Melanoidines are produced by the reaction between carbonil compounds (aldeids and ketones) and amino compounds. This reaction, known as Maillard reaction, produces high molecular weight compounds with an intense colour.
In sugar solutions the main source of carbonil compounds are invert sugars besides the compounds resulting from alkaline degradation of hexoses and poliphenol oxidation.
The formation of melanoidins take place mainly over 65º brix. The velocity of formation of these compounds is very slow in low brix solutions. As the brix increases, the contribution of Maillard products to solution colour, increases (Paton and Mc Cowage, 1987).
Through UV analysis (Bento, 1995a) we can say that melanoidins present a high anionic charge, in comparisson with HADP and caramels.
In the next figure is presented the melanoidines spectrum at pH 9 (Bento, 1995). The spectra at pH 11 and pH 3 present two peaks at 286nm and 326nm (Bento, 2002)
. Melanoidines spectrum at pH 9
In the next figure it is presented the diagram obtained by GPC with ELS detector using a melanoidins solution (Bento and Sá, 1998). Melanoidines present peaks at 39,0; 41,0; 44,1; 50,0 and 51,6 minutes of retention time, corresponding to 50,8kD, 36,0kD, 21,9kD 7,7kD and 6,1kD molecular weights, respectively.
ELS diagram of Melanoidines
In the next figure it is presented the UIV curve of melanoidines (Bento, 2002). UIV means the Indicator Value in the UV spectrum. As it is observed the curve presents a minimum at 291nm.
UIV curve of Melanoidines
In the next figure it is presented the melanoidines chromatogram obtained by sucrose chromatography (Bento, 1994). In this chromatogram it is observed that these colourants present only one group eluted with methanol at 62 minutes of Rt. This result shows that melanoidines present, in general, a lower degree of hydrophobicity than HADP.
Sucrose chromatogram of Melanoidines
Bento L.S.M., 1995, Application of UV Spectrophotometry to study sugar colourants throughout the refining
process, Proc. of S.I.T. Conf., 211-230
Bento L.S.M., 2002, Separation of beet and cane colourants through styrenic strong base resins, Proc. of
S.P.R.I. Conf., 311-327
Bento L.S.M., S. Sa, 1998, sudy of HMW compounds in sugar liquors from carbonatation and ion-exchange
resins using GPC chromatography with an evaporative light scattering detector, Proc. of S.P.R.I.
Paton N.H., Mc Cowage, 1987, Colour forming mechanisms during mill processing, Proc. of Aust. S.S.C.T.