Surface disinfection of berry crops with the natural volatile (E)-2-hexenal

We are studying the use of (E)-2-hexenal, a compound naturally produced and metabolized by fresh fruits and vegetables, as a fumigant to reduce 1) the incidence of postharvest disease, and 2) the levels of microorganisms which may cause food safety hazards. In vitro cultures of disease-causing Botrytis cinerea Pers. (gray mold) and human pathogenic organisms such as Escherichia coli 0157.H7 were exposed to the vapors of (E)-2-hexenal. At higher headspace levels, the growth of in vitro cultures was reduced. Fruit, including strawberry, blackberry, and table grape, were inoculated with the same disease and food safety microorganisms and fumigated in film-wrapped packages during cold or room temperature storage. The incidence of postharvest disease was reduced on blackberry and table grape, but the treatment was less successful on strawberry. The population of E. coli O157:H7 on strawberry was lower but not by the desired 5-log reduction in contrast to the effective 5 log reduction on table grapes. To obtain these effects upon the microorganisms, adequate headspace levels of (E)-2-hexenal must be maintained. Gas chromatography-mass spectral analysis of the volatiles in the headspace have shown that all the fruit metabolized (E)-2-hexenal to several other compounds leading to a rapid reduction in the headspace levels and a reduced impact of the compound on the microorganisms. This work shows the potential and some limitations for using (E)-2-hexenal and similar volatile compounds, natural products of fruits and vegetables which are readily metabolized and may leave minimal residues, as postharvest fumigants to reduce the incidence of postharvest disease as well as the presence of microorganisms posing food safety hazards.