Comparison of the physicochemical property and volatile flavour compounds of yoghurt made from ultra-pasteurised and membrane-filtered milk

In this study, we aimed to compare and contrast the physicochemical and flavour attributes of yoghurt crafted from ultra-pasteurised (UPM-yoghurt) and membrane-filtered milk (MFM-yoghurt). The results indicated that MFM-yoghurt required 1.5 h longer than UPM-yoghurt to reach a pH of 4.5 at the end of fermentation, primarily owing to differences in Streptococcus thermophilus growth and lactoferrin (LF) content. UPM-yoghurt exhibited greater hardness, consistency, and water-holding capacity, resulting in a firmer gel texture. Conversely, MFMyoghurt demonstrated lower viscosity but a smoother texture, possibly due to biologically active components. LF and lactoperoxidase (LPO) were absent in UPM-yoghurt, whereas MFM-yoghurt contained 106.00 mg/L of LF and 2986.25 U/L of LPO. Free amino acid analysis revealed lower levels of umami and bitter amino acids in MFM-yoghurt than those in UPM-yoghurt, while sweet amino acid levels were similar in both. The predominant volatile flavour compounds included aldehydes and ketones, with no significant differences observed in key compounds, such as 2-acetone, ethyl acetate, 3-hydroxy-2-butanone, and 2,3-butanedione, between the two yoghurts. However, notable variations were observed in 41 volatile flavour compounds between the samples, suggesting distinct flavour profiles. This study offers insights and directions for enhancing the nutritional quality of yoghurt.