**3. Valorization of agro-industrial by-products using** *lactobacillus*

At present, cellulosic materials are attractive as possible replacements for edible raw material made up of starch [22], materials such as agricultural residues are considered inexpensive and captivating materials to produce lactic acid since they are a great source of carbohydrates [23, 24]. The most used LAB to produce lactic acid by fermentation are *Lactiplantibacillus plantarum, Amylolactobacillus. amylophilus, L, delbrueckii subsp. delbrueckii, L. delbrueckii subsp. bulgaricus* and *Lactobacillus acidophilus* [25–28]. For optimal lactic acid production it is necessary to make several

considerations: strain of the microorganism with which to work, carbon source, temperature, pH, incubation time, and recycling of cells by immobilization [29]. For this reason, many attempts have been made to find low-priced substrates and interest has arisen in recycling agro-industrial by-products such as wheat bran, distillery residues, beer production residues, etc. These materials that are no longer used in different industries, could reduce the cost of lactic acid production, since raw materials such as starch and lignocellulosic materials require a physicochemical or enzymatic treatment for fermentations and that LAB can directly take advantage of these substrates [22].

For valorization of agro-industrial by-products using *Lactobacillus*, e.g., the production of lactic acid, several studies have been carried out with different types of substrates. For example, bakery waste with the microorganism *Thermoanaerobacterium aotearoense* [30], using whey with *S. thermophillus* and *L. delbrueckii subsp. delbrueckii* [31]. In addition, using cane bagasse as a substrate and *Lactiplantibacillus pentosus* [32], corn stubble has also been used to produce lactic acid by *B. coagulans* [33], coffee mucilage with *L. delbrueckii subsp. bulgaricus* [34], etc.

#### **3.1 Whey**

Today, the dairy industry is researching new technologies and looking for new products not only to meet consumer demand through innovative products but also to increase profitability. One of these alternatives is the addition of whey as a substitute for water [35]. However, some laws prohibit the sale of products derived from whey, to prevent food fraud.

Whey contributes with nutrients such as essential amino acids, in addition to the reduction of calories and improvements in technological properties [36]. The addition of this ingredient produces changes in the structure and in the case of chocolate drinks, it produces modifications in the functional and sensory properties [37].

The use of whey as an ingredient in food is regulated, for example, the FDA establishes a maximum of 5%. In white chocolate [38], a similar percentage of 5% of the total mass of chocolate has been established by the EU [39]. The use of *Lactobacillus* in whey as a substrate gives rise to new products, for example, enzymes with antihypertensive properties, which have been isolated after the fermentation of whey with *Lactiplantibacillus plantarum* QS670, *Lactobacillus amylolyticus* L6 has been used to prepare fermented tofu whey, it can be used as a starter culture to produce quagulant tofu and functional drinks [40].

Other studies indicate the suitability in the development of new foods based on lactic serum [41], whose fermentation converts its complex elements into simpler elements, facilitating assimilation in the intestinal tract [42]. Thus, the presence of probiotics increases the number of digestible amino acids, making fermented dairy products a good alternative as a source of nutrients, especially for diseases such as diarrhea [43].

An investigation ensure that salty whey fermented with the microorganism *L. acidophilus* 43S, fights harmful microorganisms such as *Escherichia coli* [6]. In addition, the fermentation of the whey favors the formation of peptides that can improve the functionality of food and beverages by reducing the taste of cheese that the whey has [17]. The way to obtain a probiotic drink based on milk serum is to drain, filter, and submit to a caloric process such as pasteurization, to later inoculate and ferment with the microorganisms of our choice. It is important to mention that the use of whey obtained by curd coagulation has an advantage over acid whey since, with sweet or deproteinized whey, clearer drinks are obtained without the formation of sediments.

#### *3.1.1 Lactic acid and PLA made from whey*

In the dairy industry, cheese is made by acidifying milk, which produces the precipitation of proteins known as casein, called curd. In this process, a by-product called whey is obtained, which contains other proteins such as lactalbumin, lactoferrin, and lactoglobulin, additionally, it has lactose, fat, and minerals such as calcium and iron that are present in milk [44].

Around 1/3 of the dairy production is destined for the production of cheese, of which between 80 and 90% of this volume corresponds to whey, which is considered a pollutant too, due to its high biological oxygen demand (BOD) and chemical oxygen demand (COD), currently, the treatment of waste from the food industry is mandatory and necessary to avoid damage to the environment [44].

Investigations have been carried out due to its multiple compounds and its ease of transformation into another useful product, to get the most out of the benefits it can provide. In the polymer industry, whey is used as a precursor for polylactic acid (PLA), a biodegradable material with uses in industry and medicine. Due to the scarcity and environmental regulations, alternatives for materials more compatible with the environment and independent of those of fossil fuels have been developed, this is why biopolymers such as PLA are adjusted to meet these needs in the industry, it is for the demand to elaborate more of these biopolymers has increased over time promoting a new industry worldwide, in the same way, other studies raise similar proposals with matrices other than PLA, focused mainly on starches and proteins [44].

