**6. Absorption and bioavailability of wheat antioxidants**

#### **6.1. Syringic acid, sinapic acid, vanillic acid, and** *p***-hydroxybenzoic acid**

The information regarding pharmacokinetic parameters or the absorption characteristics of syringic acid, sinapic acid, *p*-hydroxybenzoic acid, and vanillic acid is less. Therefore, it is need of the time to conduct some studies regarding the absorption of these particular acids. Moreover, these compound bioavailability is unknown. Which based on the derived innovative principle of bioavailability and absorption for phenolic acid, nevertheless, we can now assess their bioavailability and absorption effectiveness. The substrate of monocarboxylic acid transporter meets the structural standards of all these compounds, that is, group of mono-anionic carboxyl and a component of aromatic hydrophobic. Each phenolic acid inhibits the transport of fluorescein, and they increased by the following order: syringic acid (105.9%)<sinapic acid (75.0%)<vanillic acid (56.2%)<*p*-hydroxybenzoic acid (35.5%) [59]. Compared to fluorescein transport inhibition by *p*-coumaric acid (85.2%), ferulic acid (52.4%), and caffeic acid (116.2%), each phenolic acid monocarboxylic acid transporter affinity increased by the following order: *p*-hydroxybenzoic acid>vanillic acid ¼ ferulic acid>*p*-coumaric acid, sinapic acid>syringic acid>caffeic acid. Hence, monocarboxylic acid transporter vigorously absorbed the *p*-hydroxybenzoic acid, vanillic acid, and sinapic acid through a mediated transport system.

prepared from the white flour due to proper nutrition, healthy lifestyle, improved nutritional composition, and functional properties [42]. The prepared bread is a significant source of dietary fibers, minerals, inulin, vitamins, omega-3 fatty acids, oligosaccharides, β-glucans, and flax seeds. Gluten is a protein which is not present in pseudocereal (buckwheat) [43]. Buckwheat is enriched with carbohydrates, proteins, fiber, and minerals along with reducing the blood pressure, cholesterol levels, blood glucose level, and prevention of cancer [44]. It is also a prominent source of balanced amino acid composition and essential amino acids [45]. Furthermore, buckwheat phenolic compounds comprise significant quantity of rutin, ferulic, and quercetin along with preventing from the lipid peroxidation and activity of free radicals [46]. They also show higher antioxidant activity mainly due to high rutin content [47]. The total phenolic contents of whole wheat and refined flour were reported as 1.58 and 0.87 mg FAE/g, respectively [48]. On baking and phenolic conditions, total phenolic contents were decreased to about 72% and 67% of the average content found in whole wheat and refined flour [49, 50]. The antioxidant activity of bakery products is mainly affected by processing conditions, mixing, fermentation time, baking temperature, and formulations [51]. Phenolic acid recovery after baking was 74–80%. In comparison to baker's yeast wheat bread, sourdough wheat (durum and kamut) offered more antioxidant protection [52].

Wheat-based breakfast is proven effective by promoting the health-endorsing perspectives due to higher concentration of phenolic bioactive moieties. The acid and enzymatic hydrolysis increase the solubility of wheat bioactive compounds. Similarly, food processing conditions mainly affect the stability, distribution, and activity of wheat-based compounds [53]. The resultant breakfast of wheat has been used to prevent from the proliferation of type 2 diabetes mellitus through lowering the glycemic level in the postprandial phase [54]. The utilization of wheat in breakfast foods prevented the individuals from many disorders like obesity, hypertension, oxidative stress, diabetes complications, mental disorders, digestive ailments, and cognition due to the presence of diets higher in minerals and vitamins and lower in fat. These breakfasts are also used to reduce the body mass index and incidences of obesity and overweight [55, 56]. Similarly, wheat antioxidant-based breakfast significantly decreased hunger [57]. They also protect from the bowel disorder due to dietary fiber. They enhanced the hydrated fecal weight between 10

**5. Wheat antioxidants in breakfast foods**

370 Wheat Improvement, Management and Utilization

and 20 g/100 g diet from a baseline of 21±1.5 g/100 g diet [58].

