Acid-induced gelation of milk protein concentrates with added pectin: Effect of casein micelle dissociation

The dynamics of the formation of the acid gel network for mixtures of milk protein concentrate (MPC) and low methoxyl amidated (LMA) pectin were studied using rheological measurements. The results as a function of pectin content and casein micelle integrity, from neutral pH to approximately pH 4.2, together with the microstructural changes observed in some of these systems, are presented.The gelation profiles of a mixture of 4% w/v MPC and LMA pectin (0–0.075% w/v) after the addition of 1.2% w/v glucono-δ-lactone showed a gradual decrease in the shear modulus with the incorporation of pectin. The effects of casein micelle integrity on casein–pectin interactions were studied, by preparing MPC dispersions containing various levels of micellar casein. A gradual change in the shear modulus, from a disrupting effect of pectin added to MPC, in which the casein micelles are intact, to a clear synergistic effect of pectin added to dissociated casein systems, was found in the acid-induced milk gels.     

Controlling heat induced aggregation of whey proteins by casein inclusion in concentrated protein dispersions

Formation of soluble, heat stable whey protein (WP) particles may be achieved via caseins and their chaperone like activity. The aim of this study was to establish effects of caseins on the properties of heat induced WP aggregates. Concentrated dairy protein mixtures (10% total-solids) were prepared with various casein:WP ratios (5:95–30:70) at adjusted pH (5.7–7.5) and heated to 80–120 °C, under a constant shear (500 s⁻¹). Increasing casein fraction at higher pH reduced the average size of WP aggregates and the surface hydrophobicity with simultaneous reduction in apparent viscosity at pH 6.7. WP denaturation was minimal when 30% casein was included in the dispersions. Inhibition of WP denaturation at elevated pH with inclusion of caseins may be attributed to a chaperon like activity of the casein. Thus, by increasing pH and the casein content in the system it was possible to form nano-size whey protein particles.     

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.     

Improved emulsion stabilizing properties of whey protein isolate by conjugation with pectins

Functional properties of glyco-protein conjugates of the anionic polysaccharide pectin with whey protein isolate, obtained by dry heat treatment at 60 °C for 14 days, have been investigated in O/W emulsions containing 20% (w/w) soybean oil and 0.4% (w/w) protein both at pH 4.0 and 5.5. Emulsion stabilizing properties of mixtures and conjugates were compared at five protein to pectin weight ratios by determining changes in droplet size distribution and extent of serum separation with time. The results indicated that the dry heat-induced covalent binding of low methoxyl pectin to whey protein, as shown by SDS-PAGE, led to a substantial improvement in the emulsifying behaviour at pH 5.5, which is near the isoelectric pH of the main protein β-lactoglobulin. At pH 4.0, however, a deterioration of the emulsifying properties of whey protein was observed using either mixtures of protein and pectin or conjugates.The observed effects could be explained by protein solubility and electrophoretic mobility measurements. The protein solubility at pH 5.5 was hardly changed using mixtures of protein and low methoxyl pectin or conjugates, whereas at pH 4.0 it was decreased considerably. Electrophoretic mobility measurements at pH 5.5 revealed a much more pronounced negative charge on the emulsion droplets in the case of protein–pectin conjugates, which clearly indicated that conjugated pectin did adsorb at the interface even at pH conditions above the protein's iso-electric point. Hence, the improved emulsifying properties of whey protein isolate at pH 5.5 upon conjugation with low methoxyl pectin may be explained by enhanced electrosteric stabilization.Comparing two different commercial pectin samples, it was clearly shown that the dextrose content during dry heat treatment of protein–pectin mixtures should be as low as possible since protein–sugar conjugates not only resulted in increased brown colour development, but also gave raise to a largely decreased protein solubility which very badly affected the emulsifying properties.     

