Abstract
This study revealed long-chain fatty acids(LCFAs) on propionic acid production by lipid anaerobic acidogenesis. Oleic acid and palmitic acid, the two most common LCFAs, were added into the acidogenic system to evaluate LCFAs type and concentration on the propionic acid production capacity. The results showed that when the concentration of oleic acid was 4 g/L, the content of volatile fatty acids(VFAs) was 1.3 times higher than that of the blank group(propionic acid was the main product, >70%). In contrast, palmitic acid and excess oleic acid inhibited propionic acid production(butyric acid was the main product). Propionic acid-producing bacteria were the dominant bacteria in an oleic acid production system. According to response surface analysis, the optimal concentration of oleic acid favoring for propionic acid production was 2.3 g/L and fermentation time was 7.4 days in this study. The results showed that a proper concentration of oleic acid has a promotion to propionic acid production. This study provides a theoretical basis for oleic acid to promote propionic acid production.
Highlights
Propionic acid is one of the most common odd-carbon-number volatile fatty acids(OCFAs) in anaerobic fermentation
Due to the hydrophobicity of long-chain fatty acids (LCFAs) molecular structure, under the interaction of van der Waals force and static electricity, LCFAs attached to the surface of anaerobic bacteria may form a hydrophobic physical barrier, which can change the permeability of cell membrane and hinder the intracellular and extracellular material transportation [12]
(a), the VFAs yield of group Q2 (2382.22 mg/L) and group Q6 (2167.88 mg/L) were higher than the blank control group Q1 (2083.74 mg/L), and they were 14.3% and 4% higher than that of the blank control group, respectively. This indicated that LCFAs could promote acid production when the concentration of LCFAs was at an appropriate value, and the promotion effect of oleic acid was stronger than that of palmitic acid
Summary
Propionic acid is one of the most common odd-carbon-number volatile fatty acids(OCFAs) in anaerobic fermentation. It is worth noting that the accumulation of long-chain fatty acids (LCFAs), the hydrolysates of lipids, often exists in the process of anaerobic fermentation, on account of the β-degradation of LCFAs is a rate-limiting step [10]. Due to the similarity between LCFAs and cell membrane, LCFAs accumulated on the surface of bacteria will dissolve the lipid layer of the cell membrane, causing irreversible damage to it, destroying the life activities of anaerobic bacteria [11]. Due to the hydrophobicity of LCFAs molecular structure, under the interaction of van der Waals force and static electricity, LCFAs attached to the surface of anaerobic bacteria may form a hydrophobic physical barrier, which can change the permeability of cell membrane and hinder the intracellular and extracellular material transportation [12]
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