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1.
Food Chem ; 304: 125418, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-31479994

RESUMO

Low and high protein dairy powders are prone to caking and sticking and can also be highly insoluble; with powder storage conditions an important factor responsible for such issues. The aim of this study focused on the bulk and surface properties of anhydrous and humidified spray-dried milk protein concentrate (MPC) powders (protein content ~40, 50, 60, 70 or 80%, w/w). Water sorption isotherms, polarized light and scanning electron micrographs showed crystallized lactose in low protein powders at high water activities. High protein systems demonstrated increased bulk diffusion coefficients compared to low protein systems. Glass transition temperatures, α-relaxation temperatures and structural strength significantly decreased with water uptake. CLSM measurements showed that humidified systems have slower real time water diffusion compared to anhydrous systems. Overall, the rate of water diffusion was higher for low protein powders but high protein powders absorbed higher levels of water under high humidity conditions.

2.
J Dairy Sci ; 102(11): 9611-9621, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31447155

RESUMO

This study examined the effect of dietary factors on compositional and functional properties of whole milk powder (WMP) produced from bovine milk. Raw milk samples were obtained from 3 groups of 18 Holstein Friesian spring-calving cows randomly assigned to diets based on perennial ryegrass (GRS), perennial ryegrass/white clover sward (CLV), and total mixed ration (TMR). Raw milks obtained in late lactation were subsequently standardized for fat, heat-treated (90°C for 30 s), evaporated, and homogenized before spray drying. The WMP produced from each diet were analyzed to determine differences in color, particle size distribution, heat coagulation time, yogurt gelation, texture profile, and protein profile due to each diet. Significant differences in heat coagulation time were observed between the CLV and TMR samples, whereas color values were significantly different between GRS and TMR samples. No significant differences in gross composition, protein profile, or whey protein nitrogen index were found between the 3 WMP samples. Average D90 values (the particle size at which 90% of the particles were smaller than the specified size) for fat globules were significantly lower in the TMR sample compared with the GRS and CLV samples. Yogurts produced from GRS- and CLV-derived WMP had significantly higher elastic moduli (G') than those produced from TMR-derived WMP. Similarly, texture profile analysis revealed significantly higher firmness values in yogurt samples derived from CLV compared with TMR samples. Our data characterize the effect of these diets on the composition and functional properties of fat-standardized WMP, suggesting better yogurt functionality and thermal stability in WMP derived from pasture-based bovine diets.

3.
Food Chem ; 271: 136-141, 2019 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-30236658

RESUMO

This study investigated the effects of dephosphorylation and sodium hexametaphosphate (SHMP) salt addition on the viscosity of milk protein concentrate (MPC) solutions. Dephosphorylation (DP) of casein was performed using bovine alkaline phosphatase. Nuclear magnetic resonance (NMR) spectra showed that dephosphorylation depleted the casein-bound phosphate region (CNP). SHMP addition (5 mM) had no impact on the 31P NMR spectra of DP-MPC; addition of 5 mM SHMP to control MPC (C-MPC) resulted in a shift in peaks associated with the CNP region, possibly caused by SHMP sequestering calcium, leading to swelling of micelles. DP-MPC exhibited a lower viscosity compared to C-MPC, with SHMP addition at 12.5 and 25 mM causing gelation of C-MPC and DP-MPC solutions. This work confirmed the role that phosphate residues have in maintaining micelle structural stability and provides new insights into controlling viscosity of MPC solutions.


Assuntos
Caseínas/química , Proteínas do Leite/química , Fosfatos/química , Animais , Bovinos , Concentração de Íons de Hidrogênio , Micelas
4.
J Dairy Sci ; 101(12): 10743-10749, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30292547

RESUMO

Acid whey (AW) is the liquid co-product arising from acid-induced precipitation of casein from skim milk. Further processing of AW is often challenging due to its high mineral content, which can promote aggregation of whey proteins, which contributes to high viscosity of the liquid concentrate during subsequent lactose crystallization and drying steps. This study focuses on mineral precipitation, protein aggregation, and lactose crystallization in liquid AW concentrates (∼55% total solids), and on the microstructure of the final powders from 2 independent industrial-scale trials. These AW concentrates were observed to solidify either during processing or during storage (24 h) of pre-crystallized concentrate. The more rapid solidification in the former was associated with a greater extent of lactose crystallization and a higher ash-to-protein ratio in that concentrate. Confocal laser scanning microscopy analysis indicated the presence of a loose network of protein aggregates (≤10 µm) and lactose crystals (100-300 µm) distributed throughout the solidified AW concentrate. Mineral-based precipitate was also evident, using scanning electron microscopy, at the surface of AW powder particles, indicating the formation of insoluble calcium phosphate during processing. These results provide new information on the composition- and process-dependent physicochemical changes that are useful in designing and optimizing processes for AW.

