Use of Isotopic Analyses To Determine the Authenticity of Brazilian Orange Juice (<i>Citrus sinensis</i>)

Abstract

Isotopic analysis was used to characterize authentic samples of orange juice (Citrus sinensis) from Brazil. Site specific natural isotopic fractionation nuclear magnetic resonance (SNIF-NMR) was used to determine deuterium/hydrogen ratios at the methyl [(D/H)I] and methylene [(D/H)II] sites of ethanol produced by fermentation of orange juice. Stable isotope ratio mass spectrometry (SIRMS) was used to determine the ratio of carbon isotopes (13C/12C) in the same ethanol and the ratio of oxygen isotopes (18O/16O) in the citrus juice water. The mean ratios found for these parameters in authentic hand-squeezed orange juice were as follows: (D/H)I, 102.3 ppm (SD = 1.7); (D/H)II, 126.5 ppm (SD = 1.8); 13C/12C, δ13C = −26.6‰ PDB (SD = 0.9); and 18O/16O, δ18O = +2.27‰ SMOW (SD = 2.48). Retail samples taken from the Brazilian market place were evaluated by comparison against these data. No evidence was found for the addition of sugar to orange juice or for the dilution with tap water of samples labeled as freshly squeezed. Keywords: Authenticity; orange juice; SNIF-NMR; SIRMS; isotopic analysis; D/H; 13C/12C; 18O/16O