The generation of volatiles in model systems containing varying casein to whey protein ratios as affected by low frequency ultrasound

Abstract

The application of low frequency ultrasound has been intensively explored within the dairy field to improve product properties and processing efficiency over conventional treatments. However, the generation of undesirable volatile compounds during sonication can negatively influence the uptake of this technique within the dairy industry. Therefore, the present study was attempted to investigate the formation of volatile compounds in model milk systems containing 4% w/w fat and 3.5% w/w milk proteins with varying ratios of casein to whey proteins (50:50, 60:40, 80:20) as affected by low frequency ultrasound (20 kHz). The samples were treated for 1 and 10 min which were corresponding to energy densities of 9.54 J ml−1 and 190.8 J ml−1, respectively. The generation of volatile compounds was mainly influenced by the sonication time for all milk samples irrespective of the casein to whey ratios. The fatty acid chains and ester groups of milk fat and lipid-protein complexes increased with the increase in sonication time for all samples regardless of the casein to whey ratios. In contrast, milk proteins altered their secondary structure with an increase in random coil structure and concomitant decrease of α-helix, β-turn and β-sheet as affected both by sonication time and casein to whey ratios.