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Associative Action as a Cause of Yellow Color in Yeast Colonies

Dairy Section, Iowa Agricultural Experiment Station, Ames, Iowa

ABSTRACT

The data presented show that A. niger growing near to or in contact with certain yeast colonies on whey agar slopes or plates resulted in the yeast colonies showing an intense yellow instead of the usual white color. This condition occurred with a number of different yeasts common in dairy products, but not with all of those studied. The mechanism of this color production was not worked out, but it is probably rather complex since neither organism growing in contact with killed cultures of the other produced the yellow color.

The species of Aspergillus other than A. niger which were tried did not yield a yellow color when grown with yeasts that did give a yellow color with A. niger.

It seems that the associative action of yeasts and A. niger may be responsible for the yellow color occasionally observed with such products as cheese.