High Degree Of Methylesterification Research Articles

The transcription factors ZAT5 and BLH2/4 regulate homogalacturonan demethylesterification in Arabidopsis seed coat mucilage.

The level of methylesterification alters the functional properties of pectin, which is believed to influence plant growth and development. However, the mechanisms that regulate demethylesterification remain largely unexplored. Pectin with a high degree of methylesterification is produced in the Golgi apparatus and then transferred to the primary cell wall where it is partially demethylesterified by pectin methylesterases (PMEs). Here, we show that in Arabidopsis (Arabidopsis thaliana) seed mucilage, pectin demethylesterification is negatively regulated by the transcription factor ZINC FINGER FAMILY PROTEIN5 (ZAT5). Plants carrying null mutations in ZAT5 had increased PME activity, decreased pectin methylesterification, and produced seeds with a thinner mucilage layer. We provide evidence that ZAT5 binds to a TGATCA-motif and thereby negatively regulates methylesterification by reducing the expression of PME5, HIGHLY METHYL ESTERIFIED SEEDS (HMS)/PME6, PME12, and PME16. We also demonstrate that ZAT5 physically interacts with BEL1-LIKE HOMEODOMAIN2 (BLH2) and BLH4 transcription factors. BLH2 and BLH4 are known to modulate pectin demethylesterification by directly regulating PME58 expression. The ZAT5-BLH2/4 interaction provides a mechanism to control the degree of pectin methylesterification in seed coat mucilage by modifying each transcription factor's ability to regulate the expression of target genes encoding PMEs. Taken together, these findings reveal a transcriptional regulatory module comprising ZAT5, BLH2 and BLH4, that functions in modulating the de-methylesterification of homogalacturonan in seed coat mucilage.

Emulsions stabilized by okra polysaccharides: Physicochemical, interfacial, and emulsification properties

This study provided a comprehensive investigation about the correlation between okra polysaccharide physicochemical characteristics, interfacial behavior, and emulsification properties. Six okra polysaccharides with distinct physicochemical properties were prepared and evaluated for their emulsification performance. The kind of acid used for extraction affected the molecular weight of polysaccharides, while extraction solutions with different pH influenced the molar ratio of monosaccharides and the degree of methyl-esterification (DM), thereby affecting the behavior of polysaccharides at the oil-water interface and emulsification properties. Okra polysaccharides with higher DM and RG-I exhibited lower oil-water interfacial tension and thicker interfacial layers. Compared to the emulsion stabilized by okra polysaccharide extracted using citric acid solution at pH 2.0 (OPC-2), the emulsion stabilized by okra polysaccharide extracted using hydrochloric acid solution at pH 1.0 (OPH-1) exhibited significant advantages of smaller droplet size (0.56 μm) and less malondialdehyde content (6.25 μmol/kg oil). Under pH 2.0, OPH-1 demonstrated the highest viscosity (290.12 mPa S), along with the strongest G' (42.12 Pa) and G" (25.79 Pa), playing crucial roles in sustaining emulsion stability. Moreover, under conditions of high ionic strength, the interaction between ions and okra polysaccharide molecules diminished the emulsifying ability and emulsion storage stability. This study provides significant insights into the performance of okra polysaccharides and polysaccharide-based emulsions, thereby guiding the development of efficient and stable emulsifiers.

Polysaccharide from Inga edulis Pods: Emulsifying Potential and Evaluation of the Extraction Conditions Using Taguchi Approach

Inga edulis fruits, an important cultivation commonly associated with coffee and cacao farming, were collected from Baturité, located in Ceará, Brazil. Polysaccharides from Inga edulis pods were extracted using citric acid solution, and the impact of the extraction conditions in the properties of the resultant polysaccharide such as the degree of methyl-esterification behavior and galacturonic content were evaluated utilizing Taguchi approach, an efficient and easy statistical tool. For the study, the extraction conditions applied were pH (2.4, 5 and 7), time (1, 2 and 3 h) and temperature (70, 80 and 90 °C). The condition which provides the higher degree of methyl esterification allied to higher galacturonic acid content was pH 2.4, time 1 h and temperature 90 °C. For this condition, the extraction yield obtained was 3.97% m/m polysaccharide/botanical material. The emulsifying capacity and emulsion stability were also evaluated, and the emulsions with lower concentrations of polysaccharide provided the best results about emulsifying action. In the best of our efforts in research, the characterization of polysaccharide from fruit pods of Inga edulis is reported for the first time and this research contributes to the knowledge about botanical potential of this vegetal species and reinforces its potential as industrial crop.

