高甲氧基果胶对酸性大豆蛋白体系的稳定机理

为揭示高甲氧基果胶对酸性豆乳体系稳定的作用机理,通过添加不同质量浓度果胶,研究在pH值由7.0～3.0降低过程中大豆蛋白的粒径、ζ-电位以及微观结构变化。结果表明：当体系pH＜6.0时,果胶通过静电作用吸附在大豆蛋白胶粒上,阻止了大豆蛋白颗粒在酸性状态的聚集。果胶质量浓度≤0.2 g/100 mL,质量浓度1.5 g/100 mL的大豆蛋白聚集,体系失稳;果胶质量浓度≥0.4 g/100 mL,质量浓度1.5 g/100 mL的大豆蛋白体系在一定pH值内稳定,果胶质量浓度越大,稳定性越好。酸性大豆蛋白体系的稳定性与大豆蛋白和果胶之间的静电吸附作用以及果胶质量浓度有关。     

高甲氧基果胶对酸奶饮料的稳定作用

总结了高甲氧基果胶对酸奶饮料的稳定机理及其影响稳定效果的因素，并对不同的影响因素（饮料的pH值、蛋白质的浓度、高甲氧基果胶浓度、均质条件、调配搅拌速度、杀菌条件和酪蛋白粒子直径等）进行了详细的分析，为使用以高甲氧基果胶做稳定剂的酸奶饮料生产提供了较为全面的参考依据。     

Stability and physical properties of recombined dairy cream: Effects of soybean lecithin

Recombined dairy cream, which primarily comprises anhydrous milk fat and milk protein, has significant advantages compared to natural cream; however, its most notable disadvantage is poor stability. The objective of this study was to investigate the effects of lecithin on the stability and physical properties of recombined dairy cream (20% fat, and 1.5% protein) in terms of the creaming rate, mean oil droplet size and distribution, surface protein concentration, ζ-potential, and apparent viscosity. The results clearly showed that lecithin can significantly improve the stability of recombined dairy cream by decreasing the creaming rate, especially at a concentration of 0.6% (w/w). Increasing the lecithin concentration decreased the mean oil droplet size and the surface protein concentration but slightly increased the ζ-potential. The apparent viscosity decreased and surprisingly increased at 0.6% (w/w). We can infer that lecithin initially displaces proteins from the oil surface and may interact with both proteins and polysaccharides, forming a much more stable structure.     

Effect of pH and Ionic Strength on the Physicochemical Properties of Coconut Milk Emulsions

ABSTRACT:  Coconut milk (16% to 17% fat, 1.8% to 2% protein) was extracted from coconut ( Cocos nucifera L.) endosperm and diluted in buffer to produce natural oil-in-water emulsions (10 wt% oil). The effect of pH (3 to 7) and NaCl (0 to 200 mM) on the properties and stability, namely, mean particle size, ζ-potential, viscosity, microstructure, and creaming stability, of the natural coconut milk emulsions was investigated. At pH values close to the isoelectric point (IEP) of the coconut proteins (pH 3.5 to 4) and in the absence of NaCl, coconut milk flocculated, but did not coalesce. Flocculation corresponded to low surface charges and was accompanied by an increase in emulsion viscosity. Adding up to 200 mM NaCl to those flocculated emulsions did not change the apparent degree of flocculation. Coconut milk emulsion at pH 6 was negatively charged and not flocculated. Upon addition of salt, the ζ-potential decreased from –16 to –6 mV (at 200 mM NaCl) but this was not sufficient to induce flocculation in coconut milk emulsions. At low pH (< IEP), the positively charged droplets of coconut milk emulsions only flocculated when the NaCl concentration exceeded 50 mM, as the ζ-potential approached zero.     

Oxalic extraction of high methoxyl pectin and its application as a stabiliser

The objective of this work was to extract high methoxyl (HM) pectin with oxalic acid, characterise its physicochemical properties and evaluate its dispersion stability in acidified milk drink (AMD). HPSEC–MALLS analysis revealed that the obtained HM pectin was high in molecular weight (522.4 kDa). The ζ-potential of the obtained HM pectin in aqueous solution at pH 4.0 was −31.5 mV. The AFM images proved that the obtained HM pectin contained several long linear molecules. The apparent diameter of AMD stabilised by the obtained HM pectin was 636 nm at the concentration of 3.0‰. The stability analysis of AMD and the microscopic observation with confocal laser scanning microscopy (CLSM) proved that the obtained HM pectin was a prominent stabiliser in AMD.     

