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[13] Gao D-M, Kobayashi T, Adachi S. Promotion or suppression of
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and 51% at 5 wt%, respectively. However, the maxi-
mum productivity of maltulose increased almost seven-
fold to ca. 41 g/(h kg-solution). Besides, the selectivity
of maltulose was little affected by the change in feed
substrate concentration, and the total sugar content
was >70% at a feed substrate concentration of 5 wt%.
These results suggest that subcritical aqueous ethanol is
a suitable solvent for effectively producing the rare
keto-disaccharides from their corresponding common
aldo-saccharides.
In conclusion, it was demonstrated that maltulose,
palatinose, cellobiulose, lactulose, and melibiulose can
be produced by isomerization of the corresponding
aldo-disaccharides in subcritical aqueous ethanol. The
hydrolytic and isomerization reactions of disaccharides
were suppressed and promoted, respectively, by
increasing ethanol concentration, which lead to high
maximum yields of keto-disaccharides. The type of
glycoside linkage and constituent monosaccharides
affected the isomerization of disaccharides. Higher
yields of keto-disaccharides linked by β-glycosidic
bond than by α-glycosidic bond from the corresponding
aldo-disaccharides were produced. On the other hand,
the keto-disaccharide, palatinose, mainly underwent
decomposition rather than isomerization.
[14] Gao D-M, Kobayashi T, Adachi S.. Production of rare sugars
from common sugars in subcritical aqueous ethanol. Food Chem.
2015;175:465–470.
[15] Gao D-M, Kobayashi T, Adachi S. Kinetic analysis for the iso-
merization of glucose, fructose, and mannose in subcritical aque-
ous ethanol. Biosci. Biotechnol. Biochem. 2015;79:1005–1010.
[16] Gao D-M, Kobayashi T, Adachi S. Kinetics of sucrose hydroly-
sis in a subcritical water-ethanol mixture. J. Appl. Glycosci.
2014;61:9–13.
[17] Bazaev AR, Abdulagatov IM, Bazaev EA, et al. PVT measure-
ments for pure ethanol in the near-critical and supercritical
regions. Int. J. Thermophys. 2007;28:194–219.
Author contributions
All the authors conceived and designed the
experiments and discussed the results. D.-M.G. per-
formed the experiments, analyzed the data and wrote
the manuscript in consultation with T.K. and S.A.
[18] Sommer D, Kleinrahm R, Span R, et al. Measurement and corre-
lation of the (p, ρ, T) relation of liquid cyclohexane, toluene,
and ethanol in the temperature range from 233.15 K to 473.15 K
at pressures up to 30 MPa for use as density reference liquids. J.
Chem. Thermodyn. 2011;43:117–132.
[19] Pfeffer PE, Hicks KB. Characterization of keto disaccharides in
solution by deuterium-induced, differential isotope-shift 13C-
NMR spectroscopy. Carbohydr. Res. 1982;102:11–22.
[20] Low NH, Brisbane T, Bigam G, et al. Carbon-13 nuclear mag-
netic resonance for the qualitative and quantitative analysis of
structurally similar disaccharides. J. Agric. Food Chem.
1988;36:953–957.
Funding
This work was partly supported by the Tojuro Iijima Foun-
dation for Food Science and Technology (D.-M.G.) and JSPS
KAKENHI [grant Number 26870296]; T. K.
Disclosure statement
No potential conflict of interest was reported by the authors.
[21] Kimura H, Nakahara M, Matubayasi N. Noncatalytic hydrother-
mal elimination of the terminal D-glucose unit from malto- and
cello-oligosaccharides through transformation to D-fructose. J.
Phys. Chem. A. 2012;116:10039–10049.
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