Heat Stability Of Emulsions Research Articles

Heat stability of emulsions using functionalized milk protein concentrate generated by supercritical fluid extrusion.

In this study, thermostable oil-in-water emulsions containing high protein contents were developed using milk protein concentrate (MPC) that was functionalized by supercritical fluid extrusion (SCFX) processing at low temperature and shear. Functionalized MPC (f-MPC) emulsions (3% protein-80% oil and 10% protein-50% oil) were compared with emulsions stabilized by commercial MPC (c-MPC), sodium caseinate (NaCas), and a commercial mayonnaise for their emulsifying properties and heat stability at 70 and 90 °C for 30 min, and 121 °C for 15 min. Zeta-potentials and interfacial protein concentrations of f-MPC emulsions were higher than that of c-MPC emulsions. f-MPC emulsions remained stable against creaming for at least 8 weeks at room temperature (23 °C), while their c-MPC counterparts showed significant creaming at the same conditions. Even after heating at 121 °C for 15 min, f-MPC emulsions retained their structural integrity as observed from their confocal images, droplet size distributions, and viscosities. In contrast, c-MPC emulsions and mayonnaise disintegrated upon heating at 121 °C for 15 min, and oil droplets of mayonnaise partially coalesced during heating at 90 °C for 30 min. f-MPC emulsions revealed higher viscosities compared to c-MPC emulsions, providing them improved stability. Viscosities of f-MPC emulsions were not significantly affected by heating at 90 °C for 30 min, while other emulsions exhibited a substantial increase in their viscosities due to protein denaturation and aggregation. Thus, f-MPC emulsions can be utilized in the development of protein-enriched functional foods (e.g., spreads) that are stable against high heat treatments.

The repartition of whey protein microgels and caseins between fat droplet surface and the continuous phase governs the heat stability of emulsions

Whey protein microgels (WPM) are highly stable on heating and form Pickering-like emulsions exhibiting long-term resistance to coalescence. However, the heat stability of WPM emulsions is unclear and depends on the emulsion characteristics (WPM concentration, presence of non-microgel proteins such as caseins). The objective of this study was to investigate the heat-stability of WPM emulsions in the presence of caseins in order to clarify the role of the two types of proteins in the mechanism of heat-stabilization/destabilization. Emulsions (30 wt% milkfat) containing WPM (from 2.34 to 6.84 wt%) and non-microgel proteins, mainly caseins (from 0 to 0.81 wt%), were prepared at pH 7. A comparison of the emulsions before and after heating at 120 °C up to 30 min allowed their classification in three categories: viscous emulsions that gelled on heating (emulsions E1), fluid emulsions that gelled on heating (emulsions E2) and fluid emulsions even after heating (emulsion E3). A characterization of the fat droplet surface (protein interfacial load, protein composition, structure of the adsorbed entities by transmission electron microscopy) indicated emulsions E1 and E2 had WPM adsorbed at the fat droplet surface but their structural rearrangement did not explain the heat-induced modifications. Emulsions E3 had a fat droplet interfacial layer composed of caseins whereas the WPM were only located in the continuous phase. These results demonstrate that the WPM do not contribute to emulsion heat-stability but they do not induce heat instability as long as they are not situated at the fat droplet interface. Knowing the total interfacial area, the amount of caseins to obtain heat stable emulsions containing WPM can be evaluated because the caseins dominate WPM adsorption at the fat droplet surface. This knowledge will allow controlling the stability of dairy emulsions in a wider whey protein concentration range than when using native whey proteins.

Increasing the heat stability of whey protein-rich emulsions by combining the functional role of WPM and caseins

