Effect of surface-active stabilizers on the surface properties of coconut milk emulsions

Previously we have demonstrated improved stability of coconut milk emulsions homogenized with various surface-active stabilizers, i.e., 1 wt% sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20) [Tangsuphoom, N., & Coupland, J. N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7), 1233–1242]. This study examines the changes in bulk and microstructural properties of those emulsions following thermal treatments normally used to preserve coconut milk products (i.e., −20 °C, −10 °C, 5 °C, 70 °C, 90 °C, and 120 °C). Calorimetric methods were used to determine the destabilization of emulsions and the denaturation of coconut and surface-active proteins. Homogenized coconut milk prepared without additives was destabilized by freeze–thaw, (−20 °C and −10 °C) but not by chilling (5 °C). Samples homogenized with proteins were not affected by low temperature treatments while those prepared with surfactants were stable to chilling but partially or fully coalesced following freeze–thaw. Homogenized coconut milk prepared without additives coalesced and flocculated after being heated at 90 °C or 120 °C for 1 h in due to the denaturation and subsequent aggregation of coconut proteins. Samples emulsified with caseinate were not affected by heat treatments while those prepared with WPI showed extensive coalescence and phase separation after being treated at 90 °C or 120 °C. Samples prepared with SDS were stable to heating but those prepared with Tween 20 completely destabilized by heating at 120 °C.     

Effect of different treatments for the destabilization of coconut milk emulsion

Coconut milk is an emulsion which is stabilized by naturally occurring proteins. The main objective of the present work is to explore different methods employing thermal, pH, chilling, enzyme treatments and combination of enzyme treatments followed by chilling and thawing for effective destabilization of the coconut milk emulsion. Stability of emulsion is evaluated by measuring the creaming index and observed for the changes in structure of oil droplets, using phase contrast microscope. Combination of treatments (enzyme treatment at 37 °C followed by chilling and thawing) of coconut milk emulsion has resulted in highest yield of 94.5%. Physico-chemical properties and fatty acid compositions are evaluated for coconut oil obtained by combination of treatments and compared with that of commercial coconut oil. It is found that the oil obtained by combination of treatments is low with respect to free fatty acids and peroxide value and high in lauric acid content.     

Enzymatic synthesis of sugar esters and their potential as surface-active stabilizers of coconut milk emulsions

Sugar esters are compounds with surfactant properties (biosurfactants), i.e., capable of reducing the surface tension and promote the emulsification of immiscible liquids. On the other hand, as with all emulsions, coconut milk is not physically stable and is prone to phase separation. Therefore, the aim of this work was to evaluate the synthesis of fructose, sucrose and lactose esters from the corresponding sugars using Candida antarctica type B lipase immobilized in two different supports, namely acrylic resin and chitosan, and evaluate its application in the stabilization of coconut milk emulsions. The enzyme immobilized on chitosan showed the highest yield of lactose ester production (84.1%). Additionally, the production of fructose ester was found to be higher for the enzyme immobilized on the acrylic resin support (74.3%) as compared with the one immobilized on chitosan (70.1%). The same trend was observed for the sucrose ester, although with lower percentage yields. Sugar esters were then added to samples of fresh coconut milk and characterized according to their surface tension, emulsification index and particle size distribution. Although the microscopic analysis showed similar results for all sugar esters, results indicated lactose ester as the best biosurfactant, with a surface tension of 38.0 N/m and an emulsification index of 54.1%, when used in a ratio of 1:10 (biosurfactant:coconut milk, v/v) for 48 h experiments.     

Storage stability of coconut milk powder

Spray-dried coconut milk powder prepared with additions of skim milk and dextrin was stored in packages for 6 months at room temperature (30°C and 80% RH). The packaging materials used were aluminum laminate (vacuum and air packed) and polypropylene. The sorption isotherm of the powder showed that the monolayer of water molecules was complete when the relative humidity was 27% which corresponded to a moisture content of 5%. Measurements of water activity, moisture content, peroxide value and solubility index indicated that lipid oxidation is the limiting factor in the stability of the powder. Its maximum shelf-life was 4 months when air or vacuum packaged in aluminum laminates and 1 1/2 months in polypropylene.     

