Analytical and sensorial characterization of the aroma of wines produced with sour rotten grapes using GC-O and GC-MS: identification of key aroma compounds.
ABSTRACT In the present work, the aroma profiles of wines elaborated from sound and sour rot-infected grapes as raw material have been studied by sensory analysis, gas chromatography-olfactometry (GC-O), and gas chromatography-mass spectrometry (GC-MS), with the aim of determining the odor volatiles most likely associated with this disease. The effect of sour rot was tested in monovarietal wines produced with the Portuguese red grape variety Trincadeira and in blends of Cabernet Sauvignon and sour rotten Trincadeira grapes. Wines produced from damaged berries exhibited clear honey-like notes not evoked by healthy samples. Ethyl phenylacetate (EPhA) and phenylacetic acid (PAA), both exhibiting sweet honey-like aromas, emerged as key aroma compounds of sour rotten wines. Their levels were 1 order of magnitude above those found in controls and reached 304 and 1668 μg L(-1) of EPhA and PAA, respectively, well above the corresponding odor thresholds. Levels of γ-nonalactone also increased by a factor 3 in sour rot samples. Results also suggest that sour rot exerts a great effect on the secondary metabolism of yeast, decreasing the levels of volatiles related to fatty acids and amino acid synthesis. The highest levels of γ-decalactone of up to 405 μg L(-1) were also found in all of the samples, suggesting that this could be a relevant aroma compound in Trincadeira wine aroma.
Article: New insights into the ecological interaction between grape berry microorganisms and Drosophila flies during the development of sour rot.[show abstract] [hide abstract]
ABSTRACT: In this work, we studied the ecological interactions between grape berry microorganisms and Drosophila sp. flies involved in sour rot disease during grape ripening. After veráison the total microbial counts of grape berries affected by sour rot increased from about 2 log CFU/g of berries to more than 7 log CFU/g. Berry damage provoked a clear shift in yeast diversity from basidiomycetes to ascomycetous fermentative species. The latter were mostly Pichia terricola, Hanseniaspora uvarum, Candida zemplinina, and Zygoascus hellenicus. However, these species were not able to produce the metabolites characteristic of sour rot (gluconic and acetic acids) in inoculated berries. On the contrary, the acetic acid bacteria Gluconacetobacter saccharivorans produced high levels of these acids, mainly when berries were incubated in the presence of the insect Drosophila sp. Sour rot was not observed when grape bunches were physically separated from insects, even when berries were artificially injured. The wounds made in berry skin healed in the absence of insects, thus preventing the development of sour rot. Therefore, in the vineyard, the induction of sour rot depends on the contamination of wounded berries by a microbial consortium--yeasts and acetic acid bacteria--transported by drosophilid insects which disseminate sour rot among damaged berries. In the absence of these insects, plant defense mechanisms are effective and lead to skin healing, preventing disease spread. Thus, we showed that Drosophila sp. act as a vector for microorganisms associated with grape sour rot disease.Microbial Ecology 03/2012; 64(2):416-30. · 2.91 Impact Factor