Cellulose was hydrolyzed with hot-compressed water (HCW; ∼310 °C, 9.8 MPa) using an HCW-flow reactor. HCW was continuously delivered into a reactor charged with cellulose. The effluent from the reactor was cooled and separated into a water-soluble fraction (WS) and a water-insoluble fraction which deposited after cooling (DP). Cellulose started to decompose into WS and DP when HCW was delivered above 230 °C. The main components of the WS were hexose and oligosaccharides ranging from a dimer to a pentamer, and the DP consisted of polysaccharides ranging from a hexamer to an eicosamer or more polymerized saccharides. When HCW was delivered at 295 °C, nearly all of the cellulose decomposed after a 12-min flow of HCW, and 81 wt % of WS and 18 wt % of DP were obtained. The formation rates of WS and DP increased as the temperature of HCW increased. However, the composition of WS and DP barely changed with the HCW temperature under around 280 °C, which corresponds to the softening point of the cellulose. When the HCW temperature was further increased, the depolymerization of the products proceeded. The decomposition rate of cellulose itself was not affected by the flow rate of HCW, but the depolymerization of the products was suppressed when the flow rate of the HCW was increased.

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Despite their wide occurrence, proteoglycans (PGs) have never been isolated from the saliva of higher animals. We found that the Collocalia glycoproteins isolated from edible birds'-nests (the dried forms of regurgitated saliva of male Collocalia swiftlets) were rich in a PG containing nonsulfated chondroitin glycosaminoglycans (GAGs). We have devised a method to isolate a PG from the water extract of the white nest built by Aerodramus fuciphagus (white nest swiftlets) with a yield of 2-mg PG per gram nest. This PG contained 83% of carbohydrates, of which 79% were GalNAc and GlcUA (D-glucuronic acid) in an equimolar ratio. By using chondroitin AC lyase, the structure of GAGs in this PG was established to be chondroitin ( --> 4GlcUAbeta1 --> 3GalNAcbeta1 --> )(n) chains. The average molecular mass of the chondroitin chain was estimated to be 49 kDa by gel filtration. We have isolated a linkage region hexasaccharide, DeltaHexUAalpha1 --> 3GalNAcbeta1 --> 4GlcUAbeta1 --> 3Galbeta1 --> 3Galbeta1 --> 4Xyl, from this PG by chondroitinase ABC digestion to show that the GAGs in this PG are also linked to the core protein through the common tetrasaccharide linker, GlcUAbeta1 --> 3Galbeta1 --> 3Galbeta1 --> 4Xyl, found in various PGs. As water was not effective in extracting uronic acid-containing glycoconjugates from the black nest built by black nest swiftlets (A. maximus), we used 4 M guanidium chloride and anion-exchange chromatography in the presence of urea to extract and isolate about 30 mg of a chondroitin PG preparation from 10 g of the desialylated black nest. As the biological significance of chondroitin is still not well understood, bird's nest should become a convenient source for preparing this unique GAG to study its biological functions.

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