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

The present study describes compound-specific δ13C and δ15N analyses of fatty acids and amino acids for improving the accurate authentication of organic milk (OM) against conventional milk (CM) collected in Korea. Most δ13Cfatty‑acid and δ13Camino‑acid values were lower in OM than in CM (P 15Namino‑acid values displayed weak discriminative power for OM authentication. Higher isotopic fractionation was observed in δ13Cfatty‑acid than in δ13Camino‑acid and δ15Namino‑acid, with fractionation trends differing with individual amino acids. In particular, δ13Clinoleic‑acid of −33.5‰ and δ13Cmyristic‑acid of −28‰ were determined to be promising year-round threshold values for Korean OM authentication. The δ13Cbulk was highly correlated with δ13CAla (r = 0.92) and δ13Coleic‑acid,trans (r = 0.77), and strong positive correlations were observed between δ13CVal and δ13CIle (r = 0.98) and between δ15NThr and δ15NSer (r = 0.90). Chemometric modeling for OM authentication produced a high quality model (R2X = 0.547, R2Y = 0.865, and Q2 = 0.689) with reliable chemical markers, notably δ13Cmyristic‑acid, δ13Clinoleic‑acid, and δ13Cstearic‑acid. Furthermore, the models developed for seasonal separation in OM (Q2 = 0.954) and CM (Q2 = 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.本研究针对韩国境内采集的有机乳（organic milk, OM）与常规乳（conventional milk, CM）样本，开展脂肪酸（fatty acids）与氨基酸（amino acids）的化合物特异性δ13C、δ15N分析，旨在提升有机乳的精准鉴别准确性。多数脂肪酸δ13C与氨基酸δ13C值在有机乳中显著低于常规乳（P<0.05），而氨基酸δ15N值对有机乳鉴别的区分能力较弱。相较于氨基酸δ13C与氨基酸δ15N，脂肪酸δ13C的同位素分馏程度更高，且分馏趋势因单个氨基酸种类而异。其中，δ13C亚油酸（linoleic acid）值为-33.5‰、δ13C肉豆蔻酸（myristic acid）值为-28‰，被确定为适用于韩国有机乳鉴别的全年可靠阈值指标。整体稳定同位素比值δ13Cbulk与δ13C丙氨酸（alanine, Ala，r=0.92）、δ13C反式油酸（trans oleic acid，r=0.77）呈高度相关；同时，δ13C缬氨酸（valine, Val）与δ13C异亮氨酸（isoleucine, Ile）之间（r=0.98）、δ15N苏氨酸（threonine, Thr）与δ15N丝氨酸（serine, Ser）之间（r=0.90）均存在强正相关关系。用于有机乳鉴别的化学计量学建模构建了高质量判别模型（R²X=0.547、R²Y=0.865、Q²=0.689），其可靠化学标志物主要包括δ13C肉豆蔻酸、δ13C亚油酸与δ13C硬脂酸（stearic acid）。此外，针对有机乳与常规乳的季节分离所构建的模型同样具备良好性能（有机乳Q²=0.954，常规乳Q²=0.791）。本研究基于化合物特异性同位素数据，在单一整体稳定同位素比值分析不足以实现准确鉴别的场景下，提升了有机乳鉴别的可靠性；同时为韩国有机乳虚假标签管控提供了有价值的参考思路，且该方法在其他国家亦具备潜在应用价值。