Stable isotope (δ13C) profiling of xylitol and sugar in South Africa

Abstract

Xylitol is an alternative sweetener to sucrose, glucose and fructose, and is available under a number of brands in South Africa. Carbon stable isotope values (δ13C) of a selection of commercially available xylitol products (n=28) were analysed and compared with sugar samples (n=29). Sugarcane (C4) and beet sugar (C3) derived sugar samples aligned with published values of source, although two samples that indicated a sugarcane origin suggested a beet sugar origin. Control corn-derived samples defined a stepwise xylose to xylitol discrimination of +0.7‰. The distinction between C3- and C4-derived xylitol was less clear with three samples difficult to define (range = -14.8 to -17.1‰). The values for a suite of xylitol samples (-22.3‰ to -19.7‰; n=8) that aligned closely with a suspected C3-derived xylose, were ~8‰ more positive than known birch isotope values. Some xylitol samples may thus represent (1) a mixture of C3- and C4-derived products, (2) derivation from a CAM species source or (3) different processing techniques in which the discrimination values of xylose from corn, and xylose from birch, may differ because of the respective chemical processing techniques. No samples that claimed a birch bark origin were within the range of samples suggested to be corn derived (i.e. -13.0‰ to -9.7‰, n=16). We suggest that the threshold values provided are relatively robust for defining the origins of xylitol and sugar, and can be used in determining the authenticity and claims of suppliers and producers.

Origin of Xylitol in Chewing Gum: A Compound-Specific Isotope Technique for the Differentiation of Corn- and Wood-Based Xylitol by LC-IRMS

“…The xylitol of birch origin was found to have a δ 13 C value of −20.3‰, whereas the corn xylitol sample had a δ 13 C value of −10.4‰. Similar isotopic signatures were obtained for 28 commercially available xylitol samples that were studied in South Africa, in which xylitol of C3 origin was found to have isotope ratios in the range from −22.3 to −19.7‰ and xylitol of suspected C4 origin was found to be in a range from −13.0 to −9.7‰ …”

“…An overview of the results obtained is given in Figure . With the exception of one sample, all of the analyzed chewing gums fall into two clusters, representing the values for the C3- and C4-derived xylitol determined by EA-IRMS in this study and in the literature …”

“…In these cases, standard deviations from 1.1 to 2.4‰ (e.g., samples MRO, MRE, MFO, and SMP) were observed. However, the precision was found to be generally sufficient for a reliable classification into one of the two categories of origin, as the Δδ 13 C observed between corn- and wood-based xylitol is around 10‰, which has also been demonstrated in a larger set of EA measurements in the literature . To statistically evaluate the results and establish threshold values for the C3 and C4 xylitol classes, a one-sided t -test was performed with the results obtained for the triplicate measurements of each chewing-gum extract.…”

“…However, Symes et al observed a similar trend for the δ 13 C values of C3-derived xylitol measured as bulk samples by EA-IRMS. By analyzing different size fractions of xylitol crystals, it was proven that the obtained values were not the result of a mixture of xylitol from different sources . It was also suspected that adulteration with undeclared additives could be responsible for the overall higher δ 13 C value of the xylitol compared with that of the source.…”

“…The LC-method development focused on the separation of xylitol from different, additional sweeteners such as sorbitol, mannitol, and maltitol, which are most commonly used in chewing gums and sweets. For the classification, a combination of a statistical evaluation of the δ 13 C values from the CSIA of the chewing gums and a comparison to the bulk isotope measurements of samples from known origins by EA-IRMS (elemental-analyzer isotope-ratio mass spectrometry) as well as different published literature values for raw plant materials and xylitol were used …”