Effect of Magnesium Sulfate Solution Pretreatment on Antioxidant Properties and Chlorophyll Content of Dried Wolffia (Wolffia globosa)

Wolffia globosa, a nutrient-dense aquatic plant native to Southeast Asia, has gained attention as a sustainable source of protein and bioactive compounds. However, post-harvest processing often compromises its visual appeal and functional properties. This study investigates the effect of magnesium sulfate (MgSO4) solution pretreatment on color retention and antioxidant properties of dried Wolffia. Fresh Wolffia were blanched in varying concentrations of MgSO4 at 0.1%, 0.3%, 0.5%, and 0.7% w/v and dried under controlled conditions. Color parameters including lightness (L*), redness/greenness (a*), and yellowness/blueness (b*) were measured using a spectrophotometer, while antioxidant activity was assessed via DPPH radical scavenging assay and FRAP assay. Results indicated that while the 0.7% w/v MgSO4 treatment yielded the highest total chlorophyll content (6,147.31 mg/kg), this chemical retention did not translate to color preservation. MgSO4 pretreatments significantly decreased lightness (L*) and greenness (resulting in less negative a* values compared to the unblanched control) (p < 0.05). Furthermore, the pretreatments caused a significant reduction in total phenolic content and antioxidant capacity compared to the control dried Wolffia (p < 0.05). These findings suggest that while MgSO4 blanching effectively protects chlorophyll chemically, it negatively impacts the greenness, lightness, and antioxidant properties of dried Wolffia. Therefore, the trade-off between chlorophyll stabilization and the loss of color quality and functional compounds must be carefully evaluated for product applications.