Chemical and Physical Changes in Milk Protein Concentrate (MPC80) Powder during Storage (original) (raw)
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Maillard Reaction and Protein Cross-Linking in Relation to the Solubility of Milk Powders
Journal of Agricultural and Food Chemistry, 2011
Protein changes in relation to solubility, Maillard reaction (MR), and protein cross-linking in whole milk powder (WMP), skim milk powder (SMP), and whey protein concentrate (WPC) stored at different relative humidities (RHs) were investigated by chemical and electrophoretic methods. WMP and SMP reached minimum solubility rapidly, while WPC showed no change in solubility. The loss of solubility corresponded with development of high-molecular-weight protein complexes observed by two-dimensional electrophoresis. The maximal MR rate occurred at 66% RH for WMP and SMP (high lactose/protein ratios) and 84% RH for WPC (low lactose/protein ratios) based on the furosine and hydroxymethylfurfural contents. However, browning was greatest at 84% RH in all powders. The minimum solubility corresponded with the casein and fat contents. The retention of solubility and minimal protein cross-linking of WPC compared to casein-containing powders suggest that the casein content and cross-linking strongly influence the decrease in the solubility of milk powder.
Effects of storage temperature on the solubility of milk protein concentrate (MPC85)
Food Hydrocolloids, 2006
The effect of storage time and temperature on the solubility of milk protein concentrate (MPC85) was investigated using solubility tests, gel electrophoresis and mass spectrometry. It was found that, at a given temperature, the solubility of MPC85 decreased exponentially with time and a master curve was obtained using a temperature-time superposition. Gel electrophoresis indicated that the insoluble proteins were the caseins, whereas the whey proteins remained soluble. Mass spectrometry showed that, with storage time, the casein was lactosylated. In the light of these measurements, it is speculated that the insolubility of the MPC85 could have been due to cross-linking of the proteins at the surface of the MPC85 powder. However, other mechanisms, such as the cross-linking of the proteins by hydrophobic and/or hydrogen bonding, are not ruled out.
Journal of the Science of Food and Agriculture, 2011
As dissolution of powdered milk proteins is necessary for the expression of their functional properties, it is regarded as a critical property by the dairy industry. However, milk proteins exhibit a progressive loss of solubility during storage in the dry form, especially in the case of high-protein-containing powders such as milk protein concentrate (MPC). To further understand the mechanisms responsible for this loss of solubility, the rehydration process of MPC powder before and after storage at 23% equilibrium relative humidity and 24°C for up to two months was studied. This work clearly showed that the storage-induced loss of milk protein powder solubility was due to changed rehydration kinetics and not to the formation of insoluble material in the course of storage. The concentrations of the various constituents of MPC (caseins, whey proteins, lactose, calcium, magnesium, phosphorus, sodium and potassium) were determined in the dispersed phase during the powder dissolution process. The results suggest that the release of micelles from powder particles is the rate-limiting step of the MPC rehydration process and is inhibited upon storage. In contrast, water penetration into the powder particles is shown not to be a rate-limiting factor as molecules larger than water (whey proteins and lactose) were freely released out of the powder structure in both fresh and aged MPCs.
