Effect of Protein Content on Heat Stability of Reconstituted Milk Protein Concentrate under Controlled Shearing

Milk protein concentrates (MPCs) possess significant potential for diverse applications in the food industry. However, their heat stability may be a limitation to achieving optimal functional performance. Shearing, an inherent process in food manufacturing, can also influence the functionality of proteins. The aim of this research was to examine the heat stability of reconstituted MPCs prepared at two protein concentrations (4% and 8% w/w protein) when subjected to varying levels of shearing (100, 1000, or 1500 s-1) during heating at 90 °C for 5 min or 121 °C for 2.6 min. While the impact of shear was relatively minor at 4% protein, it was more pronounced in 8% protein MPC suspensions, leading to a considerable decline in heat stability. An increase in protein concentration to 8% amplified protein interactions, intensified by shearing. This, in turn, resulted in comparatively higher aggregation at elevated temperatures and subsequently reduced the heat stability of the reconstituted MPCs.

Comparison of milk protein concentrate, micellar casein, and whey protein isolate in loading astaxanthin after the treatment of ultrasound-assisted pH shifting

Milk proteins can be used as encapsulation walls to increase the bioavailability of active compounds because they can bind hydrophobic, hydrophilic, and charged compounds. The objective of this study was to investigate the effects of astaxanthin (ASTA) encapsulation and the functional properties of milk protein and ASTA nanocomposites by an ultrasound-assisted pH-shifting treatment of different milk proteins, including milk protein concentrate (MPC), micellar casein (MCC), and whey protein isolate (WPI). The ultrasound-assisted pH-shifting treatment of milk protein helped to improve the encapsulation rate of ASTA. Therein, MCC showed great improvement of encapsulating ASTA after co-treatment with the raised encapsulated rate of 5.11%, followed by WPI and MPC. Furthermore, the nanocomposites of ASTA with milk protein exhibit improved bioavailability, antioxidant capacity, and storage stability. By comparison, MCC-encapsulated ASTA has the best storage stability, followed by MPC, and WPI-encapsulated ASTA has the least stability over a 28-d storage period. The results of intrinsic fluorescence and surface hydrophobicity showed that milk protein underwent fluorescence quenching after binding to ASTA, which was due to the hydrophobic sites of the protein being occupied by ASTA. In general, the nanocomposites of milk protein and ASTA fabricated by using an ultrasound-assisted pH-shifting treatment have the potential to be better nano-delivery systems for ASTA in functional foods, especially MCC, which showed excellent performance in encapsulation after treatment technique.

Maturation of demineralized arabinogalactan-proteins from Acacia seyal gum in dry state: Aggregation kinetics and structural properties of aggregates

The aggregation in dry state of mineral-loaded arabinogalactan-proteins (AGPs) from Acacia seyal gum (GA) generally occurs above 70 °C. This study focuses on the aggregation sensitivity of AGPs after their demineralization. The dry incubation in mild temperature (25 °C to 70 °C) of demineralized AGPs induced the formation of aggregates, not observed with GA. AGPs aggregated following a self-assembly mechanism for which temperature only modulated the aggregation rate. The activation energy was around 90-100 kJ·mol^-1 that could correspond to chemical condensation reactions induced by the AGPs surface dehydration. The aggregation kinetics were characterized by the formation of soluble aggregates during the first times of incubation, whose molar mass increased from 1 · 10⁶ g·mol^-1 to 6.7 · 10⁶ g·mol^-1 (SEC MALS) or 12 · 10⁶ g·mol^-1 (AF4 MALS) after 1.66 days of dry heating at 40 °C. These soluble aggregates revealed they adopted a similar conformation to that of not aggregated AGPs with a ν_h value around 0.45. Above 1.66 days at 40 °C, the soluble aggregates grew up to form microparticles with sizes ranging from 10 to around 200 μm. This study highlighted the protective role of cations from AGPs whose demineralization increased their sensibility to dry heating and their chemical reactivity for aggregation.

