Expression of a bacterial lee nucleation gene in a yeast Saccharomyces cerevisiae and its possible application in food freezing processes

A 3.6 kb ice nucleation gene (ina) isolated from Erwinia herbicola was plac ed under control of the galactose-inducible promoter (GAL1) and introduced into Saccharomyces cerevisiae. Yeast transformants showed increased ice nuc leation activity over untransformed controls. The freezing temperature of a small volume of water droplets containing yeast cells was increased from a pproximately -13 degreesC in the untransformed controls to -6 degreesC in i na-expressing (Ina(+)) transformants. Lower temperature growth of Ina+ yeas t at temperatures below 25 degreesC was required for the expression of ice nucleation activity. Shift of temperature to 5-20 degreesC could induce the ice nucleation activity of Ina+ yeast when grown at 25 degreesC, and maxim um ice nucleation activity was achieved after induction at 5 degreesC for s imilar to 12 h. The effects of Ina(+) yeast on freezing and texturization o f several food materials was also demonstrated.