Inhibition of the growth of grain-storage molds in vitro by the yeast Pichia anomala (Hansen) Kurtzman

Abstract

The potential use of yeasts to control grain-storage molds was evaluated by coculturing the yeast Pichia anomala with Penicillium roqueforti and Aspergillus candidus on agar plates, using different temperatures, water activities (aw), and nutrient concentrations. Addition of 10 ppm cycloheximide to malt-extract agar inhibited Pichia anomala completely without affecting mold growth, making it possible to quantify the inhibition as a reduction in colony-forming units (cfu). For A. candidus, numbers of cfu and hyphal lengths were reduced at an initial yeast concentration of 104 cells/plate and reduced below detection limit at 108 cells/plate. A clear reduction in growth of Penicillium roqueforti was only observed at 108 yeast cells/plate. The antagonistic effect was generally more pronounced at low (6, 15 °C) and high (30, 37 °C) temperatures than at ambient ones. Pichia anomala inhibited growth of both molds more strongly in a substrate-rich medium than in a medium with a low substrate content. In water agar (low substrate concentration) the degree of inhibition of Penicillium roqueforti was larger at 0.96 aw than at 0.98 aw.Key words: biological control, Aspergillus candidus, Penicillium roqueforti.