Effects of disulphide bonds between added whey protein aggregates and other milk components on the rheological properties of acidified milk model systems

Micro- and nanoparticulated whey protein (MWP, NWP) were added to non-fat milk model systems and processed into chemically (glucono-delta-lactone) acidified milk gels. Model systems contained 5% protein in total and were made at two levels of casein (2.5% and 3.5%, w/w) with and without the thiol-blocking agent N-ethylmaleimide. The systems were characterised in terms of thiol groups, gel electrophoresis, particle size, and rheology during processing (homogenisation, heat treatment and acidification). The results showed that the formation of disulphide-linked structures in milk model systems was closely related to the increased particle size and rheological behaviour of the gels. MWP enriched systems produced, upon acidification, weak protein networks and required the addition of whey protein isolate (WPI) to increase gel strength. However, systems containing NWP exhibited pronounced increase in particle size and higher firmness of acidified gels through both covalent and non-covalent interactions.     

The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt

Yoghurt was manufactured from goat's milk and supplemented with 30 g L^?1 of whey protein concentrate (WPC). The textural properties of the yoghurt were evaluated during the shelf‐life of the product and the textural characteristics of yoghurt made from cow's milk were used as a reference. The instrumental analyses used were the puncture test, stress relaxation test and texture profile analysis. The addition of WPC to goat's milk enhanced the textural characteristics of yoghurt. These advantageous attributes included increased firmness, hardness and adhesiveness. These attributes were quantitatively similar (P > 0.05) to those obtained from yoghurt made from cow's milk. In addition, the textural properties were maintained constant throughout the shelf‐life of the product.     

Rheological, textural and microstructural features of probiotic whey cheeses

Whey cheeses have been manufactured with probiotic bacteria - viz. Bifidobacterium animalis Bo and Lactobacillus casei LAFTI^®L26, from combinations of bovine whey and milk, following protein denaturation at 90 °C; they were subsequently inoculated (at 10%) with those strains, and homogenized afterwards; additives such as salt and sugar were then incorporated; and the resulting solid matrices were stored at 7° C for up to 21 d. Oscillatory measurements and instrumental texture profile analyses were performed, and sensory analyses were carried out by a trained panel. Microstructural features were in addition ascertained by scanning electron microscopy.L. casei exhibited a higher acidifying activity than B. animalis, which produced distinct textures; higher firmness and viscoelasticity were indeed found in matrices inoculated with the former. Incorporation of sugar and L. casei favoured consumer acceptability, relative to plain matrices. Microstructural differences were detected between matrices at different times of storage and formulated with distinct additives.     

The influence of added whey protein/carrageenan gels and tapioca starch on the textural properties of low fat pork sausages

Response surface methodology (RSM) was used for simultaneous analysis of the effects of added high gelling 35% whey protein concentrate, (0-12%)/carrageenan (0-3%) preformed gels with dry addition of tapioca starch (0-3%), on the physical, textural and sensory characteristics of low-fat fresh pork sausages. Experimental design allowed for evaluation of potential interactive effects between these ingredients. Sausages were evaluated for cookloss, water holding capacity (WHC), mechanical texture and sensory attributes. Analysis of variance of regression models showed that ingredient blends had a significant influence on cookloss (p<0.01), WHC (p<0.05), purgeloss (p<0.05), texture (p<0.001) and the sensory attributes of flavour intensity (p<0.05), overall flavour (p<0.01) and juiciness (p<0.001). Addition of preformed gel and tapioca starch had a significant (p<0.01) negative interactive effect on % cook loss, and gave a significant (p<0.05) positive linear effect for mechanical textural values. Increasing levels of preformed gel blends with tapioca starch resulted in a general decrease in flavour intensity and overall flavour scores. Mixed gels containing high gelling 35% (protein) whey protein concentrate (8%) and carrageenan (1.5%), with dry addition of tapioca starch (3%) produced final low-fat (<3% fat) pork sausages with similar characteristics to those of full-fat (20% fat) controls.     