Mannans as stabilizers of oil-in-water beverage emulsions

The stabilizing effect of spruce galactoglucomannan (GGM) on a model beverage emulsion system was studied and compared to that of guar gum and locust bean gum galactomannans, konjac glucomannan, and corn arabinoxylan. In addition, guar gum was enzymatically modified in order to examine the effect of the degree of polymerization and the degree of substitution of galactomannans on emulsion stability. Use of GGM increased the turbidity of emulsions both immediately after preparation and after storage of up to 14 days at room temperature. GGM emulsions had higher turbidity than the emulsions containing other mannans. The initial turbidity increased with increasing GGM content, but after 14 days storage at room temperature, the turbidity was the highest for GGM/oil ratio of 0.10:1 when ethanol-precipitated GGM was used. Increasing the storage temperature to +45 °C led to rapid emulsion breakdown, but a decrease in storage temperature increased emulsion stability after 14 days. Confocal microscopy showed that the average particle size in the bottom part of GGM emulsions stored for 14 days was smaller than 1 μm. A low degree of polymerization and a high degree of substitution of the modified galactomannans were associated with a decrease in emulsion turbidity.     

椰子汁饮料的稳定性研究

系统地研究了椰子汁饮料的生产工艺及影响其稳定性的主要因素，得到最佳的工艺条件：椰子肉和水的质量比为1：10，pH控制在6．5左右，加糖量为4．0％，均质条件是在70℃左右保持压力为20～25MPa，杀菌条件是121℃、20min，同时探讨了不同HLB值的混合乳化剂和增稠剂对椰子汁饮料稳定性的影响，结果表明：HLB值在11．27时乳化剂具有良好的效果，Tween60的效果优于其他乳化剂，黄原胶的效果比海藻酸钠要好。通过b9（3^4)正交试验得出稳定剂配方为；0．02％单甘酯、0．08％Span20、0．10％Tween60，0．02％黄原胶、0．02％海藻酸钠。     

大豆磷脂对牛乳蛋白乳状液热稳定性的影响

研究了大豆磷脂对牛乳蛋白乳状液热稳定性的影响,并对相关作用机理进行了探讨.测定了添加磷脂前后牛乳蛋白乳状液的热凝固时间(HCT)、粒径分布、表面疏水性、Zeta位和游离巯基含量的变化.结果表明:添加大豆磷脂能够提高牛乳蛋白乳状液的热稳定性.其中添加量为2.5 g/L时热稳定性最高,最大HCT为23.49 min.大豆磷脂可能通过与乳蛋白发生疏水相互作用改变蛋白的构象、增加乳状液的负Zeta电位、抑制巯基氧化或降低游离豌基之间的反应几率来提高乳状液的热稳定性.     

稳定剂对乳体系稳定性影响的研究

通过稳定剂的单因素实验和复配试验,对乳体系的稳定性进行了研究。采用离心沉淀率、粘度及粒度相结合的方法,研究了不同稳定剂对乳体系稳定性的影响。实验结果表明：5种稳定剂中,PGA对乳体系的稳定效果最好,且最佳添加量为0.10%,PGA分别与瓜尔豆胶、黄原胶或果胶复配,都有协同增效作用,且PGA与黄原胶在添加量3∶7时对乳体系的稳定效果最好。     

Shelf life prediction of aluminum foil laminated polyethylene packed vacuum dried coconut milk powder

Shelf life of vacuum dried coconut milk powder packed in aluminum foil laminated polyethylene packages was predicted using developed mathematical models based on two limiting criteria viz., onset of caking and lipid oxidation. Accelerated storage studies for coconut milk powder packed in aluminium foil laminated polyethylene pouches were conducted at 90 ± 1% relative humidity and 38 ± 2 °C temperature. Threshold value for the shelf life prediction based on moisture migration was taken as the critical moisture content at which lump formation was observed. Shelf life prediction based on lipid oxidation involved establishing relationships between rate of oxygen absorption, package oxygen concentration, volume of O₂ absorbed, peroxide value of the powder and storage time. A peroxide value of 10 mEq. of O₂ per kg fat was considered as the threshold limit for oxidative rancidity. A good fit between experimental and predicted data with relative deviation percent below 10% was observed during storage studies.     

