**3. Applications**

#### **3.1 Food products**

Product of the lactic fermentation, bread has been, for a longtime, an important foodstuff of the diet of many cultures. The bread fermentation process has often been optimized and revisited to better meet consumer needs or to address economic and social issues. The fermentation of wheat leaven by *L. plantarum* allows the conversion of ferulic acid into vinyl guaiacol, ethyl guaiacol, and dihydro ferulic acid. This conversion improves the quality of the final bread product [22].

Corn flour is another example of a bread raw material, and its application in bakery illustrates the potential of lactic fermentation. In addition to the different ingredients of wheat bread, maize meal improves the nutritional profile after being fermented with *L. plantarum* T6B10 and *Weissella onfuse* BAN8. Indeed, an increase in amino acid (AA) and protein content, AO activity, and inhibition of lipases and phytic acid were

observed. This leads to an increase in dietary fiber, digestibility, and improves the texture, taste, and nutritional value of bread [69]. The same outcome was observed with the fermentation of brans from hullless barley, emmer and pigmented wheat varieties with the same *Lactobacillus* under the same conditions [70]. Another study highlighted the replacement of wheat flour substitute for breadmaking, a sourdough obtained from fermented djulis (*Chenopodium formosanum*) by *L. casei*. The bread produced contained higher levels of total phenolic and flavonoid compounds and increased hardness and chewiness compared with conventional bread. The addition of djulis sourdough also extended the shelf life by approximately 2 days [71].

A process to valorize semolina pasta with hemp flour, chickpea grains, and milling by-products by fermenting them with *L. plantarum* and *L. rossiae* has been proposed [72]. However, it is necessary to note that enzymatic pretreatment of the substrates must be carried out beforehand. This could affect the economic viability of the process. At a laboratory scale, they obtained extensive protein degradation and consequently digestibility, a 50% reduction in tannin concentration and also in phytic acid concentration [72]. *L. plantarum,* which has high proteolytic activities, was used for the fermentation of quinoa instead of wheat. Quinoa is an interesting cereal for celiac patients because it is gluten-free. The study revealed that quinoa is more easily fermented by lactic acid bacteria than wheat. These high proteolytic activities of the strain were evidenced by the increase of the total peptides and free AA contents from quinoa slurries compared with wheat slurries [62]. In reference [70], the potential use of oat extract from cereal processing with high protein content as an alternative to yoghurt was questioned. Fermentation of this by-product with *L. delbrüchii* subsp. *Bulgaricus* and *Streptococcus themophilus* followed by starch gelatinization by heating generated two kinds of gels with interesting rheological and organoleptic properties. Authors placed their studies in the context of plant-based products substituting dairy ones for health and environmental reasons. They discussed the consumer acceptance of these products but claimed that sensory descriptors such as soft, sweet, and smooth are highlighted by the sensory panel [73]. Another example of food products fermentation value is the fermentation of olive by *L. plantarum*. Kachouri et al. have shown that the phenolic content of olive oil increases after fermentation by this strain [74]. Other studies have shown that the fermentation of the common Spanish table olive improves preservation and the taste. Indeed, *L. plantarum* ferments olive brine, leading to a reduction in the oleuropein content of the olives [75–79]. In addition, wastewater from olive production, which is another olive coproduct, has been exploited in [80]. When fermented by *L. plantarum*, the content of phenolic compounds becomes more interesting. The antioxidant activity was tested by DPPH and ABTS assay. This coproduct has a 50% higher antioxidant activity after fermentation by *L. plantarum* [80].

In order to innovate in the food market, research is being carried out into the development of plant-based drinks rich in active compounds and with health benefits for consumers. Functional plant beverages fermented with *Lactobacillus* are being widely studied. Aqueous extracts of plants such as soy, pea, coconut, or rice represent alternatives to nondairy milk. Lactic acid fermentation of these beverages could improve the protein content, solubility, and availability of AA. Some strains of *Lactobacillus* are also responsible for the biosynthesis of vitamins during fermentation (vitamin K, vitamin B). Anti-nutritional compounds such as phytates are hydrolyzed during fermentation by some phytase-producing strains, which improves the digestibility and mineral content of the final product [81]. However, optimizing flavors and nutritional quality remains a challenge today because the latter are often criticized for their low nutritional quality and bland taste caused by their short shelf life. A color change

