NANOFILTRATION AS A TOOL FOR HIGH-YIELD PURIFICATION OF DIETARY OLIGOSACCHARIDES

Abstract

Fructo-oligosaccharides (FOS) are linear bioactive molecules consisting of one terminal glucose and other fructose units and belong to the group of prebiotics with scientifically proven benefits for human health. Physiological active compounds like trisaccharides (FOS3), tetrasaccharides (FOS4) and pentasaccharides (FOS5) can be produced from sucrose using enzyme-fructosyltransferase. The reaction mixture obtained in this way contains, in addition to the desired prebiotics, glucose, fructose and an unreacted amount of sucrose. Direct incorporation in products of food and pharmaceutical origin is limited due to the presence of unwanted carbohydrates (mono- and disaccharide), and to increase the functional value of the mixture, the attention was focused on their removal. In this regard, membrane separation techniques present a very suitable solution for obtaining a product with a higher FOS proportion. This study aimed to determine the optimal conditions for purification process of produced FOS mixture using nanofiltration membrane modules. Therefore, the influence of membranes with different MWCO (300-500Da and 600-800Da), temperature (20-45°C) and carbohydrate concentration in feed solution (1-5%) at a constant flow rate of 22 mL/min was investigated. From the initial mixture containing 60.2% FOS, 29.7% monosaccharides and 10.1% sucrose, after purification process under determined optimal conditions (membrane 300-500Da, temperature 35°C and carbohydrate concentration 3%), the product with 88.8% FOS, 10.0% sucrose and 1.2% monosaccharides in total carbohydrates was obtained. Purification yield was greater than 95% and the rejection coefficients for glucose, fructose, sucrose, FOS3, FOS4 and FOS5 were 0.17, 0.20, 0.95, 0.99, 1.00 and 1.00, respectively. Based on the calculated purification factor, it can be concluded that the initial mixture is refined 1.47 times. This result suggests a significant increase in the purity of the final mixture, which can be used as a sugar substitute or addition to numerous products that would be suitable for all consumers, including those suffering from diabetes.