Effects of different drying methods on nutritional composition, physicochemical and functional properties of sweet potato leaves

Abstract

In this study, effects of microwave‐vacuum (MVD), hot‐air (HAD), and vacuum‐freeze (VFD) drying methods on the nutritional composition, physicochemical, and functional properties of sweet potato leaves (SPL) were investigated. VFD–SPL showed higher total dietary fiber, vitamin C, E, B1, and B2, and mineral Mg, P, and Zn content than MVD– and HAD–SPL. MVD–SPL showed highest water absorb index, oil absorption capacity, swelling power and solubility. HAD–SPL had smallest particle size (D[4,3] = 56.85 μm), which was further verified by scanning electron microscopy findings. Total polyphenol content of VFD–SPL was highest (6.30 g CAE/100 g DW), followed by MVD– and HAD–SPL (6.06 and 4.72 g CAE/100 g DW, respectively), and the same order was found for antioxidant activity. Although nutritional and functional properties of MVD–SPL were intermediate, the higher physicochemical properties, drying rate, and lower cost suggest MVD has greater potential as a new drying method of SPL. Practical applications Microwave drying can be used to enhance the transportation of heat and moisture inside the drying products, and further increase drying rate and lower the drying temperature due to the fact that vacuum enables moisture to evaporate at a lower temperature, thus maintaining good product quality, particularly for materials with active ingredient and heat‐sensitive components. In this study, the higher physicochemical properties, drying rate, and lower cost than VFD– and HAD–SPL suggest that MVD has greater development potential as a new drying technology in SPL powder production.

Effects of drying methods on the characteristics of rambutan (Nephelium lappaceum L.) seed fat: An optimisation approach

“…The moisture content of oven‐ and freeze‐dried rambutan seed powders were found to be 8.33 and 8.46%, respectively, showing no significant difference between the two drying methods. Our results are in line with the results reported by Sui et al, who investigated the effects of different drying methods on nutritional, functional, and physicochemical properties of sweet potato leaves. Jinap et al studied the effects of moisture contents (1.95%‐17.64%) on cocoa butter extraction from ground cocoa nibs.…”

Osmo-predried fluted pumpkin (Telfairia occidentalis) leaf and its nutri-economic evaluation

“…There was no significant difference ( p > 0.05) between calcium concentrations determined in Suc-T and Syr-T. Calcium functions as a constituent of bone and teeth, and regulation of nerve and muscle. Calcium is also associated with vitamin D metabolism; and calcium-containing substances are required by children, pregnant and lactating women for bones and teeth development (Olusanya et al , 2019; Sui et al , 2019). The value obtained in this study was high enough to activate the conversion of prothrombin to thrombin (in blood coagulation) and also takes part in milk clotting (Soetan et al , 2010).…”

Bioactive Compounds, Antioxidants, and Health Benefits of Sweet Potato Leaves

“…These results imply that drying at low temperatures (<30 °C) may be a suitable method to maintain the nutritional value and bioactive compounds in SPL [ 15 ]. In addition, Sui et al [ 75 ] investigated the influences of vacuum-freeze, hot-air, and microwave-vacuum drying methods on the nutritional composition of SPL, and indicated that the vacuum-freeze drying method maintained the highest vitamins (B1, B2, C, and E), minerals (Zn, P, and Mg), total dietary fiber, and TPC.…”