*7.1.1 Probiotics*

Antioxidants are chemicals that significantly slow down or stop an oxidizable substrate from oxidizing when present in a low amount as compared to the other substrate [87]. According to Blazheva et al. [6], oxidative stress is a pathological situation that occurs when reactive oxygen species (ROS) overtake the body's antioxidant defenses, causing tissue damage, accelerated cell death, and oxidative modification of biological macromolecules (such as lipids, proteins, and DNA). Oxidative stress is just a body-wide imbalance between free radicals and antioxidants. In this circumstance, reactive nitrogen species (RNS), which cause oxidative stress, and ROS are mostly captured by antioxidants [6]. Antioxidants act as scavengers of ROS and RNS, protecting living organisms from the damaging effects of oxidative stress; as a result, compounds having antioxidant activity are of special importance. Probiotic bacteria thus have special properties that can give antioxidant effects to humans, according to recent studies, and this helps to avoid disorders linked to oxidative stress. Additionally, probiotic bacteria influence the intestinal barrier's permeability and inhibit the overabundance of dangerous bacteria in the gut microbiota [6].

Bifidobacteria are one category of microorganisms that are often regarded as probiotics since they live naturally in the human GIT and have been linked to a healthy colon microbiota [6]. Because Bifidobacteria are strict anaerobes, the oxygen being present in the GIT acts as a stressor, causing it to create antioxidant molecules

#### *Lactic Acid Bacteria: Review on the Potential Delivery System as an Effective Probiotic DOI: http://dx.doi.org/10.5772/intechopen.111776*

to scavenge these free oxygen radicals. Nonetheless, the amount of these antioxidants produced has not been reported in the literature [6]. Bifidobacteria can produce a variety of chemicals that can impede free radical oxidation processes and decrease oxidized molecules. These chemicals and other metabolites are known as the "postbiotics," and they help these probiotics in their specific actions. Some Bifidobacteria produce conjugated linoleic acid metabolites that exhibit the capacity to shield cells from damaging oxidative activity. Different species of Bifidobacteria have genomes that contain a gene for linoleic acid isomerase [88]. As byproducts of the fermentation of plant materials, Bifidobacteria are also capable of producing polyphenols, lignans, and flavonoids, all of which have an antioxidant impact and contribute to the probiotic function of the microbe [6]. A total of 25 Bifidobacterium strains were evaluated by Braune and Blaut [89] for their ability to produce lignan and flavonoid aglycones from flaxseed and soybean extracts. Most of these *Bifidobacterium* strains increased the levels of apigenin, daidzein, genistein, naringenin, and secoisolariciresinol. Additionally, the Bifidobacterium *pseudocantenulatum* and *Bifidobacterium* breve strains produced quercetin and quercetagetin, enhanced the quantity of kaempferol, and exhibited significant levels of herbaceous synthesis. The *Bifidobacterium* strains converted a wide variety of flavonoids' glycosides into their aglycones, boosting their antioxidant activity and bioavailability. According to Mayo and Van Sinderen [90], studies on the biosynthesis of vitamins by Bifidobacteria have revealed that *B. bifidum, B. breve, Bifidobacterium adolescentis, B. longum subsp. infantis,* and *B. longum subsp. longum* can all produce the vitamins nicotinate, thiamine (B1), pyridoxine (B6), and folate (B12). Vitamin B6 is a cofactor of glutathione and plays a significant part in the antioxidant process. Folic acid (B9) also boosts the lipoproteins' resistance to oxidation [90].

The gut microbiome includes another useful microbe called *Lactobacillus* as well, and they both possess strong antioxidant properties. It has been demonstrated that some strains of lactobacilli, although being facultative anaerobes or microaerophilic, may use oxygen as a substrate in processes mediated by flavin oxidases and in specific circumstances can create a minimal respiratory chain. The production of several antioxidant proteins is the main factor affecting lactobacilli's antioxidant abilities. Very infrequently, lactobacilli produce the enzyme superoxide dismutase (SOD), which neutralizes superoxide anion [6]. Included in the antioxidant abilities of lactobacilli are the same proteins that control the chelation of iron and copper ions. Numerous antioxidant substances, including riboflavin, vitamin B12, and carotenoids, are produced by different Lactobacillus strains. In addition, Lactobacilli shows antioxidant traits for the microorganisms they are symbionts for. The genes and proteins that protect lactobacilli from free radicals and their antioxidant qualities are well understood; however, little is known on the parts of lactobacilli cells and their metabolites that shield other microorganisms from free radicals. According to studies, certain strains of lactobacilli's culture fluid exhibit these characteristics in the form of exopolysaccharides, linoleic acid metabolites, histamine, vitamin K2, and soluble proteins [6]. Because probiotic bacteria from the Lactobacillaceae and Bifidobacterium families have historically been used by people to ferment food, they are widely regarded as safe (GRAS). Additionally, probiotic bacteria in the human gut have significant antioxidant activity and encourage the synthesis of antioxidant enzymes to aid in the removal of reactive oxygen species and so lessen oxidative damage. To protect cells from oxidative stress-related damage, probiotic bacteria that build up in the GIT can boost the activity of antioxidant enzymes and reduce systemic circulatory oxidative stress. In addition to being utilized to treat early stages of disorders such as ulcerative

colitis, irritable bowel syndrome, and allergic diseases, strains with antioxidant qualities can help the body's antioxidant status return [6].

#### *7.1.2 Postbiotics*

Research on the antioxidant properties of postbiotics has just become known. In an evaluation of the several postbiotic types of medications, Zólkiewicz et al. [79] investigated bacterial lysates, exopolysaccharides, enzymes, cell wall fragments, short-chain fatty acids, cell wall fragments, cell-free supernatants, and metabolites produced by the gut microbiota. According to Coelho et al. [13], *Liquorilactobacillus satsumensis, Leuconostoc mesenteroide,* and *S. cerevisiae* all have antioxidant activity that inhibited 2, 2-diphenyl-1-picrylhydrazyl (DPPH) by 20 to 28%.

Exopolysaccharide from *Lactococcus lactis subsp. lactis* has been studied *in vivo* as a postbiotics with reports of increased antioxidant enzyme levels (e.g., catalase, superoxide dismutase, and glutathione peroxidase activities) and decreased levels of lipid peroxidation in serum and mice livers [91]. Additionally, findings from *in vivo* studies support the same approach, showing that postbiotics have the capacity as an antioxidant and other health advantages. Postbiotics of lactic acid bacteria isolated from traditionally fermented sausages be potential agents of innovative pharmaceutical therapy for several illnesses associated with oxidative stress and are less dangerous alternatives to living microorganisms [6]. Studies have shown that the antioxidants of postbiotics vary and are influenced by factors that include the chelating ability of the metal ions, the antioxidant enzyme system, and the antioxidant metabolites present in them. As a result, postbiotics can be used as a treatment and feed supplements to minimize inflammation caused by disorders related to oxidative stress [6]. The above *in vivo* and *in vitro* studies provide crucial information regarding the ability of postbiotics to protect against oxidative stress, which is thought to be either a major or secondary cause of many cardiovascular illnesses, as well as to protect against damage caused by free radicals [92]. Postbiotics have also been studied for their potential antibacterial, antiviral, antioxidant, anti-obesity, anti-diabetes, antihypertensive, anti-proliferation, antimutation, and anticancer characteristics, and all these benefits have been shown *in vitro* and *in vivo* [93]. The most predominant benefits of postbiotics as natural antioxidants are generally their clinical (safety), technological (sustainability), and economical (low production costs) benefits [6].
