Changes in carbonyl compounds in Chardonnay and Cabernet Sauvignon wines as a consequence of malolactic fermentation

To study changes in carbonyl compounds in Chardonnay and Cabernet Sauvignon wines as a consequence of malolactic fermentation (MLF), wines were fermented by inoculation of commercial strains of Oenococcus oeni, and compared with unfermented (control) wines. Carbonyl compounds were determined by GC/MS analysis on the basis of their O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine derivatives after sample preparation on an ion exchange column to remove pyruvic acid. With MLF, marked changes were revealed, particularly with regard to diacetyl, acetoin and aliphatic saturated aldehydes; the presence of unsaturated aldehydes was also revealed. A significant increase in glycoladehyde was observed, which is presumed to be part of a reduction system with glyoxal. Higher acetoin/diacetyl ratios were found in Chardonnay and higher glycolaldehyde/glyoxal ratios in Cabernet Sauvignon.