Effect of addition of amino acids, treatment with β-galactosidase and use of heat-shocked cultures on the acetaldehyde level in yoghurt

In this study, the biochemical activities of nonviscous and viscous yoghurt starter cultures were investigated. Yoghurt samples produced with nonviscous and viscous cultures, and viscous cultures + methionine (10 and 30 mg/100 mL milk), + threonine (5 and 10 mg/100 mL milk), + beta-galactosidase (1 mg/100 mL milk), and with a heat-shocked culture were analysed. In the experimental yoghurts, the pH, titratable acidity, lactic acid, tyrosine and acetaldehyde contents and the number of total starter organisms were determined. According to the results obtained, the samples produced with the viscous culture had the lowest acetaldehyde levels, whereas the highest acetaldehyde level was found in the samples manufactured with the nonviscous culture. Compared with the samples inoculated with the viscous culture alone, the amino acid supplementation, lactose hydrolysis and heat-shock treatments caused a significant increase in the level of acetaldehyde.