Sequential Drying and Extraction of Lipids and Bioactives from High-Moisture Food Side Streams Using Supercritical Carbon Dioxide: A Novel Approach to Side-Stream Valorization

Supercritical carbon dioxide (SCCO2) offers multiple advantages such as low processing temperature and an oxygen-free processing environment for applications like drying food side streams and extracting lipids and bioactives. In this work, SCCO2 drying was investigated for four food side streams, including SBP (soybean pulp), brewer’s spent grain (BSG), spent coffee grounds (SCG), and cranberry pomace (CBP). The Taguchi method was used to systematically vary the processing parameters (pressure, temperature, flow rate, and extraction time) to assess their impact on moisture removal. SCCO2 drying extracted around 83–90% of the water from food side streams without affecting the properties of high-value products within the side streams. Optimal drying conditions were found to be at 100 bar and 70 °C for BSG and SCG, at 200 bar and 70 °C for SBP, and at 100 bar and 60 °C for CBP, with drying times and flow rates of CO2 ranging from 2.5 to 3 h and 90 to 150 g/min, respectively. Following drying, a sequential extraction strategy was implemented: neat SCCO2 was initially employed to extract lipids, followed by ethanol injections to recover leftover lipids and ethanol-soluble bioactives and, subsequently, sequential injections of 70% ethanol and water to extract the remaining bioactives. Nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography–mass spectrometry (LC–MS) analyses of each fraction collected from CBP demonstrated that SCCO2 not only enabled efficient drying and concurrent extraction of water-soluble bioactives but also allowed for stepwise lipid extraction and selective fractionation of bioactives at each stage. This integrated, one-pot SCCO2 process offers a sustainable and efficient approach for the comprehensive valorization of high-moisture food side streams.