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Microwave-assisted extraction (MAE) of natural antioxidants from food waste (FW) offers an economically appealing waste management strategy. Here, we characterize five single waste streams (apple, coffee, olive, tomato, and potato peel waste) and study the MAE of phenolic acids from select feedstocks and mixtures. This library of materials enables us to unravel the relationship of the FW composition and physical properties with dielectric properties, heating, and extractive yields. For example, the protein, ash, and moisture contents affect dielectric properties the most. Our study unveils the significance of moisture in free and bound states on FW dielectric properties, heating, and target acid yields. The microwaves primarily heat the solvent (dimethylformamide) due to its superior dielectric properties compared to FW (dry and moist, single and mixtures) at ≤ 0.05 solid-to-liquid ratio. High moisture content provides higher phenolic yields at lower temperatures and shorter times due to enhanced heat and mass transfer by the microwaves. We recommend extraction before drying waste streams. Further, our data indicates significant interactions between components of mixed FW that drive 2-3x higher yields than those predicted from a simple additive model from single component results. Our work provides new insights for developing versatile MAE strategies to treat complex mixed FW feedstocks. 

About 1.3 billion tons of global food production end up in landfills and composting, leading to significant anthropogenic greenhouse gas (GHG) emissions. Extracting antioxidant and antimicrobial chemicals (flavonoids, phenolic acids, etc.) from food waste is an economically lucrative valorization strategy but is hindered by efficient solvent selection. Here we perform in silico high throughput screening to identify high solubility solvents for key phenolics and reveal >100+ higher-performing solvents than the traditional ethanol and methanol. Solubilities of nine shortlisted solvents are measured and found in reasonable agreement with model predictions. Analysis of the Conductor like Screening Model for Real Solvents (COSMO-RS) σ-profiles and Hansen Solubility Parameters reveals that polarity and hydrogen bonding make dimethylformamide (DMF) an excellent single solvent. We showcase the replacement of high-solubility toxic solvents with green mixtures and demonstrate the approach to potato peel waste. Our work provides a blueprint for solvent selection and generates new insights into extraction from food waste.