Effect of high pressure - low temperature processing on composition and colloidal stability of casein micelles and whey proteins

The aim of this study was to identify the impact of high pressure treatments at sub-zero temperatures (high pressure - low temperature; HPLT) on milk proteins. Whey protein solutions, micellar casein dispersions and two mixtures (micellar caseins:whey proteins, 80:20 and 20:80, w/w) were pressure treated (100–600 MPa) at pH 7.0 or 5.8 at −15 °C, −35 °C and ambient temperature. Solubility data showed that whey proteins could only be affected by HPLT treatments at pH 7.0 if caseins were present, while effects could be induced at pH 5.8 without the presence of caseins. The caseins formed on the one hand large aggregates (flocs) and on the other hand the solubility was increased by the creation of smaller micelles. The formation of flocs could only be observed for HPLT treated samples, which indicates the formation of different protein interactions in milk protein based samples compared with common HP treatments.     

Characterization of Phase Separation Behavior, Emulsion Stability, Rheology, and Microstructure of Egg White–Polysaccharide Mixtures

ABSTRACT:  Phase separation behavior of egg white-pectin/guar gum mixtures was investigated. These systems led to phase separation arisen by either depletion flocculation or thermodynamic incompatibility. The influence of polysaccharides on the emulsifying activity index (EAI), emulsifying stability index (ESI), creaming stability, microstructure, and rheological properties was also studied at different polysaccharide concentrations (0% to 0.5%, [w/v]). Increasing pectin and guar gum concentration from 0.01% to 0.5% significantly improved EAI by 51% and 25%, respectively. The highest ESI and EAI values were obtained in the presence of 0.5% (w/v) pectin/guar gum. Microscopic images showed that emulsions containing polysaccharides had small droplets as compared to that of emulsions without polysaccharides. The addition of polysaccharides improved emulsion stability against creaming. Egg white-stabilized emulsions with and without polysaccharides reflect the pseudoplastic behavior with  n  < 1.0. Polysaccharides, especially at high concentrations, affected the viscoelastic behavior of the emulsions; storage ( G ') and loss modulus ( G ") crossed-over at lower frequency values as compared to that of emulsions containing no polysaccharide.     

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.     

Effects of pH,calcium-complexing agents and milk solids concentration on formation of soluble protein aggregates in heated reconstituted skim milk

The proportion of protein present in the supernatant after centrifugation and the formation of soluble protein aggregates in heated (90 °C for 10 min) reconstituted skim milk were investigated as a function of (a) pH, (b) milk concentration 9–21%, w/w (milk solids non-fat, MSNF) and (c) addition of calcium-complexing agents (orthophosphate or EDTA). Compositional changes in milk, resulting from pH adjustment or salt addition, altered the distribution of caseins between the serum and micellar phases of milk prior to heating, and influenced the amount and composition of soluble aggregates formed during heat treatment. Although milk pH was a good predictor of the aggregation behaviour of the proteins during heating of milk of different solids concentrations, neither the proportion of protein in the supernatant prior to heating nor the pH alone could predict the aggregation behaviour when the composition was adjusted with mineral salts.     

The stabilizing behaviour of soybean soluble polysaccharide and pectin in acidified milk beverages

The mechanisms of stabilization of soybean soluble polysaccharide (SSPS) and high methoxyl pectin (HMP) in acidified milk drinks were studied focusing on the differences in behaviour between the two polysaccharides. The changes in casein micelles size during acidification with glucono-δ-lactone or by direct acidification were measured using light scattering. When HMP was added to skim milk before acidification, pectin adsorbed on the surface of the casein micelles via electrostatic interactions and prevented casein aggregation. Results suggested that adsorption of pectin occurred from the beginning of acidification and somewhat affected the rearrangement of casein micelles in the pH range between 5.8 and 5.0. On the other hand, SSPS, at concentrations up to 2% (w/w), did not interact with caseins at pH >4.6. At pH <4.2 SSPS showed better stabilizing properties than HMP. In addition, between pH 4.2 and 3.2, SSPS-stabilized acid dispersions were not affected by pH, while dispersions homogenized with pectin showed a size distribution that depended on pH. The differences in structure between SSPS and HMP account for the unique functionalities of the two polysaccharides in acid milk systems.     

