HADP

Invert sugars, present in sugar solutions, when in high alkalinity conditions, form compounds of strong colour, named HADP (Hexoses Alkaline Degradation Products). This formation may happen during Clarification, during extraction, and in Carbonatation, in the refining process (Bento, 1999), where sugar solutions are mixed with calcium hydroxide.

HADP are polymers of carboxylic acids, of brownish yellow colour, resulting from monosaccharides degradation in alkaline conditions, through the formation of a enediol anion (Bruijn, 1986).
IV of these compounds is higher than melanoidines and caramels but it is lower than IV of phenolic compounds. 

HADP spectrum at pH 9

In the figure above it is presented the spectrum of HADP solution at pH 9.0 (Bento, 1995). The spectrum presents a peak at 265nm, at pH 11, and a peak at 267nm, at pH 3 (Bento, 2002).

In the next figure it is presented the diagram obained by GPC with ELS detector ELS using HADP solution (Bento and Sá, 1998). HADP present peaks at 41,8; 50,6 e 51,9 minutes of retention time (Rt), corresponding to a molecular weight of 31,4kD, 7,0kD e 5,5kD, respectively. 

ELS diagram of HADP

In the next figure it is presented the UIV variation of HADP (Bento, 2002). UIV is the Indicator Value in the UV spectrum.As it is observed, this curve presents a minimum at 262nm. The expression UIV means the IV in the UV radiation zone and represent the quotient between the solutions absorvancies at pH 9.0 and pH 3.0, between 220nm e 330nm. 

UIV curve of HADP 

In the next figure it is presented the HADP chromatogram obtained by sucrose chromatography (Bento, 1994). In this chromatogram it is observed that HADP are divided in two groups. The first one eluted with the less polar eluent (propanol-1) at 19min of Rt, and a second one with 62min of Rt, eluted with methanol. This result shows that HADP present a group of compounds with some degree of hydrophobicity, eluted with the less polar eluent, and another group of more polar compounds.

Sucrose Chromatogram of HADP 

Bibliography

Bento L.S.M., 1994, Separation of sugar colourants using sucrose crystals in chromatographic columns,
Proc. of S.I.T. Conf., 17-39
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.
          Conf., 233-247 
Brujn J.M., 1986, Monosacharides in alkaline medium: isomerization degradation oligomerization, PhD
           Thesis 

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