Firmness and Cell Wall Characteristics of Pasteurized Jalapeño Pepper Rings Affected by Calcium Chloride and Acetic Acid

Pepper rings packed in brine containing CaCl₂ were firmer, had higher bound calcium, chelator soluble pectin and pectin DE, and less water-soluble pectin (WSP) than peppers packed in brine containing no CaCl₂. Pepper rings packed in low acid brines (1% and 1.2% acetic acid) were firmer and had less WSP than those packed in high acid brine. Those samples (4% acetic acid) resulted in softening and pectin solubilization, but CaCl₂ resulted in less softening. Monosaccharide composition of cell walls was not affected by CaCl₂ or acetic acid. Firmness retention in CaCl₂ treated samples was probably due to greater association between calcium ions and pectic substances, which resisted acid hydrolysis.     

CELL WALL CHARACTERISTICS AND FIRMNESS OF FRESH PACK CUCUMBER PICKLES AFFECTED BY PASTEURIZATION AND CALCIUM CHLORIDE1

Changes in cell wall pectic substances, degree of pectin methylation, bound Ca⁺⁺, neutral sugar composition, and firmness were determined in mesocarp tissue of pasteurized and nonpasteurized fresh pack cucumber pickles. Large changes in solubility characteristics of pectic substances occurred in cell walls of nonpasteurized pickles that were attenuated by pasteurization. In particular, water and alkali soluble pectins declined, and nonextractable pectins increased during the first month of storage. The major changes in pectic substance solubility appeared to be related to reductions in the degree of pectin methylation with a minor influence of CaCl₂. Galactose in cell walls of nonpasteurized pickles was substantially reduced, and the reduction in galactose was hindered by CaCl₂ or pasteurization. The amount of bound Ca⁺⁺ appeared to be associated with tissue firmness after one month in storage, since firmer tissue had more cell wall bound Ca⁺⁺. While firmness was associated with the amount of bound Ca⁺⁺, the amount of bound Ca⁺⁺ was dependent on the supply of Ca⁺⁺ and the degree of pectin methylation.     

PHYSICOCHEMICAL FACTORS AFFECTING FIRMNESS OF PASTEURIZED JALAPENO PEPPER RINGS

Physical and chemical properties that influence textural properties of pasteurized pepper rings of four jalapeno pepper cultivars were determined. Hardness, cohesiveness, gumminess and chewiness were positively correlated with moisture and wall thickness, and negatively associated with water soluble pectin and alcohol insoluble solid (AIS) contents. After 90 days' storage, Veracruz peppers were firmer than the other cultivars due to their greater levels of chelator soluble pectin and bound calcium, and lower levels of water soluble pectin. Texture measurement of fresh peppers was not a reliable predictor of firmness for pasteurized peppers.     

Structure and physical properties of pectins with block-wise distribution of carboxylic acid groups

The physical and the interfacial properties of pectins de-esterified by a specific block-wise enzymatic procedure were investigated. Two major types of block-wise de-esterified pectins with different internal distribution of carboxylic acid on the pectin chains were explored. Type C and type U pectins with the same degree of methylesterification are different and a more block-wise intramolecular distribution in comparison to commercial native apple pectin. The most ordered pectin (U63 pectin, 63% methylesterified pectin) has the highest electrophoretic mobility (ζ-potential). It reveals more pronounced intermolecular interactions since it exhibited, at low pH, the lowest circular dichroism intensity at shorter wavelength. U63 pectin (at acidic pH, without calcium addition) has a higher viscosity and formed a stronger gel compared to the less ordered C63 pectin and/or native apple pectin. X-ray patterns show that powdered U63 pectin is more crystalline than C63 pectin, while apple pectin is mostly amorphous. The modified pectin also, most effectively, reduced the surface tension (55 mN/m) and the interfacial tension (5.6 mN/m), probably due to the preferred surface orientation of the carboxylic groups at the water/air or water/oil interfaces.     

Rheological and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins

Ambarella and mango peels are good sources of pectins (15–20%), with high degree of methylation (60–78%) and high molar masses. Ambarella and mango ( Améliorée and Mango varieties) peel pectins were extracted using HCl or oxalic acid/ammonium oxalate (OAAO). Purified pectins were analysed for their flow behaviour and phase diagrams were established at pH 3 as sucrose vs. pectin concentration. The gelation kinetics and mechanical spectra of these pectin gels were studied and compared to those of commercial citrus (lime) pectins. At a concentration of 1% (w/v), all pectic solutions had a shear thinning behaviour but at 0.6% (w/v), only OAAO-extracted pectins exhibited such behaviour. Phase diagrams showed that at pH 3, gelation of OAAO mango extracted pectins was possible at low polymer concentration (0.2%; w/w) for a sucrose concentration of 60% (w/w). OAAO-extracted pectins exhibited a higher gelling ability than HCl-extracted ones. Sucrose (45–50%) and pectin (0.2–0.6%) concentration had a deep impact on the gel strength. Our results enable to conclude that the OAAO extraction from mango and ambarella peels allowed the recovery of pectins that exhibit high gelling properties.     

Changes in texture qualities and pectin characteristics of fermented minced pepper during natural and inoculated fermentation process

Texture qualities and pectin characteristics in fermented minced pepper (FMP) prepared by natural fermentation (NF) and inoculated fermentation (IF) were analysed during fermentation. The results showed variation in texture qualities and pectin characteristics was similar during NF and IF process. The hardness, cell wall material, sodium carbonate-soluble pectin (SSP) and chelate-soluble pectin (CSP) content, and CSP esterification degree decreased, while water-soluble pectin (WSP) content significantly (P < 0.05) increased after fermentation. The rhamnose (Rha) molar ratio in three pectins increased, but arabinose (Ara) and galactose (Gal) molar ratios in most pectins decreased after fermentation. Changes in Ara/Gal and (Gal + Ara)/Rha ratios represented the backbone and branched chains of rhamnogalacturonan-I in three pectins depolymerised during fermentation. The decrease of molecular weight (M_w) in CSP was more obvious than that in WSP and SSP, and it was extensively depolymerised into low-M_w pectin after fermentation. Pearson's correlation analysis showed FMP hardness was extremely (P < 0.01) positively correlated with CSP content and significantly (P < 0.05) positively correlated with SSP content and CSP M_w. Hence, CSP was the main pectin to affect texture compared with WSP and SSP, and its characteristics played a crucial role for regulating FMP texture during NF and IF process.     

Gel-Forming Characteristics of Milk Proteins, 2. Roles of Sulfhydryl Groups and Disulfide Bonds

The gel-forming characteristics of milk proteins were investigated by employing skim milk either nonpreheated or preheated at 80°C, and coagulating them at 70 or 80°C with glucono-delta-lactone. The solubility of each gel in the phosphate buffer (pH 7.0) containing urea and 2- mercaptoethanol was examined. The disulfide bonds played a more important role in the gel coagulated at 80°C from skim milk preheated at 80°C than in the gel coagulated at 70°C from nonpreheated skim milk.The effect of the reduction treatment with 2-mercaptoethanol was more pronounced on preheated skim milk than on nonpreheated skim milk. Sulfhydryl groups and disulfide bonds, which were buried in the molecules of whey proteins in their native state, were rendered accessible following heat treatment at 80°C.The gel prepared from skim milk pretreated with oxidizing agent, hydrogen peroxide (i.e., skim milk has no accessible sulfhydryl groups as a result), or the gel prepared from skim milk pretreated with reducing agent, 2-mercaptoethanol, (i.e., skim milk has few disulfide bonds as a result), displayed weak gel formation. But the gel prepared from the mixture of these skim milks with appropriate ratio displayed higher gel firmness. These findings suggest that intermolecular disulfide bonds are formed by the exchange reaction between sulfhydryl groups and disulfide bonds during gel formation.     