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.     

酶水解对松子饮料稳定性的影响

通过对松子浆料先行适度水解 ,研究了不同水解度对松子饮料稳定性的影响。实验采用 AS1 398中性蛋白酶水解松子浆料 ,水解进程曲线表明 ,当加酶量为 0 .5%～ 1 .5% ,水解温度 50℃、p H8或 9时 ,水解 1 h后酶基本完全失活 ,可实现在无专门灭酶操作情况下控制蛋白水解度。由水解度为 0～ 6%的浆料制备的松子饮料 ,通过加速沉淀实验和储藏一个月后样品脂肪分布指数的测定 ,发现以水解度为 4%～ 5%的水解液制备的松子饮料稳定性最佳。     

Characterization of emulsions prepared by egg yolk phosvitin with pectin,glycerol and trehalose

Effect of pectin (34–40% esterification), glycerol and trehalose at two concentrations (0.1% and 0.5%, wt./wt%) on physicochemical and emulsifying properties of phosvitin (Pv) was investigated under the mild conditions (oil volume fraction, 0.25; protein concentration, 5 mg/mL; 10 mM sodium phosphate buffer, pH 7.0). Pv showed better emulsifying properties than sodium caseinate (Sc). Glycerol (0.5%) significantly increased the emulsifying activity index (EAI) of Pv from 19.8 to 20.9 and the emulsion stability index (ESI) from 67.6 to 75.1. The higher ESI of Pv was also obtained by 0.1% pectin and 0.5% trehalose. The results obtained from circular dichroism (CD) spectra indicated that all the tested additives displayed slight effect on the unfolded structure of Pv. Furthermore, fluorescence pattern demonstrated that glycerol and trehalose increased the hydrophobicity of Pv, while pectin displayed an opposite effect. All emulsions exhibited a shear-thinning behavior and the flow behavior was fitted to the power law model. Frequency sweeps of the emulsions illustrated that they behaved like a viscous liquid.     

Dietary fiber from coconut residue: effects of different treatments and particle size on the hydration properties

The present work is aimed at the production of dietary fiber from underutilized coconut residue left after the extraction of milk, by subjecting it to physical treatments such as water washing, hot water washing, boiling water washing and pressure cooking, as well as solvent extraction. The fat content was reduced from 62% to 45% and 41% by treatment with boiling water and pressure-cooking, respectively. Water-holding, water retention and swelling capacities increased with decreasing fat content. A marked increase was observed in hydration properties when the fat content decreased from 10 to 2%. The hydration properties were maximum for 550 m particle size coconut fiber. For the higher particle size (1,127 m), the oil was trapped inside the fiber matrix, resulting in decreased hydration properties, whereas for the lower particle size (390 m) the rupture of the fiber matrix was responsible for low hydration properties. An attempt was made to compare the hydration properties of coconut dietary fiber with other commercially available dietary fibers.     

Effect of partial whey protein depletion during membrane filtration on thermal stability of milk concentrates

