Carbohydrates from the aerial and subterranean parts of Curcuma longa

Abstract

Curcuma longa L. is a perennial herbaceous plant of the family Zingiberaceae and is indigenous to South Asia, tropical Australia, etc. The principal raw material of C. longa is the rhizomes, yellowish-gray on the outside, golden-yellow in cross section. The pear-shaped or egg-shaped I order rhizomes or cylindrical side runner II order rhizomes are used commercially. Rhizome powder is widely used as a spice to improve the taste of food, to give it a yellow color, and to improve digestion. It exhibits cholegogic, diuretic, and stimulant activity [1–4]. Our goal was to study the content and composition of the carbohydrates depending on the introduction site, in particular, under Tashkent oasis conditions. We studied air-dried powdered I and II order rhizomes, roots, and leaves. Lipophilic compounds were isolated from raw material by treatment with CHCl3:EtOH (2:1, v/v). Then sugar soluble in alcohol (SSA) was isolated by EtOH (82%). The SSA content was dominant in II order rhizomes (11.8%). The SSA composition was analyzed by descending PC on FN-13 paper using n-BuOH:Py:H2O (6:4:3). Sugars were identified using anilinium acid phthalate (hexoses) and alcoholic urea (5%, ketoses). The SSA contained arabinose, glucose, and fructose. The raw material remaining after SSA isolation was extracted exhaustively with water at room temperature, oxalic acid and ammonium oxalate (1:1) solutions (0.5%) at 70°C, and aqueous base (5%). The aqueous and acidic extracts were condensed and precipitated by EtOH to afford the corresponding water-soluble polysaccharides (WSPS) and pectinic compounds (PC). The basic extract was neutralized with CH3COOH, dialyzed against tapwater, evaporated, and treated with alcohol (three times the volume) to isolate hemicellulose (HC). The monosaccharide compositions of the polysaccharide fractions were determined after acid hydrolysis (H2SO4, 2 N, 100°C, 5–12 h). The hydrolysates were treated with BaCO3 until neutral, filtered, evaporated, and analyzed by PC and GLC. Sugars were identified using markers. GLC scans were recorded on a Chrom-5 chromatograph with a flame-ionization detector, glass column (250 0.20 mm), 5% Silicone XE-60 on inerton, super-grain (0.16–0.20 mm), 205°C, N2 carrier gas, 30 mL/min. Sugars were analyzed as aldononitrile acetates [5]. Table 1 presents the polysaccharide (PS) content and its monosaccharide composition. It can be seen that PS were distributed differently in various plant organs. There were more PS in I-II order rhizomes than in roots and leaves. The dominant PS in all plant organs were base-soluble PS, i.e., HC. The WSPS content in various organs was 0.86–2.6%; in roots, traces. The principal WSPS monosaccharide of I order rhizomes and leaves was glucose. Mainly xylose, mannose, and glucose were detected in the WSPS hydrolysate of II order rhizomes. WSPS of rhizomes were a friable white powder with a yellow tint that was soluble in water to form a slightly cloudy solution. The aqueous solution of PS gave a positive test with iodine. This suggested that the PS were glucans. Glucose dominated in the hydrolysate. Table 1 shows that PC accumulated in rhizomes. Their principal monosaccharide was glucose. There were less PC in roots and leaves. Glucose also dominated. This was consistent with the presence of starch (positive test with iodine). The isolated PC were a white powder with a yellow tint that dissolved with heating in water and formed viscous solutions. The PC differed from each other qualitatively and quantitatively. Galacturonic acid, arabinose, xylose, and glucose were detected in the PC hydrolysates.