Water sorption and hydration in spray-dried milk protein powders: Selected physicochemical properties

Can operational parameters impact spray-dried bacteria viability and production costs? An experimental study with autochthonous Lactococcus lactis subsp. lactis isolated from Amazonian artisanal cheese

Lactococcus lactis subsp. lactis Q1C2, previously isolated from artisanal cheese produced in the Brazilian Amazon region, was subjected to spray drying protocols to evaluate the impact of operational parameters on cell viability, storage stability, and production costs. Concentrated reconstituted milk was used as the drying medium, and combinations of cell concentrate flow rates (Fcell,inj) and inlet air temperatures (T°Cair,in) were tested, resulting in 12 different treatments (T1-T12). After drying (day-0), higher survival rates were obtained with lower T°Cair,in (115 °C and 130 °C), while greater viability loss was associated with higher T°Cair,in and outlet air temperatures (T°Cair,out). Moisture content and water activity (aw) were inversely correlated with cell viability, with lower values resulting in greater losses. Cell viability was evaluated during the storage at 4 °C and 25 °C on days 15, 30, and 120. Viability was more stable at 4 °C, although significant reductions were observed for some treatments (P < 0.0001). At 25 °C, all treatments exhibited significant viability losses after 120 days (P < 0.0001). Among the treatments, T6 (Fcell,inj = 0.66 kg h-1 and T°Cair,in = 130 °C) showed the best balance between high cell viability and storage temperature, 10.00 ± 0.12 log cfu g-1 and 9.93 ± 0.13 log cfu g-1 after 120 days at 4 °C and 25 °C, respectively. In terms of production costs, T6 demonstrated advantages by minimizing energy consumption and mass loss during drying. Higher Fcell,inj reduced energy costs (P < 0.0001), while elevated T°Cair,in significantly increased energy costs (P < 0.0001). T6 optimized energy efficiency and achieved a favorable balance between viability and operational costs, highlighting its potential for industrial application. These findings demonstrate the viability of spray drying for producing dairy starter cultures, offering a cost-effective solution to preserve active starter cultures without the need for refrigeration.

Spray drying of reconstituted skim milk fermented with Lactobacillus rhamnosus GG: control of glass transition and stickiness

The effects of glass transition and stickiness on the direct spray drying of reconstituted skim milk (RSM) fermented with Lactobacillus rhamnosus GG (LGG) were investigated. The fermented RSM did not spray dry properly due to severe wall depositions; however, it dried well (comparable to the control; RSM with resuspended LGG cells) when skim milk powder (SMP) was added. Adding SMP significantly increased the glass transition and sticky point temperatures of spray-dried powder, ranging from 18.2 to 72.4 °C and 34.5 to 78.5 °C, respectively, in a water activity range of 0-0.33. By adding SMP, droplets quickly shifted from a sticky plastic to a non-sticky glassy state during drying, resulting in reduced wall deposition. Although this spray-dried powder exhibited relatively high moisture sorption and lactose crystallization, the correlations between glass transition, stickiness, and moisture sorption suggested that its storage stability at 25 °C may be on par with the control powder.

Water Effective Diffusion Coefficient in Dairy Powder Calculated by Digital Image Processing and through Machine Learning Algorithms of CLSM Micrographs

Rehydration of dairy powders is a complex and essential process. A relatively new quantitative mechanism for monitoring powders' rehydration process uses the effective diffusion coefficient. This research focused on modifying a previously used labor-intensive method that will be able to automatically measure the real-time water diffusion coefficient in dairy powders based on confocal microscopy techniques. Furthermore, morphological characteristics and local hydration of individual particles were identified using an imaging analysis procedure written in Matlab©-R2023b and image analysis through machine learning algorithms written in Python™-3.11. The first model includes segmentation into binary images and labeling particles during water diffusion. The second model includes the expansion of data set selection, neural network training and particle markup. For both models, the effective diffusion follows Fick's second law for spherical geometry. The effective diffusion coefficient on each particle was computed from the dye intensity during the rehydration process. The results showed that effective diffusion coefficients for water increased linearly with increasing powder particle size and are in agreement with previously used methods. In summary, the models provide two independent machine measurements of effective diffusion coefficient based on the same set of micrographs and may be useful in a wide variety of high-protein powders.

Rapidly evaluating the caking tendency of sugar alcohols by developing a crystal bridge growth model: A case study of xylitol

Caking of crystalline sugar alcohols is a deleterious and undesired agglomeration process during storage in the food industry. Compared with the time-consuming and labor-intensive conventional caking assessment methods, this work develops a rapid methodology for evaluation of the critical caking cycle of xylitol with over 85% time-saving and 90% labor-saving while guaranteeing the precision accuracy. By developing a Caking-Hygroscopicity-Particle size crystal bridge growth model, the correlation and quantitative relationships among hygroscopic properties, particle size and the critical caking cycle are firstly established and confirmed, which can greatly simplify the most time-consuming and laborious experiments of water sorption measurements and caking tests. Besides, the knowledge obtained can help guide the rapid selection of storage humidity conditions and appropriate particle size distributions for maintaining the desired properties and competitive marketability of crystalline sugar alcohols.

