In vitro and in vivo antimicrobial activity of the fumigant, ethyl formate, against bacteria and fungi of date fruits in postharvest phase

Abstract

The search is on for safer alternatives to fumigants like methyl bromide and phosphine, which harm the ozone layer and pose other risks. Ethyl formate is a promising candidate due to its potential antimicrobial and insecticidal action in stored products like date fruits. The susceptibility of date fruits to microbial spoilage is significantly influenced by factors such as moisture content, storage practices, and environmental conditions. In the present study, the in vitro antimicrobial effect of ethyl formate against three microbial species, namely Aspergillus niger F4, Mucor circinelloides YMM22, and Pseudomonas aeruginosa B1 was tested under laboratory conditions. In addition, two common date fruit varieties, semi-dry El-Wady I and the dry Frehi, were fumigated with ethyl formate alone in a laboratory-scale prototype and with a mixture of ethyl formate and CO2 at a semi-industrial scale prototype. Both varieties had an initial moisture content of around 13.40 and 12.48% for El-Wady I and Frehi, respectively. The fumigation was conducted using the optimal concentration of 70 mg/L air for 24 h incubation period. Fumigation with ethyl formate alone or in combination with CO2 significantly reduced the number of viable bacteria and fungi (CFU/g), but the potential for a combined effect with CO2 was not investigated. The percentages of reduction in the fungal count were 78.18 and 90.76% for Frehi and El-Wady I varieties, respectively in a semi-industrial scale prototype. Moreover, the percentages of reduction in the bacterial count were 53.31 and 65.20%, respectively for Frehi and El-Wady I varieties. Ethyl formate showed promise as a natural alternative to control microbial contamination of stored date fruits. Further research suggests that increasing fumigation duration or concentration could provide comprehensive control of microbial pathogens at all stages of development.