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 CO ₂ (scCO ₂ ) extraction and thermochemical conversion. The scCO ₂ 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 scCO ₂ 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 SnCl ₄ 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 H ₂ SO ₄ , 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 scCO ₂ 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.