BIOCONTROL OF MOULDS OF CEREAL GRAINS DURING STORAGE BY THE YEAST PICHIA ANOMALA
J SCHNORER1, S PETERSSON1 and N JONSSON2
1Department of Microbiology, Swedish University of Agricultural Sciences, Box 7025, S-750 07 Uppsala, Sweden; 2Swedish Institute of Agricultural Engineering, Box 7033, S-750 07 Uppsala, Sweden
Background and objectives
Hot-air drying is commonly used to prevent mould growth in cereal grains. This is however very expensive in a temperate climate. Alternatively, grain can be stored moist in airtight silos where microbial growth is prevented by decreased oxygen and increased carbon dioxide levels, caused by respiration from the epiphytic microflora and grains. Air exchange between the silo and the atmosphere due to imperfect sealing, temperature fluctuations and grain removal makes it difficult to maintain these conditions. Yeast and mould interactions in the grain sometimes lead to complete dominance by the yeast Pichia anomala. This suggested a possibility of using this species for biocontrol of moulds.
Results and conclusions
The yeast inhibits growth of all investigated mould species in agar. In test tubes with restricted air supply an initial inoculum of between 104 and 105 P. anomala cells per g wheat completely inhibited growth of Penicillium roqueforti at temperatures between 10-30°C. Part of the inhibition may be explained by rapid yeast growth and consumption of available nutrients and oxygen. Similar inhibition patterns were observed with wheat, barley and oats, but differences in substrate quality influenced the outcome of the yeast/mould interaction. Ochratoxin A accumulation from Penicillium verrucosum was more sensitive to the presence of yeasts than mould growth. Co-cultivation with P. anomala never gave any detectable stimulation of ochratoxin A accumulation in agar or wheat. P. anomala was efficient as an inhibitor of mould growth also when applied in silos with 160 kg wheat (aw 0.94) stored outdoors during one year. The aerobic stability of grain removed from the silos and exposed to oxygen, i.e. the time to reach 105 c.f.u. of P. roqueforti, increased from 6 to 12 days in P. anomala-inoculated wheat. The yeast P. anomala thus seems to be a promising biocontrol agent, able to safeguard the microbial quality during airtight storage of high-moisture feed grains.