This chapter provides a comprehensive overview of phenolic compounds, emphasizing their role in functional foods, their biological activities, and their interactions with food components. Phenolic compounds are secondary plant metabolites that play a key role in plant defense mechanisms and significantly contribute to the color, flavor, and sensory characteristics of foods. Major classes of phenolic compounds, including flavonoids, phenolic acids, tannins, stilbenes, and lignans, are described in detail, highlighting their antioxidant, anti-inflammatory, antimicrobial, cardioprotective, and anticancer properties based on current scientific evidence.

The chapter further explores the interactions between phenolic compounds and food macromolecules such as proteins, lipids, and carbohydrates, and explains how these interactions influence food functionality, stability, and bioavailability. Protein–phenolic interactions may induce conformational changes, affecting solubility, digestibility, and technological properties, while lipid interactions contribute to enhanced oxidative stability. Environmental factors such as pH, temperature, ionic strength, and solvent conditions are discussed as critical parameters governing the strength and nature of these interactions.

In addition, the distribution of phenolic compounds in common food sources, including fruits, vegetables, cereals, legumes, nuts, beverages, and dairy products, is presented, demonstrating their nutritional and functional significance. The effects of food processing techniques on phenolic stability are also addressed, with particular emphasis on thermal treatments, fermentation, and innovative preservation strategies. Finally, emerging technologies such as microencapsulation and nanotechnology-based delivery systems are introduced as promising tools to improve phenolic stability and bioavailability. The chapter concludes by outlining future research directions aimed at optimizing the application of phenolic compounds in functional food development and enhancing their validated health benefits.