Mild acid treatments of lignocellulosic materials result in hemicellulose conversion into sugar and sugar oligomers as well as in solubilization of phenolic compounds with potential food applications. The effect of the operational conditions (measured by the severity factor) on the yield of soluble phenolics and the utilization of these compounds (with antioxidant and antimicrobial activities) as food additives are reviewed. Additional information on other biological effects of phenolics that could be of interest for the formulation of functional foods is provided.