Acid-induced gelation of milk protein concentrates with added pectin: Effect of casein micelle dissociation

The dynamics of the formation of the acid gel network for mixtures of milk protein concentrate (MPC) and low methoxyl amidated (LMA) pectin were studied using rheological measurements. The results as a function of pectin content and casein micelle integrity, from neutral pH to approximately pH 4.2, together with the microstructural changes observed in some of these systems, are presented.The gelation profiles of a mixture of 4% w/v MPC and LMA pectin (0–0.075% w/v) after the addition of 1.2% w/v glucono-δ-lactone showed a gradual decrease in the shear modulus with the incorporation of pectin. The effects of casein micelle integrity on casein–pectin interactions were studied, by preparing MPC dispersions containing various levels of micellar casein. A gradual change in the shear modulus, from a disrupting effect of pectin added to MPC, in which the casein micelles are intact, to a clear synergistic effect of pectin added to dissociated casein systems, was found in the acid-induced milk gels.     

The stabilizing behaviour of soybean soluble polysaccharide and pectin in acidified milk beverages

The mechanisms of stabilization of soybean soluble polysaccharide (SSPS) and high methoxyl pectin (HMP) in acidified milk drinks were studied focusing on the differences in behaviour between the two polysaccharides. The changes in casein micelles size during acidification with glucono-δ-lactone or by direct acidification were measured using light scattering. When HMP was added to skim milk before acidification, pectin adsorbed on the surface of the casein micelles via electrostatic interactions and prevented casein aggregation. Results suggested that adsorption of pectin occurred from the beginning of acidification and somewhat affected the rearrangement of casein micelles in the pH range between 5.8 and 5.0. On the other hand, SSPS, at concentrations up to 2% (w/w), did not interact with caseins at pH >4.6. At pH <4.2 SSPS showed better stabilizing properties than HMP. In addition, between pH 4.2 and 3.2, SSPS-stabilized acid dispersions were not affected by pH, while dispersions homogenized with pectin showed a size distribution that depended on pH. The differences in structure between SSPS and HMP account for the unique functionalities of the two polysaccharides in acid milk systems.     

Foaming and surface properties of casein glycomacropeptide–gelatin mixtures as affected by their interactions in the aqueous phase

Gelatin is widely used in food industry for the stabilization of foam products. On the other hand, casein glycomacropeptide (CMP) is a bioactive peptide with high surface activity. The aim of this work was to study the interfacial and foaming properties of CMP–gelatin mixed systems at pH 6.5 and 3.5 and evaluate the relation of these properties with the interactions in the aqueous phase. The CMP:gelatin ratio in mixed systems was 0:100 (pure gelatin), 25:75, 50:50, 75:25 and 100:0 (pure CMP). Viscosity, particle size, ζ-potential, interfacial properties and foaming properties were determined. At both pH, gelatin solutions showed the highest viscosity, CMP the lowest and the mixed systems presented behaviour more similar than CMP. Particle size and ζ-potential determinations evidenced the formation of complexes between CMP and gelatin at both pH. CMP was more surface active than gelatin and dominated the rate of diffusion of the mixed systems to the air–water interface. A synergistic effect was observed on foamability and foam stability in mixed systems that could be explained by the formation of a complex between CMP and gelatin with outstanding capacity for foams formation and stabilization.     

贮藏期间芦荟果胶含量变化及影响果胶粘度因素的研究

果胶作为由植物中提取的天然添加剂,具有良好的胶凝化和稳定化作用。从具有保健作用和药用价值的芦荟中提取果胶已广泛应用于食品工业、化妆品、医药等领域。本文对贮藏期间芦荟果胶含量态变化进行研究,并确定影响果胶粘度的因素,对芦荟果胶提取具有指导意义。本文采用酸水解醇析法提取芦荟中的果胶,确定提取果胶醇析过程中的最优pH和温度,并明确贮藏0～60d芦荟中果胶含量,此外还确定各种影响因素对果胶成品粘度的影响。结果表明,醇析过程中的最佳pH3.5,最佳温度为50℃。果胶成品的pH2.79（符合国标）,甲氧基含量为8.518%,属于高甲氧基果胶。贮藏0～60d库拉索芦荟中的果胶含量在贮藏10d时达到峰值。而后果胶含量随贮藏时间的延长而降低,并且在20d之后明显下降。因此,最适宜芦荟果胶提取和加工的时间为0～20d。所得芦荟果胶粘度与温度、柠檬酸和氯化钠添加量呈负相关,而与果胶浓度和蔗糖添加量呈正相关。     

