Impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria

Aims To investigate the impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria (LAB). Methods and results Growth studies were performed where Oenococcus oeni, Pediococcus parvulus, Ped. damnosus and Lactobacillus hilgardii were inoculated into media containing various concentrations of acetaldehyde or pyruvic acid and an equimolar concentration of SO(2) at pH 3.50 and 3.70. Low concentrations of acetaldehyde- and pyruvic acid-bound SO(2) were inhibitory to the growth of all bacteria although acetaldehyde-bound SO(2) was generally more inhibitory than pyruvic acid-bound SO(2). Inhibition was greater at pH 3.50 than 3.70, and Lact. hilgardii was the most sensitive to acetaldehyde-bound SO(2), while O. oeni was the most sensitive to pyruvic acid-bound SO(2). Degradation of SO(2)-bound acetaldehyde was observed for all LAB, and aside from O. oeni, there was also complete degradation of SO(2)-bound pyruvic acid at both pH values. O. oeni only degraded pyruvic acid at pH 3.70. Degradation of SO(2)-bound acetaldehyde or pyruvic acid did not correlate with bacterial growth as inhibition was always observed in media containing bound SO(2). Conclusions Acetaldehyde- and pyruvic acid-bound SO(2) were inhibitory to wine LAB growth at concentrations as low as 5 mg l(-1). Despite this inhibition, all wine LAB degraded SO(2)-bound acetaldehyde and pyruvic acid suggesting that bound SO(2) may have a bacteriostatic rather than bacteriocidal action. Significance and impact of the study Sulphur dioxide bound to acetaldehyde or pyruvic acid is inhibitory to growth of wine LAB and must be considered when conducting the malolactic fermentation or controlling the growth of spoilage bacteria such as Pediococcus and Lactobacillus.