Preparation, physicochemical characterization and swelling properties of composite hydrogel microparticles based on gelatin and pectins with different structure

Composite hydrogel microparticles based on pectins with different structures (callus culture pectin (SVC) and apple pectin (AU)) and gelatin were developed. Hydrogel microparticles were formed by the ionotropic gelation and electrostatic interaction of COO− groups of pectin and NH3+ groups of gelatin, which was confirmed by FTIR spectroscopy. The addition of gelatin to pectin-based gel formulations resulted in a decrease in gel strength, whereas increasing gelatin concentration enhanced this effect. The microparticle gel strength increased in proportion to the increase in the pectin concentration. The DSC and TGA analyzes showed that pectin-gelatin gels had the higher thermal stability than individual pectins. The gel strength, Ca2+ content and thermal stability of the microparticles based on gelatin and SVC pectin with a lower degree of methylesterification (DM) (14.8 %) were higher compared to that of microparticles based on gelatin and AU pectin with a higher DM (40 %). An increase in the SVC concentration, Ca2+ content and gel strength of SVC-gelatin microparticles led to a decrease in the swelling degree in simulated gastrointestinal fluids. The addition of 0.5 % gelatin to gels based on AU pectin resulted in increased stability of the microparticles in gastrointestinal fluids, while the microparticles from AU without gelatin were destroyed.

Efficacy of pectins with different degrees of methyl-esterification and of blockiness in preventing gut epithelial cell barrier disruption and the impact on sodium-glucose co-transporter expression under low and high glucose conditions.

Pectins support intestinal barrier function and have anti-diabetic effects, and can differ in the degree of methyl-esterification (DM) and the distribution of non-esterified galacturonic acid residues (DB). The mechanisms and effects of pectin type at different glucose levels are unknown. Pectins with different DM/DB on T84 cells were tested in the presence and absence of the barrier disruptor A23187 at 5 mM and 20 mM glucose. DM19 and DM43 pectins with high DB do rescue the intestinal barrier from disruption. Their effects were as strong as those of the barrier-rescuing anti-diabetic drug metformin, but effects with metformin were restricted to high glucose levels while pectins had effects at both low and high glucose levels. At high glucose levels, DM43HB pectin, which enhanced trans-epithelial electrical resistance, also increased the expressions of claudin1, occludin, and ZO-1. Low and high DM pectins decrease the apical expression of the sodium-glucose co-transporter (SGLT-1) and thereby influence glucose transport, explaining the anti-diabetogenic effect of pectin. Higher DB pectins had the strongest effect. Their impact on SGLT-1 was stronger than that of metformin. Pectin's rescuing effect on barrier disruption and its impact on glucose transportation and anti-diabetogenic effects depend on both the DB and the DM of pectins.

Fabrication and Characterization of Eco-Friendly Polyelectrolyte Bilayer Films Based on Chitosan and Different Types of Edible Citrus Pectin.

The eco-friendly polyelectrolyte bilayer films were prepared by layer-by-layer (LBL) casting method using chitosan (CS) and four types of edible citrus pectin as film substrates. The results showed that the polyelectrolyte bilayer films exhibited excellent comprehensive properties. Furthermore, the interaction between CS and pectin was closely related to the degree of methyl-esterification (DM), molecular weight (Mw), and zeta potential of pectin. The low DM, Mw, and high zeta potential of the low methyl-esterified pectin (LM) resulted in a denser internal structure of the bilayer film, stronger UV shielding performance, and stronger gas barrier ability. The high DM and Mw of the high methyl-esterified pectin (HM) endow the bilayer film with stronger mechanical properties, thermal stability, and antifogging property. The microstructural and spectroscopic analysis showed that there are hydrogen bonds and electrostatic interactions between the layers. Overall, the developed CS-pectin polyelectrolyte bilayer films provided potential applications for food bioactive packaging.

