Gamma Irradiation on Fermentation Mashes Consisting Mainly of Cane Molasses

The application of the radiopasteurization method to fermentation media consisting mainly of molasses was investigated. γ-Irradiation was found to have an excellent pasteurization effect on the fermentation media and at the same time to bring about an increase in the fermentation rate and yield of ethanol. Percent survivals in molasses decreased to ca. 70% by heating at 80°C for 30 min, to ca. 10% by irradiation with 3.0 × 10⁵ rad and to ca. 1% by 6.0 × 10⁵ rad. Irradiated mash was suitable for the medium of the “starter”, since the rate and the degree of the growth of Saccharomyces cerevisiae in irradiated mash did not differ from those of the growth in heat-pasteurized mash.

In the case of the molasses mash supplemented with nitrogen sources, the fermentation rate and yield of ethanol in irradiated mash were larger than those in heated mash. Besides, in the absence of nitrogen sources a 14% difference in fermentation yield was seen between the mash irradiated with 3.0 × 10⁵ rad and the mash heated at 80°C. With the doses ranging from 1.0 × 10⁵ to 9.5 × 10⁵ rad, concentrations of total sugar and direct reducing sugar, pH, and optical density of molasses were little affected by irradiation.