As mentioned, lactic acid has two optical isomers D (−) and L (+), these can be obtained by fermentation using a LAB. However, by means of the chemical method, racemic DL-LA is always obtained [29]. The optical purity of lactic acid is of utmost importance within different industries that seek the combination of D (−) and L (+) polymers to obtain crystalline PLA with good mechanical properties [45]. There are several studies on the production of L (+) lactic acid; however, little research regarding the production of D (−) through fermentation processes were performed. Normally, the production of lactic acid occurs by batch, but this method has the disadvantage of reducing productivity and production due to inhibition by high concentrations of substrate, due to this, different alternatives have been reported in terms of improving productivity of lactic acid [46].

The effect of the different carbon sources for the development of the *L. delbrueckii subsp. delbrueckii* to the production of lactic acid using by-products like whey was evaluated [16]. Through this study, it was possible to conclude that the production of high optical purity D (−) lactic acid is possible by the microorganism, with the use of waste raw material such as molasses and corn liquor, without the need for pretreatment of these by-products. This represents a low cost to produce acid with high productivity using a fed-batch strategy [16].

The use of whey for the synthesis of polylactic acid, with the use of lactic acid bacteria, such as *L. delbrueckii subsp. delbrueckii*, through fermentation and its use as biodegradable material for food containers, is an alternative that must be studied yet. This proposal has great technological and environmental relevance because the development and characterization of the physical–chemical and mechanical properties of a biodegradable container from a by-product such as whey, will be able to solve contamination problems in the environment and the possibility of showing that natural polymers generate a greater contribution to the term of biodegradability [44].

#### **3.2 Meat by-products**

LAB is known to be present in the fermentation processes of meat products and by-products, to produce metabolites such as lactic and acetic acid. To carry out the fermentation of these meat products, it is possible to add an inoculum or simply take advantage of the bacterial flora present in the muscle fibers of the animal [17].

The microorganisms that are commonly found in animal meat and are involved in lactic fermentation are *Pediococcus pentosaceus, Pediococcus acidilacti, Lactiplantibacillus plantarum*. These microorganisms have beneficial effects on meat since there is the production of organic acids that favors the decrease in pH, and development of aroma and flavor, in addition to the partial denaturation of meat proteins, favoring the texture of these fermented products [47].

The decrease in pH helps with the elimination of harmful microorganisms that may be present in meat, especially in the viscera of the animal which are parts where pathogens prevail. The safe pH that the meat must reach is 4.0 to 4.2. However, in the case of fish this can take 48 hours to reach this point that, compared to poultry, their viscera reach the desired pH point between 24 to 36 hours [17].

#### **3.3 Farinaceous by-products**

Studies mention that to produce lactic acid it is necessary to use substrates rich in starch, such as starch from wheat, corn, rice, etc. [46]. However, these raw materials require pretreatments so that fermentation can be carried out, which is expensive for the industrial process. For this reason, alternatives have been found that can help in the production of this acid with the use of agro-industrial by-products such as molasses and corn liquor. These substrates must comply with the nutritional requirements of the LAB, and in this way reduce the cost of production [48]. For example, a study carried out to analyze and investigate the production of stereospecific lactic acid from agro-industrial by-products using strains belonging to *Lactobacillus* and *Pediococcus* in combination with enzymatic hydrolysis shown that raw materials, wheat bran (WB), distillery grains (DGS), used brewery grains (BSG) and lupine seeds (LF) (*Lupinus angustifolius*), can be efficiently synthesized [15]. In this investigation, favorable results were obtained for the propagation of LAB and the production of lactic acid. The lowest pH that was reached was with LF after 48 hours of fermentation with the strains of *P. pentosaceus* and *Pediococcus acidilactici*, while with the strain of *Latilactobacillus sakei* the substrate with the best result was WB. Thus, it is possible to conclude that with cellulosic agro-industrial waste using LAB, L-lactic acid can be efficiently synthesized [15].

Cassava (*Manihot esculenta*) is a tuber that has a large number of complex carbohydrates, which can lead to the production of lactic acid. This root is made up of 20% bagasse made up of peel and bark and 80% per tuber. Cassava bagasse is composed of 50 to 60% starch, approximately 34% cellulose, 15% hemicellulose, and 7% lignin [49]. In Colombia, studies have been carried out where the production of lactic acid was analyzed using a cassava starch solution and the use of *Lactobacillus* strains grown from yogurt [50]. A study with two different cassava varieties widely in Ecuador inoculated with *L. delbrueckii subsp. lactis* to produce lactic acid showed the sample with high starch presented highest lactic acid at pH of 5.5 and 150 rpm of stirring [51]. The results obtained in this study show that the production of lactic acid increases with pH with which it works during fermentation if the value exceeds 5.5 there is a growth inhibition of lactic acid producing microorganisms from