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

has been observed by Do and Fan in fruit or carrot juices fermented by *Lactobacillus* strains, indicating that carotenoids are modified to cis-carotenoid isomers responsible for color change during fermentation by *Lactobacillus* [82]. Rheological studies have also been performed. Indeed, in [83], the effects of different *Lactobacillus* species on volatile and nonvolatile flavor compounds in juices fermentation were studied. The main objective of this research was to identify the marker metabolites generated by different species of *Lactobacillus* strains, which contribute to the flavor and reveal the roles of various *Lactobacillus* species in the formation of flavor compounds. The main markers were 2.3 butanedione, hexenal, acetic acid, formic acid as volatile compounds and lactic acid, malic acid, citric acid as nonvolatile compounds [83].

In another application for the beverage sector, one of the main ideas is to provide fermented products with prebiotic effects from a different matrix of vegetable juice as raw material. Consumers' demand for non-dairy prebiotic foods is constantly increasing due to drawbacks related to dairy foods such as allergy, lactose intolerance, as well as lifestyle change or religious beliefs. In this context, reference [71] presents a development of a functional drink based on soy and quinoa (*Chenopodium quinoa Willd*) obtained by fermentation by *Lactobacillus casei* LC-1. This drink presents a prebiotic effect stimulating the gut microbiota and reducing the following bacterial populations: *Clostridium spp, Bacteroides spp, Enterobacteria, and Enterococcus spp* [84]. Cabbage juice and fresh cabbage, fermented by *Lactobacillus*, are also being studied for the development of probiotic products. When mixed with other vegetables (carrots, onion, cucumber), white and red cabbage fermented with *L. plantarum, L. casei , L. acidophilus,* or *L. delbrueckii* shows a good fermentation profile and potential as a functional probiotic drink as demonstrated by Hyunah et al. [85–88]. Dunkley and Hekmat evaluated the sensory properties and worked to assess the growth and viability of *L. rhamnosus* GR-1 in carrot juice, carrot apple juice, carrot orange juice, and carrot beetroot juice over 72 h of fermentation and 30 days of refrigerated storage at 4°C. The conclusion was that carrot, carrot apple, carrot orange, and carrot beetroot juice fermented with *L. rhamnosus* GR-1 proved to be a satisfactory alternative to dairy-based prebiotic products. All juices achieved viable counts above the minimum counts required to be classified as prebiotic. The results of sensory evaluation also indicated a market potential for prebiotic vegetable juice. The development of prebiotic vegetable juice using *L. rhamnosus* GR-1 as a probiotic agent will provide consumers a viable non-dairy alternative that can provide many health benefits [89]. Co- or triculture can be used to enhance activities. Bergamot juice was fermented by three *Lactobacillus* (*L. plantarum* 107 subsp *plantarum* PTCC 1896, *L. plantarum* AF1, *L. plantarum* LP3) in triculture. This combination resulted in a higher AO activity. Bergamot juice fermented could also be used as a functional drink [90].

Other by-products are recycled, especially in the brewery sector. One study aimed to produce a polyphenol-rich beverage from brewers' spent grain. Fermentation by *L. plantarum* ATCC 8014 was realized, followed by tests on phenolic compound content and AO activity. Phenol content and AO have increased during fermentation. The beverage was more concentrated in phenolic compounds than before fermentation, and its bioactive compounds were more stable [91]. More recently, coffee cherry pulp has been used in infusion to obtain an AO drink called cascara. To improve the AO activity of this beverage, it was fermented by endophytic *L. casei* [92]. A turmericbased functional drink was also obtained by co-fermentation with *Enterococcus faecium, Lactococcus lactis subsp. Lacti, and L. plantarum*. The AO capacity was measured by titration of total phenolic compounds, and the prebiotic effect was also highlighted by *in vitro* and *in vivo* tests.

