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

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 a_w (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 a_w than to AP. At 0.90 and 0.85 a_w 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 a_w 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 a_w. 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.