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Lactic acid polymers have the advantage of being produced by renewable carbohydrates. Polymer production accounts for the largest portion of lactic acid demand (39%). In the cosmetic industry, lactic acid is used in the manufacture of hygiene and aesthetic products because of its moisturizing, antimicrobial, and rejuvenating effects on the skin. In the chemical industry, lactic acid can be converted to ethanol, propylene glycol, and acrylic polymers. In the food industry, which accounts for a large portion of the demand (35%), lactic acid has a number of uses. For applications in food and in medicine, L(+)-lactic acid is preferred because the metabolic conversion of L(+)-lactic acid in the body is faster than for D(-)-lactic acid.

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To use dairy wastes as a substrate, mainly whey, it is necessary to use an enriched mediums, due to insufficient proteolytic enzyme activity 5, 6, 7, 8. Relatively to the use of fungi, the low LA productivity disadvantage of using wild-type yeasts can be overcome by engineering genetic modification . Oryzae-based process.

Many LAB produce only one isomer of lactic acid, but sometimes, depending on operating conditions, small amounts of both isomers can be produced. Another approach for production of lactic acid is from glycerol, which is a by-product of biodiesel production. Several studies have recently reported lactic acid production using whey (Tejayadi et al. 1995, Kim et al. 2006; Li et al. 2006). Lignocellulose biomass is also a promising source for lactic acid production because its represents the most abundant global source of biomass (Hama et al. 2015; Hu et al. 2015; Eom et al. 2015).

6.2. Chemical pretreatment

In this yeast, the bovine L-lactate dehydrogenase gene (LDH) insertion and decarboxylase gene deletion were sufficient to increase the LA production to 109 g.l−1, with a productivity of 0.91 g.l−1. This modification (C. sonorensis chicken road apk expressing L. helveticus LDH) did not affect cell growth and resulted in the accumulation of lactate up to 92 g/l with a yield of 0.94 g/g glucose without ethanol production . Multiple LDH gene copies were expressed to produce suitable mutants for LA production, which produced LA and ethanol.

As far as we are aware, there are no reports that include other fungi to produce LA. Abdel-Rahman et al. 13, 14 verified that high LA production was obtained by cotton-like mycelial flocs morphology, which was formed by the culture of R. Some researchers investigated fungi morphology that enhances the LA productivity.

3.1. Cheese whey

“L (+) lactic acid fermentation and its product polymerization,” J. “Efficient production od D-(-)-lactic acid from broken rice by Lactobacillus delbrueckii using Ca(OH)2 as a neutralizing agent,” Bioresour. “Lactic acid production from recycled paper sludge by simultaneous saccharification and fermentation,” Biochem. “Utilization of white rice bran for production of L-lactic acid,” Biomass Bioenerg.

• Algae and cyanobacteria are included in the category of photosynthetic microorganisms, and they can grow almost anywhere, with a short harvesting cycle of about 1–10 days and produce various chemicals (including biofuels (H2), ethanol, lactic, AA and FA).
• 2, hydrogen cyanide (HCN) is added to liquid acetaldehyde (CH3CHO) in the presence of a base catalyst under high pressure when lactonitrile is produced (Pal et al. 2009).
• Comparatively, yeasts versus bacteria, yeasts can tolerate low pH which leads to a reduction for the need of neutralizing agents and downstream processing cost.
• “Utilization of white rice bran for production of L-lactic acid,” Biomass Bioenerg.
• “Use of lactate esters for improving the action of agricultural pesticides,” U.

Lactic acid production from urban areas or the hospitality sector, and fruits and vegetables industry (Demichelis et al., 2017). Amylolytic lactic acid bacteria (ALAB) such as Lb. Plantarum , Sporolactobacillus cellulosolvens 13, 14, Rhizopus arrhizus , Lb. Disaccharides (lactose and sucrose) and monosaccharides hexoses (glucose, fructose, and galactose) and pentoses (xylose and arabinose) sugars can be fermented by LAB via EMP and/or the pentose PK pathway . Algal biomass can be proposed as an alternative candidate to LA production without carbohydrate feed medium costs, being induced in high content of carbohydrates and proteins and also lack lignin 15, 108. The deletion of alcohol dehydrogenase 1 (ADH 1) and insertion of L-LDH (from heterologous Lb. helveticus) under the ADH1 promoter, led to an engineering P. stipitis producing 58 and 41 g/l of LA from 100 of xylose and 94 g/l glucose, respectively.

LA producing microorganisms

Generally, three leading stages could be demonstrated for efficient fermentative LA production mainly (i) feedstock pretreatment, (ii) mixed and other substrates for LA production, (iii) ion requirement 10, 134, 147, 200. Torquens, by simultaneous saccharification and co-fermentation, achieved values of 37.1 g/l and 36.6 g/l LA and D-LA, respectively, from 80 g Hydrodictyon reticulatum (47.5%) 198, 199. The microalga Hydrodictyon reticulum has been utilized as a substrate for the production of L-LA by Lb. Algal biomass is another source for LA production 15, 108, 134. Coli strains via homofermentative route could convert glycerol to D-lactate 59, 187, 196. From yogurt whey LA was obtained with a productivity of 0.76 g/L/h and a yield of 0.9 g/g by Lb.

