Effects of Conventional and Ultrasound-Assisted Washing on Pesticide Residue Reduction and Quality Characteristics of Purslane (Portulaca oleracea L.): An Artificial Surface Contamination Study

Purslane (Portulaca oleracea L.) is a nutritious leafy vegetable rich in phenolic compounds, vitamins, minerals, and dietary fiber. However, pesticide residues remaining after cultivation may pose risks to human health, making effective post-harvest decontamination treatments necessary. This study investigated the effects of different washing treatments 5% sodium bicarbonate (SB), 5% acetic acid (AA), 5% citric acid (CA), a mixture containing 2.5% acetic acid and 2.5% citric acid (AA-CA), tap water washing (TW), and ultrasound-assisted washing for 5, 10, and 15 min (US-5′, US-10′, and US-15′, respectively) on pesticide residue reduction and quality characteristics of purslane. This study used an artificial surface contamination model with a 4 h holding period before washing. Residue analyses of acetamiprid, cypermethrin, imidacloprid, and propargite were performed by LC-MS/MS and GC-MS/MS using the QuEChERS extraction method. The antioxidant capacity and total phenolic content of the SB sample were significantly lower than those of the other treatments. Color analysis showed significantly higher ΔE* values in the SB sample. Acidic treatments generally resulted in higher TA% and lower pH and chlorophyll contents than the other treatments. Depending on the pesticide and washing treatment, residue reduction efficiencies ranged from 6.33% to 72.22%. Ultrasound-assisted washing (UAW) provided a favorable balance between residue reduction and preservation of several quality attributes, including total phenolic content (TPC), antioxidant capacity, total flavonoid content (TFC), color, and chlorophyll contents in purslane. These results indicate that ultrasound-assisted washing, particularly the 5 min treatment, provided a favorable balance between pesticide residue reduction and preservation of several quality attributes; however, longer ultrasound exposure was associated with deterioration of some quality characteristics, particularly firmness and weight loss.