Reconsidering conventional and innovative methods for pectin extraction from fruit and vegetable waste: Targeting rhamnogalacturonan I

Abstract

Background: Rhamnogalacturonan I (RG-I) is composed of a backbone of repeating disaccharide units 2)-L-Rhap-(1 4)-D-GalpA-(1 with neutral sugar sidechains consisting of arabinose and galactose with variable linking types and chain lengths, corresponding to the hairy regions of pectin. This polysaccharide is abundant in the primary cell walls of fruits and vegetables. Scope and Approach: Biological functions of RG-I in immunomodulation and functional properties as a supplement and pharmaceutical expedient have increased commercial interest in RG-I extraction from fruit and vegetable waste. However, conventional extraction methods use harsh acid treatments that hydrolyze the side chains of RG-I. Innovative extraction technologies have been developed to preserve RG-I structure with better biological function. Therefore, the present review will focus on the influence of conventional and innovative methods exerts on the RG-I region of pectin from fruits and vegetables. Key Findings and Conclusions: Non-thermal processing (ultrasound, dielectric barrier discharge plasma, and enzymatic treatment) is superior to conventional and thermal processing (relying on high pressure, microwave and subcritical water extractions) in extracting branched RG-I from fruit and vegetables waste for food and pharmaceutical applications.

Environmentally Friendly Hydrothermal Processing of Melon by-Products for the Recovery of Bioactive Pectic-Oligosaccharides

“…However, these values might actually be higher, since the considerable protein content of these extracts could be showing peaks at 1650 and 1539–1558 cm −1 , overlapping with the 1606 cm −1 band [ 70 ]. The increase in DM when recovering the pectin is in agreement with the literature regarding hot water treatments, which tend to extract pectins with high DM [ 69 ]. Free carboxyl groups also show weaker bands at 1410–1440 cm −1 related to symmetric stretching [ 19 , 73 , 75 ].…”

“…The composition of the precipitated pectin can give more insight into the structure of the solubilized oligosaccharides. A recent study shows that hot water treatments are efficient for the extraction of the HG region of pectin with rhamnose contents of 0.5-0.6%, indicating a low RG-I content [69]. Our results confirm this finding, by increasing HGs and decreasing RG-I in the precipitated pectin, meaning that some of the branched oligosaccharides solubilized would be too degraded to be recovered by precipitation.…”

Development of an Affordable, Sustainable and Efficacious Plant-Based Immunomodulatory Food Ingredient Based on Bell Pepper or Carrot RG-I Pectic Polysaccharides

“…However, ginseng and other exotic plant extracts meet with regulatory challenges, are often expensive and are not derived from renewable sources [ 4 , 16 ]. Several polysaccharide-enriched extracts from more common renewable crop sources have been reported for their ability to modulate the immune system [ 17 , 18 ], and our own studies identified bell pepper ( Capsicum annuum ) and carrot ( Daucus carota ) as promising plant sources containing particularly active polysaccharides while also being affordable and potentially scalable candidate source crops.…”

“…This two-way dialogue, known as the gut–lung axis (GLA), has been demonstrated in humans with recruitment of innate immune cells from the gut to the lungs, and increased numbers of recirculating immunologically active cells [ 12 ]. It has been hypothesized that the prophylactic/therapeutic effects of polysaccharide-enriched extracts from ginseng and other traditional plants is mediated via two routes (1) recognition of specific polysaccharide domains by PRRs including toll-like receptors (TLRs), scavenger receptor and C-type lectins like Dectin-1 resulting in priming or training of innate immune responsiveness and (2) microbial fermentation of the polysaccharides (PS), resulting in modulation of the intestinal microbiota composition and production of biologically active metabolites including SCFA [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ].…”

Extraction Methods Affect the Structure of Goji (Lycium barbarum) Polysaccharides

“…According to the structure of the molecular backbone and side chains, pectic polysaccharides can be categorized into four major groups: homogalacturonan (HG), rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II) and xylogalacturonan (XG) [1]. HG (about 65% of commercial pectin) is the most abundant and structurally found to have a linear chain of (1-4)-linked α-d-GalAp units [2], while the backbone of RG-I is composed of alternating rhamnose and galacturonic acid residues (1-2 and 1-4 linked) [3]. RG-I is present in the fruits, roots, stems and leaves of plants, linking with cellulose and hemicellulose, as well as cell wall proteins [4].…”