Effect of debranching on the rheological properties of Ca-pectin gels

Water-soluble pectin (WSP) extract was subjected to controlled carrot pectin methylesterase treatment, thereby producing de-esterified pectin (DEP). Both WSP and DEP were incubated with a mixture of endo-arabinanase and α-L-arabinofuranosidase to yield partially debranched pectins (WSP_DBr and DEP_DBr respectively). Pectin samples were characterised in terms of degree of methylesterification (DM), neutral sugar content, and degree of branching (DBr). The characterised pectins were used for the preparation of pectin gels with high and low calcium ion (Ca²⁺) concentrations. The rheological characteristics of the produced gels were evaluated by means of small-amplitude oscillatory tests. These characteristics include network development of the gel, gel strength (G′), gel elastic character and gel type. Partial debranching of pectin resulted in a reduction of the arabinose content (by approximately 50%) and caused a slight decrease in polymer DBr. Gels produced from semi-dilute solutions of partially debranched pectins showed network development profiles similar to those prepared from semi-dilute solutions of the corresponding non-debranched polymers. Yet, the former gels showed lower G′ values, poor gel elastic character and a “weaker” nature as compared to the latter. Next to Ca²⁺ cross-links, the presence of long arabinose-containing side chains is suggested to play an important role in the rheological characteristics of Ca²⁺-pectin gels.     

Short communication: Stabilization of milk proteins at pH 5.5 using pectic polysaccharides derived from potato tubers

Potato pectin has unique molecular characteristics that differentiate it from commercially available pectins sourced from citrus peels or apple pomace, including a higher degree of branching and a higher acetyl content. The objective of this study was to evaluate the ability of potato pectin to stabilize milk proteins at an acidic pH above their isoelectric point, pH 5.5, at which no citrus- or apple-derived pectins are functional. Potato pectin was extracted from raw potato tubers by heating at pH 4.5 and 120°C for 30 min after removing starch solubilized using a dilute HCl solution adjusted to pH 2. The potato pectin was found to have a galacturonic acid content of 17.31 ± 3.29% (wt/wt) and a degree of acetylation of 20.20 ± 0.12%. A portion of the potato pectin was deacetylated by heating it in an alkaline condition. The deacetylation resulted in a galacturonic acid content of 19.12 ± 4.64% (wt/wt) and a degree of acetylation of 3.03 ± 0.03%. Particle size distributions in acidified milk drink (AMD) samples adjusted to pH 5.5 demonstrated that the acetylated and deacetylated potato pectins were capable of inhibiting the aggregation of milk proteins to the largest degree at a pectin concentration of 1.0 and 0.25% (wt/wt), respectively. Pectin molecules that were not bound to milk proteins in these AMD samples were quantified after centrifugally separating milk proteins and pectin bound to them from the serum. We found that, for the acetylated and deacetylated potato pectins, all or approximately half of the pectin molecules were bound to milk proteins at a pectin concentration of 0.25 or 1.0% (wt/wt), respectively. These results suggest that the presence of acetyl groups is a critical factor that determines how potato pectin molecules bind electrostatically to milk protein surfaces, form 3-dimensional structures there, and function as a stabilizer. The present results demonstrate that potato pectin can stabilize milk proteins at pH 5.5 and potentially enable the development of novel AMD products with improved functionality for casein-containing products with moderately acidic pH profiles.     

Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High‐methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.     

Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications.

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High-methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.     

Firming of fruit tissues by vacuum-infusion of pectin methylesterase: Visualisation of enzyme action

Apple pieces were vacuum-impregnated with either a pectin methylesterase (PME) and calcium solution or with water prior to pasteurization. Pasteurized apple pieces impregnated with PME and calcium showed a significantly higher firmness. Moreover, solid state ¹³C NMR spectroscopy of apple cell wall residues revealed an increase of their molecular rigidity. Exogenous PME addition involved a decrease from 82% to 45% of apple pectin degree of methyl-esterification. Microscopic observations of apple slices immunolabelled with antibodies specific for pectins showed that (i) demethyl-esterification was more intense in the cell wall region lining intercellular spaces (demonstrating a key role for these intercellular channels in the enzyme penetration in the tissue during vacuum-infusion) and that (ii) the number of calcium-dimerized deesterified homogalacturonan chains increased. The results corroborate the hypothesis that vacuum-impregnated PME action liberates free carboxyl groups along pectin chains that could interact with calcium, increasing the rigidity of pectins and finally the mechanical rigidity of apple tissue.     

