Fatty Acid- and Amino Acid-Specific Isotope Analysis for Accurate Authentication and Traceability in Organic Milk

The present study describes compound-specific delta C-13 and delta N-15 analyses of fatty acids and amino acids for improving the accurate authentication of organic milk (OM) against conventional milk (CM) collected in Korea. Most delta C-13(fatty-acid) and delta C-13(amino-acid) values were lower in OM than in CM (P < 0.05); however, most delta N-15(amino-acid) values displayed weak discriminative power for OM authentication. Higher isotopic fractionation was observed in delta C-13(fatty-acid) than in delta C-13(amino-acid) and delta N-15(amino-acid), with fractionation trends differing with individual amino acids. In particular, delta C-13(linoleic-acid) of -33.5 parts per thousand and delta C-13(myristic-acid) of 28 parts per thousand were determined to be promising year-round threshold values for Korean OM authentication. The delta C-13(bulk) was highly correlated with delta C-13(Ala) (r = 0.92) and delta C-13(oleic-acid,trans) (r = 0.77), and strong positive correlations were observed between delta C-13(val) and delta 13C(IIe), (r = 0.98) and between delta N-15(Thr) and delta N-13(Ser) (r = 0.90). Chemometric modeling for OM authentication produced a high quality model ((RX)-X-2 = 0.547, (RY)-Y-2 = 0.865, and Q(2) = 0.d89) with reliable chemical markers, notably d13Cmyristic-acid delta C-13(linoleic-acid) and delta 13C(stearic-acid) Furthermore, the models developed for seasonal separation in OM (Q(2) = 0.954) and CM (Q(2) = 0.791) were of good quality. Our findings, based on compound-specific isotope data, improve the reliability of OM authentication in cases where bulk stable isotope ratio analysis alone is insufficient. They also provide valuable insight into the control of fraudulent OM labeling in Korea, with potential application in other countries.