Comparative elucidation of bioactive and antioxidant properties of red dragon fruit peel as affected by electromagnetic and conventional drying approaches.

The effects of near-infrared (NIRD), mid-infrared (MIRD), far-infrared (FIRD), microwave (MWD), and hot air drying (HAD) on drying kinetic, colour, phytochemical composition, and antioxidant activity of red dragon fruit peel (RDFP) was evaluated. Results indicated that drying methods induced varying microstructural and chemical changes on RDFP, significantly influencing moisture removal rates and phytochemical retention. The lowest drying time was observed for MWD, while MIRD presented the highest drying time. FIRD drying was more favourable for retaining TPC, TFC, betacyanin and betaxanthin, while the ascorbic acid content was better retained during MIRD and NIRD. Enhancements in ABTS, CUPRAC and reducing power were associated with FIRD, and NIRD and MIRD enhanced DPPH and HRSA. Overall, chemical modifications induced by drying improved the phytochemical and antioxidant properties but presented adversative effects on ascorbic acid and DPPH. The study presented an essential background for the optimal drying of RDFP.

Improving drying kinetics, physicochemical properties and bioactive compounds of red dragon fruit (Hylocereus species) by novel infrared drying.

Effects of tray rotation speeds (TRS: 0, 20, 40 rpm), temperatures (50, 60, 70 °C) and wavelength spectra (mid and near-infrared) were comparatively evaluated on improving drying kinetics, physicochemical properties and bioactive content of red dragon fruits. Results indicated that successive increases in TRS and temperature led to significant reductions in drying time and increases in drying rates and moisture diffusivity. High TRS (40 rpm) and lower temperatures (50, 60 °C) also improved colour, total soluble solids, rehydration ratio, total phenolics and flavonoid contents, betalain content and antioxidant activity. Meanwhile, NIR drying presented a more energy-efficient approach, but with substantial reductions in quality properties compared with MIR drying. Overall, the results suggested the importance of wavelength absorption properties of plant tissues and potential avoidance of localized overheating for enhanced efficiency during infrared drying and prompted the development of suitable approaches and optimization studies for improving efficiency.