Effect of raw milk sonication on volatile compounds production

Introduction Among new technologies used to improve milk sanitization and shelf life, the treatment with ultrasounds (US) showed positive effects on bacterial inactivation, although it resulted responsible of some changes on milk sensory properties. The aim of this study was to evaluate the influence of different sonication parameters on volatile compounds production. Methods Ten combination of US wave amplitude (A: 70, 100%) and treatment duration (D: 0 (control), 50, 100, 200 and 300s) were applied to raw milk using a 400W ultrasonic processor, mounted with a 22 mm diameter horn. Solid-phase microextraction (SPME) was performed with a 100 µm Polydimethylsiloxane (PDMS) fibre and GC/MS analysis of volatile compounds adsorbed onto the SPME fibre was carried out taking into account spectra from M/Z 29 to M/Z 500. The experiment was replicated twice and three determinations were carried out per replicate. Data were subjected to analysis of variance using the software PAWS Statistic 18.0. Results Given that the detector response factor for each compound was not determined, the amounts of the 34 volatiles detected are only semi-quantitative and will be therefore used only to discriminate the treatments. Among detected substances, 10 belonged only to sonicated milk, while 13 showed significantly different concentrations (P<0.05) according to the treatment. Discussion Sonication led to changes in the composition of volatile compounds and in particular to the increase of several esters, ketones and aldehydes that could be responsible of milk organoleptic modification. Compounds such as nonanal, n-octyl ether and 2-nonanone increased in concentration with duration of sonication treatment, while the others showed non linear variations. The increment of nonanal, that is formed only in the auto-oxidation of oleic acid, suggests that sonication favours lipid oxidation, probably through the free radical mechanism. Further research is needed to predict sensory properties from volatiles composition.