Lactosucrose (lactosylfructoside, O-β-D-galactopyranosyl-(1 → 4)-O-α-Dglucopyranosyl(1 → 2)-β-D-fructofuranoside) is an oligosaccharide consisting of galactose, glucose, and fructose and has several benefits. This compound is 30 % as sweet as sucrose and used as functional food ingredient. Additionally, lactosucrose also plays an important role in the refinement of sugars in the food industry (Kawase et al. 2001).
Method of Production
Lactosucrose, a trisaccharide, can be synthesized either by transfructosylation of lactose with sucrose or transgalactosylation of sucrose with lactose.
10.5.1.1 Enzyme Involved
The biosynthesis of lactosucrose can be obtained with lactose and sucrose as substrates by the following enzymes:
1. Levansucrase (EC 18.104.22.168)
2. Fructofuranosidase (EC 22.214.171.124)
3. β-D-galactosidase (EC 126.96.36.199)
Levansucrase and fructofuranosidase have transfructosylation activity, whereas β-D-galactosidase has both hydrolytic and transgalactosylation activity.
Commercially, lactosucrose (lactosylfructoside) has been produced from sucrose and lactose by transfructosylation (Gänzle et al. 2008). The microorganisms such as Zymomonas mobilis, Paenibacillus polymyxa, and Bacillus subtilis have been used as a source for levansucrase whereas Bacillus circulans and Arthrobacter sp. For β-D-galactosidase and fructofuranosidase, respectively (Kawase et al. 2001; Li et al. 2009; Han et al. 2009; Choi et al. 2004; Park et al. 2005). Increase in lactosucrose yields (from 29 to 43 %) was observed by a mixed enzyme system coupling the transfructosylation of lactose to glucose removal by glucose oxidase (Han et al. 2009). The selection of strain, substrate concentration, and reaction time along with other optimal conditions play an important role in the production of lactosucrose.
B. subtilis was found to be an effective producer of levansucrase, and the maximum lactosucrose production (181 g L−1) was observed at 55 °C and pH 6.0 after 10 h of incubation (Park et al. 2005). Lactosucrose has also been produced through continuous process in a packed bed reactor using mutant strain of Sterigmatomyces elviae, which resulted in the production of 192 g L−1 of lactosucrose at 50 °C and pH 6.0 with the flow rate of 1.2 mL/min (Lee et al. 2007). Z. mobilis strain has been applied for levansucrase, and the maximum lactosucrose conversion efficiency of 28.5 % has been observed at 23 °C and pH 7.0 with lactose monohydrate (18.0 % w/v) and sucrose (18 % w/v) as substrate. The main problem associated with the low yield of lactosucrose is the presence of other carbohydrate products. To overcome this problem, a mixed enzyme system containing a levansucrase and a glucose oxidase has also been applied, and as a result of this, the efficiency of lactose and sucrose conversion to lactosucrose increases to 43.2 % (Han et al. 2009).