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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.
Carbohydr Polym ; 223: 115121, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31427011

RESUMO

Alginate microcapsules were prepared using three different alginate grades and incubated under simulated digestion conditions. Their micro- and nanostructural changes were studied using microscopy, laser diffraction and small angle X-ray scattering. Both the molecular weight and M/G ratio affected the size and nanostructural features of the capsules, but the changes in gastrointestinal conditions were mainly determined by the latter. All microcapsules swelled slightly in simulated gastric fluid (pH = 3) and swelled further in simulated intestinal fluid (pH = 7), particularly those with high mannuronic acid (M) contents. While high guluronic acid (G) beads maintained the nanostructural features characteristic of alginate gels (junction zones) in both media, these were rapidly disrupted in the M-rich capsules. Decreasing the pH of the gastric phase from 3 to 2 had dramatic structural impacts, resulting in a greater integrity of the microcapsules, thus highlighting the importance of the selected digestion protocol for rational microcapsule design.

3.
J Dairy Sci ; 101(12): 10819-10830, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30243639

RESUMO

Denaturation and consequent aggregation in whey protein solutions is critical to product functionality during processing. Solutions of whey protein isolate (WPI) prepared at 1, 4, 8, and 12% (wt/wt) and pH 6.2, 6.7, or 7.2 were subjected to heat treatment (85°C × 30 s) using a pilot-scale heat exchanger. The effects of heat treatment on whey protein denaturation and aggregation were determined by chromatography, particle size, turbidity, and rheological analyses. The influence of pH and WPI concentration during heat treatment on the thermal stability of the resulting dispersions was also investigated. Whey protein isolate solutions heated at pH 6.2 were more extensively denatured, had a greater proportion of insoluble aggregates, higher particle size and turbidity, and were significantly less heat-stable than equivalent samples prepared at pH 6.7 and 7.2. The effects of WPI concentration on denaturation/aggregation behavior were more apparent at higher pH where the stabilizing effects of charge repulsion became increasingly influential. Solutions containing 12% (wt/wt) WPI had significantly higher apparent viscosities, at each pH, compared with lower protein concentrations, with solutions prepared at pH 6.2 forming a gel. Smaller average particle size and a higher proportion of soluble aggregates in WPI solutions, pre-heated at pH 6.7 and 7.2, resulted in improved thermal stability on subsequent heating. Higher pH during secondary heating also increased thermal stability. This study offers insight into the interactive effects of pH and whey protein concentration during pilot-scale processing and demonstrates how protein functionality can be controlled through manipulation of these factors.

4.
Food Chem ; 237: 1155-1162, 2017 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-28763964

RESUMO

Surface energetics of demineralised whey (DMW), skimmed milk (SMP), phosphocasein (PCN) and infant milk formula (IMF) powders were determined by inverse gas chromatography (IGC). All four milk powders were amphoteric in nature with the dispersive (apolar) component of surface energy dominating the specific (polar) contribution. PCN and IMF had the highest and lowest extent of surface heterogeneity, respectively. PCN also demonstrated the poorest functional properties of the powders examined. In contrast, IMF had excellent flow and rehydration properties. Thermodynamic work of cohesion was highest in PCN and may have contributed to inadequate rehydration behaviour. Glass transition temperature of IMF powder, determined by IGC, suggested a surface dominated by lactose. Surface heterogeneity provided a better indicator of functional behaviour than total surface energy. IGC is a useful complementary technique for chemical and structural analysis of milk powders and allows improved insight into the contribution of surface and bulk factors to functionality.


Assuntos
Leite/química , Animais , Cromatografia Gasosa , Lactose , Pós , Propriedades de Superfície , Termodinâmica
5.
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.

6.
J Agric Food Chem ; 62(43): 10585-93, 2014 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-25251787

RESUMO

Understanding macronutrient interactions during heating is important for controlling viscosity during infant milk formula (IMF) manufacture. Thermal behavior of macronutrients (casein, whey, lactose, fat) was studied, in isolation and combination, over a range of concentrations. Addition of phosphocasein to whey protein solutions elevated denaturation temperature (Td) of ß-lactoglobulin and the temperature at which viscosity started to increase upon heating (Tv). Secondary structural changes in whey proteins occurred at higher temperatures in dispersions containing phosphocasein; the final extent of viscosity increase was similar to that of whey protein alone. Addition of lactose to whey protein solutions delayed secondary structural changes, increased Td and Tv, and reduced post heat treatment viscosity. This study demonstrated that heat-induced changes in IMF associated with whey protein (denaturation, viscosity) are not only a function of concentration but are also dependent on interactions between macronutrients.


Assuntos
Fórmulas Infantis/química , Caseínas/química , Gorduras/química , Temperatura Alta , Lactose/química , Proteínas do Leite/química , Valor Nutritivo , Viscosidade , Proteínas do Soro do Leite
7.
Org Biomol Chem ; 3(16): 3059-65, 2005 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-16186940

RESUMO

Beta-sitosterol is the most prevalent plant cholesterol derivative (phytosterol) and can undergo similar oxidation to cholesterol, leading to beta-sitosterol oxides. The biological impact of phytosterol oxides has only been evaluated in a phytosterol blend (usually of beta-sitosterol, campesterol, stigmasterol and dihydrobrassicasterol). The lack of pure phytosterols, including beta-sitosterol, hinders the collection of significant toxicity data on the individual beta-sitosterol oxides. An efficient synthetic route to multi-gram quantities of pure beta-sitosterol is described here, together with the first syntheses and characterisation of pure beta-sitosterol oxides.


Assuntos
Sitosteroides/síntese química , Cromatografia Gasosa-Espectrometria de Massas , Espectroscopia de Ressonância Magnética , Óxidos/síntese química , Óxidos/química , Sitosteroides/química
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