Lactic acid production - producing microorganisms and substrates sources-state of art

Abstract

Lactic acid is an organic compound produced via fermentation by different microorganisms that are able to use different carbohydrate sources. Lactic acid bacteria are the main bacteria used to produce lactic acid and among these, Lactobacillus spp. have been showing interesting fermentation capacities. The use of Bacillus spp. revealed good possibilities to reduce the fermentative costs. Interestingly, lactic acid high productivity was achieved by Corynebacterium glutamicum and E. coli, mainly after engineering genetic modification. Fungi, like Rhizopus spp. can metabolize different renewable carbon resources, with advantageously amylolytic properties to produce lactic acid. Additionally, yeasts can tolerate environmental restrictions (for example acidic conditions), being the wild-type low lactic acid producers that have been improved by genetic manipulation. Microalgae and cyanobacteria, as photosynthetic microorganisms can be an alternative lactic acid producer without carbohydrate feed costs. For lactic acid production, it is necessary to have substrates in the fermentation medium. Different carbohydrate sources can be used, from plant waste as molasses, starchy, lignocellulosic materials as agricultural and forestry residues. Dairy waste also can be used by the addition of supplementary components with a nitrogen source.

Keywords: Agricultural waste; Biotechnology; Fermentation; Industrial waste; Lactic acid; Microbiology; Microorganisms.

Figure 1

Pathways of lactic acid production from agro-industrial residues. Number on arrow catalyzed by enzyme and other reaction. 1: Exo β_1,4 Glucanase, 2: β -Glucosidase, 3: lactose phosphotransferase system (Lac-PTS), 4: permease, 5: Amylase, 6: β-galactosidase, 7: ATP→ADP, 8: galactose-1-phosphate uridylyltransferase, 9: phosphoglucomutase, 10: NAD→ NADH, 11: ATP→ADP, 12: ATP→ADP, 13: Phosphoenolpyruvate carboxylase, 14: ATP→ADP, 15: ATP→ADP, 16: NAD⁺→NADH, 17: arabinose isomerase, 18: ribulokinase and ATP→ADP, 19: xylose reductase and xylitol dehydrogenase, 20: ATP→ADP, 21: ribulose 5-phosphate 3-epimerase, 22: D-lactic acid Dehydrogenase, 23: Pyruvate-fomarate lyase, 24: Pta, 25: Pyruvate dehydrogenase complex, 26: Aldehyde dehydrogenase, 2NADH→ 2NAD⁺, 27: Acetate kinase, 28: 4 ADP→ 4ATP, 2 NAD⁺→2NADH, 29: 2NADH→2NAD⁺, 30: ADP→ ATP, 31: NADH→ NAD⁺, 32: NADH→ NAD⁺, 33: 2ADP→ATP, NAD⁺→NADH, 34: Lactate dehydrogenase, NADH→NAD⁺, 35: Acetaldehyde dehydrogenase, 36: Pyruvate decarboxylase. 37: Alcohol dehydrogenase. GA3P: glyceraldehyde-3-P, DHAP: Dihydroxyacetone-P. A route: D-tagatose 6-phosphate pathway. B route: Pentose phosphoketolase (PK) pathway: for Hetero lactic acid metabolism. C route: Embden-Meyerhof-Parnas (EMP) pathway: for Homo lactic acid metabolism. D route: Glycolysis pathway in E. coli, K. lactis and S. cerevisiae.

Figure 2

Pathways of lactic acid production from pentose sugars obtained from lignocellulose hydrolysate. Genes AraA, AraB, and AraD encoding arabinose isomerase, ribulokinase, and ribulose-5-phosphate 4-epimerase, respectively. XylA, and xylB encodes xylose isomerase, and xylulokinase. (1) arabinose isomerase; (2) ribulokinase; (3) ribulose-5-phosphate 3-epimerase; (4) xylose isomerase; (5) xylulokinase; (6) phosphoketolase; (7) acetate kinase; (8) phosphotransacetylase; (9) aldehyde dehydrogenase; (10) alcohol dehydrogenase; (11) lactate dehydrogenase; (12) transketolase; (13) transaldolase; (14) 6-phosphofructokinase; (15) fructose-bisphosphate aldolase; and (16) triosephosphate isomerase. PK pathway and PP pathway are phosphoketolase and pentose phosphate pathway. GA3P: glyceraldehyde-3-P, DHAP: Dihydroxyacetone-P.

Figure 3

Different modes of fermentative production of lactic acid.

Figure 4

Lactic acid production from urban areas or the hospitality sector, and fruits and vegetables industry (Demichelis et al., 2017).