Homogenization and sodium hydrogen phosphate induced effect on physical and rheological properties of ultrafilterd concentrated milk.

Ultrafiltration (UF) of buffalo skim milk (BSM) induces changes in its delicate protein-mineral equilibrium. Appling UF causes alteration in chemical composition of UF retentates as a function of protein concentration that adversely affect their physical and rheological properties. Hence, present investigation was targeted to evaluate the changes taking place in heat stability, ζ-potential, particle size, apparent viscosity, pH, turbidity and crossover temperature of storage (G') and loss (G″) modulus of high-protein BSM based UF retentates as a function of homogenization and sodium hydrogen phosphate (SHP) addition. The UF of BSM (heat treated at 85 ± 1 °C for 5 min), significantly increased (P < 0.05) the concentration of protein, fat and minerals, however, it decreased the concentration of lactose and water soluble minerals in UF retentates over BSM. The SHP addition significantly increased (P < 0.05) pH, crossover temperature of G' and G″, ζ-potential, while significantly decreased (P < 0.05) turbidity and particle size in most non-homogenized retentates. Heat coagulation time (HCT) of control and treated UF retentates were at par (P > 0.05) with each other, however, variations were observed in their viscosity values. Rheological behaviour of most of these UF retentates was efficiently described by Bingham model. The correlation among ζ-potential, particle size, apparent viscosity, pH, turbidity, HCT and crossover temperatures G' and G″ of evaluated samples was also established. Overall, this study concluded that 0.5-6% SHP addition in non-homogenized UF retentates, markedly improved their milk protein stability as advocated by higher ζ-potential, G' and G″ crossover temperature values. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13197-021-05097-2.

Effect of change in pH, heat treatment and diafiltration on properties of medium protein buffalo milk protein concentrate.

The demand of milk protein concentrate (MPC) powders is continuously increasing as high protein dairy ingredients. Presence of higher calcium and casein contents; heating, ultrafiltration (UF), diafiltration (DF) and spray drying of buffalo skim milk induces undesirable changes in milk proteins that causes problem of poor solubility in MPC powders. Therefore, this investigation was aimed to study the effect of change in pH (6.8-native, 7.0-neutral), heat treatments (74 ± 1 °C/15 s, 80 ± 1 °C/5 min, 85 ± 1 °C/5 min, 90 ± 1 °C/5 min) and DF on physicochemical, functional, reconstitution and rheological properties of medium protein buffalo milk protein concentrate (MP-BMPC) powder. Based on maximum ζ-potential and heat stability, UF retentate was selected, diafiltered and spray dried to obtain MP-BMPC powder. Despite having higher protein content, MP-BMPC powder exhibited markedly better functional (solubility, wettability, viscosity and emulsion stability) properties than buffalo milk protein concentrate 60. The interstitial air content, occluded air content, loose bulk density, packed bulk density, particle density and porosity values of MP-BMPC powder were 145.97 and 112.92 mL 100 g-1 of powder, 0.21 g mL-1, 0.30 g mL-1, 0.55 g mL-1 and 65.09%. Further, its specific surface area; particle size distribution (d10, d50, d90); Sauter (D32) and DeBroukere (D43) mean values were 97.93 m2 kg-1; 34.32, 104.42, 218.58 µm; 61.27 µm and 117.99 µm. The storage modulus (G') and loss modulus (G″) crossover temperature of UF and DF retentates were ~ 57.16 °C and 55.10 °C, respectively. Rheological behaviour of UF, DF retentates and MP-BMPC solution were best explained by Herschel-Bulkley model. Fourier-transform infrared spectroscopy best described amide I, II and III regions in 1700-1400 cm-1 and 1350-1200 cm-1 wavenumber range.

Alteration in physicochemical, functional, rheological and reconstitution properties of milk protein concentrate powder by pH, homogenization and diafiltration.

Concentration of milk proteins by ultrafiltration (UF) and diafiltration (DF) processes during manufacturing of milk protein concentrate (MPC) powders alter their natural milk protein stabilization system. Increasing calcium and protein contents often leads to poor functional properties in MPC powders. The pH adjustment using disodium phosphate (DSP, Na2HPO4) and DF with 150 mM NaCl solution of UF retentate were hypothesized to produce desirable changes in various properties of resulted MPC powders. Addition of Na2HPO4 followed by homogenization; DF of 5 × UF retentate with 150 mM NaCl solution resulted in significant improvement in the dispersibility, wettability, flowability, solubility, heat stability, buffer index, emulsification and foaming and water and oil binding capacities of the MPC powders. The solubility of developed MPC powders was significantly higher than MPC-C powder in fresh as well as even after 90 days of storage at 25 ± 1 °C. Rheological behaviour of reconstituted MPC was best explained by Herschel Bulkley model. Scanning electron microscopy micrograph indicated that MPC powders were having smooth surfaced, intact and separate smaller particles compared to rough, larger, infused aggregates with dents in MPC-C. Technological interventions applied are easier to adopt, cost-effective and efficient in producing excellent quality MPC powders that may find applications in wide range of novel food formulations.