Influence of the overall charge and local charge density of pectin on the complex formation between pectin and β-lactoglobulin

The complex formation between β-lactoglobulin (β-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMP_B and HMP_R are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pH_c, the pH where soluble complexes of β-lg and pectin are formed and pH_?, the pH of phase separation, both as a function of ionic strength. pH_c decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH_? passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between β-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of β-lg and pectin showed charge regulation in β-lg–pectin complexes. Around pH 5.5–5.0 the pK_as of β-lg ionic groups are increased to induce positive charge on the β-lg molecule; around pH 4.5–3.5 the pK_a values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with β-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.     

Pectin Extraction from Lemon By-Product with Acidified Date Juice: Effect of Extraction Conditions on Chemical Composition of Pectins

Mixtures of date and lemon pectins were extracted from lemon by-product with acidified date juice under different conditions of temperature, pH and time. Individual pectins from date and lemon, respectively, were also extracted using the same experimental conditions, then analysed and compared to pectin mixtures. It was found that the use of extreme conditions resulted in higher galacturonic acid content, lower degree of methylation, lower neutral sugar content, lower molecular weight and darker colour pectins. Examination of the individual neutral sugars showed that the main ones were galactose (1.6–5.4%), arabinose (1.6–4.2%) and rhamnose (0.5–0.8%). The Gal A/Rha molar ratios varied from ∼53 to ∼149. Moreover, mixture of pectin extracted at the optimal extraction conditions (84.34 °C, pH 2.8 during 3 h 34 min) had interesting properties, with a high galacturonic acid content (63.4%), low degree of methylation (∼35%) and a mass molecular weight of about 243 kg/mol.     

Influence of pectin structure on the interaction with bile acids under in vitro conditions

Structural parameters of pectin (a polysaccharide and important component of dietary fibre) influence the interaction with bile acids (BA). The effect of experimental conditions (concentration of pectin, BA and Ca²⁺) on such interactions was studied at pH 6.0. Series of pectins were used, prepared from virtually fully esterified pectin by gradual de-esterification with alkali or with pectinesterase from oranges. Further amidated and acetylated pectins were also tested. The greatest interaction with BA was found with a very highly esterified pectin under in vitro conditions. The interaction diminished with decreasing degrees of esterification (DE). This decrease was more intensive for pectins possessing a blockwise arrangement of free -COOH groups. Derivatives of pectin generally interacted less with BA. These results were principally confirmed with commercial pectins, with pectins prepared on a pilot-plant scale and with pectins originating from a defined botanical source. The interactions of these preparations with BA were less intensive than with those of pectins having an ideal random distribution of free -COOH groups in the polysaccharide molecules at the same DE. The interaction with pectin is also likely to be influenced by the structure of BA.     

Relationship Between Degree of Pectin Methylation and Tissue Firmness of Cucumber Pickles

The relationship between pectin methylation and tissue firmness was examined in cucumber pickles exposed to pre-brining and brining treatments. Tissue treated with CaCl₂ prior to or during brining, blanched before brining or held at 2°C during brine storage resisted softening. Although all treatments reduced the degree of esterification (DE) of pectic substances, less demethylation occurred in treatments that protected against softening. Join point regression analysis of the data indicated that maximum firmness of mesocarp tissue was attained when the DE of pectins was 12.3 ± 1.2 or greater. Firmness declined concomitantly when the DE declined below 12.3 ± 1.2. Methods that protect against excessive demethylation of pectins appear to be important in retarding softening of cucumber pickle tissue during storage in brine.     