Effects of polymerized goat milk whey protein on physicochemical properties and microstructure of recombined goat milk yogurt

Goat milk whey protein concentrates were manufactured by microfiltration (MF) and ultrafiltration (UF). When MF retentate blended with cream, which could be used as a starting material in yogurt making. The objective of this study was to prepare goat milk whey protein concentrates by membrane separation technology and to investigate the effects of polymerized goat milk whey protein (PGWP) on the physicochemical properties and microstructure of recombined goat milk yogurt. A 3-stage MF study was conducted to separate whey protein from casein in skim milk with 0.1-µm ceramic membrane. The MF permeate was ultrafiltered using a 10 kDa cut-off membrane to 10-fold, followed by 3 step diafiltration. The ultrafiltration-diafiltration-treated whey was electrodialyzed to remove 85% of salt, and to obtain goat milk whey protein concentrates with 80.99% protein content (wt/wt, dry basis). Recombined goat milk yogurt was prepared by mixing cream and MF retentate, and PGWP was used as main thickening agent. Compared with the recombined goat milk yogurt without PGWP, the yogurt with 0.50% PGWP had desirable viscosity and low level of syneresis. There was no significant difference in chemical composition and pH between the recombined goat milk yogurt with PGWP and control (without PGWP). Viscosity of all the yogurt samples decreased during the study. There was a slight but not significant decrease in pH during storage. Bifidobacterium and Lactobacillus acidophilus in yogurt samples remained above 10⁶ cfu/g during 8-wk storage. Scanning electron microscopy of the recombined goat milk yogurt with PGWP displayed a compact protein network. Results indicated that PGWP prepared directly from raw milk may be a novel protein-based thickening agent for authentic goat milk yogurt making.     

Investigation on the microstructural and textural properties of Lighvan cheese produced from bovine milk fortified with protein and gum tragacanth during ripening

The effect of 0.02% gum tragacanth, sodium caseinate or milk protein concentrate (MPC70) on the physiochemical, microstructural and textural properties of Lighvan cheese produced from bovine milk was investigated. The microstructure of cheese samples was studied by scanning electron microscopy (SEM), and the SEM micrographs were analysed using 3D images, surface plots and binarised SEM images. The texture parameters of bovine Lighvan cheese containing sodium caseinate were similar to those of ovine Lighvan cheese, and the microstructure of the MPC‐containing bovine Lighvan cheese was closest to that of ovine Lighvan cheese.     

Effect of anthocyanin-absorbed whey protein microgels on physicochemical and textural properties of reduced-fat Cheddar cheese

Reduced-fat foods have become more popular due to their health benefits; however, reducing the fat content of food affects the sensory experience. Therefore, it is necessary to improve the sensory acceptance of reduced-fat foods to that of full-fat equivalents. The aim of this study was to evaluate the effect of adding whey protein microgels (WPM) with an average diameter of 4 μm, or WPM with adsorbed anthocyanins [WPM (Ant)] on the textural and sensory properties of reduced-fat Cheddar cheese (RFC). Reduced-fat Cheddar cheese was prepared in 2 ways: (1) by adding WPM, designated as RFC+M, or (2) by adding WPM (Ant), designated as RFC+M (Ant). For comparison, RFC without fat substitutes and full-fat Cheddar cheese were also prepared. We discovered that the addition of WPM and WPM (Ant) increased the moisture content, fluidity, and meltability of RFC, and reduced its hardness, springiness, and chewiness. The textural and sensory characteristics of RFC were markedly inferior to those of full-fat Cheddar cheese, whereas addition of WPM and WPM (Ant) significantly improved the sensory characteristics of RFC. The WPM and WPM (Ant) showed a high potential as fat substitutes and anthocyanin carriers to effectively improve the acceptance of reduced-fat foods.     

Zeta potential of pectin-stabilised casein aggregates in acidified milk drinks

High-methoxy (HM) pectin is commonly used to improve the stability of acidified milk drinks (AMDs) and zeta potential measurements can aid in elucidating the mechanisms responsible for the improved stability. Pectin was added to an AMD model system in concentrations of 0.0%, 0.1%, 0.3% or 0.5% and the samples were subjected to heat treatment at 75 °C for 20 min; control samples were not heated. A change in zeta potential from positive to negative values with addition of pectin was observed. Increasing the pectin concentration resulted in a more negative zeta potential. Heat treatment caused a decrease in the numeric value of the zeta potential, which indicates a partial desorption of pectin from the protein aggregates.     

