Download Sugar Analysis and Utilization of Dietary Fiber from Sweetpotato as

Foods Food Ingredients J. Jpn., Vol. 213, No.8, 2008
Sugar Analysis and Utilization of Dietary Fiber from Sweetpotato as a Foodstuff
-Application of Un-Utilized Polysaccharide Resources in Southern KyushuToshihiko Suganuma, Kanefumi Kitahara, and Kiyotaka Fujita
Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University
1-21-24, Korimoto, Kagoshima 890-0065, Japan
Summary
Sweetpotato is one of the major crops in Southern Kyushu, utilized mainly for starch and in
shochu-manufacture. Sweetpotato starch residues and shochu distillation waste are at present
generally discarded without recycling.
In our laboratory, we have therefore focused our research on sweetpotato cell wall material (CWM)
and its conversion to dietary fiber resources. CWM was separated into pectin, hemicellulose and
cellulose fractions, and comparisons were made with samples from potato and cassava. Sugar
composition analysis by HPEAC-PAD indicated that sweetpotato CWM had the most abundant
pectin fraction among the three CWM's. Hemicellulose fractions from the three plants showed
marked differences in sugar composition.
Some bacteria strain (Bacillus sp. M4) isolated from soil produces CWM solubilizing enzymes
which attack protopectin moieties. Protopectinase activity is due to a complex of several
related-degradation enzymes and to assess individual primary enzymes, we determined sugar
alcohols derived from reducing-end residues of solubilized products. Rhamnitol and galactitol were
the major products from the large and small molecule fractions, respectively, indicating that
rhamnogalacturonase first attacks the protopectin moieties in sweetpotato CWM to solubilize and
thereafter a galactanase removes galactan side chains. Animal testing in rats showed positive
effects of solubilized products on triglycerides in blood.
As an additional project, in order to reduce shochu distillation waste in Southern Kyushu, we have
developed a new process of shochu making without emission. Before the distillation, fermented
moromi is separated into liquid and solid fractions, which are distilled separately to give new types
of shochu and residue as a foodstuff. The solid distillation residue contains rich dietary fiber and
anti-oxidant substances, and thus might provide beneficial foodstuffs for metabolic syndrome
patients.