## 1 Introduction  
Plant derived polysaccharides are major components in the human diet and although widely regarded as primary sources of energy, they revealed numerous more complex biological properties [1]. They have beneficial effects on reducing the risk factors for some chronic diseases, including cardiovascular diseases, certain types of cancer and diabetes, also explored such as immunomodolatand wound healing agents, plasma substitutes and scaffolds in tissue engineering [2; 3; 4; 5]. The variety in the biological behavior of plant polysaccharides is due to diverse nature of their structure characteristics as molecular weight, the presence of different monosaccharides as building blocks, variations in sequence, linkage, branching, and distribution of side chains [2; 4]. Furthermore, the possibility of modulating their structure make them particularly attractive. In recent years, lower molecular fractions of plant polysaccharides, and especially non-digesiblec oligosaccharides, gained attention regarded as functional foods with prebiotic activities [1; 6; 7]. Prebiotics, according to the International Scientific Association for Probiotics and Prebiotics, are defined as substrates that are selectively utilized by host microorganisms conferring health benefits [8]. The physiological benefits include stimulation of the intestinal microbiota with production of short-chain fatty acids (lactate, acetate, propionate, butyrate) and reduction of intestinal pH; inhibition of pathogen growth in the gastrointestinal tract; decreased insulin response and glucose uptake; reduction of blood lipid levels; enhancement of mineral bioavailability, etc. [9; 10]. Investigations on the precise mode of action of prebiotics are still being conducted. Nowadays, only several types of oligosaccharides with prebiotic properties, such as galactooligosaccharides (GOS) and fructooligosaccharides (FOS), are commercially available but there is an increasing interest in the development of \"second generation\" novel prebiotics with added functionality and lower cost [9; 11]. The improved functional properties include ability for modulating microbiota, protection of colonic cells against pathogens and toxins, stimulation of apoptosis of human colonic adenocarcinoma cells, synergistic empowerment of immunomodulation caused by GOS and FOS, dermatological applications, and others [12]. On this point, pectic oligosaccharides (POS), have been considered as promising prebiotic agents [7; 13]. POS are derived from the parent compound, \"pectin,\" which is a complex of plant cell-wall matrix polysaccharides consisting of homogalacturonan, rhamnoman I and II in the backbone with arabian, galactan, arabinogalactan and xylogalacturonan side-chains attached to rhamnose in rhamnogenalacturonan regions [14; 15]. Given the complexity and the heterogeneity of the pectin polymer, POS can vary significantly in their molecular weight and monosaccharide composition [14]. In this respect, the major advantage of POS is that regarding the different structural blocks comprising pectins, a variety of POS as rhamnogalacturonan oligosaccharides, galacturonan oligosaccharides, arabinogalactan oligosaccharides, galactooligosaccharides, arabinogalactan oligosaccharides can be obtained [11; 14]. Mostly, three different pathways are applied for the production of POS: (1) extraction from plants; (2) depolymerization of polysaccharides; (3) synthesis from mono- and disaccharides [1; 16; 17]. The process of depolymerization is considered as one of the most effective pathways because a wide variety of oligomers can be produced from one polymer [16]. Depolymerization strategies as physical, chemical and enzymatic hydrolysis have been developed [1; 18; 16]. Unlike the non-specific chemical and physical treatments, enzyme-catalyzed degradation is the major pathway to obtain more defined oligosaccharides with desired molecular weights and minimum adverse chemical modifications in the end products [7; 9; 18; 19].