Influence of Bulk Nanobubbles Generated by Acoustic Cavitation on Powder Microstructure and Rehydration Characteristics of Spray-Dried Milk Protein Concentrate Powders

Bulk nanobubbles (BNBs) have widespread applications in various fields of science due to numerous peculiar characteristics. Despite significant applications, only limited investigations are available on the application of BNBs in food processing. In the present study, a continuous acoustic cavitation technique was used to generate bulk nanobubbles (BNBs). The aim of this study was to evaluate the influence of BNB incorporation on the processability and spray drying of milk protein concentrate (MPC) dispersions. MPC powders were reconstituted to the desired total solids and incorporated with BNBs using acoustic cavitation as per the experimental design. The control MPC (C-MPC) and BNB-incorporated MPC (BNB-MPC) dispersions were analyzed for rheological, functional, and microstructural properties. The viscosity significantly decreased (p < 0.05) at all the amplitudes studied. The microscopic observations of BNB-MPC dispersions showed less aggregated microstructures and greater structural differences compared with C-MPC dispersions, therefore lowering the viscosity. The viscosity of BNB incorporated (90% amplitude) MPC dispersions at 19% total solids at a shear rate of 100 s^-1 significantly decreased to 15.43 mPa·s (C-MPC: 201 mPa·s), a net decrease in viscosity by ~90% with the BNB treatment. The control and BNB incorporated MPC dispersions were spray-dried, and the resultant powders were characterized in terms of powder microstructure and rehydration characteristics. Focused beam reflectance measurement of the BNB-MPC powders indicated higher counts of fine particles (<10 μm) during dissolution, signifying that BNB-MPC powders exhibited better rehydration properties than the C-MPC powders. The enhanced powder rehydration with the BNB incorporation was attributed to the powder microstructure. Overall, reducing the viscosity of feed by BNB incorporation can enhance the performance of the evaporator. This study, therefore, recommends the possibility of using BNB treatment for more efficient drying while improving the functional properties of the resultant MPC powders.

Effect of Storage of Skim Milk Powder, Nonfat Dry Milk and Milk Protein Concentrate on Functional Properties

The physicochemical changes during the storage of high protein powders, such as skim milk powder (SMP), nonfat dry milk (NDM), and milk protein concentrates (MPC), can result in a variation in the functional properties of the powders. The objective of this study was to evaluate the effects of the storage of various milk powders (SMP, NDM, MPC40, and MPC70) on their functional properties. Three different lots of the powders were collected from US manufacturers and were analyzed for functional properties after 3, 9, and 15 months of storage at 25 °C. Additionally, this study also evaluated the effects of seasonal variation on the functionality of SMP and NDM. Functional properties, such as solubility, emulsification ability index (EAI), foaming, and surface hydrophobicity index (SHI), were evaluated at each storage time point. The solubility of MPC70 and the foam overrun of SMP, MPC40, and MPC70 decreased significantly (p < 0.05) with an increase in the storage time. The emulsification properties of MPC70 were significantly higher than other powders. Except for foam drainage, there was no effect of the season on the SMP and NDM functional properties. The storage of milk powders has an impact on some functional properties, and a proper selection of powders based on end-use is recommended.

Improving rehydration properties of spray-dried milk protein isolates by supplementing soluble caseins

Spray-dried milk protein isolates (MPIs) are important dairy ingredients but may not have desirable rehydration properties for industrial applications. In the present study, rehydration properties of MPIs were improved by spray-drying MPI dispersions containing different amounts of soluble caseins in the form of derivatized MPI (dMPI). dMPI was prepared by alkalizing MPI dispersions to pH 11.0 and subsequently acidifying to pH 6.8 (the pH-cycle). All the spray-dried MPIs had the similar bulk density (around 0.33 g/cm^-3), composition, size distribution (1-100 µm), and SEM morphology. However, the decrease of hydrodynamic diameter, dissolution of total solids and proteins, and disruption of particles during the dynamic rehydration were accelerated as the dMPI content increased, indicating the improved rehydration properties. The improvement in rehydration properties was not due to the wettability that decreased as the dMPI:MPI mass ratio changed from 0:8 to 8:0, but resulted from the reduced cross-linking of casein micelles on powder surface and the increased surface porosity during the hydration as observed for partially hydrated samples. The present work may assist industrial applications of spray-dried MPIs.

Design of a new lyoprotectant increasing freeze-dried Lactobacillus strain survival to long-term storage

Background

Stabilization of freeze-dried lactic acid bacteria during long-term storage is challenging for the food industry. Water activity of the lyophilizates is clearly related to the water availability and maintaining a low a_w during storage allows to increase bacteria viability. The aim of this study was to achieve a low water activity after freeze-drying and subsequently during long-term storage through the design of a lyoprotectant. Indeed, for the same water content as sucrose (commonly used lyoprotectant), water activity is lower for some components such as whey, micellar casein or inulin. We hypothesized that the addition of these components in a lyoprotectant, with a higher bound water content than sucrose would improve lactobacilli strains survival to long-term storage. Therefore, in this study, 5% whey (w/v), 5% micellar casein (w/v) or 5% inulin (w/v) were added to a 5% sucrose solution (w/v) and compared with a lyoprotectant only composed of 5% sucrose (w/v). Protective effect of the four lyoprotectants was assessed measuring Lactiplantibacillus plantarum CNCM I-4459 survival and water activity after freeze-drying and during 9 months storage at 25 °C.

