Effect of alcohols on the mycological production of citric acid in surface and submerged culture. I. Nature of the alcohol effect.

There has been a steady increase in the consumption of citric acid during the past 25 years. An estimate by Cochrane (1948) places annual manufacture at approximately 35 million pounds. Commercial production of citric acid is reputedly based on fermentation by Aspergillus niger of a suitable grade of beet syrup in shallow pans. A submerged process appears to be highly desirable, and many articles and patents (Perquin, 1938; Karow, 1942; Szucs, 1944; Waksman and Karow, 1946; Karow and Waksman, 1947; Shu and Johnson, 1948a, b; Perlman, 1949; Schweiger and Snell, 1949; and Snell and Schweiger, 1949)'have appeared in this field. Proposed procedures all require a source of highly purified carbohydrate and in most cases also the use of oxygen for aeration. Large-scale production of citric acid in submerged culture has not been reported. Several improvements in the submerged culture process are needed. These include the use of less inoculum, greater fermentation speed, and the use of crude, cheap carbohydrate sources. Investigations on these problems have been in progress for several years in the Fermentation Division of this laboratory. It was discovered in the course of the work that the use of low molecular weight alcoholsmethanol, ethanol or isopropanol-as adjuncts to the culture medium greatly increased citric acid production in both surface and submerged culture.2 Such use has made it possible to ferment directly crude carbohydrate substrates which other investigators have found necessary to purify, especially for use in submerged culture. This paper deals with the nature of the alcohol stimulation as related to the presence of trace elements as well as to initial acidity of the medium and to the quantity of inoculum used.