**6. Absorption and bioavailability of wheat antioxidants**

**6.1. Syringic acid, sinapic acid, vanillic acid, and** *p***-hydroxybenzoic acid**

The information regarding pharmacokinetic parameters or the absorption characteristics of syringic acid, sinapic acid, *p*-hydroxybenzoic acid, and vanillic acid is less. Therefore, it is need of the time to conduct some studies regarding the absorption of these particular acids. Moreover, these compound bioavailability is unknown. Which based on the derived innovative principle of bioavailability and absorption for phenolic acid, nevertheless, we can now assess their bioavailability and absorption effectiveness. The substrate of monocarboxylic acid transporter meets Syringic acid absorption is particularly absorbed through paracellular diffusion; lesser amount is absorbed by monocarboxylic acid transporter, same in the case with caffeic acid [60]. Conjugating enzyme susceptibility, for instance, sulfotransferase and glucuronosyltransferase, bioavailability also affects by that enzyme. Vanillic acid, having a group of hydroxymethoxy aromatic ring, may be a good aim for conjugation [61]. The ferulic acid and vanillic acid affinities for monocarboxylic acid transporter, their conjugation susceptibility together, show that these two compounds have similar bioavailability. While the caffeic acid absorption efficiency is alike to the syringic acid, conjugation susceptibility is different. Component of catechol lacks in syringic acid and therefore unlikely to be conjugation [62]. These results propose a syringic acid has a greater bioavailability over caffeic acid. The understood fact, that is, syringic acid, *p*-hydroxybenzoic acid, and sinapic acid bioavailability, is alike to that of *p*-coumaric acid, while the vanillic acid bioavailability is alike to that of ferulic acid. Germano et al. stated that after hydrolyzed extraction from the root of *Trichilia emetica* including numerous phenolic acids which is orally ingested in rats such as free caffeic acid, syringic acid, *p*-coumaric acid, vanillic acid, and gallic acid, free vanillic acid absorption was comparatively efficient and fast [63].

The bran of oat powder rich in phenol-fed hamsters to find the total bioavailability of vanillic acid, sinapic acid, syringic acid, *p*-coumaric acid, *p*-hydroxybenzoic acid, and ferulic acid, including each phenolic acid, is present in conjugated and free forms, calculated by plasma Cmax/oral dose ratio [64]. The expected bioavailability and absorption of these phenolic acids, depend on our new protocol of fluorescein assay, are generally constant with these two reports. Nevertheless, a number of factors influenced by the bioavailability and absorption came from these studies (i.e., impacts of numerous phenolic acid medicated concurrently and considerable differences of bioavailability between intact and total phenolic acid). Both in vivo and in vitro studies must be done for accurate determination of engagement and bioavailability of these phenolic acids. It has already been performed for caffeic acid and *p*-coumaric acid [30, 65, 66].

#### **6.2. Soluble, insoluble, and free conjugate-bound phenolic acid present in wheat**

In grains, phenolic acid contributes the major portion, for instance, corn, wheat, and rice, which are typically esterified with arabinose or galactose in pectic and hemicellulosis residues in cell wall as well as occur as insoluble fraction (corn 85%, wheat 75%, and rice 62%) [67]. The major phenolic compounds present in grains is ferulic acid with free, soluble conjugated and bound form present in 0.1:1:100 ratios [67]. Furthermore, the major contributors to the total antioxidant activity are the bound phytochemicals e.g. 71% in rice, 90% in wheat, 58% in oats and 87% in corn. The health consequences of dietary phenolic acid in wheat based food materials depends mainly on the bioavailability and absorption of soluble/ insoluble and free/ conjugate phenolic acids.

In case of insoluble fiber, the greater number of bound ferulic acid, for example, wheat bran, is believed to evade from the stomach or intestinal digestion or absorption to hold out the colon. Microbial enzymes of the colon, for instance, esterase and xylanase, release and solubilize feruloylated oligosaccharides (FOs) (i.e., feruloyl-arabinoxylan, 5-o-feruloyl-arabinofuranose) or free ferulic acid, just after reaching the colon. An esterase from mucosa acts on a part of bound ferulic acid during the flow within the gastrointestinal tract leading to the colon, and feruloylated oligosaccharides or free ferulic acid is released [68, 69]. The newly emancipated phenolic acid is absorbed through the gastrointestinal epithelium into the bloodstream jointly with ingested free phenolic acid and delivered to various tissues. The microbial esterases and mucosal substrates like 5-o-feruloyl-arabinofuranose are examples of soluble free and conjugate phenolic acids which are used for absorption of nutrients [70].

In short, phenolic acid in wheat which is of various forms (i.e., insoluble, soluble, and free conjugated bound forms) is converted by the breakdown reaction of free phenolic acid involving colonial and mucosal enzymes. These free phenolic acids destined to blood stream after distribution and metabolized into the body by the action of different enzymes. Wheat phenolic acids have different stages where various factors affects absorption and bioavailability. These factors include (a) the absorption of phenolic acids in the lumen of digestive system and capacity of the biomembrane and monocarboxylic acid transporter; (b) conjugating enzyme susceptibility, tissue having free phenolic acid metabolism, and transporter of monocarboxylic acid affinity; (c) ingestion of wheat phenolic acid, phenolic acid-bound content in conjugated, free, insoluble, and soluble; and (d) discharge of free phenolic content and soluble and insoluble bound of phenolic acid which are attacked by enzymes and the area of GI tract. In recent studies the effect of ingested food components having phenolic acid has been discussed in Ref. [71]. The health benefits of whole grain such as rice and wheat should be studied in detail to find the effect of different aspects on bioavailability and absorption of phenolic acid present in wheat.
