Effects of Osmotic and Ultrasound-Assisted Osmotic Dehydration Pretreatments on Vacuum-Dried Purple Sweet Potato Powder

Lee, Xin (2026) Effects of Osmotic and Ultrasound-Assisted Osmotic Dehydration Pretreatments on Vacuum-Dried Purple Sweet Potato Powder. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Purple sweet potato (PSP) is a nutritionally rich yet highly perishable crop. Vacuum drying is an effective preservation method for producing PSP powder; however, prolonged processing time remains a challenge. This study investigated the effects of sugar-to-maltodextrin (S:M) ratios (100:0, 90:10, 50:50, 10:90, and 0:100) in osmotic solution on osmotic dehydration (OD) and ultrasound-assisted osmotic dehydration (UAOD) as pretreatments prior to vacuum drying. Purple sweet potato slices subjected to OD and UAOD were evaluated for weight reduction (WR), water loss (WL), solute gain (SG), and moisture content (MC), while vacuum-dried PSP powders were analysed for physicochemical, chemical, and antioxidant properties. Results showed that increasing S:M ratios significantly increased WR (-2.02–7.31%) and reduced SG (15.86 to −2.02%) at p < 0.05. UAOD significantly increased WL (8.42–13.85%) and SG (3.01–15.86%), but resulted in lower WR (-2.01–5.41%) and MC (54.99–65.05%) compared to OD (p < 0.05). However, OD-pretreated PSP powders exhibited significantly higher total anthocyanin content (TAC) of 51.74–71.84 mg/100 g dry solids, total phenolic content (TPC) of 325.45–398.03 mg GAE/100 g dry solids, total flavonoid content (TFC) of 64.82–86.83 mg QE/100 g dry solids, and antioxidant activities including DPPH (226.45–303.20 mg AAE/100 g dry solids), FRAP (812.50–1031.84 mM FSE/100 g dry solids), and ABTS (456.15–735.60 mg TE/100 g dry solids) than UAOD-pretreated PSP powders (p < 0.05). Specifically, OD at an S:M ratio of 10:90 showed significantly (p < 0.05) higher TFC (86.83 mg QE/100 g dry solids), ABTS (635.34 mg TE/100 g dry solids), and FRAP (1031.84 mM FSE/100 g dry solids) than the control PSP powder. Overall, OD combined with mixed sugar-maltodextrin osmotic solutions is a promising pretreatment strategy for producing vacuum-dried PSP powder with improved antioxidant retention. Future studies are recommended to optimise conditions to balance drying efficiency and product quality.