A Study of the Pectin Present in the Bark of Amabilis Fir (Abies Amabilis)

Abstract

X pectic material has bee11 isolated frorn the bark of Abies anzabilis (Do~rgl.) F~r b e s in a yield of 2y0. On hydrolysis it yielded D-galact~ironic acid, ~-galactose, and L-arab~nose in a ratio of S5:4:ll, and also traces of rhanlllose. The product, when submitted to several conventional fractionation methods, a p p p r e d homogeneous. Further resolution could b e effected by acidihcation of an aqueous solut~on of the pectin, followed by ultracentrifugat~on. 'The insoluble portion (50y0) was an electrophoretically hon~ogeneous galactzrronan with [ a ]~ +246'. The material remaining in solution (30y0), here referred to as a pectic acid, had [ a ]~ +225" and on hydrolysis gave D-galacturonic acid, D-galactose, and L-arbabinose in a ratio of 74:7:19, as well as traces of rhamnose.The structure of the galacturonan was established by partial hydrolysis and methylatio~~. I t consisted of a-D-galacturonic acid residues linked together by ( I --t 4)-glycosidic bonds t o a linear macromolecule. T h e same techniques were applied to the pectic acid. While a unique str~rctural formula could not bc assigned in this case, one probable alternative involved a framework of (1 + 4)-linked a-D-galacturoIIic acid residues together with a few residues of 1,2,4-linlced L-rhamnose. Some of the galacturollrc acid units carried a t C-2 and C-3 side chains which were terminated by D-galactopyranose and L-arabinofuranose residues. A few of the latter also occurred as inner units, probably in the side chains. This appears to be the hrst t i~u e a pectic material has been resolved into a galacturonan and a pectlc a c~d containing the four sugar residues usually found in pectitls. I t is probable that the pectin occurring to a limited extent in wood has a similar composltlon.In previous investigations several polysaccharides were isolated from the bark of amabilis fir (Abies amabilis) ( I ) , namely a cellulose (2), a galactoglucoinannan (3), a gluco~nannan (4), and a xylan (5). The present study is concerned with the pectic substances also present in this bark. Pectin has previously been isolated from both wood and bark by Anderson and his co-worlters (6-9). Painter and Purves (10) obtained pectin in a yield of 770 froln white spruce inner bark. Similarly, inner bark of white birch has yielded a pectin in a yield of 3-4y0 (11). During the early stages of cell differentiation, the primary wall and the middle lamella consist largely of pectin. The pectic substances of cell walls in the phloem, cambial, sapwood, and heartwood regions have recently been studied by Thornber and Northcote (12).The pectic group of polysaccharides is based on residues of D-galacturonic acid, Dgalactose, L-arabinose, and L-rhamnose, with the galacturonic acid usually, albeit not always, predominating. A polymer containing only D-galacturonic acid residues (a galacturonan) seems to have been isolated only on one occasion, namely from sunflower heads (13). Lately, it has become evident that most of the so-called pectic acids probably also contain neutral...

Fractionation of Pectins From Sunflowers, Sugar Beets, Apples, and Citrus Fruits

“…From the evidence presented in Table 111 and discussed above it is very likely that the two coinponents in pectic acids are a linear galacturonan free of neutral sugars and a linear galacturonan t o which neutral sugars are attached as side chains. This conclusion fully confirms the results of a study of pectin from the bark of amabilis fir (12) and supports the conclusion, based on a study of sisal pectic acid (3), that the pectic acid consisted of "a mixture of acidic polysaccharides, one composed solely of D-galacturonic acid residues and the other or others containing both neutral sugar and D-galacturonic acid residues". Barrett and Northcote (22) have shown that apple pectin is degraded when heated in buffer a t pH 6.8 to give a galacturonan and an acidic polysaccharide which contains neutral sugars.…”

“…T h e galacturonic acid contents decreased with increasing sodium acetate concentration and were markedly lower in the fractions precipitated by ethanol. T h e specific rotations were directly related to galacturonic acid content and, in the purest fractions, were considerably higher than those which have been reported for pectins or pectic acids (2,12,16). T h e limiting viscosity numbers increased with increasing sodium acetate concentration except for apple pectic acid, in which the first fraction had the highest limiting viscosity number and subsequent fractions a lower and nearly constant value.…”

“…The present paper describes the fractionation of pectins from sunflower heads, sugar beets, apples, and citrus fruits. While this work was in progress it was reported that a galacturonan from amabilis fir pectin could be precipitated from aqueous solution by sodium chloride (12) ; however, in contrast t o the present work, ultracentrifugation was required to separate the galacturonan.…”

“…There have been only txvo reports of the isolation of homoglycans from pectins. Both were galacturonans \vl~ich yielded only D-galacturonic acid on hydrolysis; one was isolated from sunflower heads (13), the other from the bark of amabilis fir (12). The galacturonan from sunflower heads was obtained by extraction with ammonium oxalate:oxalic acid and reprecipitation in 60% ethanol.…”

Lemon-peel pectin. III. Fractionation of pectic acids from lemon-peel and lucerne

“…The galacturonan isolated by Bhattacharjee and Time11 (6) from Amabilis fir bark rnay provide a second example. This pectin, however, was extracted from bark which had been treated previously with hot potassium acetate (6). In the light of Barrett and Northcote's observations that homogeneous apple pectin may be degraded on heating with phosphate buffer at p H 6.8 to give two structurally dissimilar degraded polysaccharides, one of them a galacturonail (lo), the occurrence of a native undegraded galacturonan in Amabilis fir bark remains open to doubt.…”