## 2 Natural Bioactive Compounds for Food and Therapeutic Applications  
Natural bioactive compounds are obtained from some natural sources. These natural bioactive compounds are of two types: (a) those which show functional effects in the food systems, such as antioxidants, antimicrobials, flavor enhancers, colorants, and stabilizers, and (b) those which show functional effects in consumers, such as antioxidant, anti-inflammatory, antidiabetic, and antihypertensive compounds. Some natural antimicrobials are very effective in controlling both, the pathogenic and spoilage microorganisms [8]. Essential oils [9; 10] and plant extracts [11; 12; 13; 14; 15; 16; 17] have been used for improving the oxidative and microbial shelf-life of foods. Natural bioactive compounds prevent oxidative processes in food products [18]. This strategy is vital since the oxidative reactions are the most important degradative process in foods, including both lipid [18; 19] and protein oxidation [20], which result in important losses of food quality (chemical composition and physicochemical characteristics) and also produce a significant reduction of nutritional properties of foods. Moreover, the encapsulation of natural colorants is also a promising strategy in order to limit the use of synthetic dies in the food and pharmaceutical industries [21]. Thus, natural functional therapeutic compounds are either used directly or incorporated in the food systems to provide necessary therapeutic effects in consumers. Similar to the natural ingredients for food applications, these natural functional therapeutic compounds are preferred over synthetic [22]. The use of natural bioactive compounds as food ingredients or therapeutic agents has some limitations because their bioactivity is affected by processing and storage conditions [23] since these compounds are degraded with high temperature, pressure, light, extreme pH, etc. [24; 25]. Physical and chemical transformations are other problems that affect their stability and bioactivity [3]. Therefore, a high concentration is required to obtain the similar antimicrobial effect in food products as in in vitro tests; however, a higher concentration may impart negative consequences in food quality (estrange flavors, colors, appearance, etc.). Hence, the direct incorporation of these natural compounds in the food product formulations results in their degradation and transformation at faster rates, which substantially destroys their bioactivity [3; 25]. However, the encapsulated compounds have benefits on human health, since this process increases both the bioaccessibility and bioavailability of these compounds, which also improves their absorption efficiency [21]. On the other hand, many phytochemicals have been shown to have anticancer, antiinflammatory, and antidiabetic potential, which are being used for the development of functional food products. Their stability, bioactivity, as well as their bioavailability, are important attributes that decide their therapeutic potential [26]. The liberation, absorption, distribution, metabolism, and elimination of these compounds are required in order to obtain their health benefits. Thus, the bioavailability of different therapeutic compounds depends on different factors. For instance, the phenolic compounds have lesser stability, poor solubility, and slow intestinal permeability; hence, they have poor bioavailability when they are used in free form. The pH range of various sections of the gastrointestinal tract also differs, hence, the free forms of bioactive compounds have different bioavailability, and this also affects their degradation rate at different sections of the intestinal tract. Anthocyanins are very sensitive to pH and temperature changes, the bioavailability of carotenoids largely depends on particle size and processing conditions, the antimicrobial and antioxidant potential of natural extracts are diminished by the gastrointestinal environment.