The effect of cooking and washing temperature during pilot-scale rennet casein manufacture on casein hydration characteristics in disodium orthophosphate solution

Variations were observed in the hydration behaviour of rennet caseins in a solution (0.4%, w/w) of disodium orthophosphate (DSP). These caseins were manufactured on a pilot scale from curds cooked at 45, 65 or 75°C and from curds washed at a hot-wash temperature of 60, 70, 78 or 86°C. The influence of cooking temperature and hot-wash temperature on various compositional characteristics, the electrophoretic resolution and particle size parameters of the milled rennet caseins were determined. Relationships between all of these parameters and hydration characteristics in DSP solution were also investigated. Cooking temperature or hot-wash temperature did not influence electrophoretic resolution, the level of Maillard reaction compounds or the particle size parameters of the caseins. Increasing the cooking temperature increased whey protein levels and decreased calcium levels in the curd, leading to slower hydration rates. This suggested that increased whey protein denaturation and its precipitation onto the rennet casein curd retarded subsequent rennet casein hydration. Hot-wash temperature influenced certain aspects of rennet casein hydration in 0.4% (w/w) DSP; however, the hydration characteristics of these caseins did not appear to be related to any of the other characteristics investigated.     

Rennet caseins manufactured from seasonal milks: composition, hydration behaviour and functional performance in pilot-scale manufacture of mozzarella cheese analogues

Compositional and hydration properties of edible rennet caseins prepared from Irish milks over three production seasons were studied. The ash content of the caseins declined during early to mid-lactation and increased sharply in late-lactation. Protein content was independent of season of manufacture, while moisture content showed no clear relationship to season of manufacture. The hydration properties of the rennet caseins on dispersion in a solution of a calcium-sequestering salt were assessed in a simple model system relevant to mozzarella cheese analogue manufacture. The maximum viscosity index reached and the time taken to reach maximum viscosity index on dispersion of rennet casein both decreased as the season of manufacture progressed. Poor performance of rennet caseins in pilot-scale mozzarella cheese analogue manufacture was observed for some caseins manufactured from both early lactation milks and late-lactation milks, while caseins manufactured from mid-lactational milks generally performed well in pilot-scale mozzarella cheese analogue manufacture.     

曲拉凝乳酶干酪素生产工艺研究

优化了曲拉凝乳酶干酪素的生产工艺,并通过中试实验验证。设计正交实验对影响曲拉溶解速率的4个因素、改善曲拉凝乳酶干酪素色泽的4种护色剂配比和曲拉溶解液离心脱脂效果的3个因素工艺参数进行了优化,实验结果确定了曲拉溶解的最佳工艺参数:pH10.5,温度55℃,搅拌转速300r/min,物料浓度10%;4种护色剂最佳配比:低亚硫酸钠0.2%、亚硫酸氢钠0.2%、乙二胺四乙酸二钠0.05%、焦亚硫酸钠0.23%;曲拉溶解液离心脱脂的最佳工艺:重力环内径为108mm、进料流量为2.5t/h、排渣间隔时间为5min。对15批次产品进行感官评价和理化检测,感官评价结果:呈淡黄色粉末,无嗅无味;各项目理化检测平均结果为:蛋白质91.0%,脂肪0.6%,乳糖0.19%,水分10.3%,灰分5.0%,pH7.07。工艺优化后,原料曲拉的溶解速率提高20.7%;曲拉凝乳酶干酪素感官指标得到很好改善;脂肪质量分数下降了50%,同时其他理化指标均优于优化前指标,大大提高了产品品质。      

酶凝干酪素生产过程中酶凝工艺的优化

研究了凝乳酶添加量、凝乳温度和凝乳时间对酶凝干酪素酶凝工艺的影响,通过对凝乳过程的感官评价,最终确定了酶凝干酪素的最佳酶凝工艺参数。结果表明:凝乳温度和凝乳时间对酶凝干酪素酶凝状态有显著影响,确定最优工艺条件为:凝乳酶添加量的体积分数为0.078%,凝乳温度为32℃,凝乳时间28 min。此条件下生产的酶凝干酪素与市售酶凝干酪素理化指标接近。     

Influences of rennet and container types on proteolysis of traditional Kurdish cheese during the ripening

