Plant components, primarily secondary metabolites that have health-promoting properties are called phytonutrients. In vitro studies indicate phytonutrients may play a signifi cant role, in addition to vitamins, in protecting biological systems from the effects of oxidative stress (Kalt, 2005). Various molecular processes, as well as environmental, dietary and lifestyle factors can invoke the production of a variety of reactive oxygen, nitrogen and iron species that are responsible for the irreparable damage to molecules, such as DNA, lipids, and proteins. It is well accepted that oxidative damage plays an important role in the etiology of many chronic diseases and the process of aging (Ames et al., 1993). In addition to natural defense mechanisms, diet may play an important role in disease prevention through ingestion of antioxidant compounds that reduce the oxidative threat to the biological systems. The prevention of chronic diseases by phytonutrients is not limited to direct antioxidant activity. Other proposed mechanisms include the induction of disease-preventive enzymes, inhibition of disease-promoting enzymes, and inhibition of various cancerinducing signals (Lambert and Yang, 2003; Waladkhani and Clemens, 2001). It has also been demonstrated that phytonutrients may possess anti-infl ammatory and estrogenic activities (Hou, 2003) and may provide health benefi ts through modulation of cell signaling pathways and gene expression (Williams et al., 2004). Phenolics and carotenoids represent two major classes of phytonutrients found in fruits and vegetables. Phenolics are ubiquitous plant components that are primarily derived from phenylalanine via the phenylpropanoid metabolism (Dixon and Paiva, 1995). They serve a major role in protecting plants from biotic and abiotic stresses. The hydroxylated aromatic ring characteristic of phenolics is an excellent reducing agent, enabling compounds present in the plant to donate a hydrogen radical to reactive free radicals in biological environments. The aromatic ring is capable of stabilizing the unpaired electron by resonance and terminating the propagation of additional radicals or damaging species. The antioxidant potency of phenolics has been documented in many in vitro studies (Duthie et al., 2000). Carotenoids are synthesized through the isoprenoid pathway in plant plastids and are stored in the chloroplasts with the function of protecting chlorophyll during photosynthesis (Cunningham and Gantt, 1998). The primary sources of dietary carotenoids include carrots (Daucus carota L.), tomatoes (Lycopersicon esculentum Mill.), sweet potatoes (Ipomoea batatas), spinach (Spinacia oleracea L.), and other green leaf vegetables (Block, 1994). In addition to pro-vitamin A activity, carotenoids act as potent antioxidants in vivo. The conjugated double bond structure is capable of stabilizing an additional electron from a free radical or other reactive compound (Mortensen et al., 2001). Processing can have a dramatic effect on the phytonutrient content of fruits and vegetables. In this paper, we review various processing factors that infl uence phytonutrient losses in carrots, a common vegetable and major source of β-carotene in the U.S. diet (Block, 1994; Simon and Wolff, 1987).