Physicochemical and functional characterization of pectin extracted from Moroccan citrus peels

Three Moroccan citrus peels, such as orange, lemon, and bigarade, were chosen to extract the pectin using Box Behnken Design. At a temperature of 90 °C, pH = 1.5, and extraction time = 120 min, a high pectin yield was recorded with 28.57, 26.86, and 26.55% for lemon (LPP), bigarade (BPP), and orange (OPP) peel pectins respectively. The extracted pectins have a less branched linear structure with high GalA contents for BPP (86.0 mol%), LPP (82.0 mol%), and OPP (79.0 mol%), and a high degree of methyl esterification (>74%), but a low degree of acetylation (<4%). A narrow and homogeneous distribution was recorded with a higher average Mw for LPP (90.0 kDa) than OPP (88.0 kDa) and BPP (80.0 kDa). One gram of Moroccan citrus pectin could hold more than 23.0 g of water. The high emulsifying activity was recorded for the three citrus pectins (∼50%), with higher emulsion stability for BPP pectin at 4 °C (94.42%). Furthermore, all extracted pectins exhibit a significantly non-Newtonian pseudoplastic behavior when the concentration increases. At 3% concentration, the apparent viscosity of BPP was higher than that of OPP and LPP with 40.26, 13.45, and 6.85 Pa s, respectively.

A pair of non-Mendelian genes at the Ga2 locus confer unilateral cross-incompatibility in maize

Maize unilateral cross-incompatibility (UCI) that causes non-Mendelian segregation ratios has been documented for more than a century. Ga1, Ga2, and Tcb1 are three major UCI systems, described but not fully understood. Here, we report comprehensive genetic studies on the Ga2 locus and map-based cloning of the tightly linked male determinant ZmGa2P and female determinant ZmGa2F that govern pollen-silk compatibility among different maize genotypes. Both determinants encode putative pectin methylesterases (PME). A significantly higher degree of methyl esterification is detected in the apical region of pollen tubes growing in incompatible silks. No direct interaction between ZmGa2P and ZmGa2F is detected in the yeast two-hybrid system implying a distinct mechanism from that of self-incompatibility (SI). We also demonstrate the feasibility of Ga2 as a reproductive barrier in commercial breeding programs and stacking Ga2 with Ga1 could strengthen the UCI market potentials.

Pectins with commercial features and gelling ability from peels of Hylocereus spp

Peels of edible fruits from Hylocereus genus have been investigated as possible sources of pectins. In the present study, peels of H. undatus (red peel and white pulp) and H. costaricencis (red peel and red pulp) were extracted using the enzyme preparation Celluclast® (111 μL/g, pH 5, 50 °C for 1.5 h) and conventional acid extraction (boiling 0.1 M nitric acid for 60 min). The monosaccharide composition and the degree of methyl-esterification (DM) were determined by chromatographic and spectroscopic methods. It was possible to obtain pectins with GalA ≥65% from H. undatus and H. costaricencis peels by acid and enzymatic extractions with similar yields. Pectins obtained by acid extraction had higher DM (>50%) and GalA content. The enzymatic extraction resulted in pectins with DM < 50% and higher molar mass. High methoxyl pectins obtained by acid extraction were characterized by NMR analysis. Oscillatory rheological measurements showed they were able to form gel at concentration ≥1% (w/w), 60% sucrose at pH 2.5. Comparing the two species, the pectin obtained from H. undatus peels had longer side chains, higher DM and molar mass than the pectin from H. costaricencis peels. It was demonstrated for the first time that pectins with commercial features can be obtained from peels of H. undatus and H. costaricencis by acid extraction.

