Development of a Rapid On-Site Method for the Detection of <i>Kazachstania servazzii</i> and <i>Candida sake</i> in Kimchi Using Loop-Mediated Isothermal Amplification

Kimchi has recently gained considerable global interest for its health benefits, including its probiotic properties and anticancer and antioxidative effects. However, in the later stages of kimchi fermentation, an increase in the number of yeast species that form a white film on the surface of kimchi, such as <i>Kazachstania servazzii</i> and <i>Candida sake</i>, takes place, which can negatively affect kimchi quality. Thus, we developed loop-mediated isothermal amplification (LAMP) assays for the on-site detection of <i>K. servazzii</i> and <i>C. sake</i> in kimchi. The internal transcribed spacer (ITS) region of 24 yeast strains were aligned to identify the specific region of the target yeasts, after which the LAMP primer for each target species was designed. The developed LAMP primer sets specifically amplified <i>K. servazzii</i> and <i>C. sake</i> and detected 0.4 and 4 pg of <i>K. servazzii</i> and <i>C. sake</i> DNA, respectively. In addition, the limits of detection were 10³ CFU/ml for <i>K. servazzii</i> and 10² CFU/ml for <i>C. sake</i>, respectively. The LAMP methods were validated by applying them to fermented kimchi samples, with the LAMP reactions being completed within 35 min. Overall, we found that the developed LAMP assays had excellent potential to be used for advanced on-site detection of <i>K. servazzii</i> and <i>C. sake</i> due to their specificity, sensitivity, and rapidity.