The effect of free Ca2+ on the heat stability and other characteristics of low-heat skim milk powder

Low-heat skim milk powder (SMP), reconstituted to 25% total solids, was found to have poor heat stability. This could be improved by reducing the free Ca²⁺ concentration to 1.14 mm, or lower, by the addition of either Amberlite IR-120 ion-exchange resin in its sodium form or tri-sodium citrate in skim milk prior to evaporation and spray drying. Reduction in Ca²⁺ concentration was accompanied by increases in pH, particle size, and kinematic viscosity, and by a reduction in ζ-potential and changes in colour. In-container sterilisation of the reconstituted powder increased particle size, ζ-potential, kinematic viscosity and a* and b* values. However, Ca²⁺ concentration, pH and whiteness decreased. This study elucidated the importance of Ca²⁺ concentration and pH on heat stability of low-heat SMP, suggesting that Ca²⁺ concentration and pH in bulk milk are useful indicators for ensuring that spray dried milk powder has good heat stability.     

Physiochemical Properties,Microstructure, and Probiotic Survivability of Nonfat Goats’ Milk Yogurt Using Heat‐Treated Whey Protein Concentrate as Fat Replacer

There is a market demand for nonfat fermented goats’ milk products. A nonfat goats’ milk yogurt containing probiotics (Lactobacillus acidophilus, and Bifidobacterium spp.) was developed using heat‐treated whey protein concentrate (HWPC) as a fat replacer and pectin as a thickening agent. Yogurts containing untreated whey protein concentrate (WPC) and pectin, and the one with only pectin were also prepared. Skim cows’ milk yogurt with pectin was also made as a control. The yogurts were analyzed for chemical composition, water holding capacity (syneresis), microstructure, changes in pH and viscosity, mold, yeast and coliform counts, and probiotic survivability during storage at 4 °C for 10 wk. The results showed that the nonfat goats’ milk yogurt made with 1.2% HWPC (WPC solution heated at 85 °C for 30 min at pH 8.5) and 0.35% pectin had significantly higher viscosity (P < 0.01) than any of the other yogurts and lower syneresis than the goats’ yogurt with only pectin (P < 0.01). Viscosity and pH of all the yogurt samples did not change much throughout storage. Bifidobacterium spp. remained stable and was above 10⁶CFU g^‐1 during the 10‐wk storage. However, the population of Lactobacillus acidophilus dropped to below 10⁶CFU g^‐1 after 2 wk of storage. Microstructure analysis of the nonfat goats’ milk yogurt by scanning electron microscopy revealed that HWPC interacted with casein micelles to form a relatively compact network in the yogurt gel. The results indicated that HWPC could be used as a fat replacer for improving the consistency of nonfat goats’ milk yogurt and other similar products.     

Charge domain of modified pectins influence interaction with acidified caseins

The interaction of non-fat dry milk, caseinate and casein (CSN) fractions with charge modified pectins (B-Pec and U-Pec) and unmodified pectin (O-Pec) in acidified dispersion systems was investigated. U-Pec led to more precipitation of proteins than O-Pec or B-Pec. Casein dispersions with pectin had larger particle size, especially U-Pec and B-Pec, than dispersions without pectin. Dispersions with charge modified pectins showed more negative ζ-potential than dispersions with unmodified pectin or dispersions without pectin. U-Pec enhanced negative ζ-potential of β-CSN more than B-Pec. There was no significant difference in flow behavior among non-fat milk samples regardless of pectins added. In contrast, non-Newtonian behavior, shear thinning behavior was observed in modified pectin added κ-CSN. Analysis by light microscopy of non-fat milk and κ-CSN showed that sizes and shapes were changed by addition of O-Pec and U-Pec. The results suggest a specific affinity between pectin and κ-CSN, which is related to the charge distribution of pectin.     