Physicochemical and swelling properties of composite gel microparticles based on alginate and callus cultures pectins with low and high degrees of methylesterification

Composite gel microparticles based on alginate and callus culture pectins with low and high degrees of methylesterification or apple pectin were produced. By varying the chemical composition of the pectic samples and the ratio of alginate to pectin, the gel strength, morphology, and swelling properties of composite microparticles can be altered. The inclusion of increasing concentrations of alginate in gel formulations promoted an increase in the microparticle gel strength and the formation of a smoother surface microrelief independently of the pectin chemical composition. Microparticles based on the pectin with a low degree of methylesterification (DM) and a higher concentration of alginate exhibited an increased swelling degree in the simulated digestive fluids. Microparticles based on the pectin with high DM and low alginate concentration were destroyed in the simulated intestinal fluid within 1 h due to the low Ca2+ content, gel strength, and grooved and rough surface of these microparticles. An increase in alginate concentration of gel formulations based on pectin with high DM led to increased stability of the microparticles in the simulated intestinal and colonic fluids due to increased Ca2+ content, microparticle gel strength and degree of crosslinking.

Molecular binding between anthocyanins and pectic polysaccharides – Unveiling the role of pectic polysaccharides structure

The interaction between cyanidin-3-O-glucoside and four citrus pectic fractions was investigated using a combined molecular approach, including isothermal titration calorimetry (ITC), magnetic nuclear resonance (NMR) and UV–Visible spectrophotometry. These pectic fractions differed on their type and degree of esterification (amidated (AHG 30%), low (HG 30%) and high methyl esterified fractions (HG 70%)) and on the pattern of esterification (blockwise (HG-B 70%) vrs random (HG-R 70%)). The binding constant (Ka) and the associated thermodynamic parameters determined showed weak noncovalent interactions, particularly due to electrostatic interactions, hydrogen bonding and hydrophobic effect. The degree and the type of esterification of each pectic fractions had a significant effect on the binding constants determined by ITC and NMR experiments. The binding constants ranged from 102 to 104 M−1, with the highest Ka value observed for the interaction between cy3glc and low methylesterified fraction, followed by the amidated fraction. Pectic fractions with a higher degree of methyl esterification, resulted on lower binding affinities, with these interactions being mostly driven by hydrophobic effect compared to enthalpy. The different binding affinities could be correlated with anthocyanins colour impact, as a higher red colour intensity could be observed for a cy3glc model solution fortified with a low methylated fraction. However, this colour improvement was not observed for amidated fraction, presumably due to charge repulsive forces, lowering the stability of the flavylium cation.

Pectin biopolymer mechanics and microstructure associated with polysaccharide phase transitions.

Polysaccharide polymers like pectin can demonstrate striking and reversible changes in their physical properties depending upon relatively small changes in water content. Recent interest in using pectin polysaccharides as mesothelial sealants suggests that water content, rather than nonphysiologic changes in temperature, may be a practical approach to optimize the physical properties of the pectin biopolymers. Here, we used humidified environments to manipulate the water content of dispersed solution of pectins with a high degree of methyl esterification (high-methoxyl pectin; HMP). The gel phase transition was identified by a nonlinear increase in compression resistance at a water content of 50% (w/w). The gel phase was associated with a punched-out fracture pattern and scanning electron microscopy (SEM) images that revealed a cribiform (Swiss cheese-like) pectin microstructure. The glass phase transition was identified by a marked increase in resilience and stiffness. The glass phase was associated with a star-burst fracture pattern and SEM images that demonstrated a homogeneous pectin microstructure. In contrast, the burst strength of the pectin films was largely independent of water content over a range from 5 to 30% (w/w). These observations indicate the potential to use water content in the selective regulation of the physical properties of HMP biopolymers.