Lactose crystallization and Maillard reaction in simulated milk powder based on the change in water activity

Maillard reaction (MR) and lactose crystallization (LC) are important reactions in the storage of milk powder. In this study, three models with different proteins based on skimmed milk powder were established to investigate the relationship between MR and LC at different water activities (a_w ). Moisture sorption isotherm, glass transition temperature (T_g ), and glycation products were evaluated, and the protein structure and lactose crystallinity were determined. The results indicated that MR product content, browning, and LC subsequently enhanced with the increase in a_w . The T_g value dropped lower than 0 at a_w 0.43 in whey protein isolate-lactose (WP-Lac) model and at a_w 0.54 in casein-whey protein isolate-lactose (CN-WP-Lac) model and casein-lactose (CN-Lac) model. The crystallinity of α-lactose monohydrate and anhydrous β-lactose in WP-Lac model was more significant than CN-WP-Lac and CN-Lac models (p < 0.05). The molecular band of whey protein gradually blurred in the Sodium dodecyl-sulfate polyacrylamide gel electrophoresis image, and the content of α-helix of WP-Lac model increased by 45.15% from a_w 0.33 to 0.53 (p < 0.05), while that of CN-WP-Lac model increased by only 3.95% (p < 0.05). With the increase in a_w , WP-Lac model formed more browning and crystallization products than CN-WP-Lac model, indicating that the presence of micelle macromolecules and the interaction between casein and whey proteins limited the browning and crystallization in CN-WP-Lac model. Practical Application Maillard reaction and lactose crystallization are important reactions in the storage of milk powder, and the result will provide theoretical guidance for the development of milk powder in the food industry.

Investigation of breakage behavior and its effects on spray-dried agglomerated whey protein-lactose powders: Effect of protein and lactose contents

Particle breakage of dairy powders occurs easily during many processes, reducing the powder functionality. The characteristics of particles and the applied stress from processing conditions on the particles are 2 main factors that can be manipulated to reduce breakage. In this study, we explored the effect of whey protein and lactose contents on dynamic breakage in agglomerated whey protein-lactose powders to provide useful information, in terms of particle characteristics, for controlling unwanted dairy powder breakage. A series of model agglomerates with different whey protein:lactose ratios were produced under the same spray-drying conditions, through a pilot plant trial. We evaluated physical characteristics, composition, and structure of samples; analyzed dynamic breakage under different mechanical stresses; and investigated the rehydration and water adsorption properties of model powders before and after breakage. The particle size and irregularity of agglomerates with more lactose was significantly higher than of samples that contained more protein. This resulted in higher particle breakage during dynamic breakage for samples with more lactose. The breakage of agglomerates was affected by the moisture content of powders and fatigue, where particle breakage happens when mechanical loads, lower than the strength of particles, occur multiple times. Breakage changed the morphology and surface composition of particles and decreased particle size. It also decreased the dispersibility of powders and increased the wetting time of wettable samples but decreased the wetting time of powders with poor wettability. Breakage accelerated time-dependent crystallization and decreased the crystallization temperature but did not affect the glass transition temperature of samples. Thus, under the same drying conditions, composition of powders significantly affected breakage, mainly by altering the physical properties of their particles, which resulted in deteriorated functionality.

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.

Dynamic Mechanical Analysis as a Complementary Technique for Stickiness Determination in Model Whey Protein Powders

The α-relaxation temperatures (T_α), derived from the storage and loss moduli using dynamic mechanical analysis (DMA), were compared to methods for stickiness and glass transition determination for a selection of model whey protein concentrate (WPC) powders with varying protein contents. Glass transition temperatures (T_g) were determined using differential scanning calorimetry (DSC), and stickiness behavior was characterized using a fluidization technique. For the lower protein powders (WPC 20 and 35), the mechanical T_α determined from the storage modulus of the DMA (T_α onset) were in good agreement with the fluidization results, whereas for higher protein powders (WPC 50 and 65), the fluidization results compared better to the loss modulus results of the DMA (T_α peak). This study demonstrates that DMA has the potential to be a useful technique to complement stickiness characterization of dairy powders by providing an increased understanding of the mechanisms of stickiness.

Study of Polyphenol Content and Antioxidant Properties of Various Mix of Chocolate Milk Masses with Different Protein Content

The aim of the study was to analyze the antioxidant character of conched chocolate milk masses, taking into account different protein content in milk. For the study, cocoa liquor obtained from roasted and unroasted cocoa beans from different regions, as well as milk powder obtained by spray and cylindrical drying were used. The analysis that was carried out showed that the protein content of powdered milk products ranged from about 11.6% (w/w) to over 31% (w/w). Lower content of polyphenols and lower antioxidant activity were shown in the masses to which the addition of milk with higher protein content was applied. The analysis of antioxidant character of chocolate milk masses showed higher total polyphenols content in masses prepared from unroasted cocoa beans liquor.

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.