pH值对低酯果胶/酪蛋白酸钠复合体系流变及结构特性的影响

为研究pH值对低酯果胶/酪蛋白酸钠复合体系流变及结构特性的影响,分别在不同酸性条件下（pH 3.0、3.5、4.0、4.5、5.0、5.5）对复合体系的静态剪切及动态黏弹流变特性、Zeta电位、粒径、浊度、微观结构进行测定。结果表明：复合体系流变特性呈两段式变化,在pH 3.0～4.0时,随pH值的增大,复合体系流体指数n和tanδ均增大,稠度系数K减少;在pH 4.5～5.5时,体系n和tanδ骤减后继续增加,且增加程度更大,K骤增后继续减少。复合体系Zeta电位值随着pH值的增大而降低。Zeta电位值在pH 3.0～4.0时为正,在pH 4.5～5.5时为负。复合体系粒径和浊度值均随着pH值的增大呈先增大后减小的趋势,在pH 4.5时达到最大。随着pH值的降低,复合体系微观结构由杂乱变得细密。在pH 3.0～4.0时,体系以低酯果胶附着在酪蛋白表面结构为主;在pH 4.5～5.5时,体系中低酯果胶的网状结构更明显。因此,pH值的变化会改变复合体系的流变及结构特性,从而影响体系的稳定性。     

Comparison of rheological properties of acid gels made from heated casein combined with β-lactoglobulin or egg ovalbumin

Gelation of heat-treated milk protein solutions by acid fermentation was performed using a model system of micellar casein alone (systR), micellar casein and β-lactoglobulin (systB) or micellar casein and egg ovalbumin (systO) dissolved in a milk ultrafiltrate and heat-treated at 90°C for 24 min. Solubility of globular proteins at given pH values and their interactions with casein were determined. Particle size and ζ-potential of the protein systems were measured before and after heat treatment. Acid gelation of the heated systems was monitored using dynamic low-amplitude strain oscillation. Ovalbumin alone or with casein produced larger particles than casein alone or with β-lactoglobulin upon heat treatment. The systems gelled at different pH values, i.e. 4.88, 5.47 and 5.88 in systR, systB and systO, respectively. The latter two pH values were clearly related to the pH of the loss of solubility of the heated globular proteins. While the gelation pattern for systR resembled unheated milk, the pattern for systB and systO showed the usual maximum for tan δ of heated milk.     

Influence of molecular weight and degree of substitution of carboxymethylcellulose on the stability of acidified milk drinks

The influence of molecular weight (M_w, 250,000, 700,000) and degree of substitution (DS, 0.7, 0.9 and 1.2) of carboxymethylcellulose (CMC) on the diameter and ζ-potential of casein micelles during acidification in diluted dispersions and on the stability of acidified milk drinks was investigated. The experimental results suggested that CMC with high M_w or low DS would result in thick adsorbed layer onto casein micelles. The ζ-potential of CMC-coated casein micelle increased with increasing the M_w of CMC with the same DS while at a fixed M_w the ζ-potential for CMC with high DS (1.2) increased in comparison with those for CMC with low DS (0.7 and 0.9). Both M_w and DS of CMC influenced the stability of acidified milk drinks. CMC with high M_w increased the viscosity of acidified milk drinks significantly and therefore contributed to the stability. CMC with high DS resulted in high ζ-potential of CMC-coated casein micelles, increasing the electrostatic repulsion between casein particles, which prevented the phase separation in acidified milk drinks. It was also found that the amount of CMC needed for efficient coverage of casein micelles increased with increasing the M_w of CMC. Above the efficient coverage concentration, the long-term stability of acidified milk drinks with high M_w CMC was better than that with low M_w CMC.     