Membrane filtration technologies are widespread unit operations in the dairy industry, often employed to obtain ingredients with tailored processing functionalities. The objective of this work was to better understand the effect of partial removal of whey proteins by microfiltration (MF) on the heat stability of the fresh concentrates. The micellar casein concentrates were compared with control concentrates obtained using ultrafiltration (UF). Pasteurized milk was microfiltered (80 kDa polysulfone membrane) or ultrafiltered (30 kDa cellulose membrane) without diafiltration (i.e., no addition of water) to 2× and 4× concentration, based on volume reduction. The final concentrates showed no differences in pH, casein micelle size, or mineral concentration in the serum phase. The micellar casein retentates (obtained by MF) showed a 20 and 40% decrease in whey protein concentration compared with the corresponding UF milk protein concentrates for 2× and 4× concentration, respectively. The heat coagulation time decreased with increasing protein concentration, regardless of the treatment; however, MF retentates showed a higher thermal stability than the corresponding UF controls. The average diameter for casein micelles increased after heating in UF but not MF concentrates. The turbidity (measured by light scattering) increased after heating, but to a higher extent for UF retentates than for MF retentates at the same protein concentration. It was concluded that the reduced amount of whey protein in the MF retentates caused a significant increase in the heat stability compared with the corresponding UF retentates. This difference was not due to ionic composition differences or pH, but to the type and amount of complexes formed in the serum phase.     

On the stability of oil-in-water emulsions to freezing

Oil in water emulsions (40 wt%) were prepared from a homologous series of n-alkanes (C10–C18). The samples were temperature cycled in a differential scanning calorimeter (two cycles of 40 °C to −50 °C to 40 °C at 5 °C min⁻¹) and in bulk (to −20 °C). The emulsions destabilized and phase-separated after freeze–thaw if the droplets were solid at the same time as the continuous phase and were more unstable if a small molecule (SDS or polyoxyethylene sorbitan monolaurate) rather than a protein (whey protein isolate or sodium caseinate) emulsifier was used. The unstable emulsions formed a self-supporting cryo-gel that persisted between the melting of the water and the melting of the hydrocarbon phase. Microscopy provides further evidence of a hydrocarbon continuous network formed during freezing by a mechanism related to partial coalescence which collapses during lipid melting to allow phase separation.     

Effects of bacteriostatic emulsifiers on stability of milk-based emulsions

For milk-based emulsion products such as canned coffee or tea, the addition of bacteriostatic emulsifiers is necessary to inhibiting the growth of heat-resistant sporeformers. Since bacteriostatic emulsifiers often cause the destabilization of emulsions, other type of emulsifiers, such as stability-enhancing ones, are necessary for the long-term stability of emulsions. Four milk-based emulsions were prepared from powdered milk combined with several types of emulsifiers. The long-term stability of emulsions, which was detected by the occurrence of a creaming layer after 3 months of storage, differed according to the composition of emulsifiers. To understand the reason for the differences in the stability of emulsions, particle size, distribution, ζ-potential, and the amount of proteins and phospholipids present in the cream layer (separated oil droplets) in the emulsions were measured. Only the amount of proteins adsorbed onto oil droplets was found to be closely related to the difference in emulsion stability, that is, the more proteins adsorbed, the higher the emulsion stability. SDS–PAGE analyses revealed that κ-casein and β-lactoglobulin play an important role in emulsion stability by adsorbing onto the oil droplet surface.     

Rheological properties and stability of model salad dressing emulsions prepared with a dry-heated soybean protein isolate–dextran mixture

The rheological characteristics of model salad dressing emulsions, incorporating a dry-heated soybean protein isolate (SPI)–dextran mixture as emulsifier, were investigated by applying dynamic rheometry tests in an attempt to probe the emulsion structure and to elucidate the mechanism of their stability against creaming. Both the viscoelastic properties and the creaming behaviour of the dressings were greatly influenced by the extent of protein–dextran conjugation and also by xanthan gum addition. The results are discussed in terms of emulsion droplet interactions which, depending on the extent of glyco-conjugation, may be dominated by depletion or ‘bridging’ flocculation effects and, thereby, influence the droplet network structure collapse during ageing.     

