Mesoscopic structure of pectin in solution

Structural characteristics and gelling properties of citrus pectins after chemical and enzymatic modifications: Conformation plays a vital role in Ca2+-induced gelation

Due to the excellent health benefits of rhamnogalacturonan I (RG-I)-enriched pectin, there has been increasing research interest in its gelling properties. To elucidate its structure-gelation relationship, chemical modifications were used to obtain RG-I-enriched pectin (P11). Then, enzymatic modification was performed to obtain debranched pectins GP11 and AP11, respectively. The effects of RG-I side chains on structural characteristics (especially spatial conformation) and gelling properties were investigated. Among the low-methoxylated pectins (LMPs), AP11, with a loose conformation (Dmax 52 nm) showed the poorest gelling, followed by GP11. In addition to primary structure, spatial conformation (Dmax and Rg) also showed strong correlations (r2 > 0.8) with gelation. We speculate that compact conformation may shorten distance between pectin chains and reduces steric hindrance, contributing to formation of strong gel network. This is particularly important in LMPs with abundant side chains. The results provide novel insights into relationship between spatial conformation and gelling properties of RG-I-enriched pectin.

Gelling properties of lysine-amidated citrus pectins: The key role of pH in both amidation and gelation

The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation. Pectin was amidated over the range of pH 4-10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3-10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and β-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.

Antioxidant activity and semi-solid emulsification of a polysaccharide from coffee cherry peel

In order to further improve the economic benefits of the coffee industry chain, we carried out the following systematic research on processing by-products. In this research, the obtained coffee cherry peel polysaccharide (CCP) which was removed from the coffee cherry peel by hot acid method had a galacturonic acid content of 20.50 % and a molecular weight of 3.05 kg/mol. According to the results of monosaccharide analysis, Fourier transform infrared spectroscopy, molecular weight distribution, and thermal analysis, CCP was a typical high methoxy polysaccharide. In vitro antioxidant results showed that CCP had better antioxidant capacity than commercial citrus polysaccharide (APC). When it came to emulsification performance, the water-oil bonding ability and disturbance resistance to the fluid of CCP were also significantly higher than that of APC. Specially, we found that 0.50 % (wt%) CCP could form a solid-liquid gel with very high plasticity at low oil phase fraction. In conclusion, the coffee cherry peel could be used as a natural source of a novel emulsifier, providing a promising alternative for polysaccharide in the food industry.

A critical review of RG-I pectin: sources, extraction methods, structure, and applications

In recent years, RG-I pectin isolated by low-temperature alkaline extraction methods has attracted the attention of a large number of researchers due to its huge health benefits. However, studies on other applications of RG-I pectin are still lacking. In this study, we summarized the sources (e.g. potato pulp, sugar beet pulp, okra, apple pomace, citrus peel, pumpkin, grapefruit, ginseng, etc.), extraction methods, fine structure and applications of RG-I pectin in physiological activities (e.g. anti-cancer, anti-inflammatory, anti-obesity, anti-oxidation, immune regulation, prebiotics, etc.), emulsions, gels, etc. These neutral sugar side chains not only endow RG-I pectin with various physiological activities but the entanglement and cross-linking of these side chains also endow RG-I pectin with excellent emulsifying and gelling properties. We believe that this review can not only provide a comprehensive reading for new workers interested in RG-I pectin, but also provide a valuable reference for future research directions of RG-I pectin.

Effect of the addition of soluble polysaccharides from red and white grape skins on the polyphenolic composition and sensory properties of Tempranillo red wines

Soluble polysaccharides from white (PSW) and red (PSR) grape skins were obtained to be evaluated as potential modulators of the unbalanced astringency of a Tempranillo red wine. The modulation of astringency was evaluated by a sensory panel and it seemed to be related to the changes in the polyphenolic profile. Isothermal Titration Calorimetry (ITC) studies, employed to characterize flavan-3-ol-polysaccharide interactions, showed that PSR decreased noticeably wine astringency causing a great flavan-3-ol loss (ca. 40 %), since they interacted more spontaneously with the flavan-3-ols (ca. ΔGtotal = -2.14 × 10⁴ cal/mol) than PSW (ca. ΔGtotal = -1.32 × 10⁴ cal/mol). The strength of these interactions seems to be related to the polysaccharide molecular size and to the presence of arabinogalactans in the structure. On the contrary, PSW showed no relevant effects on wine astringency. Furthermore, potential variations of color were also assessed and no deleterious effect was observed after the addition of any polysaccharide.