#### *Use of* Lactobacillus *for Lactic Acid Production from Agro-Industrial By-Products DOI: http://dx.doi.org/10.5772/intechopen.106697*

glucose [52]. The determining factors in this work were the substrate and the pH, it is also important to mention that the used microorganism directly consumes glucose to produce lactic acid; however, in the hydrolysis of starch, reducing sugars were obtained that include maltose, dextrins, and glucose. Regarding the pH and density, it was possible to determine a correlation between higher density values with the presence of lactic acid in the product obtained by fermentation, and consequently, the pH of this will be lower. Finally, it is possible to conclude that at higher pH with stirring, the microorganism works optimally in a fermentation process with hydrolyzed cassava bagasse, obtaining relevant yields. Thus, with the analyzes carried out on the lactic acid obtained, its quality was verified, and it may have value in the market for the sustainable development of Ecuador. However, the starch obtained from cassava bagasse for fermentation should be studied in greater depth, directly in the hydrolysis of the lignocellulosic material present [51].

Most of the biodegradable packaging developed for food use is based on the use of starches, among them those of cassava, potato, and achira, these by-products are subjected to fermentation by LAB to obtain lactic acid, precursor of PLA [51], also proteins such as zein are used, in both cases, the use of a source food to produce an inedible product poses a risk to food safety. There are few by-products used as raw material to produce biodegradable packaging, one of them is starch from cassava husk, there are no studies on the production of dairy packaging from PLA of whey from milk which must be inert and heat resistant [44].

Bakery waste is other product that can be fermented for obtain new foods, usually is used mainly to obtain breadcrumbs and for feed for livestock. It is possible to market it as a food with added value, for this, it is necessary to subject the by-products to crushing and drying to obtain a fine powder with low moisture content for these processes such as drying, mixing with other elements, and crushing is important [17]. Bakery by-products and other food waste have been subjected to fermentation to improve their physicochemical characteristics using LAB such as *Ligilactobacillus salivarius* [53]. The changes that can be seen due to anaerobic fermentation with LAB is the increase in soluble carbohydrates and nutritional improvement. However, it is achieved through a short fermentation of 10 days; thus, the microbial load is not so elevated. To carry out a fermentation process like this, it was considered that 0.2% inoculum is the optimal amount for improving the nutritional properties of bakery coproducts using LAB [47].

#### **3.4 Fruit by-products**

To produce lactic acid, the use of fruit waste as liquid pineapple could be beneficial since it is an element rich in glucose and nutrients [14]. The pineapple canning industry is one of the food industries that generates a large amount of both solid and liquid waste and that must follow strict environmental regulations. For this reason, there is a special interest in this productive sector. In addition, the use of effluents as carbon sources for lactic acid fermentation helps to reduce or eliminate pollution and reduce costs [14]. However, there is the presence of metals such as copper, zinc, magnesium, calcium, iron, etc., which can cause problems in the fermentation to produce lactic acid. These can inhibit the growth of LAB, influence the pH of the substrate, and also be involved with the inactivation of enzymes that participate in the synthesis of products [26]. Currently, the most widely used microorganism immobilization matrix has been sodium alginate, this matrix has been used for *Saccharomyces cerevisiae, Bacillus amyloliquefaciens,* and *Kluyveromyces*. The advantage of the use of this matrix

is its stability; The substrates and products easily diffuse in and out. However, there is much work on the production of lactic acid, the use of pineapple residues and the immobilization of lactic microorganisms have not been explored [54]. In this study, it was found that sodium alginate in a concentration of 2% generates the maximum production of lactic acid in comparison with the other concentrations tested. Regarding pH, the best yield in the production of lactic acid was 6.5 and finally, the optimal temperature during fermentation was 37°C [14]. Thus, it is possible to conclude that the production of lactic acid using effluents from the pineapple canned industry is viable, if the optimal sodium alginate conditions, the working pH, and the temperature are considered [14].

#### **3.5 Marine by-products**

The main elements of interest from shellfish by-products are pigments such as carotenoids and melanin. Carotenoids are responsible for the coloring of the meat and skin of some fish such as salmonids, they have warm colors such as yellow, orange, and red, Furthermore, they are found in the exoskeletons of crustaceans such as crabs, lobsters, and shrimp. Melanin is a dark pigment that ranges from brown to black, this product of an oxidation reaction of phenolic compounds is present in the peritoneal lining, skin, and eyes of some species [17].

For the extraction of carotenoids from the by-products of crustaceans, several studies have been carried out, using enzymatic or fermentative methods, that are more preferable for compounds such as carotenoids, thus, obtaining higher yields and higher quality carotenoids for their possible applications [17]. Regarding very unstable carotenoids, the silage method by fermentation with lactic acid has been tried, in order to stabilize astaxanthin [55]. The extraction of carotenoids by means of silage of shrimp by-products (*L. delbrueckii subsp. indicus*) by *Lactiplantibacillus plantarum* was studied, in addition, extraction with a mixture of hexane and isopropanol as solvents and refined sunflower oil and the effect of each of the procedures to analyze the stability of the carotenoids, obtaining that the fermentation turned out to be better compared to acid silage, in solvent as in oil [17].
