Obesity is a major public concern in modern society, resulting in increased health risks of related diseases. Natural fruit juices, that in general are considered healthy and nutritious, are now getting negative criticism due to their high sugar and calorie contents. The primary objective of this research is to develop an enzymatic process to reduce the calorie content of fruit juices. The main sugar in citrus juices is the disaccharide sucrose. In nature there are several enzymes (fructansucrases) capable of catalyzing both sucrose hydrolysis (to glucose and fructose) and the polymerization of fructose to beta-D-fructofuranose polymers (fructans). Fructans are indigestible, low-calorie fibers, and are considered as prebiotic food ingredients. Thus, by introducing fructansucrases into natural juices it should be possible to convert half of the calorie content of sucrose into the indigestible fructan. This approach may not only reduce the calorie content of the juice without releasing any byproducts, but also should upgrade its nutritional value.
We have identified a suitable fructansucrase, the Zymomonas mobilis levansucrase, capable of working at typical juice processing conditions of low pH and temperature. The gene encoding the enzyme was cloned and overexpressed in E. coli. An efficient and scalable procedure for purifying the enzyme was developed based on its unique properties at different pHs (1). Our results indicate that the enzyme can function in natural juice with high catalytic efficiency, hydrolyzing more than 95% of the available sucrose and converting fructose to the high molecular weight polymer, levan. The process can be performed on a time scale that actually enables the enzymatic treatment to be integrated in a commercial process.
(1) Goldman D, Lavid N, Schwartz A, Danino D and Shoham Y. (2008) Two active forms of Zymomonas mobilis levansucrase: An ordered microfibril structure of the enzyme promotes levan polymerization. J. Biol. Chem. 283:32209-32217.
