**2.1 Antioxidant activity**

Many *Lactobacillus* enzymes can generate compounds with strong AO activity from plant by-products. For example, β-galactosidase releases isoflavone and oleuropein aglycone while tannases generate propylgallate [16].

#### **Figure 1.**

*Summary of the biomolecules, bioactivities generated by the fermentation by* Lactobacillus *strains of plant products or by-products, and their application domains.*

Glycosylated polyphenols such as tannins, lignans, isoflavones, flavonols, and anthocyanins are widespread in plant products. Absorption in the intestine depends mainly on their degree of glycosylation. Some strains of *Lactobacillus,* such as *L. plantarum*, possess glycosidases that are crucial for the absorption of glycosylated polyphenols and consequently for the resulting AO activity [19]. In most cases, the AO activity is studied with classical biochemical antioxidant assays such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), hydrolxyl or alkyl radical scavenging activities, the ferric-reducing antioxidant power (FRAP), superoxide dismutase (SOD) -like activity, β-carotene bleaching, and oxygen radical absorbance capacity (ORAC). In addition to *in vitro* biochemical tests, other studies have investigated the antioxidant capacity of fermented products with *in vitro* cell-based assays. Reference [16] demonstrated that the fermentation of *L. plantarum* increased the AO properties of a kiwi extract. They correlated this result with increased amounts of protocatechic and chlorogenic acid in the fermented products, which were less represented in the starting extract [20]. Gallic acid production was also observed with the fermentation of red chicory leaves by *L. plantarum* et *L. hilgardi* thanks to tannases [21]. In addition, co-fermentation by *L. gassieri* and *Bifidobacterium animalis* resulted in the release of caffeic acid and conjugated chlorogenic acid after fermentation of sunflower seeds through the action of cinnamoyl esterase. Tannins are also the product of biomass fermentation by *Lactobacillus.* Tannases hydrolyze the ester bond, and gallate decarboxylase converts gallic acid to pyrogallol; thus, *Lactobacillus* generates gallic acid, glucose, and pyrogallol [22].

Several studies have illustrated the fermentation of plants such as Indian chilli pepper, grape pomace, dandelion beverage, and cereal-based plant beverages by *Lactobacillus spp*., resulting in polyphenol compounds (caffeic acid, succinate, pyruvate, pyroglutamate) with AO capacity [23–25]. In [26], they evidenced that rice bran and wheat bran fermented with *L. plantarum* possessed AO capacity through their hydroxyl and oxygen radical scavenging activities. Furthermore, the purified fractions exerted reactive oxygen species (ROS) scavenging activity in HUVEC cells and decreased the senescence of the cultured cells, also conferring an antiaging activity to the fermented fractions. These activities were attributed to the acids and ketones [26]. Co-cultivation of *L. johnsonii* and *Bacillus coagulans* was undertaken in [27] to produce a soybean meal with improved AO properties. Interestingly, the co-cultivation resulted in a significant increase in total phenolic content [27]. Fruits are also an excellent matrix for fermentation due to their high content of dietary fiber, sugars, vitamins, minerals, and phenols. Furthermore, lactic fermentation preserves and improves food safety, nutritional value and preserves the organoleptic quality. In particular, when plants are fermented by *Lactobacillus* endophyte, it preserves of color, firmness, AO activity, growth of fermentation starters and inhibits pathogens in media. Many studies have been conducted on the lactic fermentation of polyphenol-rich berries and red fruits. *L. casei* has been studied for the fermentation of blueberry pulp [28]. In another example studied in [29]*,* mulberry juice fermented in coculture by three different strains (*L. plantarum, L. acidophilus*, and *L. paracasei*) showed a higher AO capacity [29].

In reference [30], they investigated the fermentation of cherry silverberry fruits (*Elaeagnus multiflora Thunb*.) fermented with pure cultures of *L. plantarum* KCTC 33131 and *L. casei* KCTC 13086 alone or in mixed culture. In reference [31], they studied the fermentation by *L. plantarum* FNC 0027 of Jamaican cherry (*Muntingia calabura Linn.*), which induces the production of phenolic compounds and the inhibition of diabeticrelated enzymes (α-glucosidase, α-amylase, and amyloglucosidase). They demonstrated the production of gallic acid, 5,7 dihydroxyflavone, and dihydrokaempferol [31].

