Evolution of colorants in sugarbeet juices during decolorization using styrenic resins Mónica Coca * , M. Teresa García, Silvia Mato, Ángel Cartón, Gerardo González Departamento de Ingeniería Química y Tecnología del Medio Ambiente, Universidad de Valladolid P° Prado de la Magdalena s/n, 47011 Valladolid, Spain article info Article history: Received 26 November 2007 Received in revised form 13 March 2008 Accepted 17 May 2008 Available online 2 July 2008 Keywords: Melanoidins Sugar technology Size exclusion chromatography Color removal Ion exchange abstract Molecular size distribution of coloring impurities in sugar beet juices was studied in order to get a better understanding of the evolution of colorants during ion exchange decolorization processes using styrenic resins as well as to provide useful information about the influence of operating decolorization conditions and regenerant consumptions on the removal of harmful colorants. A study of resin life was also per- formed. Size exclusion chromatography (SEC) of sugar beet thin juices confirmed the presence of colo- rants with molecular masses above 100 kDa, 20 kDa and 2 kDa. The global color reduction percentages achieved in the decolorization stage were about 75–80%. The colorants with a molecular mass of 20 kDa were completely removed whereas components above 100 kDa and 2 kDa presented lower removal efficiencies, showing lower affinity for the styrenic resin. Colored impurities are likely to be related to melanoidins, Maillard reaction products. Low regenerant consumptions, about 57 L of solution per m 3 of treated juice, removed adsorbed colorants from the styrenic resin without reducing its decol- orization capacity considerably. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Many factors affect the quality and quantity of beet sugar. These factors are related to the formation of non-sugars, mainly colored compounds. These components are formed through beet process- ing as a result of pH changes, thermal and autocatalytic effects. These impurities are of high molecular masses, polymeric and with tendency to occlude within the sugar crystal (Bento and Sá, 1998). The nature of beet coloring matter is quite different to cane colo- rants (Godshall et al., 2002). The mechanisms concerning color for- mation in beet sugar processing are very complicated because of the many parameters involved. The main mechanisms related to color formation during purification stage are Maillard reaction and alkaline degradation of invert sugars. Maillard reaction prod- ucts, melanoidins, are formed by the reaction of monosaccharides and carbonyl compounds with amino acids. Melanoidins are recog- nized as being acidic and polymeric compounds, with a highly complicated structure (Cämmerer and Kroh, 1995; Cämmerer et al., 2002; Yaylayan and Kaminsky, 1998). The formation of mela- noidins proceeds much faster at high temperature and basic pH conditions. In concentrated juices, the Maillard reaction also pro- ceeds faster. Alkaline degradation products of hexoses (HADP) may be responsible for up to 80% of color in sugar beet juices (Heitz, 1995). The production of colored HADP takes place at the common pH of a beet sugar factory (8–11). The formation of deg- radation products takes place mainly in the purification step where temperature increases up to 85 °C and pH rises up to strong basic values (11–12). The nature and structure of colored HADP have not been elucidated but they are probably due to the extensive aldolisation of intermediate di-carbonyl compounds in alkaline solutions (De Bruijn, 1986). To meet standards of whiteness, it is necessary to undertake ef- forts to reduce color levels in the end product. In addition to pre- ventive industrial actions, a decolorization stage becomes necessary. Most of resin applications for decolorization have been made in cane sugar industry (Bento, 1992, 1997; Godshall, 1999). Ion exchange technology has also considerable potential to decol- orize beet sugar juices, removing colorants by adsorption as well as by ion exchange (Broughton et al., 1991; García Agudo et al., 2002). At usually process pH conditions, most of these colorants exhibit an anionic nature thereby anion styrenic resins are efficient decolorizing materials (Bento and Sá, 1998; Guimaraes et al., 1996; Gula and Paillat, 2005). Styrenic matrices increase the affinity of colorants, showing higher decolorization efficiencies than acrylics but the regeneration stage is more complicated (Bento, 1997). The extent of decolorization depends on colorant properties: molecular size, ionic charge and hydrophobicity. However, colo- rants in sugar solutions are usually managed as a single substance. The global color measurement by spectrophotometric analysis at 420 nm wavelength does not make possible to distinguish the different characters of colorants. Therefore, it is necessary to advance in the knowledge of beet colorants through the decolor- ization processes for a sound factory scale design. This paper is concerned with the removal of colored compo- nents from beet sugar solutions using a commercial polystyrenic 0260-8774/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2008.05.025 * Corresponding author. Tel.: +34 983 423 166; fax: +34 983 423 616. E-mail address: monica@iq.uva.es (M. Coca). Journal of Food Engineering 89 (2008) 429–434 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng