Sulfur Dioxide Fumigation of Table Grapes: Relative Sorption of SO₂ by Fruit and Packages, SO₂ Residues, Decay, and Bleaching

Abstract

Table grapes are fumigated with SO₂ to control decay during storage and marketing. The efficacy of the treatment is affected by the type of packaging material used. Most fumigation schedules in commercial use were developed for grapes packed in wooden or wood/kraft veneer (WKV) boxes. In laboratory experiments, grapes packed in expanded polystyrene foam (EPF) boxes sorbed ca 50% less SO₂ as did those in WKV boxes; grapes packed in fiberboard boxes sorbed ca 50% more SO₂ than did those in WKV boxes. Adjusted fumigation dosages were developed that compensated for sorption by packaging materials and provided comparable concentration x time (CT) products in the fumigation chamber. Free SO₂ residues in grapes packed in the three types of boxes and treated with the adjusted dosages were similar (0.11 - 0.13 µg/g); total SO₂ residues were 2.3, 1.8, and 1.0 µg/g in grapes packed in WKV, EPF, and fiberboard boxes, respectively. All residues were below a proposed tolerance of 10µg/g. The adjusted schedules had comparable effects on decay control, stem condition, and bleaching of the berries.