Effect of disodium phosphate and homogenization on physico-chemical and rheological properties of buffalo skim milk based ultrafiltered retentate.

The concentration of pasteurized buffalo skim milk (PBSM) employing ultrafiltration (UF) alters the chemical composition of ultrafiltered retentate that adversely affect its proteins and salts equilibrium. Effect of stabilizing salts addition in concentrated milks or retentates was majorly dedicated to their thermal stability only. Therefore, this study was aimed to investigate the effect of disodium phosphate (DSP) addition and homogenization of 2.40 × UF retentate (0.60 protein to total solids ratio) on its ζ-potential, particle size, heat stability, turbidity, pH, viscosity and crossover temperature of storage (G') and loss (G″) modulus. Concentration of PBSM in UF process, significantly (P < 0.05) increased its percent TS, protein, fat and ash contents, but markedly decreased its lactose content. DSP addition significantly increased (P < 0.05) the ζ-potential, pH, viscosity and particle size in majority of the homogenized and non-homogenized retentates. Homogenized retentates containing 2.5 and 5% DSP exhibited Newtonian and Power law flow behaviour. However, rheological behaviour of non-homogenized retentates containing zero (control), 1 and 4% DSP was best explained by Bingham model. Further, non-homogenized retentates with 0.5, 2, 3, 5% DSP exhibited Newtonian flow, but retentates containing 6 and 7% DSP was best explained by Power law. The correlation among different attributes of DSP added non-homogenized and homogenized samples were also studied. Particle size and turbidity (r = + 0.999, P < 0.05) as well as ζ-potential and crossover temperature of G' and G″ (r = + 0.999, P < 0.05) showed positive correlation in 4% DSP added non-homogenized retentate.

Application of ohmic heating for concentration of milk.

The concentration of milk through evaporation is the most commonly employed unit operation for the production of a wide array of traditional and industrial dairy products. Major problems associated with thermal evaporation are a loss of aroma, flavor and color change. Ohmic heating (OH) has an immense potential for rapid and uniform heating of liquid, semi-solid and particulate foods, yielding microbiologically safe and high-quality product. The effect of ohmic heating on physico-chemical, rheological, sensorial and microbial properties during concentration of cow milk, buffalo milk and mixed milk (50:50) was studied and compared to conventional evaporation. OH significantly increased free fatty acids (FFA), apparent viscosity, hydroxymethylfurfural (HMF) content, instrumental color values i.e. redness (a*) and yellowness (b*) values. However, pH value and whiteness (L*) of the concentrated milk decreased significantly. OH caused a drastic reduction in microbiological counts and treated milk can be kept for a longer period.

Effect of change in pH of skim milk and ultrafiltered/diafiltered retentates on milk protein concentrate (MPC70) powder properties.

Poor solubility of milk protein concentrate (MPC) powders are attributed to their high protein and calcium contents. Concentration of skim milk in ultrafiltration (UF) and diafiltration (DF) increased total solids, protein and mineral contents and changed pH and ζ-potential values of the retentates that leads to milk proteins destabilization in 7× UF/DF retentates. Hence, this investigation was aimed to study the effect of change in pH of skim milk (no change; native pH maintained) and DF retentates (5.85 and 7.10) with KOH, NaOH and NaH2PO4∙2H2O on physicochemical, reconstitution, functional and rheological properties of fresh MPC70 powders. MPC70-7.10 powder had significantly higher (P < 0.05) solubility, but MPC70-NaOH and MPC70-5.85 showed significantly lower solubility than control. However, after two months storage at 25 ± 1 °C, control powder had significantly lower solubility (27.78% decrease) than treated powders. These changes in pH, significantly decreased calcium content and specific surface area; significantly improved viscosity, water binding, oil binding, emulsifying, foaming and buffering capacities, L*, a*, flowability, pH (except MPC70-5.85) and packed bulk density (except MPC70-NaOH) of treated powders over control. However, rennet coagulation time of all reconstituted powder solutions was similar. Hershel Bulkley, a best fit model, efficiently explained the pseudoplastic rheological behavior of all reconstituted MPC70 powders. This investigation had established that change in pH could improve the functional properties of MPC70 powders and is a simple, cheap, compatible and easy to use approach. Treated MPC70 powders could replace control in several food formulations owing to their improved functional properties.

Effect of pH adjustment, homogenization and diafiltration on physicochemical, reconstitution, functional and rheological properties of medium protein milk protein concentrates (MPC70).

Poor solubility is the major limiting factor in commercial applications of milk protein concentrates (MPC) powders. Retentate treatments such as pH adjustment using disodium phosphate (Na2HPO4), also responsible for calcium chelation with homogenization and; its diafiltration with 150 mM NaCl solution were hypothesized to improve the functional properties of treated MPC70 powders. These treatments significantly improved the solubility, heat stability, water binding, dispersibility, bulk density, flowability, buffer index, foaming and emulsifying capacity of treated powders over control. Rheological behaviour of reconstituted MPC solutions was best explained by Herschel Bulkley model. Compared to rough, large globular structures with dents in control; majorly intact, separate, smaller particles of smooth surface, without any aggregation were observed in SEM micrograph of treated powders. Applied treatments are easy, cost-effective and capable to improve functional properties of treated powders that could replace control MPC70 powder in various food applications where protein functionality is of prime importance.