The effect of rennet and container types was evaluated on proteolysis of traditional Kurdish cheese during 60 days ripening. The enzymes involved were commercial chymosin and traditional rennet from lamb abomasum. Goat skin (traditional container) and plastic containers were used as storage containers. The trend of proteolysis was determined by measuring the content of nitrogen (N) in compounds soluble in water, 12% trichloroacetic acid and 5% phosphotungstic acid along with the urea–polyacrylamide gel electrophoresis method. The results showed that the nitrogen in compounds soluble in water, 12% trichloroacetic acid and 5% phosphotungstic acid was higher in ripened cheeses into plastic containers; however, the containers had no significant effect on the breakdown of α‐ and β‐caseins (P < 0.05). Using commercial rennet caused the breakdown of α‐ and β‐caseins and the level of nitrogen in compounds soluble in water to increase. Finally, however, the amount of α‐ and β‐caseins breakdown was trivial, and α‐casein was decreased more than β‐casein in all samples.     

Effect of manufacture and reconstitution of milk protein concentrate powder on the size and rennet gelation behaviour of casein micelles

Samples of raw skim milk, ultrafiltration/diafiltration retentate, concentrated retentate and milk protein concentrate powder (MPC80) from a single commercial production run were analysed using photon correlation spectroscopy. Measurements revealed insignificant differences in casein micelle size between the samples. In addition, there was no discernable difference between raw skim milk and MPC powder dissolved at 60 °C in the amount of casein remaining in supernatants from centrifugation at either 25,000 × g or 174,200 × g. Casein micelles did not appear to be altered during manufacture of MPC. The rennet gelation behaviour of reconstituted MPC was compared with raw skim milk. Reconstituted MPC did not coagulate unless supplemented with approximately 2 mm calcium chloride, which was attributed to the mineral removal during ultrafiltration/diafiltration. Addition of sufficient calcium could restore rennet coagulation kinetics and gel strength of reconstituted MPC to approximately that of raw skim milk.     

Effect of inlet temperature on the physicochemical properties of spray-dried seed-watermelon seed protein powder

Here, we studied the effects of inlet temperature on the physicochemical properties of the hydrolyzed protein (seed-watermelon seed hydrolyzed protein [SWSP]) powder in seed-watermelon seeds. The inlet temperature of the study was in the range of 150 to 180 °C, and the remaining experimental parameters remained constant, that is, the feed flow rate was 0.2 L/hr, the concentration of maltodextrin was 30%, and the outlet temperature was 80 °C. We studied the water activity and moisture content, bulk density, flowability (Carr index and Hausner ratio), angle of repose, solubility, color, hygroscopicity, powder morphology, particle size, crystallinity, and odor of the sample. Inlet temperature of 170 to 180 °C reduced the moisture content and increased the particle size. It was found that the value of measured water activity was less than 0.5, which helped in maintaining stability of the sample. Powders produced at the temperatures showed smoother particle surfaces, whereas higher inlet temperature showed spherical particles with some shrinkage as analyzed by scanning electron microscope. The inlet temperature affected the color of the sample, thus at high temperature, the sample had a brighter color. The sample was approximately 18% crystalline. At a preparation temperature of 160 °C, the sample showed significant antioxidant activity (P < 0.05).     

喷雾干燥入口温度对草莓粉品质的影响

研究喷雾干燥入口温度对草莓粉品质的影响。当喷雾干燥入口温度由160℃升高到180℃时,草莓粉在水中溶解时间延长,草莓粉的晶型转变温度由41.8℃提高至47.3℃,水分活度由0.108下降到0.0887,花青素含量下降20.3%;草莓粉的粒径分布峰值由9.21μm下降到8.00μm,粒径分布宽度由11.39μm下降到10.85μm;同时,草莓粉的包埋率下降、颜色变浅、表面形态发生变化。在喷雾干燥入口温度为170℃时,草莓粉的包埋率最高达94.1%,粒径分布最均匀,稳定性较高。      

Influence of the degree of hydration on the thermal expansion of muscle tissue

The variation of expansivity, α, of beef M. semitendinosus with moisture content was determined by measurement of the temperature change induced by adiabatic compression over the moisture content range 2 to 90%, at temperatures (T) of 1, 8 and 15°C. At low levels of hydration, α increased with moisture content, reached a maximum around 35% water, and thereafter decreased. The data suggested that thermal expansivity is related to water binding, and the application of a simple expansivity model based on 'free' water, 'bound' water and dry-solids, gave a value for the expansivity of 'bound' water at 8°C of 8.9±1.7x10-⁴°C-¹, about seventeen times that of 'free' water.     

