Geographical origin of Chinese wolfberry (goji) determined by carbon isotope analysis of specific volatile compounds

Chinese wolfberry or goji berry (Lycium barbarum) is an important traditional Chinese medicine. Its price and function has a close correlation with its geographical provenance. Illegal mislabeling motivated by commercial gains brings serious food safety problems and damages consumer confidence. In this work, a novel analytical strategy combined with chemometrics statistic tools was developed to determine the geographical origin of wolfberries from different provinces in China. Stable carbon isotopic ratios (δ¹³C) of wolfberry volatile compounds (i.e. limonene, tetramethylpyrazine, safranal, geranylacetone, and β-ionone) were determined by gas chromatography-combustion-isotope ratio mass spectrometry (GC-IRMS) with headspace-solid phase micro extraction (HS-SPME). Five types of SPME fiber (i.e. DVB/CAR/PDMS, CAR/PDMS, PDMS/DVB + OC, PDMS, and PA), extraction time, temperature and GC-IRMS conditions were comprehensively optimized to obtain the best adsorption of volatile compounds in wolfberry. Method integrity was assessed by comparing volatiles extracted using HS-SPME GC-IRMS with direct injection GC-IRMS and were in good agreement with each other. The geographical variations of volatile compounds using one-way analysis of variance (ANOVA) were explored for individual δ¹³C values in wolfberry samples from Gansu, Ningxia and Qinghai. Geographical origin of wolfberry was differentiated by linear discrimination analysis (LDA), with an accuracy of 89.16%, 87.77% and 85.87% for these three provinces, respectively. These results showed the combination of SPME and IRMS provides a rapid and valid method to determine the geographical origin of wolfberry.