The Glutathione Content of Grape Berries Is Reduced by Fumigation With Methyl Bromide or Methyl Iodide

¹ Department of Viticulture and Enology, University of California, Davis, CA 95616
² Kern County, Bakersfield, CA 93303.

The mean glutathione content of 26 Thompson Seedless clusters collected from a single vineyard in Chile was 34 µg/g fresh weight (sd = 7.8, range = 20.6 to 48.3 µg/g). Clusters of Thompson Seedless grapes from four separate Chilean vineyards were taken immediately after harvest and shipped by air freight to the United States. They were fumigated with methyl bromide to meet import regulations. These fruit contained less than 10% of the original glutathione content. It was suspected that methyl bromide fumigation was responsible for the decline in glutathione in the berries, since this fumigant reduces the glutathione content of other products. Experiments conducted with methyl iodide as a model compound demonstrated that fumigation with this methyl halide reduced grape berry glutathione content by 85%. Methyl bromide under simulated commercial conditions had a similar effect. The results are discussed with regard to possible direct or indirect effects that glutathione may have on internal browning of Thompson Seedless table grapes and how the decline in glutathione caused by methyl bromide fumigation might influence the disorder.

Key words: fumigation, glutathione, internal browning, methyl bromide, methyl iodide, storage

Submitted on December 20, 1991