Le Lait, 2005
Lactose crystallisation and Maillard reaction are two major modifications occurring in milk and whey powders during processing and storage. In this work, the aim was first to monitor the solid-state early Maillard reaction (EMR) in whey protein concentrates (WPC) heated at 60 °C and various water activities, and then, to characterise the physical changes that occur as a consequence of heat treatment in skim milk powder (SMP) and WPCs. After a w adjustment, SMP and WPC were heated at 60 °C in hermetic conditions to induce an amino-sugar reaction. Furosine analysis (% of blocked lysine) was used to monitor the progress of EMR. The results showed that the kinetic of EMR was linked to the initial a w of the powders. Heating of SMP may lead to the crystallisation of lactose in humidified powders, without apparently affecting the progress of EMR. Surprisingly, lactose crystallisation-monitored by micro-Differential Scanning Calorimetry-was easily induced in heated SMP, whereas it was delayed or even inhibited in WPC. The results showed that this effect was dependent on the protein/lactose ratio in WPCs. lactose crystallisation / early Maillard reaction / whey protein concentrate / water activity
International Dairy Journal, 2013
Protein cross-linking, a possible cause of loss of solubility of milk protein concentrate (MPC) powder, may occur via advanced Maillard reaction products (e.g., methylglyoxal) or dehydroalanine. This study was designed to determine the relevance of these cross-linking pathways with the aid of proteomic techniques. Cross-linked proteins in the insoluble fraction of reconstituted MPC80 contained all major caseins, with a S1-casein predominating, and a small amount of b-lactoglobulin. To investigate the mechanism of protein cross-linking, model heating experiments were carried out on a S1-casein. Dephosphorylation of a S1-casein did not prevent protein cross-linking, suggesting that dehydroalanine was not involved in the cross linking. However, densitometric analysis showed that the amount of cross-linked a S1-casein was considerably enhanced by adding lactose or methylglyoxal. Protein cross-linking in MPC induced by methylglyoxal was also shown on 2-dimensional electrophoresis gels, confirming a possible pathway of protein cross-linking in milk powders involving advanced Maillard reaction products (e.g., methylglyoxal).
The oxidative status of high-heat, medium-heat and low-heat whole milk powder was investigated at moderately accelerated storage conditions, with exposure to atmospheric air at 25 or 45°C and at three water activities (0.11, 0.23 and 0.33 at 25°C and 0. II, 0.17 and 0.31 at 45°C) for 2 months using: (i) electron spin resonance spectrometry for measurement of the level of free radicals, (ii) determination of thiobarbituric acid reactive substances (TBARS) as a measurement of secondary lipid oxidation products, (iii) size-exclusion HPLC for measurement of fluorescent protein polymerization products, and (iv) sensory evaluation. Lipid oxidation was affected greatly by storage temperature, with a maximum level of free radicals being detected after 47 days at 45°C and with the highest level in low-heat powder, irrespective of water activity. The sensory quality dropped to an unacceptable level for low-heat powder within 33 days of storage, as confirmed by measurement of TBARS, and the increasing TBARS value was parallelled by a decrease of 'free' thiol groups to an unmeasurable level in low-heat powder, in contrast to medium-and high-heat powders, in which the initial level of free thiol groups was only reduced by one-third after 63 days of storage. In contrast to common beliefs, initial powder quality was retained best at water activities between 0.11 and 0.23, where powders showed no significant differences in sensory quality, irrespective of preheat treatment. No difference in sensory score was found for storage at different water activities at 25°C whereas storage at water activity 0.31 at 45°C markedly affected all powders. This effect was ascribed to a combination of increased autoxidation rate and increased Maillard reaction rate giving rise to protein polymerization, in effect decreasing the powder solubility, as often seen during storage under tropical conditions. 13: 1997 Elsevier Science Ltd. All rights reserved
Effect of powder source and processing conditions on the solubility of milk protein concentrates 80
2012
Two milk protein concentrates powders with 80% protein content (MPC80) were reconstituted with either water or permeate at 4C or 37C to contain 3.5% protein content. Samples were homogenized at 0 or 13800 kPa. The objective of this research was to determine how different solubility measures such as solubility index, soluble solids and particle size were affected by powder source, reconstitution solvent type, temperature of reconstitution and homogenization. A separate analysis of variance was run with each solubility measure as a response. The relationship between treatment effects on the results for solubility index and mean particle size were the most similar. A combination of solvent type, temperature, and homogenization affected both the solubility index and mean particle size significantly. Powder source also affected solubility and particle size and the effect of powder source was not modified by any other factors. These studies indicate that the reconstitution temperature and...
