Adriana C. Flores-Gallegos,1 Juan C. Contreras-Esquivel,1 Jesús A. Morlett-Chávez,2 Cristóbal N. Aguilar,1 and Raúl Rodríguez-Herrera 1*
1 Food Research Department, School of Chemistry, Universidad Autónoma de Coahuila, Boulevard Venustiano Carranza and José Cárdenas s/n, República Oriente, Saltillo 25280, Coahuila, Mexico.
2 Clinical and Molecular Diagnosis Department, Universidad Autónoma de Coahuila, Boulevard Venustiano Carranza and José Cárdenas s/n, República Oriente, Saltillo 25280, Coahuila, Mexico.
Fructose and fructo-oligosaccharides (FOS) are important ingredients in the food industry. Fructose is considered an
alternative sweetener to sucrose because it has higher sweetening capacity and increases iron absorption in children,
and FOS’s are a source of dietary fiber with a bifidogenic effect. Both compounds can be obtained by enzymatic hydrolysis of inulin. However, inulin presents limited solubility at room temperature, thus, fructose and FOS production is carried out at 60C. Therefore, there is a growing interest to isolate and characterize thermostable inulinases. The aim of this work was to evaluate the capacity of different fungal strains to produce potential thermostable inulinases. A total of 27 fungal strains belonging to the genera Aspergillus, Penicillium, Rhizopus, Rhizomucor and Thermomyces were evaluated for production of inulinase under submerged culture using Czapek Dox medium with inulin as a sole carbon source. Strains were incubated at 37C and 200 rpm for 96 h. Crude enzyme extract was obtained to evaluate inulinase and invertase activity. In order to select the fungal strain with the highest thermostable inulinase production, a selection criterion was established. It was possible to determine the highest inulinase activity for Rhizopus microsporus 13aIV (10.71 U/mL) at 36 h with an optimum temperature of inulinase of 70C. After 6 h at 60C, the enzyme did not show any significant loss of activity and retained about 87% activity, while it only retains 57% activity at 70C. According to hydrolysis products, R. microsporus produced endo and exo-inulinase.