Kombucha is a sweet infusion of green tea leaves usually fermented with Kombu, a fungus. One study shows that replacing Kombu with *L. casei* and *L. plantarum*, which are derived from kefir, enhances the production of glucuronic acid, leading to greater antimicrobial and antioxidant activities [93]. Another study showed that a mixture of LAB from kefir and kombucha (*L. casei, L. plantarum*, *L. acidophilus. L. casei,* and *L. plantarum*) increases the glucuronic acid concentration, antimicrobial and antioxidant activities and allows the use of Kombucha as a health drink [94]. Hou et al. demonstrated the link between antimicrobial activities of kombucha with polyphenols and LAB, especially against *Escherichia coli, Salmonella tiphy, Vibrio cholerae,* and *Shigella dysenteriae* [95]. Green tea used in Kombucha may have activity when fermented by *L. plantarum*. Indeed, fermented extract derived from *Camellia sinensis* is able to mitigate ethanol-induced liver damage. *In vitro* and *in vivo* tests on hepatic cells (HepG2,) and murin model exposed to fermented green tea extract show after exposure of ethanol a better viability and an increase of hepatic alcohol dehydrogenase [96].

#### **3.2 Livestock feeding**

The products of plant fermentation by *Lactobacillus* strains can be used in many fields ranging from livestock feeding, such as ruminant by decreasing gas production [97]. *Lactobacillus* strains can also be used for silage preparation. Silages are grass or other green fodder that is compacted and stored under airtight conditions, typically in a silo, for use as livestock feeding in the winter. Many studies focus on using *Lactobacillus* strains to improve the quality of the silage. In reference [98], the effect of *L. brevis* and *L. parafarraginis* used as inoculants and the microbial communities of corn stover silage were studied. After 20 days, the two *Lactobacillus* strains were predominant, and a reduction in lactic acid content coupled with an increase in acetic acid and 1.2-propanediol contents was observed. An improvement in the silage quality and reproducibility of the ensiling process were observed [98]. Recently in [99], the effect of *L. plantarum* addition on the nutritive value of dwarf elephant grass (*Pennisetum purpureum* cv Mott) silage was presented. The aim was to examine the effects of different *L. plantarum* addition on the physical quality, pH, and nutritional value (dry matter, organic matter, crude protein, crude fiber). After incubation, a good silage quality (fresh and acidic odor, good texture, and no fungi) and a pH around 4 were observed. *L. plantarum* addition accelerates ensilage fermentation [99]. In [100], an increase in silage quality by adding waste molasses to *L. plantarum* MTD1 was observed. In the same context, the addition of cellulase was studied to evaluate the effects on the chemical composition, bacterial communities, stability of mixed silage made with high-moisture amaranth and rice straw fermented by *L. plantarum*.

Cellulases increased the abundance of *Lactobacillus* bacteria and reduced the abundance of other lactic acid bacteria. It decreased pH, acetic acid content, ammonia nitrogen content and increased lactic acid concentration after 7 days of ensiling [101]. In conclusion, silage treated with both *Lactobacillus* bacteria and cellulase showed the best silage quality. Optimizing the digestibility of feeds and thus increasing their nutritional value are a challenge for the livestock feeding industry. In another study, the fermentation product of a mixture of ginger and turmeric extract by *Lactobacillus* spp. was supplemented to chickens. Biological analyses of AO enzymes and analysis of gut microbiota and lymphoid organs showed a prebiotic effect, an AO effect, and an improvement in resistance to bacterial infections [102].

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

#### **3.3 Lactic acid production from plant biomass**

The use of low-cost by-products is of primary interest as it reduces production costs compared with the use of complex culture media made with pure and refined products. Consequently, many by-products have been tested in the last few years, in association with screening of the best microbial strains, the best fermentation process, and the best conditions to make them work together [103]. Lactic acid is one of the most widely used organic acids for a long time in various industries, such as food, cosmetics, pharmaceutical, and textile industries, and flavor, conservation, AO, and antimicrobial activity [104]. In the last decade, it has also become an essential platform molecule in the biomaterials sector to produce poly-lactic acid (PLA), a biobased polymer. This new interest has led to an explosion in worldwide demand. One of the characteristics of polylactic acid is its thermal resistance, a critical parameter for manufacturing thermoformed materials (packaging, film, etc.). *Lactobacillus* have been traditionally used for lactic acid production [105, 106]. When using large-scale fermentation bioprocesses, the biomass feedstock must be carefully selected as it accounts for almost half of the biopolymers production costs [105]. To address this production cost issue, scientists and industrials have been focused on lignocellulosic biomass as a fermentation substrate for lactic acid production. Nevertheless, in order to be easily usable, saccharification pretreatments are needed to break down the cellulose into fermentable carbohydrates. Moreover, *Lactobacillus* are classified as either homofermentative or heterofermentative. *L. delbrueckii* is a homofermentative strain commonly used for the production of lactic acid [107]. Homofermentative strains of *Lactobacillus* cannot use pentose carbohydrates from hemicellulose, but heterofermentative ones, such as *L. brevis*, can use these carbohydrates through the phosphoketolase pathway [106].

