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Valorization of Waste and By-products from the agrofood Industry using Fermentation processes and enzyme treatments
Published in Quan V. Vuong, Utilisation of Bioactive Compounds from Agricultural and Food Waste, 2017
Phuong Nguyen Nhat Minh, Thien Trung Le, John Van Camp, Katleen Raes
Lactic acid is a common organic acid that can be derived from renewable resources like mango peel, potato peel, cassava waste, etc. Lactic acid can be produced either by fermentation or by chemical synthesis. Ninety per cent of the world’s production of lactic acid is through bacterial fermentation. Metabolic pathways for lactic acid production from various sugars by lactic acid bacteria are divided into pentose phosphate/Glycolytic pathway (homolactic acid metabolism) and phosphoketolase pathway (heterolactic acid metabolism) (Abdel-Rahman et al. 2013). Homo-fermentative lactic acid bacteria produce nearly pure lactic acid (90 per cent) (Vijayakumar et al. 2008). There are several studies outlining the use of fruit and vegetable waste as well as agricultural residue to produce lactic acid. Peels of potato, green peas, sweet corn, orange and mango were used for producing lactic acid through fermentation, using the strains of Lactobacillus casei and Lactobacillus delbrueckii. The highest lactic acid yield of 63.3 g/L was obtained for mango peels by L. casei, whereas it was 54.5 g/L for orange peels by L. delbrueckii. The amount of lactic acid from the other substrates was obtained at lower levels, ranging from 13.4 to 38.9 g/L (Mudaliyar et al. 2012). These value could be compared with the yield of lactic acid obtained from a normal carbon source, for example, the yield of lactic acid of 67 g/L for waste sugarcane bagasse (Adsul et al. 2007) and 28 g/L for defatted rice bran (Tanaka et al. 2006). In a recent study, three types of waste substrates—wasted bread and wasted potato stillage from bioethanol production and beer production—were studied as substrates for the production of L(+) lactic acid by Lactobacillus rhamnosus ATCC 7469 (Djukić-Vuković et al. 2016). A maximal lactic acid productivity of 1.28 g/L/hr, lactic acid concentration of 46 g/L and a highest lactic acid yield of 0.8 g/g were obtained on wasted potato stillage media after 36 hours of fermentation (Djukić- Vuković et al. 2016).
Biosynthetic Pathways for Metabolic Products of Microorganisms
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Four pathways for the catabolism of carbohydrates up to pyruvic acid are known. All four pathways exist in bacteria, actinomycetes, and fungi, including yeasts. The four pathways are the Embden-Meyerhof-Parnas Pathway, the Pentose Phosphate Pathway, the Entner- Duodoroff pathway, and the Phosphoketolase Pathway. Although these pathways are for the breakdown of glucose, other carbohydrates easily fit into the cycles.The Embden-Meyerhof-Parnas (EMP Pathways): The net effect of this pathway (Fig. 5.2) is to reduce glucose (C6) to pyruvate (C3). The system can operate under both aerobic and anaerobic conditions. Under aerobic conditions, it usually functions with the tricarboxylic acid cycle which can oxidize pyruvate to CO2 and H2O. Under anaerobic conditions, pyruvate is fermented to a wide range of fermentation products, many of which are of industrial importance (Fig. 5.3). The Pentose Phosphate Pathway (PP): This is also known as the Hexose Monophosphate Pathway (HMP) or the phosphogluconate pathway. While the EMP pathway provides pyruvate, a C3 compound, as its end product, there is no end product in the PP pathway. Instead, it provides a pool of triose (C3) pentose (C5), hexose (C6), and heptose (C7) phosphates. The primary purpose of the PP pathway, however, appears to be to generate energy in the form of NADPH2 for biosynthetic and other purposes and pentose phosphates for nucleotide synthesis.’The Entner-Duodoroff Pathway (ED): The pathway is restricted to a few bacteria especially Pseudomonas, but it is also carried out by some fungi. It is used by some organisms in the anaerobic breakdown of glucose and by others only in gluconate metabolism.The Phosphoketolase Pathway: In some bacteria, glucose fermentation yields lactic acid, ethanol, and CO2. Pentoses are also fermented to lactic acid and acetic acid. An example is Leuconostoc mesenteroides.
Production of chemicals in thermophilic mixed culture fermentation: mechanism and strategy
Published in Critical Reviews in Environmental Science and Technology, 2020
Kun Dai, Wei Zhang, Raymond Jianxiong Zeng, Fang Zhang
In the acidogenesis step (Figure 2), the thermophilic fermentative microorganisms convert the simple substrates of glucose and xylose into VFAs, alcohols, H2, and CO2 (Hoelzle, Virdis, & Batstone, 2014; Madigan, Martinko, Bender, Buckley, & Stahl, 2015; Regueira, González-Cabaleiro, Ofiţeru, Rodríguez, & Lema, 2018). Glucose is converted to pyruvate in the Embden-Meyerhof pathway (Equation (1)). Xylose is initially converted to D-xylulose-5-phosphate that is further converted to pyruvate and acetate through the pentose phosphate pathway (Equation (2)) and/or phosphoketolase pathway (Equation (3)).