Carbohydrate Polymers 117 (2015) 370–376 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me pa g e: www.elsevier.com/locate/carbpol Chemical structure of the arabinogalactan protein from gum ghatti and its interaction with bovine serum albumin Kanika Ghosh, Sayani Ray, Debjani Ghosh, Bimalendu Ray ∗ Natural Products Laboratory, Department of Chemistry, The University of Burdwan, Golapbag, Burdwan 713 104, West Bengal, India a r t i c l e i n f o Article history: Received 24 June 2014 Received in revised form 14 September 2014 Accepted 22 September 2014 Available online 7 October 2014 Keywords: Anogeissus latifolia gum Arabinogalactan protein Smith degradation ESMS analysis AGP–BSA interaction a b s t r a c t Exudate gums, because of their beneficial properties, have been significant items of international trade in various industries for centuries. This manuscript sets out to gain insight into the fine structural details of an arabinogalactan protein (AGP) of gum ghatti (Anogeissus latifolia gum). The presence of a highly branched 554 kDa AGP having 1,6-linked Galp, 1,2-linked Manp, 1,3-linked Araf and 1,4-linked GlcpA main chain, substituted at O-4,6 of 1,2-linked Manp, and O-3/O-3,4 of 1,6-linked Galp residues by Araf, Arap and Galp units was revealed by chemical, chromatographic, ESMS, and NMR analyses. In particular, ESMS analysis of per acetylated oligomeric fragments derived from AGP by Smith degradation followed by acetylation was described as a commanding tool for providing critical structural information on a spectrum of glycerol tagged oligosaccharides. In addition, formation of an electrostatically driven com- plex between the isolated AGP and bovine serum albumin resulting in changes in the microenvironment around the tryptophan residues of BSA was established. A moderate radical scavenging activity compa- rable with those of standard antioxidants was observed from the AGP fraction (∼94% at 1 mg/mL) that could be valuable in foods or pharmaceutical products as alternatives to synthetic antioxidants. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction For thousand of years exudates gums have been important arti- cles of international trade in the food, pharmaceutical, adhesive, paper, textile, and other industries. Gum ghatti, the exudates from the large deciduous tree Anogeissus latifolia (Combretaceae, Myr- tales), is one such item that have been widely evaluated in food and certain biotechnology industries (Deshmukh, Setty, Badiger, & Muralikrishna, 2012). The generally regarded as safe status of gum ghatti in USA is affirmed in 1976, but the EEC because of the lack of the more detailed safety evaluation deleted it from the Euro- pean list of approved additives (Stephen & Churms, 1995). Renewed interest in gum ghatti is primarily due to its excellent emulsifi- cation properties (Castellani, Al-Assaf, Axelos, Phillips, & Anton, 2010a; Castellani et al., 2010b; Kaur, Singh, & Singh, 2009), which is probably better than gum Arabic (Ido et al., 2008). Moreover, the cost is attractive, comparable with that of gum Arabic. Also, the quality of this gum has been improved and its emulsification mech- anism is clarified (Ido et al., 2008; Katayama et al., 2008). Indeed, the acceptance of gum ghatti in food in Japan, Latin America and ∗ Corresponding author. Tel.: +91 342 2557709; fax: +91 342 2564452. E-mail addresses: bimalendu ray@yahoo.co.uk, bimalendu.ray@gmail.com (B. Ray). other countries, have made it an alternative hydrocolloid for the food industry as a thickener and emulsifying agent (Castellani et al., 2010a). Despite the well-recognized importance of the polysaccharide from gum ghatti and more than fifty years of investigation fol- lowing their first description (Aspinall, Hirst, & Wickstrom, 1955), finer structural details are still missing. The complex nature of the molecular core and extreme size heterogeneity presents a major technical difficulty defying detailed structural analysis. To date, principal findings from two complementary analytical approaches essentially conceptualize and confine our current understanding of the polysaccharide from gum ghatti. First, chemical and chro- matographic analyses of the oligosaccharides generated from gum ghatti has led to recognition of a molecular core comprising of alternating 1,4-linked -d-GlcpA and 1,2-linked d-Man residues to which extremely complex arrays of neutral sugar units (Galp, Araf, and Arap) and GlcpA are attached (Aspinall et al., 1955; Aspinall, Auret, & Hirst, 1958; Aspinall, Bhavanan, & Christen, 1965; Aspinall & Christen, 1965; Aspinall & McKenna, 1968; Aspinall, 1969). Technically, this chemical strategy was powerful but tedious. In contrast, using methylation analysis and NMR spectroscopy Kang and coworkers reported the presence of a highly branched polysac- charide containing 1,4-linked GlcpA, 1,6-linked Galp and 1,2-linked l-Araf main chain substituted at O-3 and O-4 of 1,6-linked -d- Galp residue by side chains (Kang et al., 2011a,b, 2012). A major http://dx.doi.org/10.1016/j.carbpol.2014.09.084 0144-8617/© 2014 Elsevier Ltd. All rights reserved.