Bulk and Compound-Specific Stable Isotope Analysis for the Authentication of Walnuts (Juglans regia) Origins

Walnuts are grown in various countries, and as product origin information is becoming more important to consumers, new techniques to differentiate walnut geographical authenticity are needed. We conducted bulk stable isotope analysis (BSIA) and compound-specific stable isotope analysis (CSIA) on walnuts grown in seven countries. The BSIA consisted of delta C-13(bulk), delta N-15(bulk), and delta S-34(bulk), and CSIA covered delta H-2(fatty acid), delta C-13(fatty acid), delta C-13(amino acid), delta N-15(amino acid), and delta H-2(amino acid). Analysis of variance (ANOVA) and linear discriminant analysis (LDA) were used for statistical analysis to compare samples from the USA and China. Parameters that yielded significant variations are delta H-2(C18:1n-9), delta C-13(C18:2n-6), delta C-13(C18:3n-3), delta C-13(Gly), delta C-13(Leu), delta C-13(Val), delta H-2(Glu), delta H-2(Ile), delta H-2(Leu), and delta H-2(Thr). Our findings suggested that CSIA of fatty acids and amino acids can be useful to differentiate the geographical provenance of walnuts.