Butyric acid is a short chain fatty acid (C3H7COOH). Its esters exist naturally in animal fats and certain vegetable oils [18]. Butyric acid can be used as an ingredient in varnishes, perfumes, pharmaceuticals, disinfectants and used to produce plastics, plasticizers, surfactants and textile auxiliaries [18]. It can be applied in animal feed and used as a flavoring agent in food products in the form of esters and salts [18]. It can also serve as a substrate to produce butanol [1, 2]. Butyric acid can be produced by petrochemical or biological methods [18,76]. Although today butyric acid is mainly produced from petroleum feedstocks, its production from renewable feedstocks through microbial fermentation attracts more attention due to limited resources and its application as food additives or products cosmetics [18,22]. In microbial fermentation, a number of gram-positive obligate anaerobic microorganisms have the capacity to produce butyric acid in significant quantities such as Clostridium sp. and Butyrivibrio fibrisolnes [18]. Among these, Clostridium tyrobutyricum, a Gram-positive and obligate anaerobic bacterium, is the most promising due to its ability to produce butyric acid with high selectivity, its tolerance to high product concentrations [22] and its relatively high and stable production [3, 4, 5, 6]. The metabolic pathway of Clostridium tyrobutyricum is shown in the figure. 1. The final products are butyrate and butanol, while acetate and acetone are by-products. Lactate and ethanol are produced but in small quantities [77]. Solvents include butanol, ethanol and acetone are produced when pH <5 during the solvogenesis phase. Acids are produced during the acidogenesis phase when the pH is higher (77). Acetyl-CoA is a branch point intermediate...... middle of paper ......spectively after dilute acid pretreatment and enzymatic hydrolysis [26]. Some research also chose 1 g/l [27, 28] or 2 g/l [21, 29] as the maximum concentration of furfural. The furfural concentrations in this research were divided into four levels to study: 0.6 g/l, 1.2 g/l, 1.8 g/l and 2.4 g/l. As for syringaldehyde and vanillin, similar to furfural, concentrations of 0.06 g/l and 0.04 g/l were found respectively in the strover corn solution after hydrolysis of sulfuric acid and the author has also tested both at 2 g/l [24]. S. cerevisiae and Z. mobilis cells are mainly killed by 2 g/l vanillin or 1.5 g/l syringaldehyde [23]. So, even though the concentrations in the hydrolysis solution were not high, this research still chose a maximum of 2.8 g/l of both to carry out the study. They had the same concentration levels: 0.7 g/l, 1.4 g/l, 2.1 g/l and 2.8 g/l..