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 δ¹³C_bulk, δ¹⁵N_bulk, and δ³⁴S_bulk, and CSIA covered δ²H_fatty acid, δ¹³C_fatty acid, δ¹³C_amino acid, δ¹⁵N_amino acid, and δ²H_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 δ²H_C18:1, δ¹³C_C18:2, δ¹³C_C18:3, δ¹³C_Gly, δ¹³C_Leu, δ¹³C_Val, δ²H_Glu, δ²H_Ile, δ²H_Leu, and δ²H_Thr. Our findings suggested that CSIA of fatty acids and amino acids can be useful to differentiate the geographical provenance of walnuts.