Biocontrol of mold growth in high-moisture wheat stored under airtight conditions by Pichia anomala, Pichia guilliermondii, and Saccharomyces cerevisiae

Abstract

Pichia anomala inhibits the growth of Penicillium roqueforti and Aspergillus candidus on agar. In this investigation, antagonistic activity on agar against 17 mold species was determined. The abilities of Pichia anomala, Pichia guilliermondii, and Saccharomyces cerevisiae to inhibit the growth of the mold Penicillium roqueforti in nonsterile high-moisture wheat were compared by adding 103 Penicillium roqueforti spores and different amounts of yeast cells per gram of wheat. Inoculated grain was packed in glass tubes, incubated at 25°C with a restricted air supply, and the numbers of yeast and mold CFU were determined on selective media after 7 and 14 days. Pichia anomala reduced growth on agar plates for all of the mold species tested in a dose-dependent manner. Aspergillus fumigatus and Eurotium amstelodami were the most sensitive, while Penicillium italicum and Penicillium digitatum were the most resistant. Pichia anomala had the strongest antagonistic activity in wheat, with 105 and 106 CFU/g completely inhibiting the growth of Penicillium roqueforti. Inhibition was least pronounced at the optimum temperature (21°C) and water activity (0.95) for the growth of Penicillium roqueforti. Pichia guilliermondii slightly reduced the growth of Penicillium roqueforti in wheat inoculated with 105 and 106 yeast CFU/g. S. cerevisiae inhibited mold growth only weakly at the highest inoculum level. Pichia anomala grew from 103 to 107 CFU/g of wheat in 1 week. To reach the same level, Pichia guilliermondii had to be inoculated at 104 CFU while S. cerevisiae required an inoculum of 105 CFU to reach 107 CFU/g of wheat.