Towards the development of a membrane reactor for enzymatic inulin hydrolysis

Abstract

Ultra high fructose syrup is of increasing importance, because of its sweetening properties. Fructose is often obtained by glucose isomerization. However, this process has a relatively low conversion (around 45%), and it uses a complex purification scheme. An alternative process involves the hydrolysis of natural products, such as inulin, a polymer which contains between 5 and 65 molecules of fructose. The use of enzymes in such hydrolysis reactions would add the benefit of mild reaction conditions and a better product profile. In this work, the enzymatic hydrolysis of inulin has been studied in a membrane reactor (EMR). A first set of experiments aimed to find the optimum operating conditions, in terms of pH (a value of 4.5 was obtained as optimum), substrate concentration (a maximum of 100 g/L is recommended, because of the ease of inulin precipitation), and substrate/enzyme ratio. All experiments were conducted at 50 °C. Then, enzymes were immobilized in order to be able to reuse them, which would result in a more economically feasible process. As immobilization supports both hollow fibre membranes and particulates have been used and compared, and methods of improving the amount and/or the stability of the immobilized enzymes have also been proposed and tested. The results show that the EMR is capable to retaining more than 50% of the initial activity that the enzyme has in solution over at least five repeated reaction cycles. This work can provide a preliminary basis for the production of fructose syrups with a commercial inulinase preparation immobilized onto a membrane.