The separation of GMP from milk whey using the modified chitosan beads
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P RO C E E D I N G S O F P B A S T 5
The separation of GMP from milk whey using the modified chitosan beads Cunben Li · Xianghua Song · San Hein · Kean Wang
Received: 2 August 2009 / Accepted: 19 April 2010 / Published online: 28 April 2010 © Springer Science+Business Media, LLC 2010
Abstract The cationic property of chitosan was used to adsorb glycomacropeptide (GMP) molecules from milk whey proteins. β-cyclodextrin was immobilized to native chitosan beads by cross-linking with 1,6-hexamethylene diisocyanate (HMDI). The resultant modified beads (CS-HMDI-BCD) presented superior adsorption affinity and capacity towards GMP. At pH 3.0, 90.23% of GMP was adsorbed with a maximum adsorption capacity corresponding to 12.87 mg of sialic acid/g-adsorbent. Desorption experiments showed that the modified beads could be regenerated and used in many cycles without significant decreases in the capacity and selectivity. Keywords Chitosan · β-cyclodextrin · Glycomacropeptide · Adsorption · Milk whey
1 Introduction Glycomacropeptide (GMP), which is released from κ-casein by the action of chymosin during cheese making (Eigel et al. 1984), is an acidic C-terminal glycopeptides containing 64 amino acid residues. GMP lacking aromatic amino acids (phenylalanine, tyrosine, and tryptophan) is useful in the diet for patients with phenylketonuria, an important innate error in phenylalanine metabolism. It also contains sugars such as N -acetylneuraminic acid (sialic acid), galactose, and N acetylgalactosamine (Abd ElSalam et al. 1996). Due to its
C. Li · X. Song · S. Hein · K. Wang () School of Chemical & Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore e-mail: [email protected]
biological activities (Dziuba and Minkiewicz 1996) and potential as an ingredient for functional food and pharmaceuticals, great attention has been given to GMP isolation and purification in recent years. GMP has been purified from sweet whey by different techniques including ultrafiltration (Chu et al. 1996), gel chromatography (Nakano and Ozimek 2002), hydrophobic interaction chromatography (Nakano and Ozimek 2000b), and ion exchange chromatography (Doultani et al. 2003; Nakano and Ozimek 2000a; Silva-Hernandez et al. 2002). Heat treatment, ethanol precipitation, and trichloracetic acid precipitation were usually combined with the above methods as pretreatment to improve the purity (Li and Mine 2004; Saito et al. 1991; Thoma et al. 2006). With anion exchange chromatography, GMP can be separated from other major whey protein with relatively high yield and purity due to its lower isoelectric point (Nakano et al. 2004). Thus, this technique is considered as one of the most practical approaches for large scale production of GMP. The major issue of this method, however, is the cost and efficiency of the adsorbents used. Chitosan (CS), a polysaccharide comprising copolymers of glucosamine and N -acetyl-glucosamine, is a derivative of the naturally abundant bio-polymer, chitin. In acidic condition, its cationic property makes it
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