The heat stability of whey protein emulsions remains a real challenge due to the rapid denaturation/aggregation of native whey proteins on heating. The use of heat-stable Pickering-like whey protein microgels (WPM) makes it possible to develop heat-stable emulsions in a large range of whey protein concentrations. In this study, emulsion heat stability was evaluated with a special focus on the contribution of WPM adsorbed at the fat droplet surface and in the continuous phase of the emulsion. Dairy emulsions were prepared with 30% milk fat and 70% suspension of WPM in the dispersed phase of milk. The protein interfacial load and the composition of the fat droplet surface were determined immediately after emulsion formation, and the heat stability of the emulsions at 120 °C was assessed visually and at microscopic scale. WPM are heat stable in the continuous phase of the emulsion, but the presence of WPM at the surface of the fat droplets is responsible for a rapid gelation of the emulsions. In the heated emulsions, the fat droplets seemed to be crosslinked by WPM. The presence of caseins instead of WPM at the fat droplet surface allowed the heat stability of the emulsion to recover at low and high whey protein concentrations. This study shows that it is possible to prepare heat-stable whey protein–rich emulsions by using whey proteins previously aggregated as heat-stable WPM and a sufficient amount of caseins in order to fully cover the fat droplet surface. These results will contribute to the development of heat-stable whey protein–rich emulsions.

Aggregated whey proteins and trace of caseins synergistically improve the heat stability of whey protein-rich emulsions

Heat treatments are used to extend the shelf life of manufactured food emulsions, which in turn require excellent heat stability. Whey protein aggregation prior to homogenization is a means to modify emulsion heat stability but the underlying mechanism of heat stabilization has hardly been studied in an industrial context where whey protein ingredients contain caseins. Emulsions were prepared with 30% anhydrous milk fat and 70% whey protein/casein solutions with protein concentrations ranging from 3 to 6%. The proteins were either unheated (WP/Cas samples) or heat-aggregated (A-WP/Cas samples). After homogenization, the fat droplet interface was characterized and emulsion stability was analyzed visually and at microscopic level. WP/Cas emulsions were heat stable at low protein concentrations but exhibited a gradual decrease in heat stability when the protein concentration increased (>3%). This instability was due to the co-gelation of the protein-coated fat droplets and the proteins in the dispersing phase. In contrast, A-WP/Cas emulsions were rapidly heat destabilized at low protein concentrations (<4%) but were more heat stable than WP/Cas emulsions at higher protein concentrations. The stability of the A-WP/Cas emulsions at protein concentrations higher than 4% was correlated with the heat stability of the whey protein aggregates in the dispersing phase and the decrease in the proportion of whey protein aggregates at the oil/water interface due to increasing competition with caseins present in the whey protein ingredient. This study contributes to greater understanding of the functional role of aggregated whey proteins and residual caseins in emulsions stabilized by industrial WP ingredients.

ارزیابی خواص عملکردی موسیلاژ دانه بِه استخراج شده به کمک فراصوت

موسیلاژ دانه به از جمله هیدروکلوئیدهای بومی است که استخراج آن به علت ویسکوزیته بالا نیازمند روشی است که علاوه بر کاهش زمان و مصرف انرژی، از بازدهی بالایی نیز برخوردار باشد. استخراج به کمک فراصوت به عنوان یکی از روش‌های نوین می‌تواند در دستیابی به این هدف نقش داشته باشد. به این منظور در ابتدا شرایط استخراج رایج (زمان 45 دقیقه، دمایC˚47 و نسبت آب به دانه 1: 5/32)، با هدف تعیین بهترین شرایط هیدراسیون بهینه‌سازی گردید . در این پژوهش از فراصوت (پروب با فرکانس KHz24 و توان W400) با شدت‌ها (20،60،100 درصد) و زمان‌های مختلف صوت‌دهی (5، 15و 30 دقیقه) استفاده شد. نتایج حاکی از آن بود که طی 30 دقیقه استخراج با شدت 100 درصد، بازده نسبت به نمونه کنترل 7/42 درصد افزایش داشت. مدل هرشل بالکی بهترین مدل رئولوژیکی برای توصیف رفتار جریان نمونه‌ها انتخاب شد. به علت شکست ساختار پلی‌ساکاریدی موسیلاژ توسط امواج فراصوت، حلالیت نمونه‌ها بین 66 تا 92 درصد متغیر بود اما در مقایسه با نمونه کنترل به شدت افزایش یافت. در شدت 60 درصد نیز بالاترین پایداری نمونه‌ها مشاهده شد. پایداری کف نمونه‌ها نسبت به نمونه کنترل 31/17 درصد افزایش نشان داد. با وجود کاهش جذب آب موسیلاژهای استخراج شده طی زمان طولانی با شدت بالا، اما این پارامتر تقریبا در بسیاری از تیمارها فراتر از نمونه کنترل بود. نتایج این پژوهش نشان داد استفاده از فراصوت به دلیل تاثیر مثبت بر بسیاری از خواص علمکردی می‌تواند روش مناسبی برای استخراج موسیلاژ دانه به معرفی گردد.

