# Analytical Methods for Exploring Nutraceuticalticals Based on Phenolic Acids and Polypphenols
## 2 Polyphenols and Related Compounds
Flavanones consist of flavan-4-one structures without the double bond in the heterocycle so that they have chiral carbons. As in the other cases, phenyl rings display varied hydroxylation (and methoxylation), with some representative aglycones being hesperetin, naringenin, taxifolin, and eriodictyl. They are predominantly combined with saccharides, resulting in compounds such as hesperidin, naringin, or narirutin. Flavanones are the main polyphenols in species of the Citrus genus, reaching concentrations of 100 to 3000 mg kg\({}^{-1}\)[22]. The main flavanone bioactivities deal with the antioxidant and radical scavenging power, thus being used as prophylactics to reduce the risk of cancer and cardiovascular diseases. Anthocyanin glycones and anthocyanin glycosides are charged species containing the flavylium cation (the oxygen of the heterocyclic is an oxonium cation). The principal aglycones (e.g., cyanidin, delphinidin, malvidin, and pelargonidin) are often attached to sugars. They are the largest group of pigments found in nature responsible for the cyan and red colors of berries, grapes, tomatoes, and wine [23]. Flavanols, also referred to as flavan-3-ols or catechins, are one of the most important families of polyphenols from both quantitative and qualitative issues [24; 25; 26]. Flavanols are present in high amounts in cocoa, coffee, fruits (berries, grapes, pears, and apples), legumes (peas, lentils, and beans), nuts (walnut, hazelnut, and peanut), and tea. For example, overall concentrations in fresh fruits are about 50 to 250 mg kg\({}^{-1}\), reaching even higher values in green tea (ca. 700 mg kg\({}^{-1}\)) and cocoa (ca. 2000 mg kg\({}^{-1}\)). As flavanones, the heterocycle lacks the double bond so that they have chiral carbons. (--)-Epicatechin and (+)-catechin, (--)-epigallocatechin, (--)-epigallocatechin gallate, and (--)-epigallocatechin gallate are the most remarkable flavanols. They are prone to condense to form the so-called proanthocyanidins (PACs) or condensed tannins, which consist of two or several flavonoid moieties attached in different ways, thus resulting in dimers, trimers, and largeroligomers [9; 27]. Monomers are often connected via the C4 of the upper unit with the C6 or C8 of the lower counterpart (B-type bond). However, in specific cases, they have an additional link between the C2 of the upper monomer and the hydroxyl group of C5 or C7 of the lower one (i.e., C2-O-C5 or C2-O-C7), thus resulting in the so-called A-type bond. As detailed below, B-type compounds are more abundant in nature but the A-type ones possess a noticeable antimicrobial activity [28]. 3. Stilbenes are characterized by a double-bond connecting two aromatic rings. Despite being found in low quantities in the human diet, the significance of compounds such as trans-resveratrol is outstanding. Apart from the more controversial antiaging effects, chemopreventive, chemotherapeutic, cardioprotective, and neuroprotective benefits have been attributed to resveratrol and its derivatives [29]. Curcuminoids are structurally related stilbenoids exhibiting a great range of nutritional and health beneficial properties [30]. Their structure has been used as the basis to design new drugs for the treatment of several types of cancers and microbial infections [30]. 4. Lignans are a minor class of polyphenols consisting of two phenylpropane units. The main food source of lignans is linseed, although they are also found at lower concentrations in cereals, fruits, and vegetables [31]. Recently, lignans have attracted the attention of researchers because of their potential anti-inflammatory, anti-neurodegenerative, antiviral, antimicrobial, and phytoestrogenic activities.