International Journal of Biological Macromolecules 32 (2003) 209–216 Enzymatic degradation of hydroxypropyltrimethylammonium wheat starches Ali Ayoub a , Sebastien Gruyer b , Christophe Bliard a,∗ a Laboratoire de Pharmacognosie, Faculté de Pharmacie, UMR 6013 CNRS, Bˆ at 18 Europol’Agro, Moulin de la Housse, URCA, 51687 Reims Cedex 2, BP 1039, France (UE) b Laboratoire de Microbiologie Industrielle, Faculté de Sciences, 51687 Reims Cedex 2, France (UE) Received 14 March 2003; received in revised form 4 June 2003; accepted 27 June 2003 Abstract The enzymatic degradation of hydroxypropyltrimethylammonium modified starches synthesised by dry process was compared with that of hydroxypropyltrimethylammonium modified starches synthesised in glycerol–water plasticised molten medium. The enzymatic degradation rate of products from both origins decreased as the degree of substitution increased. However, two distinct enzymatic degradation profiles were obtained. Dry process products displayed a regular decrease pattern as DS increased. Molten medium synthesised cationic starches displayed a constant degradation level on a wide DS range with ,-amylase and amyloglucosidase, whereas isoamylase degradation rapidly reached its degradation limit at DSs 0.05. The various plasticising conditions used to synthesise cationic starch in molten medium show no influence on the enzymatic degradation. By measuring the affinity of -amylase, -amylase and isoamylase for native, extruded non-modified and hydroxypropyltrimethyl- ammonium-modified starches. It was evident that the enzymes’ affinity for the substrate diminishes with increasing chemical modification, particularly in the case of -amylase, suggesting that the location of cationic groups impairs the enzyme’s recognition of the substrate. Structural elements of limit dextrins were analysed by 1 H NMR. © 2003 Elsevier B.V. All rights reserved. Keywords: Cationic starch; Enzymatic degradation; Kinetics 1. Introduction Chemically modified starches have found numerous appli- cations in food and non-food industries. Functional groups are introduced on the macromolecules by reaction on the hydroxyls groups [1,2]. Cationic starches are widely used in industrial paper-making process [3], where they bind to negatively charged cellulose fibres by ionic association. Hydroxypropyltrimethylammonium (HPTMA) is one of the most widely used cationic modifying groups. In indus- trial process, the chemical modification is performed either in solution or by dry process [2]. In a previous paper we described an alternative chemical modification procedure in microhydric molten medium using glycerol-plasticised starch [4]. Hydrolysis has been widely used to study the molecular architecture of complex carbohydrate polymers. Hydrolysis ∗ Corresponding author. Tel.: +33-3-2691-3495; fax: +33-3-2691-3596. E-mail address: christophe.bliard@univ-reims.fr (C. Bliard). of starch can be performed by acidic treatment [5], or by enzymatic degradation [6,7]. Enzymatic degradation is the base of the largest starch transformation industries. Hamdi and Ponchel [8] have studied the influence and the sensi- tivity to enzymatic degradation of starch microspheres with -amylase. Brandam et al. [9] describe the - and -amylase activities on starch. Several research groups have investigated the enzymatic degradation of starch in order to determine the location of the chemical modifications. Based on the results of specific en- zymatic degradations, Kavitha and BeMiller [10] concluded that hydroxypropyl modification was preferentially located in amorphous regions as opposed to crystalline regions. Steeneken and Woortman [11] reported that the polymers obtained by methylation of granular starches were substi- tuted in a more block-wise manner, while starch polymers methylated in solution were substituted in a more random fashion. We used a similar selective degradation procedure to investigate structural differences between cationic starches 0141-8130/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0141-8130(03)00057-6