Effect of heat treatments and homogenisation pressure on the acid gelation properties of recombined whole milk

The homogenisation pressure and the order of heating and homogenisation were varied in the preparation of recombined whole milks. The fat globule sizes decreased from ∼2 to 0.2 μm as the homogenisation pressure increased from 50 to 850 bar for samples heated before (HEHO) or after (HOHE) homogenisation. For acid gels prepared from the milks, small increases in elastic modulus of the set gels were observed with decreasing fat globule size. The yield strain of the acid gels increased linearly with decreasing fat globule size, and HOHE gels had higher yield strains than HEHO gels. The yield stress of the set gels increased with decreasing fat globule size, and the yield stress for HOHE gels were higher than the HEHO gels. Confocal micrographs of the gels revealed an almost continuous protein network structure without pores for gels from milks treated at low homogenisation pressures, and the large fat globules did not actively interact with the strands in the gel network. In contrast, a porous protein network structure with distinct strands was observed for the samples treated at high homogenisation pressures, and the small fat globules were intimately involved in the strands in the network structure. The HOHE gels had a more porous protein network with thicker strands than the HEHO gels. The size of the fat globules and their incorporation in the protein network during acidification is proposed to affect the acid gel structure and properties.     

Interfacial and emulsifying properties of sucrose ester in coconut milk emulsions in comparison with Tween

In this study, sucrose esters were presented as a promising alternative to petrochemically synthesized Tweens for application in coconut milk emulsions. The interfacial and emulsifier properties of sucrose ester (SE), mainly sucrose monostearate, had been investigated in comparison with Tween 60 (TW), an ethoxylate surfactant. The interfacial tension measurement showed that SE had a slightly better ability to lower the interfacial tension at coconut oil–water interface. These surfactants (0.25 wt%) were applied in coconut milk emulsions with 5 wt% fat content. The effects of changes in pH, salt concentration, and temperature on emulsion stability were analyzed from visual appearance, optical micrograph, droplet charges, particle size distributions, and creaming index. Oil droplets in both SE and TW coconut milk emulsions extensively flocculated at pH 4, or around the pI of the coconut proteins. Salt addition induced flocculation in both emulsions. The pH and salt dependence indicated polyelectrolyte nature of proteins, suggesting that the proteins on the surface of oil droplets were not completely displaced by either added nonionic SE or TW. TW coconut milk emulsions appeared to be thermally unstable with some coalesced oil drops after heating and some oil layers separated on top after freeze thawing. The change in temperature had much lesser influence on stability of SE coconut milk emulsions and, especially, it was found that SE emulsions were remarkably stable after the freeze thawing.     

Changes in the physical properties,solubility, and heat stability of milk protein concentrates prepared from partially acidified milk

A limiting factor in using milk protein concentrates (MPC) as a high-quality protein source for different food applications is their poor reconstitutability. Solubilization of colloidal calcium phosphate (CCP) from casein micelles during membrane filtration (e.g., through acidification) may affect the structural organization of these protein particles and consequently the rehydration and functional properties of the resulting MPC powder. The main objective of this study was to investigate the effects of acidification of milk by glucono-δ-lactone (GDL) before ultrafiltration (UF) on the composition, physical properties, solubility, and thermal stability (after reconstitution) of MPC powders. The MPC samples were manufactured in duplicate, either by UF (65% protein, MPC65) or by UF followed by diafiltration (80% protein, MPC80), using pasteurized skim milk, at either the native milk pH (~pH 6.6) or at pH 6.0 after addition of GDL, followed by spray drying. Samples of different treatments were reconstituted at 5% (wt/wt) protein to compare their solubility and thermal stability. Powders were tested in duplicate for basic composition, calcium content, reconstitutability, particle size, particle density, and microstructure. Acidification of milk did not have any significant effect on the proximate composition, particle size, particle density, or surface morphology of the MPC powders; however, the total calcium content of MPC80 decreased significantly with acidification (from 1.84 ± 0.03 to 1.59 ± 0.03 g/100 g of powder). Calcium-depleted MPC80 powders were also more soluble than the control powders. Diafiltered dispersions were significantly less heat stable (at 120°C) than UF samples when dissolved at 5% solids. The present work contributes to a better understanding of the differences in MPC commonly observed during processing.