In vitro regeneration of two Populus hybrid clones. The role of pectin domains in cell processes underlying shoot organogenesis induction

An efficient plant regeneration protocol has been established for two commercial Populus hybrid clones, MC (Populus × euramericana) and UNAL (Populus × interamericana). The culture of internode segments on Murashige and Skoog (MS) medium with 0.5 μM α-naphthalene acetic acid (NAA) and 4 μM N6-benzyladenine for 7 weeks (2 weeks in absence of activated charcoal and 5 weeks in its presence) resulted in the highest frequency of shoot regeneration (100 % for MC and 82 % for UNAL). All regenerated shoots longer than 2 cm rooted on half-strength MS medium, independent of the addition of 0.1 μM NAA. Nevertheless, shoots developed better-formed roots in NAA-free medium, which had a positive effect on the acclimatization of plants. In order to know the cellular processes underlying in vitro shoot organogenesis, a histological study was made in UNAL internode-explants. Results revealed that in vitro culture caused swelling around the cut-off zones in all explants, but only those undergoing organogenesis formed proliferation centers under subepidermal cells, which led to formation of bud primordia. Moreover, in vivo tissues and explants with different in vitro response showed different immunolabelling patterns when they were treated with fluorescentmonoclonal antibodies directed to several pectin-polysaccharides of the cell wall. Results allow us to assign a predominant role of homogalacturonan with a low degree of methyl-esterification in the initiation of bud primordia, a role of β-1,4-D-galactan side chains of rhamnogalacturonan-I in the cellular differentiation, ra ole of α-1,5-L-arabinan side chains of rhamnogalacturonan-I and of homogalacturonan with a high degree of methyl-esterification in cell division and growth.

Ultrasonic-microwave assisted extraction, characterization and biological activity of pectin from jackfruit peel

Extraction and application of pectin from jackfruit (Artocarpus heterophyllus) peel could add value to the waste products arising from processing of the jackfruit. In this study, pectin from jackfruit peel was extracted using different organic acids and mineral acids. A response surface methodology was employed to optimize the ultrasonic-microwave-assisted extraction (UMAE) of pectin with citric acid. The pectins obtained from UMAE (UM-P) and conventional heating (CH-P) were compared in terms of their physicochemical and antioxidant properties. The optimum UMAE conditions were: extraction temperature 86 °C, extraction time 29 min, and solid-liquid ratio 1:48 (w/v). Under these conditions, the yield of pectin was 21.5%. Physicochemical analysis suggested that two pectins (UM-P and CH-P) were major in galactose, rhamnose, arabinose, glucose, and galacturonic acid with a high degree of methyl-esterification. UM-P and CH-P possessed considerable antioxidant activities, while UM-P had stronger antioxidant abilities than CH-P in certain tests. The current work showed that critic acid is a ‘green’ and safe acidic solvent that could be used to effectively extract pectin from jackfruit peel. The UMAE method is considered to be a potential alternative conventional extraction method. Pectins from jackfruit peel could potentially be used as natural antioxidants by the food industry.

Dynamic Changes of Pectin Epitopes in Cell Walls during the Development of the Procambium-Cambium Continuum in Poplar.

The change of pectin epitopes during procambium–cambium continuum development was investigated by immunolocalization in poplar. The monoclonal antibody JIM5 labels homogalacturonan (HGA) with a low degree of esterification, and the monoclonal antibody JIM7 labels HGA with a high degree of methyl-esterification. Arabinan, rather than galactan, and HGA with low degree of esterification were located in the cell walls of procambial, while HGA with a low degree of esterification was located in the tangential walls, and galactan was located in both the tangential and radial walls of procambial, yet nearly no arabinan was located in the tangential walls of the cambial cells. The changes in pectin distribution took place when periclinal divisions appeared within a procambial trace. The distribution difference of pectin epitopes was also present in procambium–cambium derivatives. The arabinan existed in all cell walls of primary xylem, but was absent from the tangential walls of secondary xylem cells. The galactan existed only in mature primary phloem. Furthermore, 19 pectin methylesterases (PMEs) genes were identified by RNA sequencing, six genes presented highly differentially and were supposed to be involved in the cell wall esterification process. The results provide direct evidence of the dynamic changes of pectin epitopes during the development of the procambium–cambium continuum in poplar.

