Methods and procedures applied


IV. Honey adulteration analysis (determination of added HFCS)

Method:

Carbon isotope analysis is a powerful tool in monitoring the identity, origin or purity of foodstuff of various types. Most of the isotopic analyses are performed for quality control in the food technology.

The δ13C values found in C3 plants range from about –22 ‰ to about –35 ‰, while carbon from C4 plants are somewhat heavier, ranging from about –8 ‰ to about –20 ‰. Values for CAM plants, which use features of both the C3 and C4 pathways, spread throughout most of the ranges of values found for C3 and C4 plants. Pineapples and cactus are notable examples of CAM plants.

Normally honey is derived from flowering plants, which are almost exclusively C3 in their photosynthetic behavior. HFCS (high fructose corn syrup) is derived from corn, which is a C4 photosynthetic plant.

The purity of the honey sample is judged by the difference between the isotope ratio value of the whole honey sample and the isotope ratio value of its separately prepared protein fraction. This principle was proposed by Parker and was further examined by Bricout and Koziet.

The procedure consists in diluting a known amount of honey in distilled water adding sodium tungstate solution and sulphuric acid to precipitate proteins. The centrifuge tube is immersed in a 80° C water bath until visible flocculates form (10-15 min). After drying the protein the samples are weighted into Sn boats, combusted and measured by mass spectrometry like the initial honey samples.

The apparent corn/cane sugar content might be calculated as follows:

Adulteration (%) = 100* ( δ13C protein – δ13C honey) / δ13C protein (-9.7)

reporting negative values for % adulteration as 0%. –9.7 ‰ is considered the mean δ13C value of HFCS. The method permits the objective evaluation of possible adulteration especially in case of small quantities of corn/cane sugar (7-20%).

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