Cold-Pressing as an Energy-Saving Dewatering Pretreatment for the Valorization of Vegetable Processing By-Products

In this study, an integrated process combining cold-press dewatering and thermal dehydration was proposed to reduce the energy required for powder production while simultaneously recovering a liquid fraction enriched in soluble bioactive compounds. Asparagus, broccoli and artichoke by-products were selected as representative vegetable matrices because of their markedly different anatomical organization and physicochemical characteristics, allowing the robustness of the proposed approach to be evaluated across heterogeneous biomasses. By-products and the corresponding solid residues obtained after cold-press dewatering were dehydrated under identical conditions and subsequently milled into powders. Moisture content, drying kinetics and nutritional quality of whole by-products and corresponding residues were assessed and compared. The specific energy consumption and the percentage increase in specific energy consumption associated with the omission of the cold-press dewatering step were also calculated using an approach already available in the literature. The preliminary dewatering step significantly reduced the amount of water entering the dryer, resulting in lower thermal energy demand for all investigated by-products. Nevertheless, the extent of the energy saving depended on the structural characteristics of the biomass, with asparagus, broccoli and artichoke exhibiting different dewatering efficiencies because of their distinct tissue organization and water distribution. The recovered liquid fractions contained appreciable amounts of water-soluble bioactive compounds, demonstrating that the proposed strategy not only can decrease the energy required for dehydration but also generate an additional value stream.