**2. Phenolic compounds in chickpea, pea, and common bean: chemistry, distribution, and beneficial effects**

Legumes are an excellent source of phytochemicals, including phenolic acids, flavonols, flavones, flavanols, flavanones, isoflavones, anthocyanins, tannins, and other phenolics [14, 16, 28, 29]. The structure of polyphenols and their composition and interaction in a food matrix are important determinants of their bioavailability and bioactivity [12, 15, 30]. **Figure 1** shows the structures of phenolic compounds present in chickpea, pea, and bean. Differences in the phenolic profile of various legumes influence the specific health benefits. The presence of phenolic acids and flavonoids in legumes such as chickpea, pea, and beans have been reported in different units of concentration and are presented in **Table 1**.

Phenolic compounds are present in soluble and insoluble forms. Therefore, it is very important to optimize the polyphenols extraction process [9, 10]. Most of the phenolic compounds associated with whole seed are in insoluble bound forms, mainly phenolic acids, linked covalently to cell wall structural components like cellulose, hemicellulose, lignin, and pectin [14, 20, 30, 45].

Chickpea contains several phenolic compounds, including lignans (secoisolariciresinol, pinoresinol, and lariciresinol), isoflavones, flavonoids, phenolic acids, and anthocyanins [20, 49]. Besides, it has significant amounts of flavonoids, especially isoflavones, the main ones being biochanin A and formononetin, to a lesser extent genistein and daidzein [5, 9, 12, 47].

The main compounds in peas are glycosylated flavonols, condensed tannins, as well as hydroxybenzoic and hydroxycinnamic acids, such as quercetin, kaempferol, luteolin, apigenin, flavan-3-ols, apigenin-7-glucoside, quercetin-3-rhamnoside, kaempferol-3-glucoside, flavonols, flavones, and stilbenes; the main compounds identified in the whole seed are hesperidin and catechin [26, 47]. In beans, phenolic acids and flavonoids represent 50% of the total content of phenolic compounds like vanillic, ferulic, 4-hydroxybenzoic, sinapic acids; quercetin, myricetin, and catechin are the major phenolic acids contained in bean seeds and determine the seed color [10, 14, 28].

#### **Figure 1.**

*Main phenolic compounds in legumes [20, 28, 31].*


*Phenolic Compounds in Legumes: Composition, Processing and Gut Health DOI: http://dx.doi.org/10.5772/intechopen.98202*


#### **Table 1.**

*Polyphenols reported in chickpea (*C. arietinum*), pea (*P. sativum*) and common bean (*P. vulgaris*) seeds.*

The phenolic composition of legumes has been particularly interesting for metabolic health because of their protection against oxidative damage [45]. Phenolic compounds constitute an important group of secondary plant metabolites, important for health by preventing multiple degenerative conditions in the body [16]. These compounds are biologically active and have been associated with antidiabetic, anticarcinogenic, antihypertensive, antimutagenic, antioxidant, antimicrobial, anti-inflammatory, anticholesterolemic, cardioprotective, immunostimulant, and anti-angiogenic properties [11, 14, 16, 20, 21, 29, 35, 41, 49, 50].

#### **3. Impact of processing on phenolic compounds**

Processing of legumes may result in an increase or decrease in the content of phenolic compounds. During processing, phenolic compounds may undergo various changes, altering the antioxidant activity of the products. Changes in phenolic content depend on the species, variety, and processing conditions [12, 18, 22]. Processes such as soaking, cooking, extrusion, germination, fermentation, and roasting improve the release of bound phenolic compounds, which influences the sensory properties of the seeds [51–54].

During processing, a reduction in the content of condensed tannins has been reported. In legumes, soaking has been found to decrease tannic acid content by approximately 20%, and germination reduces tannin content by 50%. The decrease of phenolic compounds during soaking and cooking may be due to several factors during the heat treatment, such as 1) polyphenol-protein interactions that decrease the extraction capacity, 2) the formation of tannin complexes with other watersoluble components, and 3) the lixiviation and thermal degradation of phenolic compounds [12, 14, 30]. However, unlike traditional processing or pressure cooking, the extrusion process is carried out in the absence of effluents, so the impact on phenolic content is less [52, 55, 56]. Arribas et al. [55] observed that extrusion does not affect the phenolic groups to the same extent; they reported that the anthocyanin content in extruded pea decreased from 4 to 50% as opposed to the flavonol content, which increased approximately three times.

On the other hand, the germination process increases bioactive compounds, like phenolic compounds, improving the seeds functionality. The increase is attributed to biosynthesis through the Shikimate pathway and the release of phenolic compounds. During germination, enzymatic reactions are activated, such as the enzyme phenylalanine ammonia lyase, which promote the phenolic compounds'

biosynthesis. The endogenous esterases action allows the liberation of hydroxycinnamic acids linked to arabinoxylans and lignin in the cell wall [20, 57, 58]. Nevertheless, changes in isoflavones during this process may be related to genetic regulation. They may be induced by the metabolic pathways of naringenin chalcone and isoliquiritigenin, the precursors of isoflavonoids, present in legumes. Therefore, germination is an efficient alternative to increase antioxidant activity and has been used in legumes such as chickpeas, peas, and beans [9, 12, 48, 50]. Domínguez-Arispuro et al. [20] observed that the germination process in chickpeas induced an increase of 97 and 111% of the total phenolic and flavonoid content, respectively, as compared to the raw seed. Moreover, formononetin and biochanin contents of 0.10 and 0.18 mg/g, respectively, have been reported in raw chickpea; during a 10-day germination process, they increased to 1.42 and 2.10 mg/g respectively [48].

The fermentation process has been reported to cause an increase in free radical scavenging capacity. Changes in phenolic composition are associated with sensory, nutritional, and biochemical properties and depend on fermentation conditions such as optimal time and temperature to avoid a further reduction, mainly in tannin content [53, 59, 60]. Bulbula & Urga [53] reported the effect of different traditional processing methods on tannins in chickpea, noting that during boiling, toasting, and fermentation at 0 h, there are no differences from raw seed beans. However, during fermentation for 24, 48, 72 h and chickpea germination, tannin content decreased by 3.1, 14.4, 18.5, and 43.4%, respectively. The reduction of tannins during germination is generally attributed to enzymatic hydrolysis by polyphenolase.
