Quantification of progesterone in beef with marbling using liquid chromatography-tandem mass spectrometry with stable isotope-labelled standards.

Progesterone (P4) is contained naturally in animal tissue, and it is also used as a veterinary drug in cattle for treatment purposes. To assess the risk from P4 residues in beef derived from treated cattle, it is essential to quantify the P4 contained naturally in cattle tissue (endogenous P4). Therefore, we performed a method validation for the quantification of endogenous P4 (method quantification limit = 0.06 ng g-1) by using isotope-labelled P4s, and investigated the P4 contents in Japanese beef (n= 112; 0.07 to 121 ng g-1). The P4 contents in cattle muscle ranged from 0.07 to 54.3 ng g-1 in males, and from 0.27 to 121 ng g-1 in females. Our investigation also indicated that the developed method using both 13C- and deuterium-labelled P4 standards could be used to certify the recovery of P4 from cattle muscle containing various amounts of intramuscular fat, and enabled the determination of the P4 content in all Japanese beef samples that exceeded the method quantification limit.