Identification of undesirable white-colony-forming yeasts appeared on the surface of Japanese kimchi

<p>To identify yeasts involved in white-colony formation on Japanese commercial kimchi products, three types of kimchi were prepared and fermented at four different temperatures. At 4 °C, yeast colonies did not appear until 35 days, while more rapid white-colony formation occurred at higher temperatures (10, 15, and 25 °C). Combination of PCR-DGGE and direct isolation of yeasts from white colonies revealed that <i>Kazachstania exigua</i> and <i>K. pseudohumilis</i> were responsible for the white-colony formation. Inoculation of the isolated <i>Kazachstania</i> strains into fresh kimchi successfully reproduced white-colony formation at 15 °C but not at 4 °C. Growth experiments in liquid medium revealed that <i>Kazachstania</i> spp. grew fast at 15 °C even in the presence of acidulants, which are commonly added to Japanese kimchi products for prevention of yeast growth. These results suggest that white-colony formation on Japanese kimchi is caused by the genus <i>Kazachstania</i>, and that one of important factors determining white-colony formation is its fermentation temperature.</p> <p>Kimchi inoculated with 10<sup>2</sup> CFU g<sup>−1</sup> of <i>Kazachstania pseudohumilis</i> after fermentation at 15 °C for 21 days (left) or at 4˚C for 51 days (right).</p>