Abstract
ABSTRACTThe effect of three levels of hop extract (0.5, 1.5, 2.5%) on the formation of mold colonies in laboratory culture media, adjusted to six levels of water activity between 0.98 and 0.77, was investigated. Nutrient agar plates containing hop extract were inoculated with dilute suspensions of asexual spores of Penicillium and two Aspergilli isolated from intermediate moisture food. The plates were wrapped with a moisture barrier and oxygen permeable film to prevent drying, and incubated at room temperature for 30 days. The data suggest that at levels of 1.5–2.5%, the hop extract inhibited vegetative growth of all three organisms. Reduction in the number of visible colonies was caused independently by both the reduced water activity and the presence of the hop extract. Hop extract inhibited mycelial growth and allowed development of the germ tube. The combined effect of reduced water activity and the addition of hop extract may be usable in imparting biological stability to intermediate moisture foods.
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