Characterization of citrus pectin samples extracted under different conditions: influence of acid type and pH of extraction.

BACKGROUND AND AIMS: Pectin is a complex macromolecule, the fine structure of which is influenced by many factors. It is used as a gelling, thickening and emulsifying agent in a wide range of applications, from food to pharmaceutical products. Current industrial pectin extraction processes are based on fruit peel, a waste product from the juicing industry, in which thousands of tons of citrus are processed worldwide every year. This study examines how pectin components vary in relation to the plant source (orange, lemon, lime, grapefruit) and considers the influence of extraction conditions on the chemical and macromolecular characteristics of pectin samples. METHODS: Citrus peel (orange, lemon, lime and grapefruit) from a commercial supplier was used as raw material. Pectin samples were obtained on a bulk plant scale (kilograms; harsh nitric acid, mild nitric acid and harsh oxalic acid extraction) and on a laboratory scale (grams; mild oxalic acid extraction). Pectin composition (acidic and neutral sugars) and physicochemical properties (molar mass and intrinsic viscosity) were determined. KEY RESULTS: Oxalic acid extraction allowed the recovery of pectin samples of high molecular weight. Mild oxalic acid-extracted pectins were rich in long homogalacturonan stretches and contained rhamnogalacturonan I stretches with conserved side chains. Nitric acid-extracted pectins exhibited lower molecular weights and contained rhamnogalacturonan I stretches encompassing few and/or short side chains. Grapefruit pectin was found to have short side chains compared with orange, lime and lemon. Orange and grapefruit pectin samples were both particularly rich in rhamnogalacturonan I backbones. CONCLUSIONS: Structural, and hence macromolecular, variations within the different citrus pectin samples were mainly related to their rhamnogalacturonan I contents and integrity, and, to a lesser extent, to the length of their homogalacturonan domains.

Utilization of industrial citrus pectin side streams for enzymatic production of human milk oligosaccharides.

This study reports the enzymatic upgrading of fucosylated xyloglucan from depectinized citrus residues into 2'-fucosyllactose, a fucosylated human milk oligosaccharide. Alkaline and enzymatic xyloglucan extractions were compared. Of the original fucose present in the depectinized residues of lemon and orange, 35-36% and 48-51% were extracted as fucosylated xyloglucan by enzyme- or alkaline treatment, respectively. Furthermore, the enzymatically extracted xyloglucan structures had a narrower molecular weight distribution around 1 kDa, contrary to a more polydisperse distribution of the alkaline extracted xyloglucans, ranging from 1 to 500 kDa. The applicability of the fucosylated-xyloglucan extracts in transfucosylation reactions, was determined by use of a selected fungal fucosidase, resulting in yields of 10.2-11.4% enzymatic extracts, and 6.5-7.4% for alkaline extracts (orange and lemon respectively). The results demonstrate that depectinized citrus side streams are a useful source of fucosylated xyloglucan, preferably extracted by an enzyme catalyzed approach.

A multivariate approach for high throughput pectin profiling by combining glycan microarrays with monoclonal antibodies.

Pectin-one of the most complex biomacromolecules in nature has been extensively studied using various techniques. This has been done so in an attempt to understand the chemical composition and conformation of pectin, whilst discovering and optimising new industrial applications of the polymer. For the last decade the emergence of glycan microarray technology has led to a growing capacity of acquiring simultaneous measurements related to various carbohydrate characteristics while generating large collections of data. Here we used a multivariate analysis approach in order to analyse a set of 359 pectin samples probed with 14 different monoclonal antibodies (mAbs). Principal component analysis (PCA) and partial least squares (PLS) regression were utilised to obtain the most optimal qualitative and quantitative information from the spotted microarrays. The potential use of microarray technology combined with chemometrics for the accurate determination of degree of methyl-esterification (DM) and degree of blockiness (DB) was assessed.