Chemistry Reference
In-Depth Information
and specificity. Some may prefer lactose as an acceptor, others sucrose. Thus,
research has been conducted into the characteristics of the enzyme from a
number of microorganisms (Takaichi et al., 1995; Choi et al., 2004b; Park
et al., 2005). The reaction conditions, such as substrate concentration and
reaction time, are also important (Fujita et al., 1992a). The
-fructofurano-
sidase is sometimes called ''levansucrase''. Microorganisms belonging to the
genera Arthrobacter and Bacillus are mostly used both in research and
industrially to produce
-fructofuranosidase (Fujita et al., 1992b; Hara
et al., 1992; Kawase et al., 2001; Pilgrim et al., 2001). A variety of methods
have been used in production - some in which whole microbial cells are used,
others have used crude cell extracts and still others have used purified enzyme.
Fujita et al. (1992a) describe an industrial method for producing lactosucrose
using
-fructofuranosidase from Arthrobacter sp. strain K1, which seems to
be the one used by Ensuiko Sugar Refining Co., Ltd. and by the Hayashibara
Company. These two Japanese-based companies are the main producers of
commercial lactosucrose. The yield of lactosucrose from the two substrates
(sucrose and lactose) is low (5-30% of total sugars in the reactants). By careful
selection of strains and the use of optimal conditions, batch reactions have
been able to produce 181 g lactosucrose from 225 g sucrose and 225 g lactose
(40% conversion), but the concentration of lactosucrose in the reactor has
only been about 18% (see Park et al., 2005). Those authors used a strain of
B. subtilis at pH 6 and 558C for a 10 h reaction. This result is typical of the
published data for batch reactions. Kawase et al. (2001), who described the
production of lactosucrose using a simulated moving bed reactor, claim that
this continuous process increases the yield to 56% compared to 48% typical of
a batch fermentation.
There is a major problem with the presence of other carbohydrate
products and residual amounts of unused lactose and sucrose in the process.
Thus, it is typical for crude product to be decolourized, demineralized and
purified by column chromatography using a strongly acidic cation-exchange
resin. A fermentation method to remove monosaccharides, like glucose, has
also been used. The lactosucrose is spray dried (Hara et al., 1992, 1994a). The
aim is to obtain a purified solution of lactosucrose of 45%, w/v, prior to spray
drying. The two major producers sell lactosucrose as a powder with different
degrees of purity (40, 55 or about 70% lactosucrose in the powder). Thus, a
considerable concentration of other carbohydrates remains in the product.
In a series of publications, Petzelbauer et al. (1999, 2000, 2002a,b) used
thermostable purified enzymes from S. solfataricus and Pyrococcus furiosus
to produce lactosucrose in a continuous stirred-tank reactor at 708C, coupled
to a cross-flow ultrafiltration module. They also used an immobilized enzyme
system. Their data do not show that they were able to achieve the yields
obtained in commercial systems. However, they demonstrated the stability of
