Quality of two table grape guard cultivars treated with single or dual-phase release SO₂ generators

Abstract

Berries of seeded table grapes (cultivars Napoleón and Aledo) were trimmed in commercial packing houses, inoculated with Botrytis cinerea, packed with single and dual-phase release SO₂ pads, and stored for up to four months at 0 ºC and 85±5 % relative humidity. Control grapes with or without inoculation, but without SO₂ pads, were stored for up to 2 months. Botrytis cinerea rot (grey mould) limited the shelf-life of Aledo grapes to one month, while a two month shelf-life was established for Napoleón grapes, which suffered from berry splitting, Cladosporium herbarum and Botrytis cinerea rots. Yeasts of the Candida genera and secondary fungi were also identified in fruit suffering sour rot after 2 months at 0^oC. No differences in grey mould development in the treatments without SO₂ pads with or without inoculation. The native grey mould of these grapes was purified and included as the B. cinerea strain 20248 in the Spanish Type Culture Collection. Storage time, but not SO₂ pads, slightly affected fruit quality. During the first month at 0^oC, total soluble solids decreased by 1^oBrix in 'Áledo' and berry hardness temporarily increased by around 30% in both cultivars. The pads provoked an SO₂ taste acceptable for consumption, which was slightly higher in Napoleón than in Aledo grapes. The dual-phase release SO₂ pads showed better performance for the long-term storage of grapes than single-release pads (both as regards berry sensory attributes and stem appearance, with lower stem browning). The dual-phase release SO₂ pads extended the shelf-life of grapes by around 1 month, depending on the cultivar. Napoleón grapes showed a better potential for longterm storage than Aledo grapes due to thicker and more compact epidermis, thicker cell walls, and different epidermal microstructure including the transition cells between epidermis and the parenchyma.