Results

The addition whey and inulin were not effective in increasing Lactiplantibacillus plantarum CNCM I-4459 survival to long-term-storage (4 log reduction at 9 months storage). However, the addition of micellar casein to sucrose increased drastically the protective effect of the lyoprotectant (3.6 log i.e. 0.4 log reduction at 9 months storage). Comparing to a lyoprotectant containing whey or inulin, a lyoprotectant containing micellar casein resulted in a lower water activity after freeze-drying and its maintenance during storage (0.13 ± 0.05).

Conclusions

The addition of micellar casein to a sucrose solution, contrary to the addition of whey and inulin, resulted in a higher bacterial viability to long-term storage. Indeed, for the same water content as the others lyoprotectants, a significant lower water activity was obtained with micellar casein during storage. Probably due to high bound water content of micellar casein, less water could be available for chemical degradation reactions, responsible for bacterial damages during long-term storage. Therefore, the addition of this component to a sucrose solution could be an effective strategy for dried bacteria stabilization during long-term storage.

Rehydration characteristics of milk protein concentrate powders monitored by electrical resistance tomography

Electrical resistance tomography (ERT) is a robust and low-cost method offering real-time visualization of processes. In this work, we developed an ERT-based method to characterize the rehydration behavior of milk protein concentrate (MPC) powders. Circular-type and linear configurations were used to achieve high resolution in the radial and axial directions, respectively. To evaluate the rehydration profile, MPC powders were reconstituted to 2.5% (wt/wt) total solids at room temperature, and the rehydration behavior of the MPC powders [MPC with 85% protein (MPC85) and milk protein isolate with 90% protein (MPI90)] was monitored for a dissolution time of 30 min using the ERT system. The MPC powders were characterized in terms of overall mean conductivity, area under the mean conductivity curve, slope at a dissolution time of 3 min, and the relative dissolution index. Additionally, the focus beam reflectance measurement (FBRM) was used as a reference method to follow rehydration characteristics. Particle count changes from the FBRM measurements showed that MPI90 had higher larger particle counts and more resistance to dispersing in water. As the dissolution time proceeded, mineral ions and proteins were released and consequently increased the overall conductivity, confirming the transfer of water into MPC particles. At lower protein contents, the particle dispersion rate was higher and an increase in overall mean conductivity was observed, indicating better powder dissolution. Both configurations were able to effectively monitor differences in the dissolution behavior of MPC powders. In the ERT circular configuration, MPC85 and MPI90 showed maximum conductivity of 0.201 ± 0.006 and 0.162 ± 0.001 mS/cm, respectively. In the linear probe configuration, MPC85 and MPI90 showed maximum conductivity of 0.161 ± 0.001 and 0.136 ± 0.001 mS/cm, respectively, suggesting increasingly inhibited water transfer as the protein content of the powder increased. In this study, we demonstrated the capability of ERT using the circular and linear probe configurations to offer, in addition to qualitative tomographic images, reliable quantitative data by which to characterize the dissolution behavior of high-protein dairy powders.

Influence of Glycomacropeptide on Rehydration Characteristics of Micellar Casein Concentrate Powder

Glycomacropeptide (GMP) shows potential for enhancing the rehydration properties of high-protein dairy powders due to its hydrophilic nature. This study involved formulating micellar casein concentrate (MCC) solutions (8.6% final protein content) with 0, 10, and 20% GMP as a percentage of total protein, and investigated the physicochemical and rehydration properties of the resultant freeze-dried powders (P-MCC-0G, P-MCC-10G, and P-MCC-20G, respectively). The surface charges of caseins in the control MCC and 10 or 20% GMP blended solutions were −25.8, −29.6, and −31.5 mV, respectively. Tablets prepared from P-MCC-10G or P-MCC-20G powders displayed enhanced wettability with contact angle values of 80.6° and 79.5°, respectively, compared with 85.5° for P-MCC-0G. Moreover, blending of GMP with MCC resulted in faster disintegration of powder particles during rehydration (i.e., dispersibility) compared to P-MCC-0G. Faster and more extensive release of caseins from powder particles into solution was evident with the increasing proportion of GMP, with the majority of GMP released within the first 15 min of rehydration. The results of this study will contribute to further development of formulation science for achieving enhanced solubility characteristics of high-protein dairy powder ingredients, such as MCC.

