 μmol TEAC/g dm, respectively. The creation of compounds during food dehydration at moderately high temperatures can enhance the antioxidant capacities and phenolic contents.

Practical applications

Rubus fruticosus is a berry with nutraceutical potential by the presence of bioactive compounds. The removal of water from a fruit extends the conservation time of the product during storage and transportation, facilitating the access to such foods when required. One of the most economical and sustainable ways to do the drying is to use solar dryers. Direct and indirect solar drying are technologies that have effects that must be taken into account according to the food that is to be dried and the final characteristics that are desired to obtain. However, the phenolic compounds present in the fruit are sensitive to the thermal process. Thus, it is important to know its consequences phenolic compounds and antioxidant activity for better use of the fruit.