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Autolysate of Whey-Grown Kluyveromyces fragilis As a Substitute for Yeast Extract in Starter Culture Media

Department of Microbiology

James W. Ayres

School of Pharmacy Oregon State University, Corvallis 97331-3804

ABSTRACT

Autolysates prepared from cells of Kluyveromyces fragilis grown in deproteinized and supplemented whey medium were used to replace commercial yeast extract in an industrial bulk starter medium formulation (PHASE 4). Lactic streptococcal cell count and acid production in this medium, as well as acid production upon subsequent transfer to nonfat milk at 1 and 2%, were used as criteria for evaluation of yeast autolysates. Among seven strains tested, Kluyveromyces fragilis NRRL Y-610 produced the highest quality autolysate. Initial pH of 5.5 and temperature of 55°C were suitable for autolysis of this strain, which was carried out for 12 h without agitation, from initial solids 15%. The product showed a concentration-dependent effect on lactic streptococcal growth and acid production and compared favorably with commercial yeast extract.