چكيده لاتين
Esters derived from alcohols and carboxylic acids constitute a large group of value-added chemicals that typically have fruity flavors and aromas and have numerous applications. In particular, butyl butyrate is known for its unique fruity scent, resembling pineapple and banana. In nature, butyl butyrate is commonly found in flowers, fruits, and fermented beverages. Therefore, butyl butyrate is used as a flavoring and aromatic compound in the beverage, food, fragrance, and cosmetic industries. Additionally, butyl butyrate serves as a solvent in the plastics, textiles, and fiber industries and as an important extractant in petroleum product processing.
In recent years, esters have gained attention as a potential biofuel due to their flammable nature. The enzymatic esterification process of butanol and butyric acid in the presence of lipase enzyme has been introduced as a "bridge" for the renewable production of this important ester from carbohydrate sources. However, this process is an equilibrium reaction, and shifting the equilibrium requires the separation of the ester from the reaction medium, which can be achieved through solvent extraction.
In this study, a multi-step simultaneous process was developed, including (1) the production of butanol and butyric acid, (2) the enzymatic conversion of butanol and butyric acid to butyl butyrate, and (3) the extraction of butyl butyrate into an organic solvent (hexadecane). In this regard, to enhance the production of butyl butyrate and butanol, a co-culture of Clostridium acetobutylicum and Nesterenkonia was utilized. Due to the simultaneous production of butyric acid and butanol during acetone-butanol-ethanol (ABE) fermentation, along with the catalytic role of the lipase enzyme, the equilibrium esterification reaction was driven towards increased butyl butyrate production.
Under optimal conditions (50 g/L enzyme loading and pH adjustment to 5.3 at the beginning of the esterification reaction), 4.79 g/L butyl butyrate was obtained with complete consumption of 40 g/L glucose as the primary substrate. In examining other influencing factors, an increase in the initial pH of the esterification reaction from 5.3 to 6.2 resulted in a decrease in butyl butyrate production, with an optimal enzyme loading of 25 g/L. Additionally, fermentation with co-culture and equilibrium esterification was performed on starch, xylose, and pectin substrates, yielding acceptable results compared to glucose.
