Supercritical Carbon Dioxide Extraction of Value-Added Products and Thermochemical Synthesis of Platform Chemicals from Food Waste

Immense global generation of food waste calls for advanced technologies to maximize the use of such renewable carbon-based resources. In this study, corn, taro, lettuce, and bean sprout, were valorized for the production of value-added chemicals via sequential supercritical CO2 (scCO2) extraction and thermochemical conversion. The scCO2 extraction was performed at 350 bar and 50 °C for 60 min. The extracts of the lettuce contained sterols (764 μg g–1) that have potential anticancer properties. While bean sprout extracts had a higher content of saturated fatty acids (641 μg g–1), corn extracts comprised polyunsaturated fatty acids (405 μg g–1) as one of the major compounds, which are beneficial to cholesterol control. There were also notable amounts of wax esters (75–774 μg g–1) in these food waste extracts. Taro extracts were rich in both saturated (2313 μg g–1) and unsaturated fatty acids (1605 μg g–1) and, in particular, contained difatty acids that exhibit pharmaceutical activities. Moreover, the solid residues after scCO2 extraction served as the substrates for platform chemical production. The starch-rich substrates, i.e., taro and corn, resulted in 11–20% hydroxymethylfurfural (HMF) after microwave heating at 140 °C for 5–10 min using SnCl4 catalyst. In comparison, due to the high fiber content, lettuce and bean sprout required a higher temperature of 170–190 °C for chemical decomposition over H2SO4, generating a levulinic acid yield of ∼7%, in company with glucose and fructose as the coproducts. This study on the combined technologies suggested good compatibility between scCO2 extraction and subsequent thermochemical conversion, producing a wide spectrum of value-added chemicals from biomass waste. We herein highlight the vast potential of integrated technologies for food waste valorization in achieving sustainable and carbon-efficient biorefineries.