Stability and Rheological Properties of Egg Yolk Granule Stabilized Emulsions with Pectin and Guar Gum

The effects of pectin and guar gum on rheology, microstructure and creaming stability of 1% (w/v) egg yolk granule stabilized emulsions were investigated. While the addition of low amount of pectin (0.1% (w/v)) had no effect on the emulsion viscosity, the addition of 0.5% (w/v) pectin greatly increased the viscosity. Granule-stabilized emulsion without hydrocolloids reflects the pseudoplastic behavior (shear-thinning behavior with flow behavior index, n < 1.0). Hydrocolloids, especially at high concentrations, affected the viscoelastic behavior of the emulsions and both storage (G′) and loss modulus (G′′) were regarded as frequency dependent. Emulsions behaved like a liquid with G′′ > G′ at lower frequencies, and like an elastic solid with G′ > G′′ at higher frequencies. Emulsion microstructure indicated that the presence of hydrocolloids induced flocculation. Creaming stability of emulsions was enhanced by the presence of hydrocolloids and increasing hydrocolloid concentration decreased the creaming by restricting the movement of oil droplets.     

Optimisation of acid extraction of pectin from sweet potato residues by response surface methodology and its antiproliferation effect on cancer cells

The response surface methodology was employed to study the acid extraction of pectin from sweet potato residues. The effects of extraction temperature, extraction time, solution pH and liquid/solid ratio on yield and galacturonic acid content of pectin were investigated. Experimental data were fitted to quadratic polynomial models and analysed using appropriate statistical methods. The determined optimum conditions were extraction temperature 93 °C, extraction time 2.2 h, solution pH 1.7 and liquid/solid ratio (v/w) 30:1. Under these conditions, the experimental extraction yield and galacturonic acid content of pectin were 5.09% and 70.03% (w/w), which were in good agreement with predicted values, 5.08% and 69.40%, respectively. In addition, sweet potato pectin exhibited remarkable antiproliferation effects on human colon cancer cells HT‐29 and human breast cancer cells Bcap‐37 by 46.64% and 42.64% at 1.00 mg mL^?1 separately, indicating that it could potentially be used as a natural supplement in functional foods.     

Pectin extraction from citron peel: optimization by Box–Behnken response surface design

In this study, the effect of acidic extraction conditions (time of 30–90 min, temperature of 75–95 °C and pH of 1.5–3) on the yield and degree of esterification (DE) of citron peel pectin was investigated applying Box–Behnken design. The highest production yield of pectin (28.31?±?0.11%) was achieved at extraction time of 90 min, temperature of 95 °C and pH of 1.5, as optimal extraction conditions, which was close to the predicted value (29.87%). Under optimum extraction conditions, the DE and the emulsifying activity were 51.33 and 46.2%, respectively. In addition, the emulsions were 93.9 and 93.5 stable at 4 °C, 93.7 and 93.1 at 23 °C after 1 and 30 days, respectively. The determination of flow behavior showed that the pectin solutions had a Newtonian behavior at low concentrations (<?1.0% w/v), while this behavior was changed to pseudoplastic with increasing concentration.     

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.     

Isolation and characterisation of κ-casein/whey protein particles from heated milk protein concentrate and role of κ-casein in whey protein aggregation

Milk protein concentrate (79% protein) reconstituted at 13.5% (w/v) protein was heated (90 °C, 25 min, pH 7.2) with or without added calcium chloride. After fractionation of the casein and whey protein aggregates by fast protein liquid chromatography, the heat stability (90 °C, up to 1 h) of the fractions (0.25%, w/v, protein) was assessed. The heat-induced aggregates were composed of whey protein and casein, in whey protein:casein ratios ranging from 1:0.5 to 1:9. The heat stability was positively correlated with the casein concentration in the samples. The samples containing the highest proportion of caseins were the most heat-stable, and close to 100% (w/w) of the aggregates were recovered post-heat treatment in the supernatant of such samples (centrifugation for 30 min at 10,000 × g). κ-Casein appeared to act as a chaperone controlling the aggregation of whey proteins, and this effect was stronger in the presence of α_S- and β-casein.     

