The cell wall materials (CWMs) from sweetpotato (Ipomoea batatas cv. Kokei 14), cassava (Manihot esculenta), and potato (Solanum tuberosum cv. Danshaku) and commercial sweetpotato fiber as well as their polysaccharide fractions were analyzed for sugar composition by the high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) method. The separation of arabinose and rhamnose, and xylose and mannose, by this method has been improved using a CarboPac PA 10 column. Pretreatment of the CWMs and cellulose fractions with 12 M H(2)SO(4) was required for complete hydrolysis to occur. Commercial sweetpotato fiber was found to be mainly composed of glucose (88.4%), but small amounts of other sugars were also detected. Among the root crops, sweetpotato CWM had the highest amount of pectin and galacturonic acid. Fucose was detected only in cassava CWM and its hemicellulose fraction, while galactose was present in the highest amount in potato CWM. Among the polysaccharide fractions, it was only in the hemicellulose fraction where significant differences in the sugar composition, especially in the galactose content, were observed among the root crops.

The potential chemopreventive properties of the dietary fiber prepared from sweetpotato (Ipomoea batatas L.) roots were examined to promote the demand of this residue from the starch industry. Dietary fiber was prepared by treating starch granules-removed residue with α-amylase. The dietary fibers at 1% concentration enhanced the growth of Bifidobacterium adolescentis and Bifidobacterium breve in vitro among 5 species of Bifidobacterium, which exist in the human intestinal tract. Analysis of the components of these fibers suggested that their pectin and hemicellulose were concerned with a promotion effect on the growth of bifidobacteria. Water-and oil-holding capacity of the fibers in the varieties with orange-colored flesh was relatively superior to ones from the varieties with yellow-or purple-colored flesh. Furthermore, the dietary fibers adsorbed about 90% of the mutagen, Trp-P-1. Commercial sweetpotato fiber, a byproduct of citric acid production from the residue from the starch industry, had slight effect on the growth of bifidobacteria and was lower in adsorption capacity of Trp-P-1 than the fibers prepared from sweetpotato roots. These results indicate that the residue from the sweetpotato root starch industry is available as a dietary fiber with physiological functions. Discipline: FoodAdditional key woods: residue from starch industry, bifidobacteria, fiber component, water-holding capacity, oil-holding capacity

Cell wall materials (CWMs) from sweetpotato, cassava, and potato starch residues were degraded using a crude enzyme solution from the culture filtrate of a Bacillus sp. isolated from soil, Bacillus sp. M4. This organism has been found to secrete polygalacturonic acid lyase (PGL) and glycan depolymerase activities, especially arabinanase, but cellulase activity was nearly absent. Sugar analysis of the solubilized product after enzyme treatment at pH 7.0 revealed that it is mainly composed of galacturonic acid, galactose, and arabinose, the sugars found commonly in the pectin fraction. This suggested the presence of a protopectinase (PPase) activity in the culture filtrate. The presence of EDTA completely inhibited PGL but PPase activity was almost retained, suggesting that the PGL is not the primary activity responsible for pectin solubilization. The mode of action of the crude enzyme was determined by terminal sugar analysis using HPAEC-PAD after hydrolysis of the reduced products. Results revealed that galactose is the main neutral sugar at the reducing terminal of the products, although rhamnose was also present in the higher molecular weight component. This suggested that at neutral pH, the primary activity in the culture filtrate of Bacillus sp. M4 is a B-type PPase, which attacked the galactan as well as rhamnogalacturonan moieties of the protopectin, resulting in the release of a soluble pectin fraction.

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