Tailoring physicochemical and structural properties of protein extracted from sweet potato wastewater

This study investigates the valorization of sweet potato starch-processing wastewater through the recovery and characterization of its protein fraction. The effects of different ascorbic acid and thermal pretreatments applied prior to protein extraction on protein properties were evaluated. Among the evaluated treatments, immersion in ascorbic acid for 10 min (A10) showed the greatest PPO inhibition, reaching approximately 73% after 60 s, while the thermal treatment at 50 °C for 3 min (B50) resulted in the highest protein recovery (30.04%). Treatment at 100 °C for 30 s resulted in the lowest protein recovery and purity and was associated with pronounced structural changes, evidenced by a marked shift of the isoelectric point toward more negative values, lower solubility, and a decrease in α-helix content accompanied by an increase in β-sheet structures. In contrast, treatment at 50 °C for 3 min resulted in proteins with a higher isoelectric point than the control sample and increased –SH group content, together with measurable antioxidant activity. Among the ascorbic acid treatments, immersion for 10 min resulted in the highest protein purity (47.41%) and was associated with more disordered structures, higher hydrophobicity, and greater thermal stability. Overall, the results demonstrate that the applied pretreatments modulated the recovery, structural characteristics, solubility, and antioxidant properties of sweet potato proteins. These findings highlight the importance of controlling pretreatment conditions during protein recovery from sweet potato starch-processing wastewater and suggest that the resulting protein-enriched fractions may have potential as sustainable plant-based ingredients, although further techno-functional evaluation is required to establish their performance in food applications.