Effect of temperature and aggregation rate on the fractal dimension of renneted casein aggregates

This study deals with the influence of chymosin/casein ratios and temperature on the fractal dimension of renneted casein aggregates in diluted milk. The angular dependence of static light scattering, from 50 to 110 degrees, was used to determine fractal dimension from double logarithmic plots of intensity versus scattering vector. No significant effect was observed when varying chymosin/casein ratios from 3.3 to 79.2 microg of chymosin/g of casein at 30 degrees C with a resultant fractal dimension value of 2.20. Temperature, on the other hand, influenced the aggregation mechanisms with fractal dimension values equaled to 2.32, 2.22, and 2.15 at 25, 30, and 35 degrees C, respectively, for a chymosin/casein ratio at 13.2 microg of chymosin/g of casein. The importance of hydrophobic interactions in fractal aggregation of renneted casein particles is discussed.     

提高劣质原料生产的干酪素色泽质量的研究

在生产干酪素过程中，加碱、加热及混入其他杂质，都会促进酪蛋白中的赖氨酸与还原糖发生美拉德反应，影响干酪素的质量。用美拉德初始产物羟甲基糖醛（HMF）值作为美拉德反应程度的标准，分别对抗氧化剂Na2SO3、H2O2的作用，烘干温度、杀菌温度的选定，酸沉、碱溶的效果进行初步探讨，为解决该生产问题进行初步尝试。     

Effect of chelating salt type on casein hydration and fat emulsification during manufacture and post-manufacture functionality of imitation cheese

Imitation cheese (50% moisture) was manufactured in a Farinograph using different ratios of disodium orthophosphate (DSP) and trisodium citrate (TSC) as chelating or emulsifying salts (ES). The ES:casein ratio was kept constant at 0.2549 mol ES/kg casein. The effects of DSP:TSC ratio on cheese manufacture and post-manufacture functional properties were investigated. Hardness, assessed by texture profile analysis, heat-induced flowability and dynamic rheology were studied. Microstructural analyses were performed using light and cryo-scanning electron microscopy. Increasing the DSP:TSC ratio from 0:1 to 1:0 caused a decrease in processing times (from ∼18 to 12 min) and lowering of the final mixing torque values (from ∼180 to 20 F.U.) and, post-manufacture led to a decrease in cheese hardness (from ∼360 to 165 N) and G′ values at 25 °C (from ∼81 to 38 kPa) and to increased cheese fat globule size (from ∼8 to 32 μm). The results suggest that changing the ratio of DSP:TSC may be used to alter cheese properties, but both ES are needed for optimum functionality.     

Influence of mixtures of calcium-chelating salts on the physicochemical properties of casein micelles

Calcium-chelating salts (CCS), such as phosphates and citrates, are often added to milk systems to modify physical properties like heat stability. The objective of this study was to investigate the effect of binary CCS mixtures on the properties of casein (CN) micelles including the distribution of Ca between the soluble and CN-bound states. Six binary CCS mixtures were prepared from 4 different types of CCS [i.e., trisodium citrate (TSC), disodium phosphate (DSP), tetrasodium pyrophosphate (TSPP), and sodium hexameta phosphate (SHMP)] by combining 2 CCS at a time in 5 different proportions (8.3:91.7, 29.2:70.8, 50:50, 70.8:29.2, and 91.7:8.3). Different concentrations of these mixtures (0, 0.1, 0.3, 0.5, and 0.7% wt/wt) were added to milk protein concentrate solutions (5% wt/wt) at pH 5.8. The ability of CCS to disperse CN particles and its interaction with Ca were assessed from turbidity measurements, acid-base titration behavior, and the quantity of CN-bound Ca and inorganic phosphate (Pi). Turbidity and the buffering peak at pH ∼5.0 during acid titration decreased with an increasing concentration of CCS. This was due to the chelation of Ca and the dispersion of CN micelles. The presence of TSC in mixtures decreased the amount of CN-bound Ca and Pi; however, the presence of TSPP in mixtures increased CN-bound Ca and Pi. When DSP was present at high proportions in mixtures of CCS, the CN-bound Ca and Pi slightly increased. When SHMP was used in mixtures of CCS, CN-bound Ca and Pi increased with the use of a low proportion of SHMP but decreased when SHMP was used at high proportions in the mixture. Combinations of DSP-TSPP used in the proportions 29.2:70.8, 50:50, and 70.8:29.2 resulted in the gelation of milk protein concentrates when the total CCS concentration was ≥0.3%. These results indicated that the type of CCS present in a mixture modified CN properties by various mechanisms, including chelation of Ca, dispersion of CN micelles, and formation of new types of Ca-CCS complexes. The type of interaction between the newly formed Ca-CCS complexes and the dispersed CN depended on the proportion, concentration, and type of CCS present in the mixtures. This information is useful in understanding how mixtures of CCS affect CN properties.     