Effect of glycerol and vegetable oil on physicochemical properties of Arabic gum-based beverage emulsion

The effect of two emulsion components namely glycerol (0.5, 1 and 1.5% w/w) and vegetable oil (2, 3 and 4% w/w) on ζ-potential, conductivity, pH, apparent viscosity, fluid behavior, turbidity and cloud stability of orange beverage emulsion was investigated. The negatively charged ζ-potential significantly (p < 0.05) increased with increasing glycerol content. A slight increase in ζ-potential was observed by adding 2% (w/w) vegetable oil to the emulsion formulation, while it was slightly decreased when vegetable oil content was increased up to 4% (w/w). Apparent viscosity, pH and turbidity of orange beverage emulsions significantly (p < 0.05) increased when the concentration of glycerol or vegetable oil was increased. All prepared beverage emulsions behaved as non-Newtonian (i.e., pseudoplastic or shear thinning) fluids. The addition of different concentration levels of both supplementary emulsion components except for 0.5% (w/w) glycerol significantly (p < 0.05) improved the cloud stability of orange beverage emulsions.     

Factors that affect the aggregation of rennet-altered casein micelles at low temperatures

The effects of temperature, CaCl₂ concentration, pH and ionic strength of milk on the aggregation of casein micelles in milk renneted at 15ºC were studied using particle size analysis determined by laser-light scattering. The rate of aggregation of rennet-altered casein micelles became significantly slower on reducing the temperature of renneting from 30 to 10ºC. At 15ºC, the rate of aggregation of rennet-altered casein micelles increased significantly on adding CaCl₂, on reducing the pH of renneted milk or on adding NaCl (up to 50 m m ). These results indicate that particle size analysis can be used successfully to study the aggregation of rennet-altered casein micelles.     

Diffusing wave spectroscopy and rheological studies of rennet-induced gelation of skim milk in the presence of pectin and κ-carrageenan

The effect of the presence of κ-carrageenan on casein micelle stability and their rennet-induced aggregation was studied using diffusing wave spectroscopy and rheology measurements. Different concentrations of κ-carrageenan, below the gelation regime, were added to skim milk at pH 6.7. No changes in casein stability and on the aggregation kinetics of casein micelles were observed at κ-carrageenan concentrations <0.015% (w/v). The effect of mixing different concentrations of high methoxyl pectin (HMP) (0.04, 0.12 and 0.18%, w/v) with 0.015% (w/v) κ-carrageenan in skim milk was then studied. It was observed that κ-carrageenan protects the system from HMP-induced destabilization. The study of the synergistic effect of κ-carrageenan and HMP on the structuring of casein micelles in milk opens new avenues for the development and control of processes where different mechanisms of aggregation and destabilization occur simultaneously.     

Structure and physical properties of pectins with block-wise distribution of carboxylic acid groups

The physical and the interfacial properties of pectins de-esterified by a specific block-wise enzymatic procedure were investigated. Two major types of block-wise de-esterified pectins with different internal distribution of carboxylic acid on the pectin chains were explored. Type C and type U pectins with the same degree of methylesterification are different and a more block-wise intramolecular distribution in comparison to commercial native apple pectin. The most ordered pectin (U63 pectin, 63% methylesterified pectin) has the highest electrophoretic mobility (ζ-potential). It reveals more pronounced intermolecular interactions since it exhibited, at low pH, the lowest circular dichroism intensity at shorter wavelength. U63 pectin (at acidic pH, without calcium addition) has a higher viscosity and formed a stronger gel compared to the less ordered C63 pectin and/or native apple pectin. X-ray patterns show that powdered U63 pectin is more crystalline than C63 pectin, while apple pectin is mostly amorphous. The modified pectin also, most effectively, reduced the surface tension (55 mN/m) and the interfacial tension (5.6 mN/m), probably due to the preferred surface orientation of the carboxylic groups at the water/air or water/oil interfaces.     

辛烯基琥珀酸酐酯化改性阿拉伯胶的工艺优化

提纯原始阿拉伯胶(OGA),采用乳化剂替代有机溶剂处理的辛烯基琥珀酸酐(OSA)对阿拉伯胶进行酯化改性。通过单因素和响应面试验优化工艺条件,并研究酯化改性后的阿拉伯胶的性质。试验结果表明:酯化改性的最佳工艺参数为OSA添加量3%(以OGA干重计),OGA质量分数40%,反应pH 8.5,反应时间1.56 h,反应温度23℃。此条件下所得产物中辛烯基琥珀酸的接入量为1.97%。结合粒径、电位及微观结构数据进行分析,发现较高的表观黏度有利于避免乳液中液滴的聚集及分层,酯化改性提高了CGA的乳化性能。