Lactobacillus *Use for Plant Fermentation: New Ways for Plant-Based Product Valorization DOI: http://dx.doi.org/10.5772/intechopen.104958*

The valorization of argan press cake was also carried out by lactic acid fermentation using a specifically isolated strain of *L. plantarum* Argan-L1. Argan press cake is a waste of oil production containing polyphenols and saponins. The authors demonstrated that sucrose from argan press cake was easily converted to lactic acid during the fermentation process. Furthermore, the fermented extract presented an increased AO capacity, but the total phenolic compound was slightly decreased [32].

*L. plantarum* KCCM 11613P isolated from Kimchi allowed the production of ginsenosides after fermentation of Korean red ginseng (*Panax ginseng*) [33]. In reference [34], it was shown that fermented soymilk products exhibited improved AO capacity associated with increased isoflavone aglycone content. In addition, fermented extracts inhibited the DNA oxidation induced by the Fenton reagent [34]. All these studies show the interest in using *Lactobacillus* to increase the antioxidant properties of fermented products. Moreover, this antioxidant activity is often associated with the anti-inflammatory activity of certain extracts. Fermentation of other plant matrices can induce antioxidant activity of the products, as shown in **Table 1**.

#### **2.2 Anti-inflammatory activity**

Vegetables, fruits, and plants (tomato, cucumber, pear, apple, mandarin, parsley, carrot, celery, onion, burdock, kale, spinach, aloe vera, civet, grape, jujube, cabbage, and perilla) fermented by *L. plantarum* offer interesting AI molecules [51]. These molecules include organic acids (OAs) such as lactic acid, 3-phennyl-lactate, indole-3-lactate, β-hydroxybutyrate, gamma-aminobutyric acid (GABA), and glycerol. When investigating the AI (and AO) capacity of these compounds, the parameters studied werethe levels of nitric oxide (NO), IL-6 (interleukins) and tumor-necrosis factor-alpha (TNF-alpha), and the DPPH test on RAW cells [52]. Another study showed the AI properties of a fermented plant extract (*Artemisia capillaris*) in RAW 264.7 cells, which stimulated NO and IL-10 secretion without cytotoxic effects [53]. Thus, the fermentation of *Aronia melanocarpa* extract by *L. plantarum* was investigated to produce GABA, polyphenol, and flavonoid compounds. The fermented extract was shown to exert AI effects inhibiting the production of proinflammatory cytokines in RAW 264.7 cells and modulating the immune response in mice [54]. Furthermore, several molecules derived from the fermentation of red fruit juices have been studied for their AI effects. For example, anthocyanins from these products are thought to produce the TNF-alpha and proinflammatory cytokines [23].

Fermented Asian products were highly investigated for their AI properties. For example, a specific strain of *L. plantarum* is involved in the fermentation of the traditional korean fermented vegetable food, the kimchi. It has been shown to secrete exopolysaccharides able to protect against rotavirus-induced diarrhea [55]. Turmeric, another plant originating from Asia, has been also extensively studied for its AI properties and particularly after fermentation. The development of turmeric extracts with potential health applications, particularly for inflammation, is increased.

The production of curcuminoid molecules, such as curcumin, has been enhanced by fermentation of turmeric (*Curcuma longa*) by *L. johnsonii*. The turmeric extracts showed AI and antiallergic effects in atopic dermatitis mice and induced a decrease in serum immunoglobulin E and proinflammatory cytokines in lipopolysaccharideinduced inflammation (LPS) [56]. Supplementation of turmeric extract fermented by *L. rhamnosus* (GG-ATCC 53103) and *Bifidobacterium animalis* (BB12) strains maintained bacterial growth of the gut microbiota in case of inflammation.


#### Lactobacillus *– A Multifunctional Genus*

