1. Sara López-Sanz 1, F. Javier Moreno 1, Antonia Montilla 1, Rodrigo Moreno 2, Mar Villamiel 1 1 Instituto de Investigación en Ciencias de la Alimentación, CIAL (CSIC-UAM) C/Nicolás Cabrera 9, 28049 Madrid, Spain 2 Instituto de Cerámica y Vidrio, ICV (CSIC), C/ Kelsen 5, 28049 Madrid, Spain. In the last few years, the increasing interest toward prebiotic carbohydrates as functional food ingredients has promoted the enzymatic synthesis of commercial galactooligosaccharides (GOS) and new lactose derivatives such as those derived from lactulose (OsLu) [1]. GOS are known oligosaccharides that can be used in a number of applications due to their nutritional, bioactive and technofunctional properties [2]. OsLu are new oligosaccharides having potentially better bioactivity than GOS, as it has been demonstrated by recent in vitro and in vivo studies. However, the development of novel bioactive oligosaccharides will be of commercial interest only if they are formulated into foods and placed in the market. In this sense, the different formed structures determine not only the physiological effects of the commercial preparations, but also their physicochemical properties and, consequently, their applications. To the best of our knowledge hardly any information is available on the rheological properties of GOS and, in the case of OsLu, no investigation has been done on their technological properties. To study the rheological behavior of both ingredients, Vivinal ® GOS and OsLu, including the flow and viscosity curves and the effect of temperature and time on viscosity. Objetive Introduction Vivinal ® GOS // OsLu - Rheometer rotational Haake MARS in controlled shear rate mode. - Measurement system: plate-plate (PP35), ø = 35 mm and distance = 1 mm - Temperature regulated with thermostatic bath -The rheological behaviour of both ingredients, Vivinal ® GOS and OsLu, is strongly influenced by the shear rate, shear time and temperature. -These data provide important information on the application of prebiotic carbohydrates in food processing, because better rheological characteristics could give rise to an equivalent functionality with smaller amount of ingredient, helping in the reduction of cost production. Materials and methods Conclusions References: [1] Moreno F.J. et al. (2014) Analysis, structural characterization, and bioactivity of oligosaccharides derived from lactose. Electrophoresis. 35, 1519-1534. [2] Lamsal. (2012) Production, health aspects and potential food uses of dairy prebiotic galactooligosaccharides. Journal of the Science of Food and Agriculture 92, 2020–20 Results and discussion Effect of share rate (Figure 1 and 2) At 4°C, in the shear rate range applied (0-10 s -1 ), the flow and viscosity curves of GOS and OsLu were very close to Newtonian, whereas at temperatures higher than 25°C in the shear rate range applied (0-500 s -1 ), became pseudoplastic, suggesting structural changes of the sample. Viscosity of OsLu was higher than that of Vivinal ® GOS, probably ascribed to the differences in the chemical composition. Effect of share time (Figure 3) An increase in viscosity was observed in both ingredients, indicating their rheopexy. This demonstrates that shearing promotes the formation of a network structure associated with the modification of the sample. Acknowledgments: Project AGL2011-27884 Effect of temperature (T) Effect of time of share (t) Effect of temperature (Figure 4) A decrease of viscosity was observed in both ingredients. OsLu seemed to be more stable than Vivinal ® GOS, because in the latter, more irregular behaviour was found. Figure 3. Variation of viscosity with time at constant share rate (10 s -1 ) and temperature (25 ºC). Figure 1. Flow and viscosity curves of Vivinal ® GOS at 35ºC. Figure 4. Variation of viscosity with temperature at constant share rate (10 s -1 ) during 1 h. Figure 2. Flow and viscosity curves of OsLu at 35ºC.