Improving thermal stability of hydrolysed whey protein-based infant formula emulsions by protein–carbohydrate conjugation

Whey protein hydrolysate (WPH) ingredients are commonly used in the manufacture of partially-hydrolysed infant formulae. The heat stability of these emulsion-based formulae is often poor, compared with those made using intact whey protein. The objective of this study was to improve the heat stability of WPH-based emulsions by conjugation of WPH with maltodextrin (MD) through wet heating. Emulsions stabilised by different protein ingredients, whey protein isolate (WPIE), whey protein hydrolysate (WPHE), heated WPH (WPH-HE), and WPH conjugated with MD (WPH-CE) were prepared and heat treated at 75°C, 95°C or 100°C for 15min. Changes in viscosity, fat globule size distribution (FGSD) and microstructure, evaluated using confocal laser scanning microscopy (CLSM), were used to monitor the effects of hydrolysis, pre-heating and conjugation on the heat stability of the emulsions. Heat stability increased in the order WPHE<WPIE<<WPH-HE<<<WPH-CE; emulsions WPHE, WPIE and WPH-HE destabilised on heating at 75°C, 95°C or 100°C, respectively. Flocculation and coalescence of oil droplets were mediated by protein aggregation (as evidenced by CLSM) on heat treatment of WPH-HE emulsion at 100°C, while no changes in FGSD or microstructure were observed in WPH-CE emulsion on heat treatment at 100°C, demonstrating the excellent thermal stability of emulsions prepared with the conjugated WPH ingredient, due principally to increased steric stabilisation as a result of conjugation.

Characteristics and emulsifying properties of acid and acid-heat induced egg white protein

This study investigated the influence of acid (pH 3.0) or moderate heat (60 °C, 15 min, pH 3.0) treatments on physicochemical characteristics (ζ-potential and hydrophobicity), structure (Raman spectra) and emulsifying capacity of EWP after re-adjusted to various pH. Simultaneously, the stability of the emulsions prepared with acid and acid-heat induced EWP (AEP and AHEP) was tested by measuring particle diameter and microstructure of the droplets after salt (0–200 mM NaCl) and heat (90 °C, 30 min) treatments at pH 3.0–4.2. The results revealed that the emulsifying capacity of EWP was enhanced after acid or acid-heat treatment with more hydrophobic amino acids and charged groups exposed on the surface, but little changes in secondary structure. Proteins adsorbed at the oil-water interface were mainly ovotransferrin and ovalbumin. The emulsions made with AEP and AHEP were stable to droplet aggregation with no phase separation during storage for 3 weeks at pH below isoelectric point (pI ≈ 5.0), but exhibited some aggregation at pH near or above pI. The heat stability of emulsions depended on pH and thermal history. The emulsions made with AHEP performed better heat stability than AEP-stabilized emulsions. The salt stability of emulsions depended on the net charge. At pH 3.0, the emulsions were stable in the presence of ≤100 mM NaCl. At other pH, the emulsions showed good tolerance to 50 mM NaCl. These results have important implications for the formulation and production of emulsion based acid products, using egg white protein as emulsifier.

