ABSTRACT
The increasing demand for propionic acid (PA) production and its wide applications in several industries, especially the food industry (as a preservative and satiety inducer), have led to studies on the low-cost biosynthesis of this acid. This paper gives an overview of the biotechnological aspects of PA production and introduces Propionibacterium as the most popular organism for PA production. Moreover, all process variables influencing the production yield, different simple and complex carbon sources, the metabolic pathway of production, engineered mutants with increased productivity, and modified tolerance against high concentrations of acid have been described. Furthermore, possible methods of extraction and analysis of this organic acid, several applied bioreactors, and different culture systems and substrates are introduced. It can be concluded that maximum biomass and PA production may be achieved using metabolically engineered microorganisms and analyzing the most significant factors influencing yield. To date, the maximum reported yield for PA production is 0.973 g·g-1, obtained from Propionibacterium acidipropionici in a three-electrode amperometric culture system in medium containing 0.4 mM cobalt sepulchrate. In addition, the best promising substrate for PA bioproduction may be achieved using glycerol as a carbon source in an extractive continuous fermentation. Simultaneous production of PA and vitamin B12 is suggested, and finally, the limitations of and strategies for competitive microbial production with respect to chemical process from an economical point of view are proposed and presented. Finally, some future trends for bioproduction of PA are suggested.
Subject(s)
Propionates/metabolism , Propionibacterium/metabolism , Propionates/chemistry , Vitamin B 12/biosynthesis , Carbon/metabolism , Bioreactors , Fatty Acids, Volatile/metabolism , Fermentation , Hydrogen-Ion Concentration , Nitrogen/metabolismABSTRACT
BACKGROUND & OBJECTIVES: Many traditional independent risk factors such as diabetes mellitus, hypertension, hypercholesterolaemia, smoking, male sex, old age, etc., contribute to the development of coronary artery disease (CAD). Hyperhomocysteinaemia is an independent risk factor of CAD but the role of plasma homocysteine (Hcy) in high risk patients (> or = 3 risk factors) is not known. We investigated the role of plasma Hcy, folic acid, vitamin B12 in patients with high risk (> or = 3 risk factors) of CAD and effects of supplementation of folic acid in the patients with hyperhomocysteinaemia. METHODS: The plasma Hcy levels in 152 patients with > or = 3 risk factors of CAD and 136 patients with 1-2 risk factors and 48 individuals with no risk factors were measured using high performance liquid chromatography (HPLC) with fluorescence detection. Plasma folic acid and vitamin B12 levels were also measured in these patients with immunoassays. The patients with hyperhomocysteinaemia were treated with 5 mg of folic acid for 8 wk, and plasma levels of Hcy were measured after treatment. RESULTS: The plasma Hcy level was significantly higher in the patients with > or = 3 risk factors of CAD than in those with 1-2 risk factors and controls. The plasma levels of folic acid and vitamin B12 were significantly lower in the patients with > or = 3 risk factors of CAD compared to those with 1-2 risk factors and controls. The Hcy levels in the patients with > or = 3 risk factors of CAD significantly reduced by 33.5 per cent after 8 wk folic acid administration. INTERPRETATION & CONCLUSION: Plasma Hcy level was elevated significantly in patients with > or = 3 risk factors of CAD. Hyperhomocysteinaemia appears to play an important role in the pathogenesis of CAD. Folic acid supplementation may be useful in reducing plasma Hcy level in high risk patients with hyperhomocysteinaemia.