Pectin from low quality ‘Golden Delicious’ apples: Composition and gelling capability

Pectin was acid-extracted from low quality ‘Golden Delicious’ apple fruit, yielding 16% (w pectin/w apple fruit). Composition and some of its physicochemical and functional properties were assessed. The pectin fraction presented a galacturonic acid content of 65% (w/w), an esterification degree of 57%, an intrinsic viscosity, [η], of 307 ml/g and a molecular weight (Mw) of 112 kDa. Pectin gels were obtained in 60% (w/v) fructose and pH 2.7. Pectin gels at 2.0% and 3.0% (w/v) presented hardness values of 10.2 and 20.4 g after 12 h at 4 °C. The gel hardness was greatly affected by aging (20% and 25% decrease in 48 h for gels at 2% and 3%, respectively). The results attained suggest the use of this gum as a potential texturing agent for the food industry.     

Optimising chitosan–pectin hydrogel beads containing combined garlic and holy basil essential oils and their application as antimicrobial inhibitor

Chitosan–pectin hydrogel beads that trap and release the maximal amount of combined garlic and holy basil essential oils to inhibit food microorganisms were developed based on the central composite design, with chitosan (0.2–0.7% w/v), pectin (3.5–5.5% w/v) and calcium chloride (CaCl₂) (5.0–20.0% w/v) contents. The optimal bead consisted of 0.3–0.6% w/v chitosan, 3.9–5.1% w/v pectin and 8.0–17.0% w/v CaCl₂, which had a high encapsulation efficiency (62.16–79.06%) and high cumulative release efficiency (31.55–37.81%) after storage at 5 °C for 15 days. Optimal hydrogel beads were packed into a cellulose bag to evaluate antimicrobial activity by the disc volatilisation method. The beads inhibited Bacillus cereus, Clostridium perfringens, Escherichia coli, Pseudomonas fluorescens, Listeria monocytogenes and Staphylococcus aureus but did not affect Lactobacillus plantarum and Salmonella Typhimurium. The oil-containing beads could potentially be applied in food packaging to inhibit the mentioned microorganisms.     

Effects of pectin and guar gum on creaming stability, microstructure and rheology of egg yolk plasma-stabilized emulsions

The influence of pectin and guar gum on the creaming stability, microstructure and rheological properties of 1.0% (w/v) egg yolk plasma (EYP)-stabilized 25.0% (v/v) soybean oil-in-water emulsions was studied at pH 7.0. Addition of pectin/guar gum decreased creaming percentage, and no creaming was detected in the presence of 0.5% (w/v) pectin/guar gum as a result of increasing viscosity. At the end of 10 h, creaming percentage decreased from 61 to 57% with the addition of 0.05% (w/v) guar gum and to 39% with the addition of 0.2% (w/v) guar gum. Microscopic observations represented the droplet aggregation arising from the presence of nonabsorbing biopolymers. At \mathop g^. \mathop \gamma \limits^{.}  = 10 s⁻¹, a tenfold increase in viscosity was observed in the presence of 0.5% (w/v) guar gum compared to the presence of 0.1% guar gum due to the thickening effect of polysaccharide. Increasing gum concentrations enhanced the viscosity and hence the consistency index. All emulsions, except for those containing 0.5% (w/v) guar gum, reflect the near-Newtonian behaviour with flow behaviour index, n, of 0.9–1.0. All emulsions exhibited a liquid-like behaviour at low frequencies (<7.0 Hz) where G″ values were higher than G′. Both G′ and G″ showed a frequency dependency and these two moduli crossed each other at higher frequencies (>7.0 Hz), G′ became greater than G″ and the system behaved like an elastic solid. Addition of pectin at all levels cause no significant change in G′ and G″ values, whereas addition of guar gum, especially at a concentration of 0.5% (w/v), significantly improved these values.     

