Use of alfalfa residual juice as a substrate for propagation of the red yeast Phaffia rhodozyma

Summary Alfalfa residual juice (ARJ) supported good growth of the yeast Phaffia rhodozyma but formation of astaxanthin was inhibited. Supplementary nutrients did not reverse the inhibition, indicating that the the juice probably contained some inhibitor of astaxanthin biosynthesis. Six strains of P. rhodozyma were tested and found to be susceptible to the inhibitory effects of the juice. Concentrations of ARJ above 1.25% (v/v) were inhibitory to pigmentation of the yeast. Above approximately 3.7%, total inhibition of astaxanthin formation was observed but some chromogenic components of the juice were adsorbed on Phaffia cells and appeared as artefacts in astaxanthin analyses. Phaffia biomass produced in ARJ showed greater susceptibility to autolysis than that produced in a peptone-glucose-salts medium. Supplementation of ARJ with glucose enhanced yield of cell mass and minimised the autolytic phenomenon, and is potentially useful for producing Phaffia biomass for use as a source of single cell protein.Unsupplemented brewer's malt wort and molasses, separately and in a suitable combination, were compared with ARJ and were found suitable for growth and pigmentation of P. rhodozyma.