The Modelling of Convective Drying Variables’ Effects on the Functional Properties of Sliced Sweet Potatoes

Abstract

Drying is a commonly used technology that provides a long post-harvest storage time for produce such as sweet potatoes. Convective drying (CD) is a method that, when conditions are optimized, provides produce with a better appearance and improved textural properties. In this study, changes in water activity (aw), moisture content (MC), rehydration capacity (Rc), shrinkage (Sb) and color attributes were modelled for the optimization of drying factors (temperature, thickness and time) using response surface methodology (RSM). The total phenol content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC) and antioxidant activity of CD samples (63.79 °C, 4.78 h, 3 mm) were investigated as functional aspects and compared with results for FD samples (−45 °C, one term). Optimum convective drying conditions caused an increase in general antioxidant properties, such as total phenol (TPC), total anthocyanin (TAC), DPPH and CUPRAC. The TPC was 190.94 mgGAE/100 g, the DPPH scavenging activity was 12.05%, the TAC was 11.37 mg/100 g, and the CUPRAC was 0.469 mmolTR/g in convectively dried samples under optimum conditions. Although improved appearance and textural properties are obtained by freeze drying, it is possible to produce sweet potatoes with good appearance and functional properties by optimizing the variables of the convective drying process.

Optimization of Convective Tray-Drying Process Parameters for Green Banana Slices Using Response Surface Methodology and Its Characterization

“…Furthermore, the convectively tray-dried spine gourd (Momordica dioica) slices (2.5-3 mm thick) dried at 40-70 °C presented a signifcant (p < 0.05) diference in the L * value ranging from 78.55 ± 0.66 to 83.74 ± 0.14 [19]. In the same way, the drying temperature of (45-75 °C) and sweet potato slice thicknesses (2-6 mm) had a signifcant (p < 0.05) efect on the L * , C * , and h o values of tray-dried sweet potatoes [34].…”

“…Te main efect of tray-drying temperature and sample thickness (A and B) and the quadratic efect of tray-drying temperature (A 2 ) signifcantly (p < 0.05) afected the a w of banana four (Table 3). In the same way, Savas [34] reported that the convective drying of sweet potato slices at diferent temperatures (45-75 °C) and sweet potato slice thicknesses (2-6 mm) showed a positive reduction in the a w with an increase in drying temperature and a decrease in sample thickness.…”

“…Tis signifcant variation in the L * , C * , and h o values of banana four might be due to the nonenzymatic and enzymatic reactions of polyphenols with the oxygen and polyphenol oxidase enzyme resulting from an increase in tray-drying temperature and sample thickness (independent factors). Several studies showed that various factors negatively infuence the color characteristic of the dried product, such as diferent drying temperatures, drying methods, rate of airfow, drying time, slice thickness, poor stability of pigmented compounds or thermal degradation, oxidative reactions, Maillard reactions, and caramelization of carbohydrates [12,[32][33][34][35][36]. A light yellowish color is mainly associated with green banana polyphenolic, favonoid, lutein, α-carotene, and β-carotene compounds [37].…”

“…Te favonoids are part of naturally occurring phenolic compounds which are sensitive to thermal processing, and their losses are mostly found on convective hot air drying [34,43]. Te TFC of traydried green banana four was found in a range of 1.53-3.33 mg QE/100 g (Table 3, Figure 4).…”

Sweet Potato Is Not Simply an Abundant Food Crop: A Comprehensive Review of Its Phytochemical Constituents, Biological Activities, and the Effects of Processing

“…The increase in phenolic content could also be explained, at least partially, by the formation of Maillard reaction products with a phenolic-type structure during the thermal process [ 98 ]. A recent study carried out by Savas [ 99 ] compared the effect of freeze-drying and convective drying on the TPC, total flavonoids, and total anthocyanins in sliced sweet potatoes. The TPC and total flavonoid content in freeze-dried samples, and total anthocyanin content in convectively dried samples were clearly higher than in fresh tubers.…”