Study of effects and conditions on the solubility of natural polysaccharide gum karaya Hana Postulkova a, * , Ivana Chamradova a , David Pavlinak b , Otakar Humpa c , Josef Jancar a, d, e , Lucy Vojtova a, d a CEITEC e Central European Institute of Technology, Brno University of Technology, Purkynova 656/123, 612 00, Brno, Czechia b Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlarska 2, 61137 Brno, Czechia c Josef Dadok National NMR Centre, Central European Institute of Technology, Masaryk University, Kamenice 753/5, 625 00 Brno, Czechia d SCITEG, a.s., Brno, Czechia e Faculty of Chemistry, Institute of Materials Science, Brno University of Technology, Purkynova 118, 612 00 Brno, Czechia article info Article history: Received 25 September 2016 Received in revised form 23 December 2016 Accepted 6 January 2017 Available online 6 January 2017 Keywords: Natural gum Polysaccharide Gum karaya Sterculia urens Solubilization Deacetylation abstract Natural polysaccharide gum karaya (GK, Sterculia urens) is a plant exudates widely available and rela- tively cheap biomaterial, which is used in food industry. However, GK is insoluble in water and it limits subsequent processing and broader utilization in medicine. Different conditions for the solubilization of GK were evaluated in this work (e.g. type and concentration of hydroxide, concentration of GK dispersion and time of solubilization process) which were not published before. GK samples were compared using different types of characterization techniques such as ATR-FTIR, NMR, TGA-FTIR, DSC, SEM and rheology. Optimized conditions for successful GK solubilization proceeded with 1 mol l 1 of sodium or potassium hydroxide and 2 wt% dispersion of GK at room temperature. A novel mechanism was suggested and by this mechanism the complex plant based biopolymer can be solubilized through the careful control of its ionic environment and degree of deacetylation. Resulted water soluble GK seems to be promising biomaterial forming hydrogels useful in regenerative medicine. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Natural gums are widely available and relatively cheap material with interesting properties. Gums are commonly utilised in com- mercial food additives, pharmaceutical industry and in medicine e.g. in development of hydrogels for wound dressings and drug delivery systems (Mirhosseini & Amid, 2012). However, some gums are naturally insoluble in water. For example gum karaya (also Sterculia gum) is insoluble in water which could restrict its further use. Thus, complex study of different solubilisation conditions and comparison of insoluble and soluble material is desirable. GK is a natural gum exudate of the Sterculia urens tree belonging to the family Sterculiaceae (Singh & Vashishtha, 2008; Singh, Sharma, & Pal, 2011). It is a branched and partially acetylated polysaccharide which is hydrophilic, anionic nature and it is ob- tained as a calcium and magnesium salt (Babu, Prasad, & Ramana Murthy, 2002; Silva, Brito, de Paula, Feitosa, & Paula, 2003; Singh et al., 2011). GK is a tree sap (Panda, 2010) and contains b-D- galactose, L-rhamnose, b-D-glucuronic acid and D-galacturonic acid and other residues (Verbeken, Dierckx, & Dewettinck, 2003). The wide interest in GK-based biomaterials is due to the unique combination of features such as biocompatibility, high swelling and water retention capacity, high viscosity, gel and film forming, adhesion abilities and high molecular mass (Le Cerf, Irinei, & Muller, 1990; Singh & Sharma, 2008). GK is also resistant to hy- drolysis by mild acid and it is partly resistant to bacterial and enzymatic degradation (Verbeken et al., 2003). Original gum karaya (OGK) is insoluble and only swells in water. The swelling behaviour of GK is caused by the presence of the acetyl groups (8 wt%) (Le Cerf et al., 1990; Verbeken et al., 2003). GK powder absorbs water and swells up to 60e100 times of the orig- inal volume, producing a viscous dispersion (Verbeken et al., 2003). Previous works showed increasing solubility of GK by alkali treat- ment (most commonly are used sodium hydroxide (NaOH), * Corresponding author. E-mail addresses: hana.postulkova@ceitec.vutbr.cz (H. Postulkova), ivana. chamradova@ceitec.vutbr.cz (I. Chamradova), d.pavlinak@mail.muni.cz (D. Pavlinak), humpa@chemi.muni.cz (O. Humpa), josef.jancar@ceitec.vutbr.cz (J. Jancar), lucy.vojtova@ceitec.vutbr.cz (L. Vojtova). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd http://dx.doi.org/10.1016/j.foodhyd.2017.01.011 0268-005X/© 2017 Elsevier Ltd. All rights reserved. Food Hydrocolloids 67 (2017) 148e156