5.
J Food Sci ; 83(4): 937-945, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29577287

RESUMO

Rheological modeling as a function of temperature is a useful tool for describing products undergoing thermal processing. The rheological behavior of a range of dairy-based (4%, w/w) protein beverages was investigated for applicability to semi-empirical temperature-dependent viscosity equations. The viscosity at 16.8 rad/s of the beverages was measured during heating, holding, and cooling over a temperature range of 25 to 90 o C using a rheometer with starch pasting cell geometry. Five established fitting methods were applied based on the Arrhenius and Williams-Landel-Ferry (WLF) equations using nonlinear regression analysis. A two-parameter WLF (WLF2 ) model, using viscosity at a reference temperature of 25 o C resulted in high R2 values (0.974 to 0.988) and a statistically superior fit compared to the Arrhenius, Generalized Arrhenius, and exponential equations (P < 0.001). Deviation from the WLF2 modeled equation was used to describe and investigate the effect formulation had on the changes in viscosity during thermal heating. This study successfully applied the WLF equation to a liquid protein system, proving that a consistent and close fit can be achieved across a range of formulations. A rapid, quantitative method for viscosity-temperature profile evaluation is presented, which can ease product development and optimization of product processing stability. PRACTICAL APPLICATION: This study validated the use of the Williams-Landel-Ferry equation to describe the behavior of dairy beverages during thermal processing, providing a better fit to rheological data than the widely used Arrhenius-based equations. In conjunction with the WLF equation, a method was presented which reduced the complex rheological data to a single value, which can aid in the comparison of formulations for product development and optimization in both research and industry.


Assuntos
Bebidas/análise , Laticínios/análise , Proteínas na Dieta , Análise de Alimentos/métodos , Reologia , Temperatura Ambiente , Temperatura Baixa , Temperatura Alta , Humanos , Modelos Químicos , Reprodutibilidade dos Testes , Amido , Viscosidade
6.
Food Res Int ; 89(Pt 1): 415-421, 2016 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28460933

RESUMO

Pea protein isolate (PPI) is used in many food formulations, due to its low cost, commercial availability and excellent amino acid profile. The objective of this study was to determine the emulsification properties of PPI. Particle size of PPI powders showed neither temperature (25-65°C) nor time (up to 24h) increased solubilisation of powder particles during mixing. Heating PPI dispersions (10%, w/w, protein) from 45 to 90°C led to an increase in storage modulus (G'; Pa) at 71°C, indicating the onset of protein aggregation. Gel formation occurred at 79°C (G'>1Pa). Pea protein-stabilised emulsions made using homogenization (15MPa; 1 pass) or microfluidization (50MPa; 1 pass) resulted in the formation of cold-set gels, with gel strength increasing with increasing oil concentration and fluidic pressure. Droplet size and viscosity of pea protein-stabilised emulsions decreased and increased, respectively, with increasing ultrasonication time. Overall, ultrasonication (<50°C) can create a uniform droplet size emulsion, while, homogenization and microfluidization can produce cold-set gels for use in a wide-range of food applications.

7.
Food Chem ; 138(2-3): 1304-11, 2013 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-23411247

RESUMO

Bovine ß-casein was purified from phosphocasein by rennet coagulation and cold solubilisation from the resultant curd. ß-Casein was then dephosphorylated using potato acid phosphatase. Urea-polyacrylamide gel electrophoresis (PAGE) of partially dephosphorylated ß-casein showed a number of bands, depending on the final level of phosphorylation. Dephosphorylating ß-casein increased its pH of minimum solubility from ∼pH 5 to 5.5 and reduced its net negative charge from -30.8 to -27.0 mV. During the acidification of ß-casein solutions, partially dephosphorylated ß-casein failed to form a gel, unlike the phosphorylated (i.e., control) ß-casein. Use of partially dephosphorylated ß-casein to stabilise oil-in-water emulsions resulted in larger fat globules compared to control ß-casein, but such globules were less susceptible to aggregation in the presence of 15 or 30 mM CaCl(2). Overall, the dephosphorylation of ß-casein resulted in a protein similar to human ß-casein in terms of physicochemical functionality, with increased stability against calcium-induced aggregation.


Assuntos
Fosfatase Ácida/química , Caseínas/química , Proteínas de Plantas/química , Solanum tuberosum/enzimologia , Animais , Bovinos , Emulsões/química , Fosforilação
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