Investigating the effect of acoustic waves on spoilage fungal growth and shelf life of strawberry fruit

Abstract

The effects of acoustic waves on growth inhibition of food spoilage fungi (Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus and Botrytis cinerea) on the medium and strawberry surfaces were investigated. Firstly, single-frequency sound waves (250, 500, 1000, 2000, 4000, 8000, 12,000 and 16,000 Hz) were induced on inoculated medium with fungi spores for 24 h and growth diameter of each mold was evaluated during the incubation period. In the second stage, the sound waves with two frequencies of 250 Hz and 16,000 Hz were induced on inoculated strawberries with fungi spores at 5 °C for different times (2, 4, 6, 8 and 10 days). The results from the first stage indicated that the sound waves inhibited the growth of A. niger (20.02%) at 250 Hz and B. cinerea (4/64%) at 4000 Hz on potato dextrose agar (PDA) surface. Also, comparison of the growth diameter of some species of Aspergillus revealed various responses in presence of 250 Hz frequency. In the second stage, applying a frequency of 250 Hz over a period of 10 days proved to be more effective in inhibiting the growth of A. niger and B. cinerea on strawberries inoculated with fungal spores. Consequently, the shelf lives of the strawberries significantly increased to 26 days and 18 days, respectively, under this treatment. Based on the findings, it is concluded that sounding with acoustic waves can be used as a green and cheap technology along with other technologies to improve food safety.

Keywords: Aspergillus flavus; Aspergillus niger; Aspergillus parasiticus; Botrytis cinerea; Shelf life; Sound waves.