Solubility of commercial milk protein concentrates and milk protein isolates
Journal of Dairy Science, 2011
High-protein milk protein concentrate (MPC) and milk protein isolate (MPI) powders may have lower solubility than low-protein MPC powders, but information is limited on MPC solubility. Our objectives in this study were to (1) characterize the solubility of commercially available powder types with differing protein contents such as MPC40, MPC80, and MPI obtained from various manufacturers (sources), and (2) determine if such differences could be associated with differences in mineral, protein composition, and conformational changes of the powders. To examine possible predictors of solubility as measured by percent suspension stability (%SS), mineral analysis, Fourier transform infrared (FTIR) spectroscopy, and quantitative protein analysis by HPLC was performed. After accounting for overall differences between powder types, %SS was found to be strongly associated with the calcium, magnesium, phosphorus, and sodium content of the powders. The FTIR score plots were in agreement with %SS results. A principal component analysis of FTIR spectra clustered the highly soluble MPC40 separately from the rest of samples. Furthermore, 2 highly soluble MPI samples were clustered separately from the rest of the MPC80 and MPI samples. We found that the 900 to 1,200 cm −1 region exhibited the highest discriminating power, with dominant bands at 1,173 and 968 cm −1 , associated with phosphate vibrations. The 2 highly soluble MPI powders were observed to have lower κ-casein and α-S1-casein contents and slightly higher whey protein contents than the other powders. The differences in the solubility of MPC and MPI were associated with a difference in mineral composition, which may be attributed to differences in processing conditions. Additional studies on the role of minerals composition on MPC80 solubility are warranted. Such a study would provide a greater understanding of factors associated with differences in solubility and can provide insight on methods to improve solubility of high-protein milk protein concentrates.
Journal of Dairy Science, 2014
A limiting factor in using milk protein concentrates (MPC) as a high-quality protein source for different food applications is their poor reconstitutability. Solubilization of colloidal calcium phosphate (CCP) from casein micelles during membrane filtration (e.g., through acidification) may affect the structural organization of these protein particles and consequently the rehydration and functional properties of the resulting MPC powder. The main objective of this study was to investigate the effects of acidification of milk by glucono-δ-lactone (GDL) before ultrafiltration (UF) on the composition, physical properties, solubility, and thermal stability (after reconstitution) of MPC powders. The MPC samples were manufactured in duplicate, either by UF (65% protein, MPC65) or by UF followed by diafiltration (80% protein, MPC80), using pasteurized skim milk, at either the native milk pH (~pH 6.6) or at pH 6.0 after addition of GDL, followed by spray drying. Samples of different treatments were reconstituted at 5% (wt/wt) protein to compare their solubility and thermal stability. Powders were tested in duplicate for basic composition, calcium content, reconstitutability, particle size, particle density, and microstructure. Acidification of milk did not have any significant effect on the proximate composition, particle size, particle density, or surface morphology of the MPC powders; however, the total calcium content of MPC80 decreased significantly with acidification (from 1.84 ± 0.03 to 1.59 ± 0.03 g/100 g of powder). Calcium-depleted MPC80 powders were also more soluble than the control powders. Diafiltered dispersions were significantly less heat stable (at 120°C) than UF samples when dissolved at 5% solids. The present work contributes to a better understanding of the differences in MPC commonly observed during processing.
Physico-chemical changes in whole milk powder during different storage conditions
We studied the changes of total dry matter and moisture content, solubility, titrable acidity, acid degree value and scorched particle content in whole milk powder (WMP) during storage of 18 months (shelf-life). Samples were stored at room temperature and at maximum 15°C (maximum limit stipulated in Romanian standard). The samples were analyzed after obtaining and at 3, 6, 9, 12, 15 and 18 months intervals for the mentioned physico-chemical parameters. Values indicated an increase in titrable acidity and moisture content with a decrease in total dry matter and acid degree value with the storage time in whole milk powder. No significant changes were observed with solubility index under these conditions. Scorched particle content do not exceeded disc A in whole milk powder samples in neither of two different storage conditions during shelf-life.