Authentication of pure L-leucine products manufactured in China by discriminating between plant and animal sources using nitrogen stable isotope technique

J Food Sci. 2013 Mar;78(3):H490-4. doi: 10.1111/1750-3841.12041.


L-leucine products among other branched chain amino acid supplements are highly susceptible to economically motivated adulteration. Curbing this menace is critical and timely. Hence, the δ(15) N composition of the L-leucine derived from plants and animals sources was estimated. The trophic enrichment phenomenon of δ(15) N composition was utilized to elucidate the sources. We finally established the distinction between the respective sources. Samples of plant sources (maize and soybean) and that of animal sources (pig fur and duck feather) were analyzed for δ(15) N isotopic signatures. An elemental analyzer which was connected to an isotope ratio mass spectrometer operated in the continuous flow mode was utilized. The raw materials were obtained from China. Statistical analysis was performed using descriptive statistics and one-way analysis of variance. The results indicated lower δ(15) N values of range -0.7344‰ to 2.384‰ and 1.032‰ to 2.064‰ for maize and soybean samples, respectively. Whereas, a range of 3.860‰ to 6.011‰ and 5.875‰ to 6.011‰ was, respectively, detected in pig fur and duck feather samples. The δ(15) N difference in plants and animals samples was significant (F = 165.0; P = 1.675 E-10 for maize and pig fur samples; F = 212.8; P = 0.0001284 for soybean and duck feather samples). It was observed that δ(15) N trophic enrichment is helpful in elucidating the respective sources. The authors can emphatically assert that the range of δ(15) N composition of L-leucine derived from plants sources within the study area is -1.000‰ to 3.000‰ whereas the range in animal sources is 4.000‰ to 9.000‰. Practical Application This study provides a reliable approach in verifying the authenticity of not only L-leucine products but also other branched chain amino acid supplements and thereby would help in fraud detection of any economically motivated adulteration and mislabeling of these products. When coupled with H and O stable isotope techniques, the region-of-origin of the detected adulteration can also be traced successfully. It therefore serves as a guide to food regulatory bodies, food scientists, retailers of these products, consumers, and the general public at large.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • China
  • Consumer Product Safety
  • Dietary Supplements*
  • Drug Combinations
  • Feathers / chemistry
  • Food Analysis / methods*
  • Glycine / analogs & derivatives
  • Glycine / analysis
  • Leucine / analysis*
  • Nitrogen Isotopes / analysis*
  • Soybeans / chemistry
  • Swine
  • Zea mays / chemistry


  • Drug Combinations
  • Nitrogen Isotopes
  • E 10
  • Leucine
  • Glycine