Effects of varying casein and pectin concentrations on the rheology of high-protein cultured milk beverages stored at ambient temperature

Shelf-stable cultured milk beverages that have high protein levels can be difficult to successfully manufacture. With increasing protein level, rapid phase separation and gel formation occur in cultured beverages, which may not be prevented even with the inclusion of stabilizers such as high methoxy (HM) pectin. To limit protein aggregation in cultured milk beverages we investigated micellar casein as an interesting alternative to milk, due to the absence of whey proteins, which can contribute to increased gel strength in cultured products. In this study, micellar casein dispersed in ultrafiltered milk permeate was fermented to pH 4.1, blended with HM pectin, homogenized, thermally processed, and bottled for storage at ambient temperature for 6 mo. Utilizing response surface methodology with a central composite rotatable design, the protein and pectin contents were varied between 5 and 9% and 0.0 and 1.0%, respectively. The elastic modulus, loss tangent, and yield stress of these beverages were measured during storage to observe the extent of bond restructuring, whereas particle size and visual phase separation were measured to determine stability. Response variables were measured initially after thermally processing the beverages, and after 1 and 6 mo of storage at ambient temperature. All samples quickly formed gels after homogenizing, regardless of the pectin level. The stiffness (elastic modulus) of all samples increased throughout storage and was determined mainly by the protein content; however, the growth of elastic bonds over time was slowed with high levels of pectin. At 6 mo of storage, yield stress values were significantly lower for beverages with <7.5% protein when they were stabilized with ≥0.85% pectin. Prediction models for visual phase separation in beverages stored for 6 mo were significantly affected by the protein content, with increasing instability at lower protein levels. Models were used to identify optimal protein (<7.5%) and pectin (≥0.85%) concentrations to minimize the stiffness of gels during ambient storage. Samples in this optimized region were predicted to have low yield stress values and were easily fluidized by gentle shaking of the bottle at 6 mo.     

The effect of varying the calcium-sequestering salt cation on the hydration behaviour of rennet caseins in a simple model system

Di potassium orthophosphate and di-ammonium orthophosphate were used to replace di-sodium orthophosphate in a simple model of cheese analogue manufacture. Rheological changes that occurred as eight rennet caseins, possessing widely differing hydration behaviour, were dispersed in solutions of the different calcium-sequestering salts were determined. Dispersion in the potassium salt resulted in minor differences in hydration behaviour of rennet caseins when compared to the behaviour in di-sodium orthophosphate solution, while dispersion in the ammonium salt resulted in considerably modified hydration behaviours and rheological profiles.     

Effect of cation, sodium or potassium, on casein hydration and fat emulsification during imitation cheese manufacture and post-manufacture functionality

Imitation cheeses (48 g moisture/100 g cheese), in which the salt (NaCl) and sodium emulsifying salts were partially or wholly replaced with their potassium equivalents were manufactured. The effect of the replacement on manufacture and post-manufacture functionality (microstructure, texture, flowability, dynamic rheology and NMR T₂ relaxometry) was assessed. The replacement of sodium salts with potassium equivalents led to decreased torque values throughout the manufacture and to slight changes in functional properties including increased fat globule size and flowability, decreased hardness and cohesiveness. The potassium-salt cheeses exhibited adhesiveness, which was absent in the standard cheese, and also showed lower microbial stability.     

Modelling the effect of temperature on the hydration kinetic of adzuki beans (Vigna angularis)

The Aw reduction is a widely used technique to preserve grains, which hydration kinetics needs to be studied in order to obtain optimized processes. This work evaluated the hydration kinetic of Adzuki beans, a widely consumed grain by the oriental culture, modelling its behaviour as function of temperature. The grains were soaked in water and the moisture over the time was evaluated at temperatures of 25–70 °C. The grain behaviour during water uptake showed an initial lag phase, with a low water absorption rate. Therefore, the hydration kinetic was evaluated using a sigmoidal model (R² > 0.99). When soaking temperature was increased the hydration rate increased and both the lag phase and the moisture at the equilibrium decreased. These behaviour were, then, modelled as function of the soaking temperature (R² > 0.99). The obtained results are potentially useful for future studies on product development, food properties and process design.     