2.2. Lignocellulosic biomass

Plantarum SKL-22 formed reasonable good content of lactic acid 34.26 g/l, so promising strain for production of lactic acid from lignocellulosic biomass . Different modes of fermentative production of lactic acid. Pathways of lactic acid production from pentose sugars obtained from lignocellulose hydrolysate. Lactic acid can be produced from sugar plant wastes (molasses and sugar beet juice), starchy, and lignocellulosic biomasses (Figure 2).

• Media containing nitrogen sources lead to a fast growth that induces the production of chitin instead of LA .
• The highest productivity possible for continuous fermentation is due to the high dilution ratio and the possibility of maintaining the process for a long period of time.
• The most applicable producer strains, types of carbon substrates, and current basic research for optimizing lactic acid synthesis are considered.
• The deletion of alcohol dehydrogenase 1 (ADH 1) and insertion of L-LDH (from heterologous Lb. helveticus) under the ADH1 promoter, led to an engineering P. stipitis producing 58 and 41 g/l of LA from 100 of xylose and 94 g/l glucose, respectively.

Algae and cyanobacteria are included in the category of photosynthetic microorganisms, and they can grow almost anywhere, with a short harvesting cycle of about 1–10 days and produce various chemicals (including biofuels (H2), ethanol, lactic, AA and FA). Moreover, ethanol production was reduced by 15–30 % and 70–80 % compared with the wild-type strain, by xylose and glucose utilization, respectively . The LA production improved by shifting of pyruvate flux toward homolactic fermentation with a yield level of 0.85 g g−1 (being the maximum theoretical yield 1 g.g−1) . Utilise produced 103.3 g/l of L-LA with 95.1% conversion of basal medium and 99.9% purity.

Technological characterization of lactic acid bacteria isolated from raw milk

“Scale-up of L-lactic acid production by mutant strain Rhizopus sp. “Acid hydrolysis of sugarcane bagasse for lactic acid production,” Bioresour. “Efficient production of lactic acid from sucrose and corncob hydrolysate by a newly isolated Rhizopus oryzae GY18,” J. Ind. “Modelling and simulation of continuous L (+) lactic acid production from sugarcane juice in membrane integrated hybrid-reactor system,” Biochem. “A novel process for recovery and refining of L-lactic acid from fermentation broth,” Bioresour.

Recent Advances in Lactic Acid Production by Lactic Acid Bacteria

However, LAB species including Lactobacillus, Lactococcus, Leuconostoc, Streptococcus, and Pediococcus are also used as starter cultures in industrial food fermentations. LA is produced by glycolysis pathway under anaerobic conditions, and this compound can be produced from hexoses and pentoses LAB metabolism pathways, as indicated in Figure 1. Lactic acid bacteria (LAB) are gram-positive microorganisms known as the main safe industrial-scale producers of lactic acid (LA). Molasses, juices waste, starchy biomass, agricultural residues, and forestry residues that is rich in mono and disaccharides, which in some cases need to be hydrolysed by pectinases to enhance the LA production.

The omission of KlPDC1 leads to production strains without PDC activity and increase LA production with free ethanol. Kluyveromyces lactis is crabtree-negative yeast which was used for LA production after genetic modification. Boidinii was 17% reduced by knocking out of the PDC1 gene encoding pyruvate decarboxylase when compared with the wild-type strain and with simultaneous heterologous expression of the bovine L-LDH gene resulted in 85.9 g/l of LA with a productivity of 1.79 g/l/h .

The first company to produce lactic acid by chemical synthesis in significant amounts was Monsanto (Texas, USA) in 1963. Lactic acid production by chemical synthesis using the lactonitrile route, which was a by-product of acrylonitrile technology, was discovered in 1863 by Wislicenus (Benninga 1990). Overview of the two manufacturing methods of lactic acid, chemical synthesis and microbial fermentation (Wee et al. 2006) Although demand for PLA has expanded, its current production capacity of 450 million kg per year is dwarfed by the 200 billion kg of total plastics produced per year. New applications for lactic acid have been developed, such as the production of biodegradable and biocompatible PLA polymers (Abdel-Rahman et al. 2013), solvents, and oxygenated chemicals.

Cerevisiae can efficiently produce d-lactic acid due to its capability to grow fast under anaerobic and aerobic conditions. Firstly, it is a microorganism resistant to low pH and can grow aerobically on glucose sources with the basic anaerobic growth factors including oleic acid, nicotinic acid, and ergosterol. Different research teams have been attempting to produce lactate from engineered yeasts genera including Saccharomyces cerevisiae 13, 14, 92, 94, 95, 96, 97, 98, Candida spp.

Raw material cost is one of the major factors in the economic production of lactic acid. However, waste products from food industries, agricultural industries, sugarcane mills, and biomasses can be used, which is advantageous from an environmental and economic standpoint. Several microorganisms and raw materials can be used in the production of lactic acid (Table 2). Lactic acid production by a chemical route is expensive and dependent on by-products from other industries, which are derived from fossil fuels (Datta and Henry 2006). They produced 40% (4,500 tons) of the lactic acid consumed in the USA (Trindade 2002).