The biorefinery concept is anchored to many types of biomass, including the residues of food processing (seeds, bark, roots, etc.) and agricultural residues (straws, bagasse, etc.). Brazil is recognized as a world leader in exports of food. The industrial activities of the agri-food sector generate large amounts of organic waste. These residues can become a major renewable resource for the production of new chemicals, fuels and energy. The supercritical water technology allows the hydrolysis of organic waste to obtain the so-called precursors: carbohydrates, lignin, oils and proteins and carbon-5 and carbon-6. In this work, it was studied the supercritical water hydrolysis (SWH) of two food industry residues commonly found in Brazil: defatted grape seeds and pressed palm fibre. The hydrolytic process was conducted in semi-batch at 257 °C, 20 MPa and constant water and carbon dioxide flow rates of 33 mLmin-1 and 7g min-1, respectively. The process was performed for 30 min. The results of the hydrolysis experiments with the addition of CO2 as an acid catalyst were compared to data from experiments conducted with pure water. For pressed palmfibre there was no change in the content of reducing sugars in the hydrolysate (11.5%), but the pH varied, and total fermentation inhibitors increased. For the defatted grape seed the content of total reducing sugars increased 56%, the pH also varied, and the fermentation inhibitors also increased. The results indicated large differences between raw materials. Therefore, the addition of carbon dioxide improves the SWH process, depending on the raw material used.