Influence of Fat Concentration on the Volatile Production in Model Whey Protein Systems as Affected by Low Frequency Ultrasound

Whey protein systems with varying fat concentrations (WF) of 2, 4, and 6% (w/w) were treated by ultrasound at 20 kHz up to 10 min, which corresponded to energy densities ranging from 9.54 to 190.8 J mL−1, respectively. The volatile compounds produced were extracted by solid phase micro extraction (SPME) and analysed by gas chromatography-mass spectrometry (GCMS). The results showed that hydrocarbons, aldehydes, ketones, esters, and alcohols are the predominant volatiles present within WF mixtures. These volatile compounds primarily derived from lipid oxidation of milk fat or cleavage of fatty acids, while some aldehydes, ethyl acetate, and hexanol derived from both lipid oxidation of milk fat and protein degradation. The fat content had negligible effects on the production of volatile compounds. In contrast, the fatty acids showed insignificant changes within WF systems containing 2% (w/w) fat, while some significant changes were observed with 4% and 6% (w/w) fat containing WF systems. However, the sonication time significantly influenced both the production of volatiles and the changes in fatty acids irrespective of the fat concentration highlighting the influence of both chemical and physical effects generated through acoustic cavitation.