PRODUCTION AND PROPERTIES OF 2,3-BUTANEDIOL: VIII. pH CONTROL IN AEROBACILLUS POLYMYXA FERMENTATIONS AND ITS EFFECTS ON PRODUCTS AND THEIR RECOVERY

Abstract

Comparative studies have shown that the pH of 15% wheat mashes fermented by Aerobacillus polymyxa can be as satisfactorily controlled by ammonium hydroxide as by calcium carbonate. The formation of 2,3-butanediol and ethanol was unaffected by all pH levels tested (5.8, 6.0, 6.5, 7.0) with the possible exception of pH 7.0, where a slight diminution of diol formation appeared at 96 hr. Over the pH range 5.8 to 6.0, the amount of ammonium hydroxide required, the escape of ammonia from the mash, and the production of acid were all minimized. The consumption of ammonia was greatest in the first 36 hr. of the fermentation owing to rapid acid production. Fermentation at the different pH levels did not affect the butanediol–ethanol ratio, which was approximately 1.5.Replacement of calcium carbonate by ammonium hydroxide reduced the ash content of the unfermented residue from approximately 20 to 4%. Protein contents (N × 5.7) of insoluble residues from carbonate and ammonia treated washes were 25 and 32%, respectively. In both mashes approximately 50% of the unfermented solids were soluble.Calculation of carbon balances on fermentables showed that increased acid production was accompanied by a decrease in carbon dioxide formation.Riboflavin and nicotinic acid contents per 100 gm. of fermented mash averaged 19.2 and 1270 μgm., respectively and were unaffected by pH of fermenting mash and heat treatment at 100 °C. for 10 hr. The riboflavin showed an 80% increase over that present in the original wheat; nicotinic acid showed a 40% decrease.