Fermentation higher carboxylic acids

Cachaqa and aguardente de cana are the most consumed distilled spirits in Brazil exclusively made from cane-sugar juice. Sugar and caramel maybe added for colour adjustment. The total content of congeners is between 200 and 650 mg 0.1 L p.e. Like other spirits, the flavour of cacha a is mainly characterised by the presence of fermentation by-products such as higher alcohols, esters, carboxylic acids, and carbonyl compounds [41-43]. 

Acetic acid is a weak carboxylic acid with a pungent odor that exists as a liquid at room temperature. It was probably the first acid to be produced in large quantities. The name acetic comes from acetum, which is the Latin word for sour and relates to the fact that acetic acid is responsible for the bitter taste of fermented juices. Acetic acid is produced naturally and synthetically in large quantities for industrial purposes. It forms when ubiquitous bacteria of the genera Acetobacter and Clostridium convert alcohols and sugars to acetic acid. Acetobacter, especially Acetobacter aceti, are more efficient acetic acid bacteria and produce much higher concentrations of acetic acid compared to Clostridium. 

Besides these simple fermentation alcohols, the yeast also forms higher alcohols as side products, "fusel oils," that have intense odors and play a role in wine aroma. Other components are carboxylic acids, such as tartaric and malic acids, that are important as "life-insurance" during aging of the wine. Some of the aromas perceived in wines stem from esters... 

Although increasing the catalyst concentration results in the faster overall reaction rate, enhanced rate of racemization, which is unwanted in the production of optically pure lactide may also occur. Higher synthesis temperatures, longer reaction times and presence of some metal cations such as sodium and potassium have the same effect on the stereochemical purity of the crude lactide [14, 15, 19]. Released metals through corrosion and carboxylic acid impurities formed during lactic acid fermentation are other sources of impurities [10,14, 20-22]. 

Acetic acid is sometimes mentioned as an important inhibitor (47, 48). Since acetic acid has a dissociation constant of 4.75 in water, it will be partly dissociated at a pH of 5-5.5 (typical values for the fermentation). It is generally accepted that the effect of the undissociated part of the acid is larger than the effect of the dissociated part (49). The undissociated carboxylic acids can diffuse through the cell membrane (50, 51). Since the intracellular pH is higher than diat of the extracellular medium (52), the undissociated acid which has diffused into die cell is partly dissociated into acetate and hydrogen ions, thereby potentially lowering the intracellular pH (53, 54). The optimum extracellular pH for growth... 

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