This paper describes recent progress in the isotopic analysis of the two
main aromatic constituents
of vanilla flavor (vanillin and p-hydroxybenzaldehyde
(pHB)). Some improvements concerning the
SNIF-NMR analysis of vanillin are presented. They include (i)
improvement of the analytical
precision by using new software for automatic phasing, baseline
correction and curve fitting of the
signals of the 2H-NMR spectra; (ii) significant enrichment
of the database containing measurements
performed on vanillin extracted from vanilla beans harvested in
different countries and on synthetic
vanillin; (iii) standardization of the purification process to obtain
pure vanillin, in order to avoid
isotopic fractionation; and (iv) improvement of the statistical tools
for both proving and quantifying
adulterations. All these improvements were also successfully
applied to site specific deuterium
NMR analysis of pHB. It is now also possible with the SNIF-NMR
method to discriminate between
the natural and chemical origins of pHB. New results concerning
the δ13C deviation of pHB are
also presented. Thus the lowest value of δ13C of pHB
extracted from vanilla bean can be set at
−19.5‰. We recommend the methodology presented in this paper
as a standard procedure for
purifying vanillin and pHB, without significant isotopic fractionation,
from most matrices (for example from ice cream, yogurts, etc.), in order to perform isotopic
analyses (13C IRMS and 2H-NMR).
Keywords: SNIF-NMR; vanillin; pHB; δ13C; adulteration;
vanilla flavor; vanilla extract; ice cream;
purification
The site-specific natural isotopic fractionation studied by nuclear magnetic resonance (SNIF/NMR) method measures site-specific isotope contents in a variety of organic compounds by deuterium nuclear magnetic resonance spectroscopy. This technique, together with SIRA/MS (stable isotope ratio analysis/mass spectrometry) provides a powerful tool for food authentication and characterization. By using the ethanol resulting from sugar fermentation as a molecular probe, SNIF/NMR (deuterium) and SIRA/MS (13C) have been used together for authentication of fruit juices. The influence of deu terium content of the fermentation water on the iso topic parameters is shown and a means for normal izing the results is proposed. A large number of authentic juices have been analyzed to define the variation of isotopic ratios in natural juices. On the basis of these data, a set of rules was designed to enable interpretation of isotopic parameters in terms of possible adulteration of fruit juices by sugar addition. Results of analyses of Florida orange juice are presented. Orange juice samples from Brazil and Israel are included as 2 extreme cases. Assignment limits for a sample of orange juice of unknown origin also are given. These assignment limits are also provided for apple and grapefruit juices.
The SNIF-NMR method may be used to measure the site specific isotope
concentrations in a variety
of organic compounds. The most common application of this
technique involves quantitative
deuterium nuclear magnetic resonance spectroscopy with appropriate
interpretation of the accumulated spectra. SNIF-NMR together with SIRA-MS provides a
powerful tool for food authentication and characterization. The concerted use of SNIF-NMR
(deuterium) and SIRA-MS (carbon-13)
on ethanol fermented from sugars has proven invaluable to the
authentication of wines, spirits,
and fruit juices. In this work, the analysis is extended to the
authentication of maple syrup, a
product rich in sucrose. Authentic maple syrup samples have been
analyzed in detail to characterize
the intrinsic variability of the isotopic ratios in this product.
These data constitute a data base of
authentic samples to which an unknown example of maple syrup can be
compared. The isotopic
ratios obtained from maple syrup are very different from those of both
beet and cane or corn sugars.
Therefore, the methodologies developed in this work are applicable
for the detection of beet and
cane or corn sugar added to a maple syrup. It can be shown that,
through a simple statistical
comparison between the data base and the unknown, a determination of
the occurrence and/or extent
of adulteration with added sugar can be made.
Keywords: Maple syrup; adulteration; NMR; isotopic analysis; SNIF-NMR;
sugar analysis
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