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

Abstract

Six kilograms of Emperor grapes (<i>Vitis vinifera</i> L.) were packed in vented corrugated cartons with a bottom excelsior cushion pad, then inoculated with berries infected with <i>Botrytis cinerea</i> 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 (<i>V. vinifera</i> 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.