Fe2+ adsorption on citrus pectin is influenced by the degree and pattern of methylesterification

The present study aimed at gaining insight into the potential of citrus pectin to bind Fe2+, a cation of great importance in several food products. In particular, the role of citrus pectin structural properties, namely the degree of methylesterification (DM) and the absolute degree of blockiness (DBabs – ratio of non-methylesterified GalA units present in blocks to the total amount of GalA units) on the Fe2+ adsorption in aqueous solution was explored using adsorption isotherms. Demethylesterification of high DM citrus pectin enzymatically (using plant pectin methylesterase) or chemically (alkaline demethylesterification using NaOH) generated P- and C-pectins, respectively, characterized by comparable DMs but different distributions of non-methylesterified GalA units (DBabs). Adsorption isotherms of P- and C-pectins in aqueous solutions of various Fe2+ concentrations revealed that both the DM and DBabs influenced the pectin-Fe2+ interactions: the lower DM or higher DBabs, the higher the Fe2+ binding capacity of citrus pectin. The Langmuir adsorption model was used to fit the experimental data for quantification of the maximum adsorption capacity (qGmax) and the pectin-Fe2+ interaction energy (KL) of the P- and C-pectins. It can be concluded that qGmax (mol Fe2+/mol GalA) was mainly determined by the DM and to a lesser extent by the DBabs while the pectin-Fe2+ interaction energy was mainly influenced by the DBabs. As a consequence, pectin modification to obtain targeted DM and DBabs allows optimization of its binding capacity and therefore the associated functional properties.

Polysaccharide compositions of collenchyma cell walls from celery (Apium graveolens L.) petioles

BackgroundCollenchyma serves as a mechanical support tissue for many herbaceous plants. Previous work based on solid-state NMR and immunomicroscopy suggested collenchyma cell walls (CWs) may have similar polysaccharide compositions to those commonly found in eudicotyledon parenchyma walls, but no detailed chemical analysis was available. In this study, compositions and structures of cell wall polysaccharides of peripheral collenchyma from celery petioles were investigated.ResultsThis is the first detailed investigation of the cell wall composition of collenchyma from any plant. Celery petioles were found to elongate throughout their length during early growth, but as they matured elongation was increasingly confined to the upper region, until elongation ceased. Mature, fully elongated, petioles were divided into three equal segments, upper, middle and lower, and peripheral collenchyma strands isolated from each. Cell walls (CWs) were prepared from the strands, which also yielded a HEPES buffer soluble fraction. The CWs were sequentially extracted with CDTA, Na2CO3, 1 M KOH and 4 M KOH. Monosaccharide compositions of the CWs showed that pectin was the most abundant polysaccharide [with homogalacturonan (HG) more abundant than rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II)], followed by cellulose, and other polysaccharides, mainly xyloglucans, with smaller amounts of heteroxylans and heteromannans. CWs from different segments had similar compositions, but those from the upper segments had slightly more pectin than those from the lower two segments. Further, the pectin in the CWs of the upper segment had a higher degree of methyl esterification than the other segments. In addition to the anticipated water-soluble pectins, the HEPES-soluble fractions surprisingly contained large amounts of heteroxylans. The CDTA and Na2CO3 fractions were rich in HG and RG-I, the 1 M KOH fraction had abundant heteroxylans, the 4 M KOH fraction was rich in xyloglucan and heteromannans, and cellulose was predominant in the final residue. The structures of the xyloglucans, heteroxylans and heteromannans were deduced from the linkage analysis and were similar to those present in most eudicotyledon parenchyma CWs. Cross polarization with magic angle spinning (CP/MAS) NMR spectroscopy showed no apparent difference in the rigid and semi-rigid polysaccharides in the CWs of the three segments. Single-pulse excitation with magic-angle spinning (SPE/MAS) NMR spectroscopy, which detects highly mobile polysaccharides, showed the presence of arabinan, the detailed structure of which varied among the cell walls from the three segments.ConclusionsCelery collenchyma CWs have similar polysaccharide compositions to most eudicotyledon parenchyma CWs. However, celery collenchyma CWs have much higher XG content than celery parenchyma CWs. The degree of methyl esterification of pectin and the structures of the arabinan side chains of RG-I show some variation in the collenchyma CWs from the different segments. Unexpectedly, the HEPES-soluble fraction contained a large amount of heteroxylans.