Effect of extraction conditions on the yield and chemical properties of pectin from cocoa husks

Different extraction conditions were applied to investigate the effect of temperature, extraction time and substrate–extractant ratio on pectin extraction from cocoa husks. Pectin was extracted from cocoa husks using water, citric acid at pH 2.5 or 4.0, or hydrochloric acid at pH 2.5 or 4.0. Temperature, extraction time and substrate–extractant ratio affected the yields, uronic acid contents, degrees of methylation (DM) and degrees of acetylation (DA) of the extracted pectins using the five extractants differently. The yields and uronic acid contents of the extracted pectins ranged from 3.38–7.62% to 31.19–65.20%, respectively. The DM and DA of the extracted pectins ranged from 7.17–57.86% to 1.01–3.48%, respectively. The highest yield of pectin (7.62%) was obtained using citric acid at pH 2.5 [1:25 (w/v)] at 95 °C for 3.0 h. The highest uronic acid content (65.20%) in the pectin was obtained using water [1:25 (w/v)] at 95 °C for 3.0 h.     

Butternut and beetroot pectins: Characterization and functional properties

The physicochemical characteristics and functional properties of butternut (Cucumis moschata Duch. ex Poiret) and beetroot (Beta vulgaris L. var. conditiva) pectins obtained by enzymatic extraction from by-products of vegetable processing have been evaluated. The molecular mass distribution was determined using Gel Permeation Chromatography using light scattering, refractive index and UV detectors and the samples were found to be highly heterogeneous and polydisperse. M_w values of 136,000 and 1,309,000 g/mol were determined for butternut and beetroot pectins respectively. Butternut pectin had a high degree of methyl esterification. In the presence of high concentrations of sugar and at low pH, this pectin did not form gels but instead produced viscous solutions. Solutions showed pseudoplastic flow behaviour with a shear thinning index of 0.68 as determined from the Power law model. Beetroot pectin had a low degree of methyl esterification and formed gels with addition of Ca²⁺ at concentrations of 10 mg/g pectin or higher. The maximum value of the storage modulus was obtained at a Ca²⁺/GalA ratio of 0.25. The thermal stability of gels suggested that hydrogen bond interactions prevailed in the absence of Ca²⁺, whereas electrostatic junction zones increasingly developed between pectin chains as the calcium concentration increased. Aqueous solutions of butternut and beetroot pectins significantly reduced surface tension and both samples were able to form stable oil-in-water emulsions. It was found that protein and/or polyphenol – rich fractions present in the pectins adsorbed at the oil–water interface and were responsible for the emulsification properties.     

Isolation and Characterization of Pectin in Sugar-Beet Pulp

Pectin was extracted from sugar-beet pulp by various solvent fractionation procedures. An optimal HCI-extraction method yielded 19.53% pectin from the raw material. The HCl-isolated pectin contained 81.8% galacturonic acid. The sugar-beet pulp pectin obtained from different extraction procedures had a high methoxy content ( 60% degree of methylation). The pectin also contained 10 to 17.5% neutral sugars which were mainly arabinose and galactose as analyzed by gas chromatography. The peak molecular weights (relative to dextrans) of the pectins as determined by gel permeation ranged from 35,500 to 44,700 daltons. The pectin possessed high water-holding capacity and low viscosity.     

The distribution of free and esterified carboxyl groups within the pectin molecule after the action of pectin esterase from Aspergillus niger and oranges

By reaction of pectin esterase (PE) from Aspergillus niger and oranges as well as lye, with 95% esterified citrus and apple pectin we prepared series of preparations with degrees of esterification between 35 and 77%. In these partial deesterified pectins the form of distribution of the free and esterified carboxyl groups has been determined from the activity coefficient gamma Ca2+ of the calcium counterions in the solutions of the corresponding calcium pectinates, from the electrostatic free enthalpy delta (Gel/N)KCa of the ion exchange Ca2+----2K+ in these systems as well as from the relative activity of the polygalacturonase reacting with sodium pectinate. The PE from A niger hydrolyzes the esterified carboxyl groups more or less randomly, in a manner similar to the effect of lye on pectin. On the other hand PE from oranges brings about block-like groupings of free carboxyl groups in the pectin molecule. The study revealed different reaction mechanisms of the pectin deesterification by pectin esterases from Aspergillus species and higher plants.