Effect of a CO2-acidification cycle on physicochemical and acid gelation properties of skim milk reconstituted with added pectin (original) (raw)
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Rheological and Biochemical Properties of Acidified Milk / Pectin Co-Gels
The influence of pH and Low Methoxyl Pectin (LMP) on the stability and properties of acid milk gel was studied by measuring rheology, ζ potential, particle size, micelle hydration and buffering properties. Glucono-delta-lactone (gdl) addition decreased rapidly the pH and stabilized it at ~ 4.6. During acidification stiffness (K) increased while the gel point decreased. The presence of pectin on milk reconstituted with or without gdl increased significantly the stiffness and the particle size compared with a non treated sample. On the other land lowering pH from the initial pH to pH 5.9-5.8 decreased significantly the micelle hydration of acidified milk treated with or without pectin and storage at 4°C.
Acid Milk Gel Formation as Affected by Total Solids Content
Journal of Food Science, 1997
Reconstituted skim milk with varying concentrations of total solids was coagulated using glucono-␦-lactone (GDL). Microscopic, turbidimetric and rheological procedures were used to examine mineral solubilization, buffering capacity, casein dissociation and micellar solvation during gelation. Total solids of the milk affected pH of the onset of gelation attributable to differences in colloïdal calcium phosphate in the casein particles during acidification. Firmness and elasticity of the resulting gel increased with total solids from a more direct contribution of dry matter during the last stage of acid milk gel formation.
Rennet-induced gelation of calcium and phosphate supplemented skim milk subjected to CO2 treatment
Journal of dairy science, 2004
A Doehlert design was performed to study the effect of calcium and phosphate supplementation at 0 to 25 mmol/kg and 0 to 16 mmol/kg, respectively, on the rennet gelation of reconstituted skim milk subjected to pH-reversible CO(2) acidification. Supplemented reconstituted skim milk samples were acidified to pH 5.80 by the addition of CO(2) under pressure and depressurized under vacuum to restore the initial pH value. The second-order polynomial models satisfactorily predicted the effect of salt addition on the micellar molar Ca:P ratio and the average diameter of the casein micelles, whereas only trends were used in the analysis of the rennet-clotting behavior of salt-supplemented, CO(2)-treated milk. Whether added Ca was the most determinant factor on the micellar molar Ca:P ratio, added Pi (a mixture of Na(2)HPO(4) and NaH(2)PO(4)) was the most determinant factor on the other responses studied, and its effect was most pronounced when Ca was simultaneously added. By comparison with ...
Zeta potential of pectin-stabilised casein aggregates in acidified milk drinks
International Dairy Journal, 2007
High-methoxy (HM) pectin is commonly used to improve the stability of acidified milk drinks (AMDs) and zeta potential measurements can aid in elucidating the mechanisms responsible for the improved stability. Pectin was added to an AMD model system in concentrations of 0.0%, 0.1%, 0.3% or 0.5% and the samples were subjected to heat treatment at 75 1C for 20 min; control samples were not heated. A change in zeta potential from positive to negative values with addition of pectin was observed. Increasing the pectin concentration resulted in a more negative zeta potential. Heat treatment caused a decrease in the numeric value of the zeta potential, which indicates a partial desorption of pectin from the protein aggregates. r
Gelation of high methoxy pectin by acidification with d-glucono-δ-lactone (GDL) at room temperature
Carbohydrate Polymers, 2009
Rheological comparisons have been made between preparations of high methoxy pectin (DE % 70%) gelled by acidification with D-glucono-d-lactone (GDL) on holding for 16 h at 25°C in the presence of 60 wt% sucrose, and otherwise identical preparations gelled by acidification with citric acid at high temperature and cooling from 90 to 25°C at 1°C/min. Two series of experiments were carried out for both methods of acidification. In the first series, the concentration of pectin (c) was held constant at 1.0 wt% and the final pH attained after holding (with GDL) or cooling (with citric acid) was varied from 3.75 to 2.25. In the second series, the final pH was held constant at 3.0 and c was varied from 0.25 to 2.00 wt%. All samples were then heated (1°C/min) from 25 to 90°C. Rheological changes on cooling/holding and heating were characterised by low-amplitude oscillatory measurements of storage modulus (G 0 ) and loss modulus (G 00 ) at 1 rad s À1 and 0.5% strain, and mechanical spectra were recorded at 25°C. Selected samples, gelled with GDL, were also characterised by compression testing (at 25°C), and a direct linear relationship was found between the logarithm of yield stress and log G 0 .