Pepsin-induced changes in the size and molecular weight distribution of bovine casein during enzymatic hydrolysis

Bovine casein was digested with pepsin at pH 2.0 in a batch-stirred tank reactor. To investigate the effect of peptic digestion on the aggregate size and molecular weight distribution of bovine casein, the resulting hydrolysates were examined by size-exclusion chromatography coupled with multiangle laser light scattering and dynamic light scattering. Casein was resolved by size-exclusion chromatography into 2 major peaks corresponding to aggregates and monomers, both of which showed a continuous decrease as hydrolysis proceeded. However, the ratio of aggregates to monomers was maintained at almost 1 (2:2.5) during the initial 30-min hydrolysis, indicating that the caseins in solution were in a type of equilibrium between aggregates and monomers. Upon peptic hydrolysis, casein aggregates increased in size and molecular weight, and exhibited a decrease in intermolecular repulsion. This finding was confirmed by dynamic light scattering measurements, which traced the changes in the hydrodynamic radii and light scattering intensities of casein hydrolysates. In addition, the release kinetics of peptide fractions with different molecular weights was also examined. It was concluded that the increase in hydrophobic attraction and the reduction in intermicellar repulsion might promote the growth in aggregate size of bovine casein during the limited hydrolysis.     

Effect of solvent and temperature on the size distribution of casein micelles measured by dynamic light scattering

The objectives of this study were to investigate the effect of the solvent on the accuracy of casein micelle particle size determination by dynamic light scattering (DLS) at different temperatures and to establish a clear protocol for these measurements. Dynamic light scattering analyses were performed at 6, 20, and 50°C using a 90Plus Nanoparticle Size Analyzer (Brookhaven Instruments, Holtsville, NY). Raw and pasteurized skim milk were used as sources of casein micelles. Simulated milk ultrafiltrate, ultrafiltered water, and permeate obtained by ultrafiltration of skim milk using a 10-kDa cutoff membrane were used as solvents. The pH, ionic concentration, refractive index, and viscosity of all solvents were determined. The solvents were evaluated by DLS to ensure that they did not have a significant influence on the results of the particle size measurements. Experimental protocols were developed for accurate measurement of particle sizes in all solvents and experimental conditions. All measurements had good reproducibility, with coefficients of variation below 5%. Both the solvent and the temperature had a significant effect on the measured effective diameter of the casein micelles. When ultrafiltered permeate was used as a solvent, the particle size and polydispersity of casein micelles decreased as temperature increased. The effective diameter of casein micelles from raw skim milk diluted with ultrafiltered permeate was 176.4 ± 5.3 nm at 6°C, 177.4 ± 1.9 nm at 20°C, and 137.3 ± 2.7 nm at 50°C. This trend was justified by the increased strength of hydrophobic bonds with increasing temperature. Overall, the results of this study suggest that the most suitable solvent for the DLS analyses of casein micelles was casein-depleted ultrafiltered permeate. Dilution with water led to micelle dissociation, which significantly affected the DLS measurements, especially at 6 and 20°C. Simulated milk ultrafiltrate seemed to give accurate results only at 20°C. Results obtained in simulated milk ultrafiltrate at 6°C could not be explained based on the known effects of temperature on the casein micelle, whereas at 50°C, precipitation of amorphous calcium phosphate affected the DLS measurement.     

葡萄糖对脱脂乳酪蛋白胶束稳定性的影响研究

研究了葡萄糖添加量、体系pH、热处理温度、热处理时间对脱脂牛乳酪蛋白胶束稳定性的影响。研究表明,在接近中性pH条件下,少量葡萄糖分子可降低脱脂乳酪蛋白胶束的稳定性,大量葡萄糖分子可增强其稳定性。添加葡萄糖后,在高温热处理的诱导下,酪蛋白沉淀的pH升高。随着热处理时间的延长,脱脂乳中酪蛋白胶束表现出聚集行为,致使粒径增大,浊度和沉淀率总体呈现上升趋势。该研究结论可为乳品加工提供参考依据。