A new species of Pseudomonas was isolated that produced copious amounts of an exocellular heteropolysaccharide (PS-60) after incubation for 3 days at 30°C in media containing 3% glucose as a carbon source. The polysaccharide was composed of approximately 46% glucose and 30% rhamnose and, in addition, contained 21% uronic acid and 3% O-acetyl. Upon deacetylation by a mild alkaline treatment, PS-60 produced a brittle, firm, and optically clear gel. This gelling property was thermoreversible. The PS-60 gel exhibited excellent heat stability that withstood autoclaving (i.e., 121°C for 15 min) for several cycles. The gel strength, melting point, and setting point of the polysaccharide were controlled primarily by the concentration of cations. PS-60 was not affected by a variety of enzymes. The results of tests involving various culture media and biochemical test media indicate that PS-60 is an excellent alternative gelling agent to agar.

In the past two decades, significant progress has been made in the

An arabinan and the previously characterized arabinogalactan and acidic polysaccharide complex have been isolated by extraction of defatted and deproteinized soybean cotyledon meal with water. Methylation analysis involving gas chromatography -mass spectrometry of methylated alditol acetates formed from the methylated arabinan has shown that the parent polysaccharlde is hlghly branched and of the same structural type as other arabinans associated with pectins. Methylated derivatives of mustard seed and lemon-peel arabinans and of soybean arabinogalactan have been similarly analyzed. In previous studies (1, 2) an arabinogalactan and an acidic polysaccharide complex have been isolated from soybean cotyledon meal and the main structural features of these polysaccharides have been established. In parallel investigations Morita and co-workers (3-5) have obtained similar evidence for the structure of the arabinogalactan. Morita also reported (3) that this polysaccharide, which was isolated by extraction of the meal with hot water after removal of the protein with cold dilute alkali, was accompanied by an arabinan whose structure was not examined. Arabinans of the type which are associated with pectins may be of genuine natural occurrence, e.g. in white mustard seeds (6-8), but polysaccharides containing a high proportion of arabinose residues in similar types of linkage, e.g. from sugar beet (9, 10) can also result from degradation during alkaline conditions of extraction. We have therefore re-examined the more readily soluble polysaccharides from soybean cotyledons isolated under the mildest possible conditions. Defatted soybean cotyledon meal was extracted with (i) phenol -acetic acid -water (1 :1:1) (1 1) to remove protein and (ii) water at 85" to remove the more soluble polysaccharides. Further removal of protein from the aqueous extract followed by fractional precipitation and chromatography on diethylaminoethylcellulose afforded an arabinan, an arabinogalactan, which contained arabinose and galactose residues in the proportions of 1:2.8, and an acidic polysaccharide complex. Paper chromatography of the neutral and acidic oligosaccharides formed on partial acid hydrolysis and acetolysis of the acidic polysaccharide complex showed that this preparation was at least qualitatively similar to the previously studied sample (1, 2) which had been extracted under harsher conditions. Likewise gas chromatography of the methyl glycosides formed on methanolysis of the methylated arabinogalactan showed that the parent polysaccharide was qualitatively similar to that studied previously by Morita and co-workers (3-5) and by ourselves (1, 2).Evidence for the structure of the arabinan was obtained by methylation analysis. Methanolysis of the methylated arabinan gave components with the retention times of methyl glycosides of 2,3,5-tri-and 2,3-di-0-methylarabinose. Although no methyl glycosides of a mono-0-methylarabinose were detected by g.l.c., paper chromatography of the hydrolysate of the methylated polysaccharide showed the p...

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