Converting potato peel waste into bioactive extracts: reduction of pesticides by traditional and novel pretreatment technologies

Potato peel, a primary component of potato processing waste, is rich in bioactive phenolic compounds. Nevertheless, it often contains elevated levels of pesticide residues that require reduction before further processing. This study aimed to diminish pesticide content in potato peel using water immersion (WI), ultrasound (US), liquid nitrogen immersion (LNI), and pulsed electric field (PEF) pretreatment processes while preserving its bioactive value. Specific pesticide compounds, including Chlorpropham, Spirotetramat, Azoxystrobin, Propiconazole, and Captan, were diluted in water and spiked onto potato peel samples. The spiked samples underwent WI (1 : 4 sample-to-water ratio), US (acoustic energy density: 592.46 ± 3.59 W L⁻¹, 1 to 5 min duration, 1 : 4 sample-to-water ratio), PEF (3 kV cm⁻¹, 12 to 50 pulses, 1 : 4 sample-to-water ratio), and LNI (2 min-immersion-thawing cycles: 1 to 4). Changes in total phenolic content, chlorogenic acid, hardness, color, and water electrical conductivity, along with light microscopy images, were evaluated before and after pretreatments to assess their impact on potato peel. Ultrasound treatment proved to be the most effective in reducing pesticide content, achieving a 100% reduction for Captan, followed by PEF (up to 80%) and LNI (20%). Removal of pesticides from potato peel using WI, with or without intensification processes, correlated well with the octanol–water partition coefficient of individual pesticide compounds. Furthermore, the retention of total phenolic content exceeded 90% for LNI, while for the US, it surpassed PEF (88% and 54%, respectively). Results of potato peel hardness, color, water electrical conductivity, and microscopic tissue images led to a plausible explanation of the differing polyphenol content. Overall, ultrasound pretreatment exhibited excellent potential for reducing hydrophilic pesticides in potato peel while preserving a significant amount of phenolic compounds.