Characterization of L-theanine in tea extracts and synthetic products using Stable Isotope Ratio Analysis

Abstract

L-theanine involves a great number of health benefits and dietary supplements containing this molecule are becoming increasingly popular. There is, therefore, a growing need to find ways to discriminate between natural L-theanine extracted from tea leaves and the cheaper, synthetic one obtained using specific bacterial enzymes. A first attempt of stable isotope ratio analysis characterization of the possible synthetic adulterant L-theanine (δ 13 C of −14.3 ± 1.5‰), obtained from vegetable substrates with C4 photosynthetic cycle, and of the more expensive natural L-theanine (δ 13 C of −24.4 ± 1.3‰), extracted from Camellia sinensis plants with C3 photosynthetic cycle, is reported here.

Stable carbon isotopic characterization of rice vinegar protein as an intrinsic reference for discriminating the authenticity of brewed rice vinegar

“…The δ 13 C protein values in the rice vinegar samples were from −25.99‰ to −28.26‰ ( Table 1 ) and fell within the typical δ 13 C range of −23‰ to −30‰ for C3 plants [ 24 ] due to the C3 plant derived raw materials of these samples, such as rice, waxy rice, wheat, or malt. Our previous study [ 17 ] showed that the δ 13 C acetic acid values in the A1 to A4 samples using the C4 plant derived ethanol as the main raw material shifted to the typical δ 13 C range of −9‰ to −15‰ for C4 plants [ 25 ].…”

Stable Isotope Ratio Analysis for the Authentication of Natural Antioxidant Curcuminoids from Curcuma longa (Turmeric)

“…The Global Network of Isotopes in Precipitation (GNIP) database, administered by the International Atomic Energy Association (IAEA) and the World Meteorological Organization (WMO), is recognized as a useful method to evaluate the correlation between the δ 2 H of rainwater and groundwater in the absence of direct measurement [39]. The GNIP database (http://www-naweb.iaea.org/ napc/ih/documents/userupdate/Waterloo/, accessed on 1 January 2023) contains monthly weighted average precipitation (δ 2 Hp and δ 18 Op) from all continents and islands between 1960 and the present. The temperature and the amount of precipitation significantly influence the δ 2 H values of the water.…”

“…In recent years, stable isotope ratio analysis (SIRA) found widespread use in food science [16], not only to trace the geographical origin of products, but also to guarantee their authenticity, differentiating between natural and synthetic or biosynthetic ingredients [17][18][19][20][21]. In the latter case, applications of the SIRA involved nutraceutical products or products with pharmacological properties that are increasingly in demand due to their natural origin [18,21,22]. The SIRA is based on the measurement of the ratio between the heavy and light isotopes of the elements carbon ( 13 C/ 12 C), nitrogen ( 15 N/ 14 N), sulfur ( 34 S/ 32 S), oxygen ( 18 O/ 16 O) and hydrogen ( 2 H/ 1 H).…”

Stable Isotope Ratio Analysis for Authentication of Natural Antioxidant Cannabidiol (CBD) from Cannabis sativa

“…The stable isotope analysis of bio-elements has already been successfully tested as a technique for distinguishing different natural molecules from their synthetic and/or biosynthetic counterparts. These molecules include, e.g., monacolin K from fermented red rice [22], theanine [23], curcuminoids [24], and vanillin [25]. The 13 C/ 12 C isotope ratios of carbon (expressed as δ 13 C), the 18 O/ 16 O ratios of oxygen (δ 18 O), and the 2 H/ 1 H ratios of deuterium (δ 2 H) proved to be effective in the discrimination between the active principal compound of interest obtained from natural sources and that obtained from fossil sources used in the industrial synthesis.…”