Effect of processing on nutritive values of milk protein.

Milk is an essential source of nutritionally excellent quality protein in human, particularly in vegan diet. Before consumption, milk is invariably processed depending upon final product requirement. This processing may alter the nutritive value of protein in a significant manner. The processing operations like thermal treatment, chemical treatment, biochemical processing, physical treatments, nonconventional treatments, etc. may exert positive or negative influence on nutritional quality of milk proteins. On one side, processing enhances the nutritive and therapeutic values of protein while on other side intermediate or end products generated during protein reactions may cause toxicity and/or antigenicity upon consumption at elevated level. The review discusses the changes occurring in nutritive quality of milk proteins under the influence of various processing operations.

Physico-chemical, functional and rheological properties of milk protein concentrate 60 as affected by disodium phosphate addition, diafiltration and homogenization.

Ultrafiltration and diafiltration of skim milk altered delicate salt equilibrium and composition of 5× UF retentate (5× UFR), and thus adversely affected the reconstitutional and functional properties of milk protein concentrate (MPC) powders. It might be due to interaction and aggregation of proteins during spray drying. Therefore, this study was envisaged to investigate the effect of disodium phosphate (DSP) addition, diafiltration and homogenization of retentates on physico-chemical, functional and rheological properties of MPC60 powders. Solubility of fresh control powder was significantly lower than MPC60-H powder; at par with that of MPC60-DSP and MPC60-Na-K, but remained minimum after 60 days of storage at 25 ± 1 °C. The pH (6.6) adjustment of 5× UFR with DSP, significantly enhanced the dispersability, wettability, specific surface area (SSA), heat coagulation time (HCT), emulsification capacity and stability; buffer index of MPC60-DSP powder over control. Diafiltration of 5× UFR with NaCl and KCl, significantly (P < 0.05) decreased calcium content, but enhanced pH and mineral content of MPC60-Na-K powder. This treatment led to significant improvement in dispersability, SSA, emulsification capacity and stability, HCT and oil binding properties. Flowability, wettability, dispersability, HCT, foaming capacity, emulsification capacity and stability were also improved significantly in MPC60-H powder made from homogenized 5× UFR. Rheological behavior of reconstituted powder samples exhibited pseudoplastic behavior, best explained by Hershel Bulkley model. These MPC60 powders with improved functional properties can be used for the improvement of quality attributes of various food formulations.

Effect of concentration, homogenization and stabilizing salts on heat stability and rheological properties of cow skim milk ultrafiltered retentate.

Ultrafiltration (UF) of skimmed milk altered the composition of UF retentate and decreased the heat stability. Heat stability further reduced upon its subsequent homogenization or diafiltration. Poor heat stability of UF retentate restricts its processing at elevated temperatures. Therefore, this study was aimed to investigate the effect of protein concentration, homogenization and addition of stabilizing salts on the heat stability and rheological properties of UF retentates. Changes in the heat stability of fivefold homogenized UF retentate (5× HUFR) was studied in the pH range of 6.1-7.0. Disodium phosphate and trisodium citrate significantly increased the heat coagulation time (HCT) from 1.45 min (pH 6.41) to 120 min (at pH 6.5, 6.6, 7.0) and 80 min (pH 6.6), respectively. Significant reduction in ζ-potential of UF retentates was observed with an increase in calcium and reduction in pH during UF process. Rheological behaviour of retentates above threefold concentration exhibited Herschel-Bulkley behavior with linear increase in flow behavior index (n). Changes in the viscosity of the homogenized retentates were measured at the respective pH of maximum heat stability as a function of temperature (20-80 °C). Promising approaches that might improve the heat stability, solubility and other functional properties of protein rich powders have been discussed in this article.

Development of protein fortified mango based ready-to-serve beverage.

Fruit drinks contain negligible amount of protein as nutritional component. Fortification of fruit drinks with protein is a challenge due to protein stability in acidic and ionic environment. Mango ready-to-serve (RTS) beverage was fortified with modified whey protein and its rheological properties were studied. Whey protein was hydrolysed with papain to improve its stability in acidic medium. The water holding capacity of whey protein increased about two times after hydrolysis. Hydrolysed and native whey protein was used at 2, 3 and 4% levels for fortification of mango based RTS beverage. Addition of hydrolysed whey protein at all the three levels did not significantly change the flow behaviour of the beverage. Native whey protein fortification resulted in precipitation; however, addition of hydrolysed whey protein led to stable beverage formulation at all the three levels. Hydrolysed whey protein imparted slight bitter taste to the RTS beverage, which was masked by ß-cyclodextrin @ 0.15% of total protein. The mango RTS beverage with 3.0% hydrolysed whey protein was found acceptable with good sensory appeal and stability during thermal processing as well storage in glass bottles.