Partial Calcium Depletion During Membrane Filtration Affects Gelation of Reconstituted Milk Protein Concentrates

Milk protein concentrate powders (MPC) with improved rehydration properties are often manufactured using processing steps, such as acidification and high-pressure 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

Acoustic attenuation spectroscopy and helium ion microscopy study of rehydration of dairy powder

Complete hydration is essential for the production of structured dairy products from powders. It is essential that the ingredients used hydrate completely. Determination of an end point of rehydration is non-trivial, but ultrasound-based methodologies have demonstrated potential in this area and are well suited to measuring bulk samples in situ. Here, acoustic attenuation spectroscopy (AAS) is used to monitor rehydration of skim milk powder, and recombined systems of micellar casein isolate with lactose and whey protein isolate. Dynamic light scattering, zeta-potential measurements and AAS as a function of pH characterise each component around its isoelectric point to assess its functionality. Scanning helium ion microscopy was used to image the dry powders, without any conductive coating, producing resolution equivalent to scanning electron microscopy, but with much larger focal lengths and fewer imaging artefacts. Imaging the powders provides information on particle size and morphology which can affect dissolution behaviour. Reconstituted skim milk powder and recombined samples were monitored showing there are changes occurring over several hours. Attenuation coefficients are shown to predict the end point of hydration. Model fitting is used to extract volume fractions and average particle sizes of large and small particle populations in recombined samples over time. AAS is demonstrated to be capable of tracking the dynamics in rehydrating dispersions over time. Physical parameters such as the volume fraction and particle size of the dispersed phase can be determined

EVALUATION OF VACUUM PACKAGING ON THE PHYSICAL PROPERTIES, SOLUBILITY, AND STORAGE SPACE OF DAIRY POWDERS

As many of the dairy powders manufactured have to travel long distances to reach their customers, both domestically and internationally, there is considerable interest among dairy powder manufacturers to maintain the quality of their products for relatively long storage periods. Dairy powders can have a long shelf life if packaged and stored properly. Vacuum packaging can be an attractive packaging strategy to maintain the quality of dairy powders and provide added value by improving the efficiency of using the storage space; because of the inherent compactness of these products. Vacuum packaged dry dairy ingredients may also have added ease of handling for end users. However, little is known about the impact of vacuum packaging on the physical properties of dry dairy ingredients. The main objective of this study was to determine the effect of vacuum packaging over 12 months storage on particle size, particle density, bulk density, tapped density, flowability, compressibility, color, moisture content, surface morphology, and solubility of six types of dairy powders. In addition, the effect of dairy ingredients type was also assessed. Commercial samples of nonfat dry milk powder, whole milk powder, buttermilk powder, milk protein Isolate, whey protein concentrate#80, and sweet whey powder were repackaged in duplicate using multi-wall foil side gusseted bags under varying degrees of vacuum (1, 0.7, 0.4 bar) and a control with no vacuum, then stored for 3, 6, and 12 months at 25°C and 60% relative humidity. Each powder was sampled and analyzed in duplicate for all the above listed quality attributes, upon receiving the powder and after 3, 6, and 12 months of storage. Moreover, the effect of vacuum packaging on storage space was evaluated comparing three different models; Model (1) represented a 25 kg bag of atmospheric packaged non fat dry milk with the actual dimensions of a commercial 25 kg bag of non fat dry milk. Model (2), a hypothetical model, represented a 25 kg bag of vacuum packaged non fat dry milk with a length and a width equal to those of model (1). Model (3), another hypothetical model, also represented a 25 kg bag of vacuum packaged non fat dry milk with a length equal to half of a pallet width and a width equal to one third of a pallet length, in order to achieve the highest pallet efficiency possible. The pallet used for all three models was considered to be a (48 × 40) pallet. The height of models 2 and 3 was allowed to reflect the bulk reduction effect of vacuum packaging and was determined based on the weight, density and the known dimensions of the bags. It is important to note that the density of models 2 and 3 was assumed to be equal to the density of a small bag of nonfat dry milk. The saved space per bag and pallet efficiency of vacuum packaging and atmospheric packaging were compared using the three models described above. Physical properties analyses of the dairy powders revealed statistically significant effect of vacuum pressure on only color values: L-, a-, and b but none of the other powder quality attributes examined. Powders packaged under vacuum showed a significantly higher mean of L- color value (p-value = 0.003 \u3c 0.01), but significantly lower means of (a- and b-) color values (p-values = 0.005, and 0.001, respectively). This effect was more dramatic in high fat containing powder such as whole milk powder. In fact, vacuum packaged whole milk powders were significantly whiter, less red, and less yellow. It is likely that vacuum packaging has prevented color changes due to lipid oxidation in whole milk powder. Physical properties analyses of the dairy powders also revealed statistically significant increases in the particle density, particle size, bulk density, and tapped density due to the effect of storage time (all p-values = 0.000 \u3c 0.01), statistically significant decreases in the angle of repose and compressibility due to the effect of storage time (p = 0.000 \u3c 0.01) and (p = 0.004 \u3c 0.01), respectively. The physical properties analyses also revealed a statistically significant effect of the powder type on particle density, particle size, bulk density, and tapped density, angle of repose, compressibility, and color values: L-, a-, and b- (all p-values = 0.000 \u3c 0.01). In other words, particle density, particle size, bulk density, and tapped density of the powders increased over the storage time, while angle of repose (AOR) and compressibility decreased over the storage time. The powder type had a significant effect on particle density, particle size, bulk density, tapped density, AOR, compressibility, and color values: L-, a-, and b; however, it did not have any significant effect on solubility and moisture content. In addition, observations of the surface morphology of dairy powders were made using a scanning electron microscope. This evaluation demonstrated the differences in powder particle shape and surface morphology which are believed to be partially responsible for the significant differences observed in the physical properties, due to the effect of powder type. It was shown that vacuum packaging does increase the efficiency of using the storage space by removing the interstitial air and increasing the density of the powder. As described above, the height of model (2) and the length of model (3) both were expectedly shorter compared to those of model (1). Storage space calculations for non fat dry milk were performed based on comparing the volume of the 3 models and showed 15 % saving in storage space per bag and per pallet, due to vacuum packaging. The effect of space saving on the number of bags per pallet was evaluated using CAPE PACK v2.09 software and showed an increase from 45 bags/ pallet in model (1) to 50 bags/ pallet in model (2) and 54 bags/ pallet in model (3). Overall, this study demonstrates the impact of vacuum packaging on physical properties, solubility, and storage properties of dairy powders. The data suggest that the proposed vacuum packaging method may be beneficial to maintain the quality of the powders studied and it results in space savings per unit of dairy powder compared to conventional atmospheric packaging

