Effects of In-Package Sulfur Dioxide Generators, Package Liners, and Temperature on Decay and Desiccation of Table Grapes

Abstract

Six kilograms of Emperor grapes (Vitis vinifera L.) were packed in vented corrugated cartons with a bottom excelsior cushion pad, then inoculated with berries infected with Botrytis cinerea Pers. The packs were either not treated with SO₂ or given an initial SO₂ room fumigation or provided with a quick-release (QR) in-package SO₂ generator (1.5 g NaHSO₃ affixed to a paper sheet) placed on top of the fruit. In some cartons, an unvented polyethylene liner enclosed the cushion pad, fruit, and a QR generator. After six days at 25°C, untreated vented packs with no poly liner had 90% decayed berries, those that had been room fumigated 55%, and those with the generator 80%. The stems of these packs were very dry and brown and the berries very soft from desiccation. Grapes in the unvented poly liners had 1% decayed berries, and stems were still plump and green and the berries fairly turgid. Unvented packs held for six days at 10° C and at O°C had respectively 1% and 0% decayed berries, and the condition of the packs was rated respectively good and excellent. Inoculated Thompson Seedless grape packs (V. vinifera L.) held at 25°C in unvented poly liners with a QR generator had no decay until the fourth day. Grapes with a modified QR generator (2.7 g NaHSO₃) had no decay until the fifth day. Fruit in a poly liner with 6 mm diameter vents on a 112 mm spacing (0.23% vented area) had significantly more decay than that in an unvented liner packed with either the 1.5 or 2.7 g generator. A vented area of 0.92% generally increased decay during six days, but with an area of 3.68% decay was less. Drying and browning of stems and softness of berries was related directly to the amount of vented area. The three SO₂ treatments significantly retarded browning of stems, and the amount of browning was related inversely to dose of SO₂. Weight loss was 0.1% after six days for grapes in an unvented liner, but was 3.75% if the liner had 0.23% vented area. With 0.92% vented area the loss was 4.3% and with a vented area of 3.68% the loss of 6.5%. This last value exceeds signficantly the 5.7% weight loss for the vented Kraft liner.