No abstract

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.

In this work, the effect of drying conditions on pear slices' physicochemical properties was determined. The factors investigated were drying temperature, air velocity, and addition of ascorbic acid. An analysis of variance indicated that the factors affected (P ≤ .05) the response variables significantly. The lowest drying time resulted at 60 C, 3 m s −1 , at 0%, and 1% of ascorbic acid concentration. At these drying conditions, the final moisture content in pear samples was 0.14 g H 2 O g d s −1 . The water activity of the pear samples was in the range from 0.27 to 0.39. A low value of 6.36 of color difference was obtained at 50 C, 1 m s −1 , and 0% of ascorbic acid. During the drying process, the lightness in pear samples increases as the air velocity and the drying temperature increases. The highest hue values (from 54.66 to 63.27 ) resulted in dried pear samples without ascorbic acid; therefore, the dried pear slices tended to yellowness. Chroma results ranged from 19.51 to 21.41 and from 14.96 to 19.16 in pear slices with and without ascorbic acid. Therefore, the color of the pear slices resulted in grayish-yellow. An increment in sugar content was observed from an initial value of 18 Brix to values from 37.5 to 48.7 Brix. This behavior is because the sugar core is concentrated in large amounts during the drying process as the residual water content decreases.