紫薯对炼乳流变及质构特性的影响

将紫薯粉添加至炼乳中,研制一种新型调制炼乳。向炼乳中添加质量分数为0.5%～2.5%的紫薯粉,研究炼乳体系流变、质构及微观结构的变化,并对其影响机理进行初步探讨。结果表明,紫薯炼乳表现出假塑性流体行为,流动曲线最符合Power Law模型。紫薯炼乳具有一定触变性,紫薯粉添加量低于1.5%时炼乳形变较易恢复。黏弹性测试表明,紫薯粉添加量大于1.5%时,炼乳表现出固体行为。质构测试表明,紫薯粉添加量低于2.5%时,炼乳在20℃下贮藏5个月浓稠度和黏度均较稳定。扫描电镜显示,紫薯粉添加量越高,炼乳内部网络结构表面越光滑致密。添加紫薯粉会对炼乳流动行为和食用品质产生影响,该文可为调制炼乳的工业化加工提供有效指导。     

Effect of polysaccharides with different ionic charge on the rheological,microstructural and textural properties of acid milk gels

The effects of addition of polysaccharides with different ionic charge on rheology, microstructure, texture and water holding capacity (WHC) of acid milk gels were studied and compared to that of gelatin addition. Similar to gelatin, starch (neutral) and xanthan gum (anionic) did not prevent milk gelation in the first 30 min of the acidification stage, even at high concentrations, and the typical casein network in acid milk gels could still be seen from electron micrographs; gelling and melting of these hydrocolloids were observed during the cooling and heating stages at specific concentrations. On the other hand, two neutral polysaccharides, guar gum (≥ 0.05%) and locust bean gum [LBG] (≥ 0.1%) inhibited milk gelation from the beginning of the acidification stage; the microstructure of the gel was modified greatly and no gelling/melting was observed during the cooling or heating stages. Another anionic polysaccharide, carrageenan, induced earlier milk gelation at low concentration (≤ 0.05%), but inhibited gelation entirely at high concentration (0.2%); inflections at ~ 27 °C and 21 °C were also observed during the cooling and heating stages at 0.05% concentration. The gel microstructure was not changed greatly, but showed smaller particle size at a carrageenan concentration of 0.05% than control sample. None of the polysaccharides showed as much improvement in WHC of the milk gels as gelatin did. Hence, xanthan and starch were found to be closer to gelatin in their effect on acid milk gels compared to guar gum, LBG and carrageenan.     

Effects of various whey proteins on the physicochemical and textural properties of set type nonfat yoghurt

In this study, the changes during storage in the physicochemical, textural and sensory properties of nonfat yoghurts fortified with whey proteins, namely whey protein concentrates (WPC), whey protein isolates and whey protein hydrolysates, were investigated. Enrichment of nonfat yoghurt with the whey protein additives (1% w/v) had a noticeable effect on pH, titratable acidity, syneresis, water‐holding capacity, protein contents and colour values on the 14th day of storage (P < 0.01). The addition of whey proteins to the yoghurt milk led to increases in the hardness, cohesiveness and elasticity values, resulting in improved textural properties. The addition of WPC improved the texture of set‐type nonfat yoghurt with greater sizes in the gel network as well as lower syneresis and higher water holding capacity. This study suggests that the addition of whey protein additives used for fortification of yoghurt gave the best textural and sensory properties that were maintained constant during the shelf life.     

Effect of sesame protein isolate in partial replacement of milk protein on the rheological,textural and microstructural characteristics of fresh cheese

Soft cheeses were manufactured from bovine milk with the addition of 0–12% sesame protein isolate (SPI) were utilised to investigate rheology, texture and microstructure at different stages of cheese making. SPI addition reduced the speed of milk fermentation, kappa‐casein proteolysis of rennet and elongated the time of cheese curd formation. Renneted milk storage modulus G′_60min was decreased and coagulation time increased with increasing SPI content. Low SPI supplements (4% and 8%) enhanced the hardness, cohesiveness, adhesiveness and gumminess of the soft cheese, while high SPI addition (12%) deteriorated the texture. In the cheese curd gel matrix, SPI distributed as specific SPI‐gel clusters on the surface of curd fractures, stacked or fused with ball‐shaped casein micelles and wrapped up to casein gel strands. In summary, SPI actively interacted with casein colloid throughout the cheese making process.     

果胶对酸性乳饮料稳定作用的研究

通过测定添加不同含量的果胶对酸性乳饮料的沉淀率、粘度、粒径分布、水分子流动性及Zeta电位的影响,研究了果胶对酸性乳饮料的稳定作用。结果表明,果胶对酸性乳饮料的稳定作用表现为使产品的沉淀率降低,粘度升高,在微观性质上表现为使产品的粒径减小,水分流动性减弱,Zeta电位的绝对值升高。      

