Impact of <i>Botrytis cinerea</i> on γ-Nonalactone concentration: analysis of New Zealand white wines using SIDA-SPE-GC-MS

Noble rot, caused by infection of grapes with the fungus Botrytis cinerea, is commonly used in the production of dessert-style white wines, imparting desirable aroma descriptors, including dried fruit, honey, and stone fruit. γ-Nonalactone is an aroma compound that is ubiquitous in wine yet has been overlooked in literature for some time. Previously, this compound has been found in higher concentrations in noble rot wines. New Zealand (NZ) is world-renowned for its high-quality white wines, particularly Sauvignon blanc; however, limited research has been carried out on the aroma features of wines produced in lower volumes, such as botrytised dessert styles, and those produced from aromatic grape varieties such as Riesling. Therefore, this work quantified γ-Nonalactone concentrations in 38 NZ commercial white wines, representing botrytised (18) and non-botrytised (20) styles, using SIDA-SPE-GC-MS. These wines were selected to represent a cross-section of NZ white wines, made from Sauvignon blanc, Riesling, and Sauvignon-Sémillon blends, and derived across a range of vintages (2014–2021), and NZ wine regions (Central Otago, Gisborne, Hawke’s Bay, Marlborough, Waiheke Island, Waipara Valley, and Wairarapa). Multivariate data analyses were carried out using vitivinicultural data from wine producers, wine, and measured technical parameters and γ-Nonalactone concentrations. Analyses revealed that γ-Nonalactone concentration was significantly higher in botrytised wines (p-value = 3 × 10-8), with a maximum of 43.5 µg L-1, compared to a maximum of 8.7 µg L-1 in the non-botrytised samples. No significant associations were found between γ-Nonalactone concentration and region or grape variety, suggesting that the precursors to γ-Nonalactone are produced by B. cinerea itself, or through alterations in grape metabolism induced by B. cinerea. Additional research is needed to elucidate the mechanism(s) by which noble rot leads to higher γ-Nonalactone concentrations in wines.