Factors affecting production of glycerol and D-arabitol by representative yeasts of the genus Zygosaccharomyces.

Osmophilic yeasts have been studied largely with respect to their ability to grow in high concentrations of sugar but, until recently, very little attention has been paid to the kind and amount of products formed. Nickerson (1943) isolated a yeast from sour wine that he classified as Zygosaccharomyces acidifaciens and later, together with Carroll (Nickerson and Carroll, 1945), studied the products formed. Besides ethyl alcohol and carbon dioxide, this yeast produced lactic acid, acetic acid, and high yields of glycerol (up to 22 per cent of the sugar fermented). Spencer and associates (1956a, b; 1957a, b, c; Roxburgh et al., 1956) have investigated this and other species of Zygosaccharomyces specifically for production of glycerol. In addition to glycerol, they found D-arabitol, erythritol, mannitol, and two unidentified polyhydric alcohols. Some or all of these polyhydric alcohols were shown by paper chromatograms to be formed by known species of Zygosaccharomyces and from 79 new strains of yeast isolated from honey and other sources. One of these isolates, identified as Saccharomyces rouxii, was studied in detail with respect to factors favoring glycerol production (Spencer et al., 1957a, c). Yields of glycerol and D-arabitol, each equivalent to around 30 per cent of the glucose, were obtained in flasks and small fermentors. A urea-yeast extract (or corn steep) medium of low inorganic phosphate content, at 37 C temperature, and with adequate aeration, promoted formation of the polyhydric alcohols. Addition of inorganic phosphate depressed the yield of these products. Maximum yields were obtained with 0.0017 M inorganic phosphate and a partial pressure of oxygen, around 400 mm of mercury. The use of oxygen in the fermentation and production of such large quantities of the rare alcohol, D-arabitol, are distinctive features of this work. As part of a broad program of glycerol production for Army Ordnance Corps during the last 6 years, it was decided to include a study of some representative osmophilic yeasts. It is surprising how little information is available regarding the products formed by such yeasts. Lodder and Kreger-van Rij (1952) describe