Characterization of the culture filtrate of Kluyveromyces thermotolerans IFO 1778 as a killer yeast

Natural preservatives, especially those effective in the presence of NaCl, are desired. To develop such a natural preservative, we examined the killer effect against Z. rouxii of the culture filtrate of Kluyveromyces thermotolerans IFO 1778 strain. This strain was shown to have killer activity against Z. rouxii in the presence of more than 4% NaCl. Its killer activity increased with the increase of NaCl concentration. Killer toxin of IFO 1778 was active in the range of pH 2 to 6 (optimum pH was 4). Killer activity was lost by heating at 40°C for 15min. Polyols had effect to stabilize killer activity. One percent conc. of freeze-dried culture filtrate of koji medium inhibited the growth of Z. rouxii and delayed fermentation. While killer activity was not affected by proteases, it was increased by cellulase treatment.