Samples of rice husks and corn cobs were subjected to hydrothermal treatments in aqueous media under conditions leading to maximal xylooligomer concentration, and the reaction liquors were extracted with dichloromethane (DCM) to assess the type and amount of reaction byproducts with potential application as food ingredients and cosmetics. The identified DCM-soluble compounds were classified in four categories (sugar-derived compounds, lignin-derived compounds, nitrogen-containing compounds and fatty acids). The experimental results were compared with literature data.