• Document: INTRODUCTION. Shigeru Tazawa 1, Shigeru Katayama 1,2, Masahiro Hirabayashi 2, Daiki Yamaguchi 2, and Soichiro Nakamura 1,2
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Prev. Nutr. Food Sci. 2014;19(4):327-332 http://dx.doi.org/10.3746/pnf.2014.19.4.327 pISSN 2287-1098ㆍeISSN 2287-8602 Improvement of Surface Functionalities, Including Allergenicity Attenuation, of Whole Buckwheat Protein Fraction by Maillard-Type Glycation with Dextran Shigeru Tazawa1, Shigeru Katayama1,2, Masahiro Hirabayashi2, Daiki Yamaguchi2, and Soichiro Nakamura1,2 1 Interdisciplinary Graduate School of Science and Technology, 2Department of Agriculture, Shinshu University, Nagano 399-4598, Japan ABSTRACT: The purpose of the current study was to determine the effects of the introduction of polysaccharide chains onto the molecular surface of buckwheat proteins on buckwheat protein surface functionality. The whole buckwheat pro- tein fraction (WBP) was prepared using 50 mM phosphate buffer (pH 7.5) containing 0.5 M NaCl and covalently linked with 6 kDa, 17.5 kDa, 40 kDa, 70 kDa, or 200 kDa dextran by Maillard-type glycation through controlled dry-heating at o 60 C and 79% relative humidity for two weeks. Conjugation with 40 kDa dextran improved the water solubility and emulsifying properties of WBP without causing a serious loss of available lysine; 84.9% of the free amino groups were conserved. In addition, we found that the introduction of dextran chains onto the molecular surfaces of WBP attenuated the antigenicity of WBP. Keywords: whole protein fraction, buckwheat, dextran, Maillard-type glycation, surface functionality INTRODUCTION A Maillard reaction-mediated modification technique was used to address this issue in the present study. Buckwheat is attracting much attention as a health food Previous work has indicated that controlled dry-heating due to its excellent nutritional properties, well-balanced (i.e., Maillard-type glycation) can be used to introduce amino acid composition, and richness in essential amino polysaccharide chains to the molecular surface of target acid such as lysine, methionine, and tryptophan (1). molecules, which drastically reduces the allergenicity of Buckwheat proteins have been shown to protect against food proteins without the use of chemical reagents 1,2-dimethylhydrazine-induced colon carcinogenesis in (13,14). In addition, glycation with polysaccharides could rats by reducing cell proliferation and cure chronic hu- favorably alter the surface functionalities of target pro- man diseases by protecting against the effects of blood teins (15-18). The safety of newly-developed compounds cholesterol and hyperpiesia (2,3). However, buckwheat formed by Maillard-type glycation has been confirmed proteins cause potent allergic symptoms, including ana- (18). There is concern that this type of modification may phylaxis, in hypersensitive patients (4). These symptoms reduce available lysine residues because the conjugation include anaphylactic reactions such as urticaria erup- occurs by covalent binding of the -amino groups of pro- tions, gastrointestinal disorders, and asthmatic attacks, teins to the reducing-end of polysaccharides. Therefore, etc. (4). Several studies have revealed that 8∼9 kDa, 17 we determined the number of free amino groups occu- kDa, 50 kDa, and 100 kDa buckwheat proteins display pied by carbohydrate moieties introduced onto the pro- robust binding activity against the sera of buckwheat al- tein molecules of the whole buckwheat protein fraction lergic patients (5-7). More recently, food allergy re- (WBP). In addition, we assessed the potential use of searchers have become aware that other fractions of WBP as a food-grade ingredient (i.e., emulsifier). The buckwheat proteins also produce a typical allergic re- present study demonstrates that Maillard-type glycation action (8-12). Thus, the allergenicity of buckwheat pro- of WBP with dextran improves its surface functionalities teins limits their use as a general food source and (e.g., water solubility and emulsifying properties) and additive. attenuates its allergenicity. Received 22 May 2014; Accepted 13 October 2014; Published online 31 December

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