Ultraviolet Spectrophotometric Detection of Added Sugar in Honey

Abstract

Thirty-two commercial honeys and honeys, supplied directly from beekeepers, were deproteinized by the addition of Carrez solutions, then the filtrates were subjected for ultraviolet spectrometry. Absorbances (E) at 245, 284, 285 and 325mμ were read for each honey, the 5-hydroxymethylfurfral (HMF) contents being calculated by the two methods (The methods will be called, hereafter, two points U. V. method and three points U. V. method, respectively).
a: by use of E₂₈₄-E₂₄₅
b: by use of E₂₈₅-0.5 (E₂₄₅+F₃₂₅)
HMF contents were also determined for the above-mentioned honeys by the colorimetry through the reaction of p-toluidine-barbituric acid.
There were close correlations between the HMF contents in honey estimated by the three methods, the correlation coefficients between the colorimetric results and 2 points or 3 points U. V. spectrometric results being 0.992 and 0.989, respectively.
Usually, somewhat higher results were obtained by the U. V. spectrometries than by the colorimetry. It is presumed that these differences might be attributed to the varieties of fururals contained in honey, since the methods applied were not specific for HMF only. It is provided in the Draft Provisional Standard for Honey (Joint FAO/WHO Food Standards Program) that HMF contents in honey, estimated by the p-toluidine-barbituric acid colorimetry, should not be more than 40mg/kg(4.0mg%), while it is shown in the domestic standard, that HMF contents determined by use of either the colorimetry or 3 points U. V. spectrometry must not exceed 5.0mg%. It was noted in this report, that there might happen discrepancy in the judgement, for the borderline cases of honey, when the two domestic methods were applied for the determination of HMF. It is difficult, at the present state, to conclude which of the three methods is most suitable for the estimation of HMF in honey. Promising results were obtained through direct U. V. spectrometry of honey in a 0.02cm super-thin cell by use of Shimadzu MPS-50L Multipurpose Recording Spectrophotometer. This apparatus is epecially contrived for measuring the absorbance or attenuance of opaque samples, using end-on type photomultiplication system. The troublesome procedures of dilution as well as deproteinization are omissible by use of this apparatus. The presence of small quantity of protein (from 0.04-0.22% in domestic honeys) makes no obstacle for the direct determination of HMF.