LWT - Food Science and Technology, 2004
Reconstituted skim milk samples at pH between 6.5 and 7.1 (heating pH) were heated at 80 C, 90 C or 100 C for 30 min (heating temperature). The particle size of the casein micelles was measured at pH 4.75-7.1 (measurement pH) and at temperatures of 10 C, 20 C and 30 C (measurement temperature) using photon correlation spectroscopy. The particle size of the casein micelles, at a measurement pH of 6.7 and a measurement temperature of 20 C, was dependent on the heating pH and heating temperature to which the milk was subjected. The casein micelle size in unheated milk was about 215 nm. At a heating pH of 6.5, the casein micelle size increased by about 15, 30 and 40 nm when the milk was heated at 80 C, 90 C or 100 C, respectively. As the heating pH of the milk was increased, the size of the casein micelles decreased so that, at pH 7.1, the casein micelles were B20 nm smaller than those from unheated milk. Larger effects were observed as the heating temperature was increased from 80 C to 100 C. The size differences as a consequence of the heating pH were maintained at all measurement temperatures and at all measurement pH down to the pH at which aggregation of the micelles was observed. For all samples, size measurements at 10 C showed no aggregation at all measurement pH. Aggregation occurred at progressively higher pH as the measurement temperature was increased. Aggregation also occurred at a progressively higher measurement pH as the heating pH was increased. The particle size changes on heating and the aggregation on subsequent acidification may be related to the pH dependence of the association of whey proteins with, and the dissociation of k-casein from the casein micelles as milk is heated.
International Dairy Journal, 2007
Casein micelle stability and reactivity were assessed on milk subjected to reversible acidification by carbonation. Pressurised CO 2 was injected at 4 1C, leading to controlled acidification from 6.6370.02 to a target pH (5.5 or 5.2). After holding the pressurised milk under these conditions for 15 or 60 min, the pressure was released and the milk pH returned to its initial value under stirring and vacuum degassing. Upon CO 2 treatment, calcium and protein partition, zeta potential and size of casein micelles were restored directly after neutralisation. The rheological properties of the gel obtained by acid coagulation of CO 2-treated milk did not change as a result of carbonation. Micelle hydration increased after neutralisation and during storage. Milk buffering capacity in the pH range of 4.5-5.5 decreased after neutralisation of milk acidified by carbonation, but increased during chilled storage of this milk. Holding time of carbonated milk at low pH was found to have no impact on the physicochemical characteristics of casein micelles and the rheological properties of the gel obtained by acid coagulation of this milk.
Journal of Dairy Science, 2015
Milk protein concentrate powders (MPC) with improved rehydration properties are often manufactured using processing steps, such as acidification and highpressure processing, and with addition of other ingredients, such as sodium chloride, during their production. These steps are known to increase the amount of serum caseins or modify the mineral equilibrium, hence improving solubility of the retentates. The processing functionality of the micelles may be affected. The aim of this study was to investigate the effects of partial acidification by adding glucono-δ-lactone (GDL) to skim milk during membrane filtration on the structural changes of the casein micelles by observing their chymosin-induced coagulation behavior, as such coagulation is affected by both the supramolecular structure of the caseins and calcium equilibrium. Milk protein concentrates were prepared by preacidification with GDL to pH 6 using ultrafiltration (UF) and diafiltration (DF) followed by spray-drying. Reconstituted UF and DF samples (3.2% protein) treated with GDL showed significantly increased amounts of soluble calcium and nonsedimentable caseins compared with their respective controls, as measured by ion chromatography and sodium dodecyl sulfate-PAGE electrophoresis, respectively. The primary phase of chymosin-induced gelation was not significantly different between treatments as measured by the amount of caseino-macropeptide released. The rheological properties of the reconstituted MPC powders were determined immediately after addition of chymosin, both before and after dialysis against skim milk, to ensure similar serum composition for all samples. Reconstituted samples before dialysis showed no gelation (defined as tan δ = 1), and after re-equilibration only control UF and DF samples showed gelation. The gelation properties of reconstituted MPC powders were negatively affected by the presence of soluble casein, and positively affected by the amount of both soluble and insoluble calcium present after reconstitution. This work, testing the chymosin-induced gelation behavior of various reconstituted MPC samples, clearly demonstrated that a decrease in pH to 6.0 during membrane filtration affects the integrity of the casein micelles supramolecular structure with important consequences to their processing functionality.
Effect of Controlled κ-Casein Hydrolysis on Rheological Properties of Acid Milk Gels
Journal of Dairy Science, 2003
An experimental method based on the controlled chymosin-induced κ-casein hydrolysis of milk was proposed to modify micellar reactivity. Milk samples with a degree of κ-casein hydrolysis of 19, 35, and 51% were obtained. The physicochemical properties of partially converted casein micelles were determined. The net negative charge of casein micelles was reduced with increasing degree of κ-casein hydrolysis and a small but significant decrease in hydrodynamic diameter and micellar hydration were noted. Dynamic low amplitude oscillatory rheology was used to monitor the rheological properties of acid milk gels (GDL) made with partially chymosin-hydrolyzed milks in comparison with those of strictly acid and rennet gels. An increase in the gelation pH value was observed with increasing the degree of κ-casein hydrolysis. The moduli values (G′ and G″) reached 2 h after the point of gel were, for all degrees of hydrolysis tested, significantly higher than those of strictly rennet and acid gels. Comparison of changes in ΔG′/Δt with time indicated differences in gel formation that could be related to the increased values of G′ obtained for acid gel made with chymosin-treated milk. At a given time after gelation (2 h), increasing the degree of κ-casein hydrolysis in milk led also to an increase in the loss tangent and the serum holding capacity of acid milk gels suggesting a correlation between these two parameters.