Specific screening for color precursors and colorants in beet and cane sugar liquors in relation to model colorants using spectrofluorometry evaluated by HPLC and multiway data analysis.
A comparison was made of the fluorophores in beet thick juice and cane final evaporator syrup, which are comparable in the production of cane and beet sugar; that is, both represent the final stage of syrup concentration prior to crystallization of sugar. To further elucidate the nature of the color components in cane and beet syrup, a series of model colorants was also prepared, consisting of mildly alkaline-degraded fructose and glucose and two Maillard type colorants, glucose--glycine and glucose--lysine. Fluorescence excitation--emission landscapes resolved into individual fluorescent components with PARAFAC modeling were used as a screening method for colorants, and the method was validated with size exclusion chromatography using a diode array UV--vis detector. Fluorophores from the model colorants were mainly located at visible wavelengths. An overall similarity in chromatograms and absorption spectra of the four model colorant samples indicated that the formation of darker color was the distinguishing characteristic, rather than different reaction products. The fluorophores obtained from the beet and cane syrups consisted of color precursor amino acids in the UV wavelength region. Tryptophan was found in both beet and cane syrups. Tyrosine as a fluorophore was resolved in only beet syrup, reflecting the higher levels of amino acids in beet processing. In the visible wavelength region, cane syrup colorant fluorophores were situated at higher wavelengths than those of beet syrup, indicating formation of darker colorants. A higher level of invert sugar in cane processing compared to beet processing was suggested as a possible explanation for the darker colorants.