Effects of Pasteurization and High-Pressure Processing of Camel and Bovine Cheese Quality, and Proteolysis Contribution to Camel Cheese Softness

The effects of high-pressure processing (HPP) compared to thermal treatments on the quality of camel vs. bovine cheeses were studied. The study showed that camel milk has a lower microbial load compared to bovine milk, which is maintained during 7 days' storage of the processed milk. The effect of three HPP treatments (350, 450, and 550 MPa for 5 min at 4°C) and two pasteurization treatments (65°C for 30 min and 75°C for 30 s) on the quality of soft unripened camel and bovine milk cheeses were accessed. The cheeses were evaluated for pH, yield, proximate composition, textural and rheological properties, microstructure, and protein profile by SDS-PAGE electrophoresis. The effects of the treatments on cheese's hardness were different between the camel and bovine cheeses; while heat treatment at 65°C for 30 min gave the hardest bovine milk cheese (1,253 ± 20), HPP treatment at 350 MPa for 5 min gave the highest value for camel milk cheese (519 ± 5) (p < 0.05). The hardness of the cheeses was associated with low yield and moisture content. SDS-PAGE electrophoresis revealed that extensive proteolysis might have contributed to the softness of camel cheeses compared to bovine and suggested the involvement of some residual enzyme activities.

Insolubility in milk protein concentrates: potential causes and strategies to minimize its occurrence

Milk protein concentrates (MPCs), which are produced from skim milk following a series of manufacturing steps including pasteurization, membrane filtration, evaporation and spray drying, represent a relatively new category of dairy ingredients. MPC powders mainly comprise caseins and whey proteins in the same ratio of occurrence as in milk. While bovine MPCs have applications as an ingredient in several protein enriched food products, technofunctional concerns, e.g., reduced solubility and emulsification properties, especially after long-term storage, limit their widespread and consistent utilization in many food products. Changes in the surface and internal structure of MPC powder particles during manufacture and storage occur via casein-casein and casein-whey protein interactions and also via the formation of casein crosslinks in the presence of calcium ions which are associated with diminishment of MPCs functional properties. The aggregation of micellar caseins as a result of these interactions has been considered as the main cause of insolubility in MPCs. In addition, the occurrence of lactose-protein interactions as a result of the promotion of the Maillard reaction mainly during storage of MPC may lead to greater insolubility. This review focuses on the solubility of MPC with an emphasis on understanding the factors involved in its insolubility along with approaches which may be employed to overcome MPC insolubility. Several strategies have been developed based on manipulation of the manufacturing process, along with composition, physical, chemical and enzymatic modifications to overcome MPC insolubility. Despite many advances, dairy ingredient manufacturers are still investigating technical solutions to resolve the insolubility issues associated with the large-scale manufacture of MPC.

Updating insights into the rehydration of dairy-based powder and the achievement of functionality

Dairy-based powder had considerable development in the recent decade. Meanwhile, the increased variety of dairy-based powder led to the complex difficulties of rehydrating dairy-based powder, which could be the poor wetting or dissolution of powder. To solve these various difficulties, previous studies investigated the rehydration of powder by mechanical and chemical methods on facilitating rehydration, while strategies were designed to improve the rate-limiting rehydration steps of different powder. In this review, special emphasis is paid to the surface and structure of the dairy-based powder, which was accountable for understanding rehydration and the rate-limiting step. Besides, the advantage and disadvantage of methods employed in rehydration were described and compared. The achievement of the powder functionality was finally discussed and correlated with the rehydration methods. It was found that the surface and structure of dairy-based powder were decided by the components and production of powder. Post-drying methods like agglomeration and coating can tailor the surface and structure of powder afterwards to obtain better rehydration. The merit of the mechanical method is that it can be applied to rehydrate dairy-based powder without any addition of chemicals. Regarding chemical methods, calcium chelation is proved to be an effective chemical in rehydration casein-based powder.