The Impact of Antioxidant Addition on Flavor of Cheddar and Mozzarella Whey and Cheddar Whey Protein Concentrate

Lipid oxidation products are primary contributors to whey ingredient off-flavors. The objectives of this study were to evaluate the impact of antioxidant addition in prevention of flavor deterioration of fluid whey and spray-dried whey protein. Cheddar and Mozzarella cheeses were manufactured in triplicate. Fresh whey was collected, pasteurized, and defatted by centrifugal separation. Subsequently, 0.05% (w/w) ascorbic acid or 0.5% (w/w) whey protein hydrolysate (WPH) were added to the pasteurized whey. A control with no antioxidant addition was also evaluated. Wheys were stored at 3 °C and evaluated after 0, 2, 4, 6, and 8 d. In a subsequent experiment, selected treatments were then incorporated into liquid Cheddar whey and processed into whey protein concentrate (WPC). Whey and WPC flavors were documented by descriptive sensory analysis, and volatile components were evaluated by solid phase micro-extraction with gas chromatography mass spectrometry. Cardboard flavors increased in fluid wheys with storage. Liquid wheys with ascorbic acid or WPH had lower cardboard flavor across storage compared to control whey. Lipid oxidation products, hexanal, heptanal, octanal, and nonanal increased in liquid whey during storage, but liquid whey with added ascorbic acid or WPH had lower concentrations of these products compared to untreated controls. Mozzarella liquid whey had lower flavor intensities than Cheddar whey initially and after refrigerated storage. WPC with added ascorbic acid or WPH had lower cardboard flavor and lower concentrations of pentanal, heptanal, and nonanal compared to control WPC. These results suggest that addition of an antioxidant to liquid whey prior to further processing may be beneficial to flavor of spray-dried whey protein

Changes in particle size, calcium and phosphate solubilization, and microstructure of rehydrated milk protein concentrates, prepared from partially acidified milk

International audienceAbstractThe present work studied the rehydration properties of milk protein concentrates (MPCs), prepared using ultrafiltration (UF) and diafiltration (DF). Milk was acidified to pH 6 with glucono-δ-lactone (GDL) prior to UF to alter the mineral composition of the final concentrates. The particle size distribution and the microstructure of the casein micelles in reconstituted MPCs as well as the partitioning of calcium, phosphate, and proteins between the colloidal and soluble phases were investigated. Reconstituted samples analyzed by electron microscopy showed that, even in partially dissolved particles, the particle surface was porous and similar to its inner portion and had no distinct skin layer. Partial acidification of milk did not have any significant effects on the microstructure; however, it significantly increased the average diameter of the casein micelles for both UF and DF samples and decreased the concentration of total calcium and phosphate. Sodium dodecyl sulfate (SDS)-PAGE analysis of the centrifugal supernatants of reconstituted MPC demonstrated that the amount of soluble caseins present in milk concentrates dramatically increased with acidification, and it further increased after restoring the mineral composition of the serum phase through dialysis against milk. This work contributes to a better understanding of how processing conditions, particularly partial acidification of milk prior to concentration, can alter the composition and physical properties of the caseins and the soluble phase of MPC after rehydration. Such alterations can significantly impact the technological properties of the reconstituted MPC