Effect of Conformation of Sugar Beet Pectin on the Interfacial and Emulsifying Properties

The influence of the conformation of sugar beet pectin (SBP) on the interfacial and emulsifying properties was investigated. The colloidal properties of SBP, such as zeta potential and hydrodynamic diameter, were characterized at different pH levels. Furthermore, pendant drop tensiometry and quartz crystal microgravimetry were used to study adsorption behavior (adsorbed mass and adsorption rate) and stabilizing mechanism (layer thickness and interfacial tension). A more compact conformation resulted in a faster reduction of interfacial tension, higher adsorbed mass, and a thicker adsorption layer. In addition, emulsions were prepared at varying conditions (pH 3-5) and formulations (1-30 wt% MCT oil, 0.1-2 wt% SBP), and their droplet size distributions were measured. The smallest oil droplets could be stabilized at pH 3. However, significantly more pectin was required at pH 3 compared to pH 4 or 5 to sufficiently stabilize the oil droplets. Both phenomena were attributed to the more compact conformation of SBP at pH < pKa: On the one hand, pectins adsorbed faster and in greater quantity, forming a thicker interfacial layer. On the other hand, they covered less interfacial area per SBP molecule. Therefore, the SBP concentration must be chosen appropriately depending on the conformation.

Structural and inflammatory characteristics of Maillard reaction products from litchi thaumatin-like protein and fructose

The structural characteristics and inflammatory activity of Maillard reaction products (MRPs) from fructose (Fru) and litchi thaumatin-like protein (LcTLP) with a pro-inflammatory activity were investigated. The structural changes of LcTLP-Fru MRPs were divided into two stages during the Maillard reaction. In 0-6 h, the unfolding and degradation of the LcTLP were dominant, resulting in a looser structure; the increase of β-sheets was 13.02%; the decrease of α-helices was 9.21%; and both the molecular weight and gyration radius R_g decreased. After 6 h, the enhanced glycosylation caused the molecular weight to increase, while R_g remained low, implying that the molecular structure became more compact. In addition, LcTLP-Fru MRPs reduced the inflammation response by significantly reducing the gene and protein expressions of tumor necrosis factor-α, interleukin-1β, and interleukin-6 compared with the LcTLP group in RAW264.7 macrophages. The findings provided a theoretical foundation for addressing the inflammatory response caused by litchi products consumption.

Structure and rheology of pectic polysaccharides from baobab fruit and leaves

Linkage patterns and relaxation dynamics of baobab (Adansonia digitata) polysaccharides have been investigated by means of linkage analysis and rheometry. The fruit polysaccharide was mostly xylogalacturonan, with co-extracted α-glucan. The leaf polysaccharide consists predominantly of two domains, one branched at O-4 of the →2)-Rhap-(1→ residues and another branched at O-3 of the →4)-GalpA-(1→ backbone to single GlcpA-(1→ residues. Master curves of viscoelasticity of fruit polysaccharides manifested strong pH-dependency. At pH below the dissociation constant of galacturonic acid, dispersions showed liquid-like behaviour. In contrast, at neutral pH, a weak gel network formation was observed that destabilised rapidly under the influence of flow fields. The present work identifies xylogalacturonans from baobab fruit as polysaccharides with unique rheological characteristics that may point to new directions in food and pharmaceutical formulation.

Grape polysaccharides: compositional changes in grapes and wines, possible effects on wine organoleptic properties, and practical control during winemaking

Polysaccharides present in grapes interact with wine sensory-active compounds (polyphenols and volatile compounds) via different mechanisms and can affect wine organoleptic qualities such as astringency, color and aroma. Studies on the role that grape polysaccharides play in wines are reviewed in this paper. First, the composition of grape polysaccharides and their changes during grape ripening, winemaking and aging are introduced. Second, different interaction mechanisms of grape polysaccharides and wine sensory-active compounds (flavanols, anthocyanins and volatiles) are introduced, and the possible effects on wine astringency, color and aroma caused by these interactions are illustrated. Finally, the control of the grape polysaccharide content in practice is discussed, including classical winemaking methods (applying different maceration enzymes, temperature control, co-fermentation, blending), modern vinification technologies (pulsed electric field, ultrasound treatment), and the development of new grape polysaccharide products.

The primary, secondary, and structures of higher levels of pectin polysaccharides

Pectin is a heteropolysaccharide abundant in the cell wall of plants and is obtained mainly from fruit (citrus and apple), thus its properties are particularly prone to changes occurring during ripening process. Properties of pectin depend on the string-like structure (conformation, stiffness) of the molecules that determines their mutual interaction and with the surrounding environment. Therefore, in this review the primary, secondary, and structures of higher levels of pectin chains are discussed in relation to external factors including crosslinking mechanisms. The review shows that the primary structure of pectin is relatively well known, however, we still know little about the conformation and properties of the more realistic systems of higher orders involving side chains, functional groups, and complexes of pectin domains. In particular, there is lack of knowledge on the influence of postharvest changes and extraction method on the primary and secondary structure of pectin that would affect conformation in a given environment and assembly to higher structural levels. Exploring the above-mentioned issues will allow to improve our understanding of pectin functionality and will help to tailor new functionalities for the food industry based on natural but often biologically variable source. The review also demonstrates that atomic force microscopy is a very convenient and adequate tool for the evaluation of pectin conformation since it allows for the relatively straightforward stretching of the pectin molecule in order to measure the force-extension curve which is directly related to its stiffness or flexibility.