Comparing the heat stability of soya protein and milk whey protein emulsions

The heat stability of emulsions stabilized by WPC or SPI or mixtures of the two are compared by following the change in oil droplet number during heating, and applying kinetic rate equations to calculate the rate constant (k) for destabilization. SPI emulsions were found to be unstable to heat at pH around the pI, whilst being stable at pH further from the pI. This is related to the pH dependent solubility of soy proteins. This determined that a pH close to the pI (pH 4.5) be used for further studies so as to give a heat labile emulsion. Both WPC and SPI emulsions showed a weak dependence of k on protein concentration at pH 4.5, and an increasing k as the temperature increased. Arrhenius plots for emulsions made with WPC were bilinear, whilst those for SPI followed a single straight line. The change in slope of the Arrhenius plots for the WPC emulsions occurred around 70 °C, lower than would be expected from the denaturation temperature of β-lactoglobulin, the protein that dominates the thermal behaviour of WPC. The activation energies for WPC and SPI emulsions calculated from the slopes of the Arrhenius plots are slightly lower for WPC and considerably lower for SPI than the equivalent values in the literature for these proteins in solution. This, and the apparent lower denaturation temperature of β-lactoglobulin in emulsions, we explain by hypothesizing that the WPC and SPI proteins are already partially denatured by surface adsorption when they are heated, and thus require less energy to denature, and unfold at lower temperatures than native non-adsorbed proteins.

Some physicochemical and functional properties of alfalfa soluble leaf proteins

Important physicochemical and functional properties of soluble leaf proteins (SLPs) from alfalfa herbage are presented. Subunits molecular weight (MW) distribution, denaturation temperature, and functional properties like, emulsification, foaming, and solubility are discussed. SLP concentrates were prepared by acid precipitation, and ultrafiltration of clarified alfalfa juice. The MW of major soluble protein component ribulose 1,5, bisphosphate carboxylase/oxygenase was estimated to be around 490 kDa. Denaturation temperature of soluble proteins was observed to be around 70–75 °C. Most of the functional properties were affected by concentrate preparation. Acid-precipitated SLP concentrate showed lowest emulsifying properties and nitrogen solubility. Heat stability of emulsions was good. Foam overrun for SLP concentrate depended on pH and was stable around protein's isoelectric point. Stress relaxation tests on 7/100 g SLP gels indicated that they were softer gels and relaxed faster compared to 13/100 g WPI gels. SLP preparations showed encouraging functional properties.

Heat stability of oil-in-water emulsions formed with intact or hydrolysed whey proteins: influence of polysaccharides

The heat stability of emulsions (4 wt% corn oil) formed with whey protein isolate (WPI) or extensively hydrolysed whey protein (WPH) products and containing xanthan gum or guar gum was examined after a retort treatment at 121 °C for 16 min. At neutral pH and low ionic strength, emulsions stabilized with both 0.5 and 4 wt% WPI (intact whey protein) were stable against retorting. The amount of β-lactoglobulin (β-lg) at the droplet surface increased during retorting, especially in the emulsion containing 4 wt% protein, whereas the amount of adsorbed α-lactalbumin (α-la) decreased markedly. Addition of xanthan gum or guar gum caused depletion flocculation of the emulsion droplets, but this flocculation did not lead to their aggregation during heating. In contrast, the droplet size of emulsions formed with WPH increased during heat treatment, indicating that coalescence had occurred. The coalescence during heating was enhanced considerably with increasing concentration of polysaccharide in the emulsions, up to 0.12% and 0.2% for xanthan gum and guar gum, respectively; whey peptides in the WPH emulsions formed weaker and looser, mobile interfacial structures than those formed with intact whey proteins. Consequently, the lack of electrostatic and steric repulsion resulted in the coalescence of flocculated droplets during retort treatment. At higher levels of xanthan gum or guar gum addition, the extent of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.

Structural and Functional Changes of Hen's Egg Yolk Low-Density Lipoproteins with Phospholipase A2

Structural and functional changes of hen's egg yolk low-density lipoproteins (LDL) as a result of modifying its phospholipids (PLs) using phospholipase A2 were examined. The 31P NMR spectrum and enzyme hydrolysis profiles revealed that the PLs are more susceptible in LDL complex than in small unilamellar vesicles (SUV) or PLs emulsions, suggesting higher membrane fluidity of LDL and that the interactions of proteins with PLs are not strong. Although the modification of PLs in LDL did not affect the secondary structure of proteins or immunological property of LDL, the emulsions stabilized with the modified LDL showed considerable heat stability. The differences in thermal behavior of modified LDL by DSC analysis suggested the formation of a structurally heat-stable complex of LysoPLs/polypeptides in LDL during heat treatment. The enhancement of PLs−protein interactions in LDL by phospholipase A2 could be responsible for the heat stability of emulsions made from the modified LDL. Keywords: Egg yolk; low-den...