A tale of two pectins: Diverse fine structures can result from identical processive PME treatments on similar high DM substrates

The effects of a processive pectin-methylesterase (PME) treatment on two different pectins, both possessing a high degree of methylesterification (DM), were investigated. While the starting samples were purportedly very similar in fine structure, the intermolecular DM distributions arising from their PME treatments were strikingly different. Herein, a simulation that illuminates the origin of this phenomenon is described. It is concluded that: (1) very different low-DM samples (with the same average DM) can be generated using the same processive PME, simply by a judicious choice of the high DM starting material; (2) observing the intermolecular DM distribution of the products of processive-PME-processing is an extremely sensitive discriminator of the fine structure of high DM starting materials; and (3) for PMEs with unknown action patterns the processive nature of the enzyme is most simply revealed by studying the changes it induces in the intermolecular DM distribution of very-highly-methylesterified homogalacturonans.

Pectins from food waste: Extraction, characterization and properties of watermelon rind pectin

Fresh and lyophilized watermelon rinds were treated with boiling ethanol for pigment removal and then used to extract pectins giving rise to fractions FW and LW, respectively. The pectins were characterized by chromatographic and spectroscopic methods. Both pectins had a galacturonic acid content higher than 65%, meeting the commercial requirement. However, FW had a higher yield (19.3%) than LW (14.2%). The protein contents were 3.9 and 3.6% for FW and LW, respectively. FW and LW had a high degree of methyl-esterification (∼60%) and low molar mass, 34,510 g/mol for FW and 40,390 g/mol for LW. The viscosity of 5% (w/w) aqueous solutions of watermelon rind pectins at 25 °C showed shear thinning behavior with a low shear Newtonian plateau of ∼30 Pa s for FW and ∼10 Pa s for LW. Mechanical spectra of FW and LW at 5% (w/w) at 25 °C showed a weak gel like behavior for both pectins. The dynamic surface tension, foaming ability and emulsifying properties of FW and LW were evaluated and compared with gum Arabic. FW and LW showed lower dynamic surface tension and higher foaming ability than gum Arabic at the same concentration. Emulsions were prepared with polysaccharides at concentrations ranging from 0.5% to 4% (w/w). The droplet size decreased for both pectins as the concentration increased. Values of surface weighted mean diameter D[3,2] and volume weighted mean diameter D[4,3] obtained for emulsions prepared with FW and LW were found to be similar to gum Arabic, which is well known for its emulsifying properties.

In vitro β‐Carotene Bioaccessibility and Lipid Digestion in Emulsions: Influence of Pectin Type and Degree of Methyl‐Esterification

Citrus pectin (CP) and sugar beet pectin (SBP) were demethoxylated and fully characterized in terms of pectin properties in order to investigate the influence of the pectin degree of methyl-esterification (DM) and the pectin type on the in vitro β-carotene bioaccessibility and lipid digestion in emulsions. For the CP based emulsions containing β-carotene enriched oil, water and pectin, the β-carotene bioaccessibility, and lipid digestion were higher in the emulsions with pectin with a higher DM (57%; "CP57 emulsion") compared to the emulsions with pectin with a lower DM (30%; "CP30 emulsion") showing that the DM plays an important role. In contrast, in SBP-based emulsions, nor β-carotene bioaccessibility nor lipid digestion were dependent on pectin DM. Probably here, other pectin properties are more important factors. It was observed that β-carotene bioaccessibility and lipid digestion were lower in the CP30 emulsion in comparison with the CP57, SBP32, and SBP58 emulsions. However, the β-carotene bioaccessibility of CP57 emulsion was similar to that of the SBP emulsions, whereas the lipid digestion was not. It seems that pectin type and pectin DM (in case of CP) are determining which components can be incorporated into micelles. Because carotenoids and lipids have different structures and polarities, their incorporation may be different. This knowledge can be used to engineer targeted (digestive) functionalities in food products. If both high β-carotene bioaccessibility and high lipid digestion are targeted, SBP emulsions are the best options. The CP57 emulsion can be chosen if high β-carotene bioaccessibility but lower lipid digestion is desired.