Stabilisation mechanism of various inulins and hydrocolloids: Milk–sour cherry juice mixture

Milk–fruit juice mixtures, such as the mainly acidic nutraceutical soft drinks, usually suffer from phase separation due to aggregation of caseins at low pH. In this study, short‐chain inulin (SCI), native inulin (NI), long‐chain inulin (LCI) and a combination of long‐ and short‐chain inulins (LCI:SCI) (MIX) in different ratios (20:80, 50:50 and 80:20) were added (up to 10% w/v) to a milk–sour cherry juice mixture and their stabilisation mechanisms investigated using rheological, microstructural and zeta potential observations. In addition, gum tragacanth (GT) and Persian gum (PG) as adsorbing and guar gum (GG) as nonadsorbing hydrocolloids were combined with inulin to enhance their stabilising properties. Finally, sensory analyses were carried out on the stabilised samples. According to our findings, LCI fully stabilised the mixture (8% w/v), while LCI: SCI and NI only reduced phase separation at very high concentrations, and SCI had no significant effect on the stabilisation. Moreover, no inulin aggregates and rheological changes were observed with SCI. However, LCI, LCI: SCI and NI formed inulin aggregates and the mixtures became even more viscous and thixotropic (LCI > LCI: SCL > NI). Based on these observations, it can be concluded that chain length and concentration are two important factors that affect the functionality of inulin. On the other hand, the combination of inulin with GT and PG did not have any pertinent effect on the stabilisation. However, the mixture of inulin and GG could stabilise the mixtures at certain ratios and concentrations. Furthermore, in mixtures containing GG and SCI, GG played the main role in the stabilisation by increasing the viscosity and forming gel network.     

Modelluntersuchungen zu Bedingungen der Bildung vonN ε-Carboxymethyllysin in Lebensmitteln

In model experiments with equimolar mixtures of lysinemonohydrochloride and glucose [88% (w/v) water content, 100° C heating temperature] the influence of several conditions (hydrolysis, pH) and ingredients (iron, phosphate, and nitrite) on the formation ofN ^ε-carboxymethyllysine (CML) were evaluated. CML was analysed using a reversed-phase HPLC-method after derivatisation witho-phthaldialdehyde. CML, which is an oxidative derivative of fructoselysine, is also formed during the acid hydrolysis applied for amino acid determination in food products. In model mixtures without hydrolysis only 8–21% CML compared to that in hydrolysed samples was found. Therefore, in food products all hydrolyses for CML must be performed after borohydride reduction in order to destroy fructoselysine. This can be controlled by the determination of furosine. The pH of the model mixtures considerably influenced the formation of CML. At pH 4.0 only 70 mg, at pH 7.0 370 mg, and at pH 9.0 3170 mg CML/kg lysine were determined. The CML concentration also clearly increased with higher concentrations of iron, phosphate, and nitrite. This is explained by a promoting effect on the oxidation of fructoselysine to CML.     

Interactions of (β-Lactoglobulin and High-methoxyl Pectins in Acidified Systems

The interactions that occur when β-lactoglobulin (β-lg) is mixed with a high-methoxyl pectin (HMP) and a modified pectin (mHMP, modified using plant pectinesterase) were examined at pH 3.8. Whereas soluble aggregates formed in β-lg-HMP, β-lg-mHMP precipitated upon mixing. β-lg-HMP mixtures showed soluble aggregates with larger hydrodynamic diameters when heated at 65°C than when heated at 90°C. β-lg-HMP mixtures adjusted to pH 6.0 after heating showed that the aggregates formed at 65°C could be dissociated, but the complexes were not reversible after heating at 90°C. A similar effect also was observed when resuspending the°-lg-mHMP precipitates at pH 6.0. The behavior of the 2 pectins was attributed to their differences in charge distribution.