For all dairy samples, headspace glass vials were affixed with inserts for headspace exposition and supplemented with a 1 × 10 −3 g/kg aqueous solution of the internal standard ethyl octanoate (Aldrich Chemical Co., Milwaukee, WI, USA). A polydimethylsiloxane (PDMS)-coated stir bar (0.5 mm film thickness, 10 mm length in liquid samples, and