Correlations between the solubility and surface characteristics of milk protein concentrate powder particles

The solubility of high-protein milk protein concentrate (MPC) may decrease significantly during storage, particularly at relatively high temperatures and humidity. The objective of this study was to seek correlations between the solubility loss of MPC during storage and various surface characteristics determined on the basis of simultaneous nanoscale topographical imaging and nanomechanical mapping of MPC particle surfaces using atomic force microscopy. A control MPC and a calcium-depleted MPC were stored at 45°C and 66% relative humidity for up to 60 d. The solubility of the control MPC was 56% at the beginning of the storage and gradually decreased to 10% at the end of the 60-d storage. The calcium-depleted MPC exhibited more rapid decreases from almost 100% at the beginning of the storage to 18% after storage for 45 d, after which we observed no significant difference in solubility between the control and calcium-depleted MPC. Averaged or root mean squared roughness values calculated using topographical images were found to have no correlation with the solubility. Deformation, Derjaguin-Muller-Toropov modulus, and adhesion images revealed the presence of individual casein micelles and larger clusters of aggregated casein micelles at MPC particle surfaces, whereas we observed no correlation between the solubility and averaged values of these nanomechanical properties. Furthermore, Derjaguin-Muller-Toropov modulus and adhesion images showed that the peripheral edges of individual casein micelles and their clusters had significantly higher values of the corresponding nanomechanical properties than other regions in the images, indicating the occurrence of the fusion of casein micelles. The surface area coverage or the percent area of the fused regions in an image revealed significant negative linear correlations with the solubility for both the control and calcium-depleted MPC. The present results support the hypothesis that the fusion of casein micelles at MPC powder particle surfaces is a causative factor for the solubility loss of MPC during storage and in turn suggest that the solubility loss may be alleviated by inhibiting the formation of a crust or skin on powder particle surfaces.

The Influence of Composition and Manufacturing Approach on the Physical and Rehydration Properties of Milk Protein Concentrate Powders

This study investigated the physical and rehydration properties of milk protein concentrate (MPC) powders with five different protein contents (i.e., 38.9, 53.7, 63.6, 74.1, and 84.7%, w/w) prepared by recombining the ultrafiltration (UF) retentate and UF permeate of skim milk. Powder density and flowability increased, while the powder particle size decreased with decreasing powder protein content. The amount of non-wetting MPC powder decreased with decreasing protein content, demonstrating greater wettability for lower protein powders. At protein contents >65% (w/w), the dispersibility and solubility of the powders decreased significantly, likely due to the greater hydrophobic interactions between casein proteins and a lower concentration of lactose. Therefore, as the protein content of the MPC powders was decreased, their rehydration properties improved. The results obtained in this study provide novel insights into the relationship between the composition of recombined UF retentate and UF permeate streams on the subsequent powder particle size, density, and rehydration properties, and demonstrate that such powders possess similar properties to those prepared using conventional direct membrane filtration.

Application of front-face fluorescence spectroscopy as a tool for monitoring changes in milk protein concentrate powders during storage

This study investigated the feasibility of front-face fluorescence spectroscopy (FFFS) to predict the solubility index and relative dissolution index (RDI) of milk protein concentrate (MPC) powders during storage. Twenty MPC powders with varying protein contents from 4 different commercial manufacturers were used in this study. The MPC powders were stored at 2 temperatures (25 and 40°C) for 0, 1, 2, 4, 8, and 12 wk. The front-face fluorescence spectra of tryptophan and Maillard products were recorded and analyzed with chemometrics to predict solubility of MPC powders. The similarity maps showed clear discrimination of the MPC samples stored at 25 and 40°C. Partial least squares regression models were developed using the fluorescence spectra of tryptophan and Maillard products to predict the solubility index and RDI measurements of MPC powders, and the prediction models were validated using an independent test set. Coefficients of determination (R²) of 0.76, 0.84, and 0.68 were obtained between fluorescence spectra (tryptophan emission, Maillard emission, and Maillard excitation, respectively) and solubility index. The R² values for the RDI predictions were 0.58 and 0.60 for the data set of tryptophan emission and Maillard emission, respectively. The ratio of prediction error to standard deviation was >2 for Maillard emission fluorescence spectra and solubility index measurements, indicating good practical utility of the partial least squares regression prediction models. The results indicated that the solubility and dissolution behavior of MPC powders were related to their protein content and storage conditions that could be measured using FFFS. Hence, FFFS can be used as a rapid nondestructive analytical technique to predict the solubility and dissolution characteristics of MPC powders.