In reference [105], the fermentation of 11 different carbohydrates from seaweed or plant biomass as a carbon source to produce L-lactic acid with seven different *Lactobacillus* species was investigated. A comparative analysis of the expected yield of lactic acid production revealed that seaweeds provided comparable production rates to lignocellulosic biomasses [105]. In another study, beet molasse was used to produce lactic acid using *L. delbrueckii* IFO 3202 during batch and continuous fermentation, dilution rate of 0.5 h−1 was determined to be the best one and allowed to reach a maximum productivity of 11 g L−1 h−1. Authors have demonstrated the importance of medium supplementation by yeast extract, as Lactobacilli are tedious microorganisms that require many substrates and substances to grow [108]. Nevertheless, it is estimated that the addition of yeast extract can contribute up to 30% of the cost of producing lactic acid [109]. Zhang & Vadlani studied the production of D-lactic acid by a homofermentative strain, *L. delbrueckii* ATCC 9649, through a sequential hydrolysis and fermentation process (SHF) and a simultaneous saccharification and fermentation process (SSF). In this work, first, the saccharification of pulp and corn stover was done, and then carbohydrates generated from hydrolysis were used by *L. delbrueckii* and converted to D-lactic acid with high purity (99.8 %). The authors highlighted that the SHF process, compared with the SSF process, avoids substrate inhibition and increases the productivity and the yield of D-lactic acid [107]. The same researchers' team has then engineered a strain of *L. plantarum*, introducing gene encoding isomerase and xylulokinase, for the overproduction of D-lactic acid from corn stover and soybean meal extract. In this work, the authors optimized the culture medium through response surface methodology using saccharified corn stover as carbon source and soybean meal extract as a nitrogen source to substitute YE in the

medium to produce high purity of D-lactic acid (99%). A maximum productivity of 0.82 g L−1 h−1 of D-lactic acid was obtained in the optimized medium, 10% higher than with YE as the main nitrogen source [106].

Saccharification and fermentation could be performed at the same time (simultaneous saccharification and fermentation) and have been used for instance by Tu et al. for LA production. With *L. plantarum*, they obtained up to 65.6 g L−1 of lactic acid with a cellulose conversion of 69% [110]. Using inulin from chicory, in [111] they obtained a better performance by simultaneous saccharification and fermentation to produce D-lactic acid with *L. bulgaricus*. In their process, they obtained an optically pure molecule (99.9%), which could be interesting for further chemical processes. Productivity is also high with 123 g L−1 starting from 120 g L−1 of inulin treated by inulinase. The enzymatic treatment yielded inulin, which was used instead of glucose in MRS medium for fermentation [110, 111].

In another example, lactic acid production from fermented orange peels was evaluated by ion-exchange chromatography. The solid fermentations were in mono or coculture, with *L. casei* 2246, *L. plantarum* 285, and *L. paracasei* 4186. This study showed that fermentation resulted in higher lactic acid production with the monoculture *L. casei* 2246 and the coculture *L. casei* 2246 with *L. plantarum* 285. Glucose can also be converted to lactic acid by symbiotic relationship between different lactic acid bacteria. *L. helveticus* is an AA-producing strain (alanine, serine, aspartate, glutamate, aromatic AA, and histidine), whereas *L. delbrueckii* is a lactic-acid-producing strain but produces little of these AAs necessary for its growth. Thus, this co-fermentation optimized the lactic acid yield [104]. Before industrialization of such a process, scale-up has to be demonstrated and downstream processes (purification) to be implemented and considered. However, another technology could also be used for lactic acid production by microorganisms. Indeed, solid-state fermentation was used with cassava bagasse as substrate and *L. delbruechii* as microorganism [103, 112].
