甜菜果胶制备藻油乳化液及其稳定性研究

藻油富含对人体非常重要的多不饱和脂肪酸DHA（二十二碳六烯酸）,但其极易被光、热和氧等因素诱使发生氧化反应。防止氧化反应发生,制备成稳定的油／水乳化液将其包埋成为其在食品中应用的关键问题。本研究采用甜菜果胶为乳化剂对其进行乳化包埋,研究了乳化条件如乳化剂量、油水比率、pH和均质条件对乳化液稳定性的影响。结果表明,最适的乳化条件为：乳化剂添加量在2．5％以上,油水比1：10,pH〉5,35MPa压力下均质3个循环得到比较稳定的乳化液。     

Improved emulsion stabilizing properties of whey protein isolate by conjugation with pectins

Functional properties of glyco-protein conjugates of the anionic polysaccharide pectin with whey protein isolate, obtained by dry heat treatment at 60 °C for 14 days, have been investigated in O/W emulsions containing 20% (w/w) soybean oil and 0.4% (w/w) protein both at pH 4.0 and 5.5. Emulsion stabilizing properties of mixtures and conjugates were compared at five protein to pectin weight ratios by determining changes in droplet size distribution and extent of serum separation with time. The results indicated that the dry heat-induced covalent binding of low methoxyl pectin to whey protein, as shown by SDS-PAGE, led to a substantial improvement in the emulsifying behaviour at pH 5.5, which is near the isoelectric pH of the main protein β-lactoglobulin. At pH 4.0, however, a deterioration of the emulsifying properties of whey protein was observed using either mixtures of protein and pectin or conjugates.The observed effects could be explained by protein solubility and electrophoretic mobility measurements. The protein solubility at pH 5.5 was hardly changed using mixtures of protein and low methoxyl pectin or conjugates, whereas at pH 4.0 it was decreased considerably. Electrophoretic mobility measurements at pH 5.5 revealed a much more pronounced negative charge on the emulsion droplets in the case of protein–pectin conjugates, which clearly indicated that conjugated pectin did adsorb at the interface even at pH conditions above the protein's iso-electric point. Hence, the improved emulsifying properties of whey protein isolate at pH 5.5 upon conjugation with low methoxyl pectin may be explained by enhanced electrosteric stabilization.Comparing two different commercial pectin samples, it was clearly shown that the dextrose content during dry heat treatment of protein–pectin mixtures should be as low as possible since protein–sugar conjugates not only resulted in increased brown colour development, but also gave raise to a largely decreased protein solubility which very badly affected the emulsifying properties.     

Covalent attachment of fenugreek gum to soy whey protein isolate through natural Maillard reaction for improved emulsion stability

Soy whey protein isolate (SWPI)–fenugreek gum (hydrolyzed and unhydrolyzed) conjugates were prepared by Maillard-type reaction in a controlled dry state condition (60 °C, 75% relative humidity for 3 days) to improve emulsification properties. Fenugreek gum was partially hydrolyzed using 0.05 M HCl at 90 °C for 10 min (HD10), 30 min (HD30) and 50 min (HD50) to examine if molecular weight had an effect on the emulsifying properties. The formation of SWPI–fenugreek gum conjugates was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Measurements of particle size distribution and average particle size have shown that conjugation of SWPI–fenugreek gum at 60 °C for 3 days was enough to produce relatively small droplet sizes in oil-in-water (o/w) emulsions. A ratio of 1:3 and 1:5 of SWPI:fenugreek gum was more effective in stabilizing emulsion compared to 1:1 ratio. Unhydrolyzed fenugreek gum conjugates exhibited better emulsifying properties compared to partially hydrolyzed fenugreek gum conjugates. The order of the conjugates in lowering the particle size of emulsions was as follows: SWPI–unhydrolzed fenugreek gum > SWPI–HD10 > SWPI–HD30 > SWPI–HD50.     

大豆多糖对乳清分离蛋白—乳状液稳定性与流变特性的影响

本文研究了大豆多糖（SSPS）与乳清分离蛋白（WPI）乳状液静电组装,形成乳状液聚集体,考察了不同浓度的SSPS对WPI-乳状液稳定性与流变特性的影响,以期提高体系的粘弹性,形成高流变特性的食品体系。将不同浓度的大豆多糖与2%乳清分离蛋白乳状液（油相为20%）静电组装,分析乳状液的粒径,Zeta-电位,稳定性指数,流变性质和微观结构。结合剪切流变与微流变技术,深入研究了SSPS对乳清分离蛋白（WPI）乳状液流体特性与结构的影响。结果表明:随着SSPS浓度的增加,WPI乳状液的粒径在添加0.25%SSPS时达到峰值（3350±0.35）nm,而后随着SSPS浓度的增加而降低;Zeta-电位绝对值呈递减的趋势,表明SSPS与WPI间产生静电吸附作用;SSPS静电吸附提高WPI乳状液的稳定性;剪切流变结果表明,SSPS浓度为0.5%时,其粘度最大,并在剪切速率为95.8 s-1处其粘度是WPI乳状液粘度的10倍以上;微流变结果表明,0.5%SSPS-WPI乳状液的MSD曲线出现平台区,表明其弹性指数（EI）与宏观粘度指数（MVI）均显著提高达到最大值。微观结构结果表明,0.5%SSPS-WPI乳状液形成均一的乳状液聚集体。本研究将有助于理解大豆多糖与蛋白质乳状液的相互作用,同时为低脂高流变特性的食品（如蛋黄酱、调味汁、巧克力和植脂奶油等）生产提供理论指导。      

