International Journal of Biological Macromolecules 49 (2011) 471–479 Contents lists available at ScienceDirect International Journal of Biological Macromolecules jo u r n al hom epa ge: ww w.elsevier.com/locate/ijbiomac Effect of gamma irradiation on rheological properties of polysaccharides exuded by A. fluccosus and A. gossypinus Samira Alijani, Sima Balaghi, Mohammad Amin Mohammadifar ∗ Department of Food Science and Technology, National Nutrition and Food Technology Research Institute, Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4741, Tehran, Iran a r t i c l e i n f o Article history: Received 28 March 2011 Received in revised form 10 May 2011 Accepted 25 May 2011 Available online 2 June 2011 Keywords: Gum tragacanth Gamma irradiation Viscosity Frequency sweep Particle size distribution FTIR a b s t r a c t In this study, Iranian gum tragacanth (GT) exudates from Astragalus fluccosus (AFG) and Astragalus gossyp- inus (AGG) were irradiated at 3, 7, 10 and 15 kGy. Fourier transform infrared spectroscopy (FTIR) data showed that irradiation did not induce changes in the chemical structure of either type of gum. Although particle size distribution and both steady shear and dynamic rheological properties were considerably affected by the irradiation process, the magnitude of the effect of irradiation on each of the rheological and size variables was different for the hydrocolloids. For instance, for AGG, increasing the irradiation dose from 3 to 10 kGy, the d(0.5) and D[3,2] values were reduced by one-sixth to one-eighth fold. Colour measurement revealed that the radiation process led to an increase in the yellow index and b* values for both types of GT in powder form, but it was more pronounced for AGG samples. Irradiation led to an approximate 13-fold increase in redness in AFG. Surface and shape changes of the gum crystals were studied by scanning electron microscope (SEM) and a smoother surface for irradiated samples was detected. The notable changes in functional properties of each variety of irradiated gum should be taken into consideration before using the radiation technology as a commercial tool for sterilisation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Food irradiation has been profoundly investigated, but mainly initiated as an ultimate minimal processing technology. Food is commonly irradiated with microwaves; however, the term food irradiation is used to describe a process in which food is exposed to ionising energy [1]. Sufficient energy that breaks chemical bonds is “ionising irradiation” [2]. Gamma rays involve very high-energy radiation and are able to break chemical bonds when absorbed by material [3]. The application potential of specific ionising radiation is very diverse, from inhibition of sprouting of tuber and bulb crops to production of commercially sterile food products [1]. Irradiation in doses up to 10 kGy has been approved by the IAEA, the WHO, and the FAO (IAEA, 2003) [4]. Additionally, doses as high as 75 kGy have been approved for some products (WHO, 1981) [4]. Specific appli- cations of food irradiation are approved by national legislations in over 55 countries worldwide [1]. As commercial applications of food irradiation become more accepted, the technology is increas- ingly applied not only to agricultural products but also to food ingredients and ready-to-eat meals. Irradiation is often viewed as being the last process, after packaging, used to control spoilage from pathogenic organisms. Furthermore, gamma irradiation, as ∗ Corresponding author. Tel.: +98 2122648120; fax: +98 2122376470. E-mail address: mohamdif@ut.ac.ir (M.A. Mohammadifar). an ionic and non-thermal process, has received more attention as a functional modification agent in polymer research and application. It has been applied as a physical modification method for natural polysaccharides such as starch [5]. Gamma irradiation treatment, compared to microwave, UV, ultra-high hydrostatic pressure and hydrothermal treatment, is rapid, convenient and more extensive, because ionising energy rapidly penetrates through the polysac- charide granules [6]. Polysaccharide gums provide a wide variety of functionality in foodstuffs, which includes gelling, thickening, emulsifying, and stabilising [7]. The function of polysaccharides in foods generally originates from chain entanglement, formation of junction zones between the ordered polysaccharide chains and subsequent aggre- gation. These effects are essentially governed by the molecular properties (e.g., molecular weight, degree of branching, chain rigid- ity, and functional groups) of polysaccharides and factors such as the concentration of polysaccharide and the quality of solvent, which is usually affected by the presence of sugars or salts [7]. Many studies have shown that treatments such as heating, ultra- sonication and irradiation can induce inverse changes in the desired quality of the end product by influencing the structure and func- tional properties of the polysaccharides. For example, increasing the irradiation dose in gums such as agar, guar, alginates and car- rageenan induced a decrease in the viscosity of their solutions [8–10], but for other gums, this reduction occurred only after an initial increase in the viscosity [11]. However, it was reported that 0141-8130/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ijbiomac.2011.05.030