The effects of two ammonium propionate formulations on growth in vitro of Aspergillus species isolated from hay

Abstract

The efficacy of fully neutralized (AP) and half‐neutralized ammonium propionate (H‐AP) against growth of a number of Aspergillus spp. was determined in vitro on malt extract at different levels of water availability in the range 0.995–0.85 aw (water activity) (= 40–25% water content of hay). In general, Aspergillus flavus, A. fumigatus, A. nidulans, A. niger and A. versicolor were more sensitive to the H‐AP in the range 0.995–0.95 aw than to AP. At 0.90 and 0.85 aw growth of most species occurred in the absence of chemicals but only of a few species in 27 mmol/l AP. All three members of the A. glaucus group tested, A. amstelodami, A. repens and A. sejunctus, were similarly more sensitive to H‐AP over the aw range 0.95–0.85 than to AP. Aspergillus sejunctus was most tolerant, growing in 27 mmol/l H‐AP and 54 mmol/l AP at 0.85 aw. The number of days for growth initiation in 27 mmol/l H‐AP was greater than with AP at different levels of water availability and reflected the different effects of the two chemicals on growth rate.