Effects of protein and fat levels in milk on cheese and whey compositions

Bulk tank milk was standardised to six levels of fat (3·0, 3·2, 3·4, 3·6, 3·8, 4·0%) and similarly to six levels of protein, thus giving a total of 36 combinations in composition. Milk was analyzed for total solids, fat, protein, casein, lactose and somatic cell count and was used to make laboratory-scale cheese. Cheese samples from each batch were assayed for total solids, fat, protein and salt. Losses of milk components in the whey were also determined. Least squares analysis of data indicated that higher protein level in milk was associated with higher protein and lower fat contents in cheese. This was accompanied by lower total solids (higher moisture) in cheese. Inversely, higher fat level in milk gave higher fat and lower protein and moisture contents in cheese. Higher fat level in milk resulted in lower retention of fat in cheese and more fat losses in the whey. Higher protein level in milk gave higher fat retention in cheese and less fat losses in the whey. Regression analysis showed that cheese fat increased by 4·22%, while cheese protein decreased by 2·61% for every percentage increase in milk fat. Cheese protein increased by 2·35%, while cheese fat decreased by 6·14% per percentage increase in milk protein. Milk with protein to fat ratio close to 0·9 would produce a minimum of 50% fat in the dry matter of cheese.     

Interactions in heated milk model systems with different ratios of nanoparticulated whey protein at varying pH

To better understand the interactions between nanoparticulated whey protein (NWP) and other milk proteins during acidification, milk model systems were diluted to 0.5% protein concentration and adjusted to pH of 6.0–4.5 following homogenisation and heat treatment. The diluted systems with different concentrations of NWP (0–0.5%) were characterised in terms of particle size, viscosity, surface charge and hydrophobicity. When pH was adjusted to 5.5, aggregation was initiated at levels of NWP (0.25–0.5%) leading to significant increase in particle size and viscosity. Pure NWP (0.5%) showed largest initial surface charge (−27 mv) and higher surface hydrophobicity than the other systems. The results indicated that NWP could self-associate above pH 5.5 and not only the decrease of electrostatic repulsion but also other interactions, such as hydrophobic interaction, play an important role in contributing to the early self-association of NWP.     

牛乳清蛋白与甘薯淀粉加热混合凝胶物化及微观结构特性的研究

研究了不同pH和NaCl、CaCl2浓度对WPI凝胶及WPI与甘薯淀粉混合凝胶物化特性和微观结构的影响。结果表明:随着pH的增加,凝胶的硬度和溶解度减小,添加淀粉进一步降低了混合凝胶的溶解度;盐浓度的增加使混合凝胶硬度增加,而蛋白溶解度、持水力和巯基含量则呈下降趋势;添加NaCl和CaCl2的混合凝胶分别呈现出多孔网状和颗粒状结构。     

The effect of pre-denatured whey proteins on the textural and micro-structural properties of model processed cheese spreads

Whey proteins (WP) were heated in a scraped-surface heat exchanger to produce products with different levels of denaturation. Model processed cheese spreads containing the WP were prepared. Rheological measurements showed that higher levels of denaturation in the WP produced softer (lower elastic modulus) cheeses. Temperature scans indicated that the cheeses prepared with high levels of native whey proteins did not melt (the elastic modulus was higher than the viscous modulus at all temperatures), whereas those prepared with high levels of denatured whey proteins melted on increasing the temperature. Microstructural examination of selected cheeses indicated that, when denatured whey proteins were used in processed cheeses, the whey proteins were incorporated as large aggregates dispersed within the cheese matrix. These aggregates did not contribute to, and may disrupt the structure of the cheese. When native whey proteins were used, they were incorporated into the cheese matrix, producing a denser network structure.     

Effects of different milk substitutes on pasting, rheological and textural properties of puddings

Commercial pudding powders are usually composed of starch, hydrocolloids, sugars, colorings and aromas, and are intended to be dissolved in milk. However, the use of milk substitutes is mandatory for people suffering from lactose intolerance and milk allergies, but these ingredients have an effect on pudding structure and rheological behavior that has been little studied. This work investigates the pasting, rheological and textural behavior of two commercial pudding powders dissolved in rice drink, light soy drink, partially skimmed milk (reference sample), and water (model system). The eight different puddings were evaluated both during preparation (heating and cooling phases) and a 3 day refrigerated storage period, by means of viscoamylographic tests, rotational and oscillatory measurements, and penetration tests. The two pudding powders, apparently similar in formulation, resulted in final products with large structural differences, that could be ascribed to different types and quantity of starch and carrageenans present in the formulation. Soy and rice drinks can not be indifferently used for pudding production, as the optimal texture of the final product is not always achieved. Generally, the properties of soy drink-based puddings were similar to those of the reference samples, while the characteristics of rice drink-based products were comparable to those of the water systems.