Attempt to cross-link feruloylated arabinoxylans and proteins with a fungal laccase M.C. Figueroa-Espinoza a , M.-H. Morel a , A. Surget a , M. Asther b , S. Moukha b , J.-C. Sigoillot b , X. Rouau a, * a INRA-ENSAM, Unite  de Technologie des Ce Âre Âales et des Agropolyme Áres, 2 Place Viala, 34060, Montpellier cedex 01, France b INRA, Laboratoire de Biotechnologie des Champignons Filamenteux, CP 925, Faculte  des Sciences de Luminy, 13288, Marseille cedex 09, France Received 5 August 1998; accepted 28 September 1998 Abstract A fungal laccase from Pycnoporus cinnabarinus was used to study the eect of proteins in the oxidative gelation process of wheat ¯our water-extractable feruloylated arabinoxylans (WEAX), in an attempt to provoke a covalent cross-linking between arabinox- ylans and proteins. Capillary viscometry, spectrophotometry, SE-HPLC and RP-HPLC were used. Two dierent proteins were tested: high molecular weight glutenin subunits (HMW-GS) and bovine serum albumin (BSA). BSA was used in both native or oxidized (oxBSA) and reduced (redBSA) forms, and HMW-GS in reduced form. Whereas oxBSA had no eect in gelation, both HMW-GS and redBSA, provoked a delay on the arabinoxylan thickening and in the oxidation of feruloyl groups, in the presence of laccase. This eect is attributed to the sulfhydryl groups of the reduced proteins. # 1998 Elsevier Science Ltd.. All rights reserved. Keywords: Arabinoxylan; Bovine serum albumin; Cross-linking; Ferulic acid; Glutenin; Laccase; Sulfhydryl 1. Introduction Food technologists use both proteins and poly- saccharides to confer semisolid textural attributes to food. The cross-linking of these molecules into gels is important to develop structures with desirable mechanical properties (Dickinson, 1997). Protein-macromolecule conjugates is a new ®eld in research that has attracted considerable attention. According to Kato et al. (1991), proteins may gain resistance to heat, proteolytic attack and organic solvents, by conjugation with macromolecules such as polysaccharides and synthetic polymers, which in addi- tion may lead to new functional properties. According to Van Sumere et al. (1975), phenols com- bine with proteins reversibly by hydrogen bonding, and irreversibly by covalent condensations. The existence of a speci®c interaction between proteins and phenols has been known since the discovery of phenols by Runge (1834). The complexation of quinones (intermediate products of oxidation of phenols) with substances possessing amino and thiol groups is well documented (Cheynier et al., 1986; Cooper, 1913; Finley, 1974; Hurrel et al., 1982; Mason, 1955; Nishiyama et al., 1979; Pierpoint, 1966, 1969a,b, 1970; VaÂmos-VigyaÂzo , 1981), i.e. Pierpoint (1969b) reported that BSA reacts with chlorogenoquinone either by its thiol or its amino group. According to Haider et al. (1965) methylated hydroxyl phenols do not react with amino acids. Polemic about arabinoxylan-protein cross-linking exists since long time ago. Arabinoxylans form gels by oxidative coupling of their feruloyl groups (Figueroa- Espinoza & Rouau, 1998; Geissman & Neukom, 1973; Hoseney & Faubion, 1981; Izydorczyk et al., 1990; Ng et al., 1997). According to Udy (1957), addition of pro- teins to pentosan solution enhance oxidative gel forma- tion. For Vinkx et al. (1991) and Vinkx and Delcour (1996), the role of small levels of protein present in ara- binoxylan preparations is unclear. Some authors observed that treatment of a pentosan solution with proteolytic enzymes prevented gelation, and if an arabinoxylan gel was treated with these enzymes, it lique- ®ed (Girhammar & Nair, 1995; Neukom, 1976; Neu- kom et al., 1962). However, evidence that protein-free arabinoxylan does gel was presented (Morita et al., 1974; Vinkx et al., 1991, 1993). Whereas Brenna et al. (1988) reported that BSA, in an arabinoxylan-peroxidase system, resulted in a partial 13 Food Hydrocolloids 13 (1999) 65±71 0268-005X/98/$Ðsee front matter # 1998 Elsevier Science Ltd.. All rights reserved PII: S0268-005X(98)00072-1 * Corresponding author. Tel.: 0033 4 99 61 22 02; fax: 0033 4 67 52 20 94; e-mail: rouau@ensam.inra.fr.