Biologically active (or bioactive) peptides are specific fragments that are latent in milk proteins (especially in casein fractions), but that, after being released upon proteolysis, can positively affect health (Kitts and Weiler, 2003; Korhonen and Pihlanto, 2006). Bioactive peptides can be released by enzymatic activities either during milk fermentation by food-grade microorganisms or following in vitro enzymatic (e.g., pepsin, trypsin) digestion, as well as during gastrointestinal transit. Several proteolytic strains of lactic acid bacteria (e.g., L. acidophilus, L. casei, L. delbrueckii, Lactobacillus helveticus, and Lactococcus lactis) are efficiently used to hydrolyze caseins and thus liberating bioactive peptides (Sadat-Mekmene et al., 2011). The proteolytic system of lactic acid bacteria usually includes as main components proteinase, transport system for oligopeptides, and several peptidases. Proteinase, frequently having extracellular location, cleaves polypeptides in peptides, most of which enter the cytoplasm via membrane-associated oligopeptides transport system (named Opp). Peptides are further cleaved, by cytoplasmic peptidases, to smaller peptides and free amino acids, which are partly used by bacterial cells to synthesize proteins and partly released in the food matrix (Savijoki et al., 2006).
Antihypertensive and antioxidant peptides are among the most studied bioactive peptides, due to the incidence of hypertensive individuals in Western countries and to the increase in life expectance. Hypertension is a major risk factor for cardiovascular (arteriosclerosis, stroke, and myocardial infraction) and renal diseases (Usinger et al., 2009). Use of dairy products containing antihypertensive peptides to prevent and/or treat hypertension would lead to save funds for public health. Increased life expectance in Western countries requires means to counteract ageing, a process that, at cellular level, may be retarded by exploiting the radical oxygen species (ROS) scavenging capacity of some milk-derived peptides (Kudoh et al., 2001; Virtanen et al., 2007).