Grape pectic polysaccharides stabilization of anthocyanins red colour: Mechanistic insights

Grape pectic polysaccharides-malvidin-3-O- β -d-glucoside binding was studied, aiming to unveil the impact of structural diversity of polysaccharides on anthocyanins-polysaccharides interactions. Polysaccharides were extracted with solutions of imidazole (ISP) and carbonate at 4 °C (CSP-4 °C) and room temperature (CSP-RT) and also recovered from the dialysis supernatant of the remaining cellulosic residue after the aqueous NAOH extraction of hemicellulosic polysaccharides (Sn-CR). Polysaccharides richer in homogalacturonan domains, like those present in the CSP-4 °C fraction had approximately 50-fold higher binding affinity to malvidin-3-O- β-d-glucoside, than polysaccharides with side chains (as ISP and CSP-RT extractable polysaccharides). CSP-4 °C polysaccharides showed a positive effect on malvidin-3-O- β-d-glucoside colour fading. Hydration equilibrium constant of malvidin-3-O- β-d-glucoside in the presence of CSP-4 °C polysaccharides was higher, showing the preferential stabilization of the flavylium cation. The results showed that anthocyanins colour stabilization can be promoted by pectic polysaccharide structures such as those extracted by cold carbonate.

Effect of mesoscopic structure of citrus pectin on its emulsifying properties: Compactness is more important than size

We previously explored citrus oil emulsion stabilized by citrus pectin. In this report, we characterized key parameters of the citrus pectin mesoscopic structure and their effect on emulsifying capacity, and explored the underlying mechanism by determining the interfacial properties, emulsifying ability, and micromorphology. To generate different mesoscopic structure, citrus pectins were hydrolyzed or regulated by pH and NaCl. Hydrolysis decreased the size of citrus pectin mesoscopic structure with constant compactness, leading to superior interfacial properties but inferior emulsifying ability. In contrast, pH and NaCl regulation decreased the mesoscopic structure size and increased the compactness, and pH- and NaCl-regulated citrus pectin formed a compact absorbed layer at the interface to resist droplet coalescence/flocculation during homogenization. Our results support the importance of compactness of the citrus pectin mesoscopic structure on emulsifying capacity. This study increased our understanding on the relationship between the mesoscopic structures of polysaccharide emulsifier and emulsifying ability.

Clustering of instrumental methods to characterize the texture and the rheology of slimy okra (Abelmoschus esculentus) suspensions

Okra (Abelmoschus esculentus) is one of the ingredients widely used in African gastronomy because of the unique slimy texture it gives to sauces. However, processing and formulation can affect the textural and rheological properties of these sauces, leading to unacceptable quality for the African consumer. The aim of this study was to select the instrumental measurements best enabling (a) characterization of the rheology and texture of slimy sauces prepared from okra and (b) monitoring its evolution during the preservation process. Thirty-seven slimy suspensions (sauces and purées) were measured with 16 rheological and textural parameters. A principal component analysis revealed that flow consistency index K and flow behavior index n were well correlated with visco-elastic, adhesive, and shear thinning properties, and that stringiness was well correlated with elongational, cohesive, and ductile properties. These two sets of measurement methods are sufficient to characterize their rheological and textural properties, and necessary to discriminate them according to their process and formulation.

Structure-Function Relationships in Pectin Emulsification

The emulsifying characteristics of pectins isolated from six different okra genotypes were investigated and their structure-function relationships have been evaluated. Emulsion formation and stabilization of acidic oil-in-water emulsions (pH 2.0, φ = 0.1) were studied by means of droplet size distribution, ζ-potential measurements, viscometry, interfacial composition analysis and fluorescence microscopy. Fresh and aged emulsions differed in terms of droplet size distribution, interfacial protein and pectin concentrations (Γ) depending on the molecular properties of pectin that was used. Specifically, pectins with intermediate length of RG-I branching with molar ratio of (Ara + Gal)/Rha between 2 and 3 exhibit the optimum emulsification capacity whereas samples with the molar ratio outside this range do not favour emulsification. Additionally, low amounts of RG-I segments (HG/RG-I > 2) improve long term stability of emulsions as opposed to the samples that contain high amounts of RG-I (HG/RG-I < 2) which lead to long term instability. Protein was not found to be the controlling factor for the stability of the dispersions. The present results show that rational design of pectin should be sought before application as functional ingredient in food and/or pharmaceutical systems.