Effects of ultra-high pressure homogenization on the properties and structure of interfacial protein layer in whey protein-stabilized emulsion

The effect of high pressure homogenization on the properties of whey protein adsorbed on emulsion interface was determined by competitive adsorption with Tween 20, Fourier transform infrared (FT-IR) spectroscopy, and RP-HPLC. The amount of whey proteins desorbed by Tween 20 increased at higher pressure. The results of FT-IR spectroscopy showed that higher homogenization pressures led to decrease of α-helix and increase of β-sheet indicating the formation of fewer interactions with the lipid phase and more interaction between adsorbed whey proteins, respectively. In RP-HPLC profile, the retention time of whey protein desorbed from high pressured emulsion was shorter than that from low-pressured emulsion. From these results, we have shown that higher pressures cause the formation of a more compact interfacial protein layer. Finally, “high pressure” emulsions are more stable than “low-pressure” ones, because of the protein layer formed by protein-protein interactions as well as the decrease of droplet size.     

Spray-drying microencapsulation using whey protein isolate and nano-crystalline starch for enhancing the survivability and stability of Lactobacillus reuteri TF-7

Decrease of survivability and stability is a major problem affecting probiotic functional food. Thus, in this study, Lactobacillus reuteri TF-7 producing bile salt hydrolase was microencapsulated in whey protein isolate (WPI) or whey protein isolate combined with nano-crystalline starch (WPI-NCS) using the spray-drying technique to enhance the survivability and stability of probiotics under various adverse conditions. Spherical microcapsules were generated with this microencapsulation technique. In addition, the survival of L. reuteri TF-7 loaded in WPI-NCS microcapsules was significantly higher than WPI microcapsules and free cells after exposure to heat, pH, and simulated gastrointestinal conditions. During long-term storage at 4, 25, and 35 °C, WPI-NCS microcapsules could retain both survival and biological activity. These findings suggest that microcapsules fabricated from WPI-NCS provide the most robust efficiency for enhancing the survivability and stability of probiotics, in which their great potentials appropriate to develop as the cholesterol-lowering probiotic supplements.     

Ability of whey protein isolate and/or fish gelatin to inhibit physical separation and lipid oxidation in fish oil-in-water beverage emulsion

The effect of pH on the capability of whey protein isolate (WPI) and fish gelatin (FG), alone and in conjugation, to form and stabilize fish oil-in-water emulsions was examined. Using layer-by-layer interfacial deposition technique for WPI–FG conjugate, a total of 1% protein was used to prepare 10% fish oil emulsions. The droplets size distributions and electrical charge, surface protein concentration, flow and dynamic rheological properties and physiochemical stability of emulsions were characterize at two different pH of 3.4 and 6.8 which were selected based on the ranges of citrus and milk beverages pHs, respectively. Emulsions prepared with WPI–FG conjugate had superior physiochemical stability compare to the emulsions prepared with individual proteins. Higher rate of coalescence was associated with reduction in net charge and consequent decrease of the repulsion between coated oil droplets due to the proximity of pH to the isoelectric point of proteins. The noteworthy shear thinning viscosity, as an indication of flocculation onset, was associated with whey protein stabilized fish oil emulsion prepared at pH of 3.4 and gelatin stabilized fish oil emulsion made at pH of 6.8. At pH 3.4, it appeared that lower surface charge and higher surface area of WPI stabilized emulsions promoted lipid oxidation and production of hexanal.     

Use of response surface methodology to optimise the hydrolysis of whey protein isolate in a tangential flow filter membrane reactor

Response surface methodology (RSM) was used to investigate the effects of substrate concentration (S), enzyme concentration (E) and initial permeate flow rate, (J_i), on permeate flux behaviour in a 10 kDa nominal molecular weight cut-off (NMWCO) tangential flow filter (TFF) enzyme membrane reactor (EMR) during 3 h hydrolysis of whey protein isolate (WPI) using Protease N Amano (IUB 3.4.24.28, Bacillus subtilis) at pH 7.0 and 45 °C. The average residual permeate flow rate (J_residual), residual enzyme activity (A_residual) and product recovered in permeate designated as apparent sieving (S_apparent) were monitored. The quadratic model regression equations obtained revealed that all the three factors had significant but dissimilar influences on permeate flux behaviour. J_residual, S_apparent and A_residual increased with increasing E, A_residual decreased with increasing J_i and there was substrate inhibition at low E. The optimised factors were S = 4.72% (w/v), E = 0.055% (w/v; hence E/S ≈ 1% w/w) and J_i = 6.91 mL/min (approximately 0.7% reactor volume per minute). The optimised values were 87.24%, 52.37% and 35.08% for J_residual, A_residual and S_apparent, respectively. The actual values for the responses agreed well with the predicted values implying that RSM is suitable for EMR optimisation. Covariance values showed that J_residual and S_apparent increased concomitantly while A_residual decreased with increasing S_apparent and J_residual.     

Iron‐encapsulated cold‐set whey protein isolate gel powder ‐ Part 2: Effect of iron fortification on sensory and storage qualities of Yoghurt

Iron was incorporated at 20–60 mg/kg of yoghurt using iron‐encapsulated cold‐set whey protein isolate gel powder (WPI‐Fe) and by direct addition of ferrous sulphate solution. The changes in physicochemical and sensory qualities of the yoghurt samples were determined over 14 days of storage. Quality attributes of the yoghurt fortified using WPI‐Fe particles at up to 60 mg iron/kg were similar to those of unfortified control samples, especially in terms of colour and flavour, while the samples fortified by direct addition of ferrous sulphate exhibited noticeable adverse effects even at 20 mg iron/kg.