SUMMARY: The nutritional requirements for high conversion of sugar to citric acid in shaken flask fermentations were investigated for the mutant strain 72--44 of . Single variable and factorial experiments were used to determine the effects of nitrogen, phosphorus, magnesium, manganese, copper, zinc and iron on the yield of citric acid. When 2% (v/v) peanut oil was added to the fermentation media it markedly improved the yield of citric acid. Two media were devised which yielded on average 10--10°5 g. anhydrous citric acid from 14 g. sugar, with occasional yields as high as 13 g. Both media contained 2% (v/v) peanut oil and the following trace metals (mg./l.): Fe 2°0; Cu 0°3; Zn 0°1. In medium A the major nutrients were (g./l.): ion-exchange purified cane sugar, 140; KHPO, 1°0; MgSO.7HO, 0°25; NHNO, 1°87; and in medium B (g./l.): ion-exchange purified cane sugar, 140; KHPO, 0°3; MgSO.7HO, 0°15; NHNO, 1°4. Interactions were found between: zinc and iron, nitrogen and iron, nitrogen and phosphorus. The implications of these findings for the fermentation of crude sugar substrates in citric acid production are discussed.


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