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Douglas D. Archbold, Thomas R. Hamilton-Kemp, Ann M. Clements and Randy W. Collins

Seedless table grapes (Vitis vinifera L.) cv. Crimson Seedless were exposed to (E)-2-hexenal vapor during cold storage to determine its potential as a fumigant for long-term control of postharvest mold. Fruit were fumigated with 0.86 or 1.71 mmol (100 or 200 μL neat compound, respectively) (E)-2-hexenal per 1.1-L container for 2 weeks during 2 °C storage. Containers were moved to 20 °C storage after 4, 8, and 12 weeks for determination of mold incidence and berry quality over 12 days. The headspace concentration of (E)-2-hexenal, measured by gas chromatography, reached a maximum of 2.5 and 4.2 μmol·L–1 for 0.86 and 1.71 mmol per container, respectively, after 1 day and declined to <1 μmol·L–1 for both treatments by 14 days. Upon removal from cold storage at 4, 8, and 12 weeks, the incidence of mold was significantly lower for (E)-2-hexenal–treated fruit. Control of mold by (E)-2-hexenal fumigation persisted through 12 days of 20 °C storage, even though mold generally increased in all treatments. The two levels of (E)-2-hexenal were similar in their suppression of mold. Fumigation did not affect O2 or CO2 concentrations within the containers, nor were fruit firmness or soluble solids content affected. Postharvest fumigation of seedless table grapes with the natural volatile compound (E)-2-hexenal shows promise for control of mold.

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Elazar Fallik, Douglas D. Archbold, Thomas R. Hamilton-Kemp, Ann M. Clements, Randy W. Collins and Margaret M. Barth

Some plant-derived natural volatile compounds exhibit antifungal properties and may offer an opportunity to control the causes of postharvest spoilage without affecting quality of, or leaving a residue on, fresh produce. The natural wound volatile (E)-2-hexenal has exhibited significant antifungal activity in earlier studies, but effects on spore germination and mycelial growth have not been separated, nor has the inhibitory mode of action been determined. To determine the efficacy of (E)-2-hexenal for control of Botrytis cinerea Pers. ex Fr. spore germination and mycelial growth, and to examine the mode of action, in vitro and in vivo studies were performed. Under in vitro bioassay conditions, spore germination was more sensitive to the compound than was mycelial growth. Vapor from 10.3 μmol of (E)-2-hexenal in a 120-mL petri dish completely inhibited spore germination. However, 85.6 μmol of (E)-2-hexenal was required to completely inhibit mycelial growth. Lower concentrations of the compound (5.4 and 10.3 μmol) significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Mycelial growth did not occur as long as the vapor-phase concentration was 0.48 μmol·L-1 or greater. Light microscopy analysis indicated that a high concentration of volatile compound dehydrated fungal hyphae and disrupted their cell walls and membranes. Exposure of B. cinerea-inoculated and non-inoculated strawberry (Fragaria ×ananassa Duch.) fruit in 1.1-L low-density polyethylene film-wrapped containers to vapor of (E)-2-hexenal at 85.6 or 856 μmol (10 or 100 mL, respectively) per container for durations of 1, 4, or 7 days during 7 days of storage at 2 °C promoted the incidence of B. cinerea during subsequent shelf storage at 20 to 22 °C. Loss of fruit fresh mass and fruit firmness during storage at 22 °C was increased by (E)-2-hexenal treatment, but fruit total soluble solids, pH, titratable acidity, and color (L, C, and H values) were not affected. Thus, maintenance of a high vapor-phasel level of (E)-hexenal, perhaps >0.48 μmol·L-1, may be necessary to inhibit mycelial growth and avoid enhancing postharvest mold problems, while significantly higher levels may be necessary to completely eliminate the pathogen.