Water-soluble pectins

This paper concerns the main properties of water soluble pectins in sol and gel states. First of all, the methods of purification and characterization are discussed. The method of steric exclusion chromatography equipped with different detectors is demonstrated as the most useful to determine the macromolecular characteristics of these polymers the role of aggregation is pointed out. 

Aspinall, G.O., Craig, J.W.T., and Whyte, J.L. (1968) Lemon-peel pectin. Part I. Fractionation and partial hydrolysis of water-soluble pectin. CarbohydrJies. 1 442-452. 

Figure 2 Ion-exchange chromatography on DEAE-Sepharose CL-6B (elution by acetate buffer pH 4.8) of (a) dialysed water-soluble pectins from extruded citrus fibres (SME = 250 kWh/t) and (b) dialysed acid extracted pectins from the same raw material, (empty symbols neutral sugars full symbols= galacturonic acids)...

The gel/sol transitions cannot be distinguished for pectins extracted by after acid treatment and water-soluble pectins after extrusion. A minimal pectin concentration of 0.2% is required for gelation and no gels can be obtained below a sucrose concentration of 45 %. Commercial pectin (Hercules) with a dm 73 % has a lower phase transition line with a minimal pectin concentration of 0.1 % and sucrose concentration of 40 %. 

The results showed (16) that the extruded products contained a large amount of water soluble pectins of high molecular weight which were able to gel. It has been shown that the all the extruded citrus fibres were able to gel in presence of sucrose at acidic pH without prior extraction of the pectins. 

The AIS of fresh and canned carrots were sequentially fractionated into water-soluble pectin (WSP), oxalate-soluble pectin (OXSP), acid-soluble pectin (HSP), alkah-soluble pectin (OHSP), hemicellulose and cellulose. The distribution of uronic acid among various fractions is presented in Table 1. WSP of fresh carrots accounted for 19.0% of the total pectin, while OXSP constituted 29.6%. HSP represented the lowest (12.0%) pectin fraction, whereas OHSP was the highest (35.6%) In the hemicellulose and cellulose fractions significant amounts of uronic acid were found. Heat treatments during canning altered the proportion... 

The ripening process has been subject of many studies [2,6,8]. Due to the large variety of plant tissues investigated, the results of these studies are quite heterogeneous. In general an increase in water-soluble pectins is observed, which is related to the combined action of... 

II. Fractionation and partial acid hydrolysis of water-soluble pectin. An Acad Brasil Cienc 1974 46 349. Molina, M. R., G. De LaFuente, M. A. Batten, and R. Bressani. Decaffein-ation. A process to detoxify coffee pulp. J Agr Food Chem 1974 22(6) 1055. 

Pectin is often divided into three categories on the basis of solubility (13). Water soluble pectin, that which can be extracted from tissue with hot water, usually has a high D.E. 

Goto, A., Araki, C. and Uzumi, Y. 1981. Molecular weight distribution of water soluble pectins in citrus juices, Proceedings of the International Society of Citriculture, pp. 931-934. 

Ralet, M.-C. and Thibault, J.-F. 1994. Effect of extrusion-cooking on plant cell-walls from lemon. I. Characterisation of the water soluble pectins and comparison with acid-extracted pectins, Carbohydr. Res., 260 283-296. 

Extraction and purification. An alcohol-insoluble residue was prepared from sugar-beet pulp. Products successively extracted from this material were water-soluble pectin (WSP), oxalate-soluble pectin (OXP), acid-soluble pectin (HP) and alkali-soluble pectin (OHP). Extractions were done according to the procedure described by Barbier and Thibault (7). The pectins were purified by chromatography at pH 4.8 on Whatman DEAE-cellulose DE 52 under the conditions described by Barbier and Thibault (7). As the alkali-soluble pectin binds irreversibly to this column, this fraction was purified by precipitation with CuSO and extensive washing of the precipitate. Cupric ions were subsequently removed by dialysis against Na2EDTA at pH 4.8. 

The water-soluble pectins include the more highly methoxylated pectlc acid, while the oxalate-soluble pectlc compounds are the calcium pectates of the middle lamellas of the cell wall. Sodium hydroxide easily hydrolyzes both the methoxylated pectates and the calcium pectate. Thus, extraction with dilute alkali of the AIS wuld Include all these pectlc fractions. 

Gas-Liquid Chromatography. — All reports are concerned with the use of crq>illaiy columns. G.c.-(e.i.)m.s. analysis of partially methylated alditol acetate derivatives has been used in the study of water soluble pectins, and the partially ethylated alditol and aldononitiile acetate derivatives of galactose and mono-O-methyl-galactoses have been similarly examined. ... 

Pectin in almond kernels can be determined by extracting ground samples with water (soluble pectins) and then 0.05 M HCL at 100 °C for 90 min (insoluble pectins). Pectins can be determined as uronic acid by the carbazole method, using galacturonic acid as standard (Bitter and Muir 1962). 

The alcohol insoluble solids (AIS) of the heated, pressurized and untreated guava juice samples were obtained by the procedure proposed by Plat et al (1991). The AIS were fractionated into water soluble pectin (WSP), oxalate soluble pectin (OSP) and alkali soluble pectin (ASP) fractions, according to the procedure given by Dietz and Rouse (1953) and quantified using the carbazole colorimetric method given by Ting and Rouseff (1986). 

Figure 2. Separation of soluble pectin extracted from the alcohol-insoluble solids of guava juice on DEAE-cellu-lose. Guava juice (30%) was adjusted to pH 3.8 and 12 Brix. A, untreated guava juice B, guava juice was pressurized at 6,000 atm and 25 °C for 10 min. C, Guava juice was heated at 95 °C for 5 min. Chromatographic conditions Column, 2.0 x 40 cm (packed with DEAE-cellulose) Elution solvent, 50 nm potassium phosphate buffer (pH 6.3) Flow rate, 30 mL/h Fraction volume, 2.0 mL/fraction Pectin extraction sequence, water-soluble pectin oxalate-soluble pectin - alkali-soluble pectin.

In general, there is some evidence to support a 5—8% reduction (approximately 0.5 mmol/L) in total cholesterol after the intake of three apples per day. Moreover, apple juice consumption is associated with no effects or increased levels of TAG. Clear apple juice lacks water-soluble pectin and has a low polyphenol content due to a clarification process. The production of cloudy apple juice does not include clarification and, thus, may maintain an important polyphenol and pectin content.Apple pomace, a by-product of juice production, consists of approximately 25% of fresh apple weight, and is a high source of fiber and polyphenols and therefore a valuable material for functional food products. Apart from the pol3q>henol and fiber content, food matrix may also play an important role whole apples contain intact cell wall components, which could contribute to the effects on lipid and glucose metabolism as will be described below. 

---