Table grapes are a nonclimacteric fruit with a low rate of physiological activity (Peynaud and Ribereau-Gayon, 1971) but are subject to serious water loss and decay during postharvest handling (Nelson, 1985). Gray mold caused by the fungus Botrytis cinerea and rachis browning as a result of desiccation are the two main factors that reduce table grape postharvest quality (Nelson, 1985). The means for preventing decay during storage is the use of sulfur dioxide (SO2), which was first tried in 1925 (Winkler and Jacob, 1925). In subsequent years, a SO2-releasing pad was developed that consists of sodium metabisulfite grains enclosed in paper–plastic pockets inside a pad. Since the late 1960s a two-stage or dual-release (DR) SO2 generator consisting of formulations that allow quick release plus slow release of the gas have been widely used for table grape storage and transport (Nelson and Ahmedullah, 1976). The DR pad contains sodium metabisulfite enclosed between paper sheets of differing permeability. Moisture within the package of grapes is absorbed by the pads and reacts with the sulfite, releasing SO2. The quick-release part of the pad gives a flush of SO2, which peaks after ≈24 h and then diminishes in ≈1 week. The slow-release part of the pad emits a low concentration of SO2 over a long period. Laminated pads are a further development in which the salt is impregnated between polymers.
Of interest is how the generator pads behave in different packaging systems. In South Africa, it has been shown that a SO2 concentration around the grapes of 10 to 20 ppm is safe and effective (Laszlo et al., 1981). It was found that concentrations of less than 7 ppm in the fruit did not control decay if the storage temperature fluctuated above 0 °C and that concentrations higher than 20 ppm could injure the grapes by bleaching. Therefore, an SO2 concentration of 7 to 10 ppm was recommended for long-term storage of grapes (Laszlo et al., 1981).
There are two main concepts in use for packing grapes for extended storage: packing with a SO2 generator pad and fumigation of cold storage chambers with SO2. In the United States during static cold storage, the grapes are subjected to an initial fumigation with SO2 during forced-air cooling and then given weekly fumigations during storage. Packaging with SO2 pads is used for both exporting and static storage in other countries (Lichter et al., 2006). One method of packaging is to pack the grapes with an SO2 generator inside a perforated liner in a box. The liner limits moisture loss from the rachis and berries, and the perforations prevent the humidity from causing water condensation on the grapes. However, this method slows the rapid cooling of the grapes after harvest. A second method is to pack the grapes in a box with an SO2 generator pad, arrange the boxes on a pallet, rapidly cool the grapes to 4 °C or below, and after they have been in the cold for 1 d, to wrap the pallet with linear low-density polyethylene (LLDPE) on all sides and the top, leaving the bottom of the pallet unwrapped. This wrapping process is mechanized and allows for rapid cooling of the grapes. There is greater free air space inside the resulting large package.
The SO2 generator pads were developed for use in liners inside boxes. The two methods of packing were compared for grape quality during sea shipment and storage for a period of 3 weeks and were found to be comparable (Ben-Arie et al., 1984). However, in recent years, late-season grapes such as ‘Redglobe’, harvested in September, are being stored for longer periods. In these cases, it is important to find the best method of packaging that will minimize water loss while preventing the decay that would occur if the SO2 level was too low or the SO2 damage that would occur if it was too high. The purpose of the present study, therefore, was to compare two methods of packaging table grapes destined for storage: boxes with perforated liners and palletized boxes wrapped with LLDPE. In addition, in some trials, the dual-release SO2 pad was compared with a laminated pad. The kinetics of SO2 concentration in the atmosphere around the grapes were monitored, and the quality of the grapes after storage and holding for 3 d at 20 °C was examined. The SO2 generators used were commercially available dual-release and laminated pads. Three grape cultivars were examined, ‘Redglobe’, ‘Thompson Seedless’, and ‘Zainy’, and the storage periods in different experiments ranged from 33 to 117 d.
Association of Official Analytical Chemists International 2005 Sulfites in foods—Optimized Monier-Williams. Method 990.28 18th ed AOAC International Gaithersburg, MD
Ben-Arie, R., Haas, A., Shoshani, Z., Bar-Lev, E., Zeidman, M. & Zutkhi, Y. 1984 The effect of pre-cooling ‘Perlette’ table grapes wrapped in various plastic films on their keeping quality during air or sea export HaSadeh 64 1380 1387 (in Hebrew).
Crisosto, C.H., Smilanick, J.L., Dokoozlian, N.K. & Luvisi, D.A. 1994 Maintaining table grape post-harvest quality for long distant markets Int. Symp. Table Grape Production Soc. Enol. Viticult. 1 195 199
Harvey, J.M., Harris, C.M., Hanke, T.A. & Hartsell, P.L. 1988 Sulfur dioxide fumigation of table grapes: Relative sorption of SO2 by fruit and packages, SO2 residues, decay and bleaching Amer. J. Enol. Viticult. 39 132 136
Laszlo, J., Combrink, J.C., Eksteen, G.J. & Truter, A.B. 1981 Effect of temperature on the emission of sulphur dioxide from gas generators for grapes Deciduous Fruit Grower 31 112 119
Lichter, A., Gabler, F.M. & Smilanick, J.L. 2006 Control of spoilage in table grapes 5 Aug. 2007 <http://www.stewartpostharvest.com/December_2006/Lichter.pdf>.
Lichter, A., Zutahy, Y., Kaplunov, T., Aharoni, N. & Lurie, S. 2005 The effect of ethanol dip and modified atmosphere on prevention of botrytis rot of table grapes HortTechnology 15 284 291
Marois, J.J., Bledsoe, A.M., Gubler, W.D. & Luvisi, D.A. 1986 Control of Botrytis cinerea on grape berries during postharvest storage with reduced levels of sulfur dioxide Plant Dis. 70 1050 1052
Nelson, K.E. & Ahmedullah, M. 1976 Packaging and decay control system for storage and transit of table grapes for export Amer. J. Enol. Viticult. 24 74 79
Palou, L., Crisosto, C.H., Garner, D., Basinal, L.M., Smilanick, J.L. & Zoffoli, J.P. 2002 Minimum constant sulfur dioxide emission rates to control gray mold of cold-stored table grapes Amer. J. Enol. Viticult. 53 110 115
Peynaud, E. & Ribereau-Gayon, P. 1971 The grape 172 206 Hulme A.C. The biochemistry of fruits and their products Academic Press New York
Smilanick, J.L., Hartsell, P.I., Henson, D.J., Fouse, D.C., Assemi, M. & Harris, C.M. 1990 Inhibitory activity of sulfur dioxide on the germination of spores of Botrytis cinerea Phytopathology 80 217 220
Smilanick, J.L. & Henson, D.J. 1992 Minimum gaseous sulphur dioxide concentrations and exposure periods to control Botrytis cinerea Crop Prot. 11 535 540
Zutkhi, Y., Kaplunov, T., Lichter, A., Ben Arie, R., Lurie, S., Kosto, I. & Raban, E. 2001 Extended storage of Redglobe grapes Acta Hort. 553 617 618