Compositional and functional properties of buttermilk: a comparison between sweet, sour, and whey buttermilk

Buttermilk is a dairy ingredient widely used in the food industry because of its emulsifying capacity and its positive impact on flavor. Commercial buttermilk is sweet buttermilk, a by-product from churning sweet cream into butter. However, other sources of buttermilk exist, including cultured and whey buttermilk obtained from churning of cultured cream and whey cream, respectively. The compositional and functional properties (protein solubility, viscosity, emulsifying and foaming properties) of sweet, sour, and whey buttermilk were determined at different pH levels and compared with those of skim milk and whey. Composition of sweet and cultured buttermilk was similar to skim milk, and composition of whey buttermilk was similar to whey, with the exception of fat content, which was higher in buttermilk than in skim milk or whey (6 to 20% vs. 0.3 to 0.4%). Functional properties of whey buttermilk were independent of pH, whereas sweet and cultured buttermilk exhibited lower protein solubility and emulsifying properties as well as a higher viscosity at low pH (pH ≤ 5). Sweet, sour, and whey buttermilks showed higher emulsifying properties and lower foaming capacity than milk and whey because of the presence of milk fat globule membrane components. Furthermore, among the various buttermilks, whey buttermilk was the one showing the highest emulsifying properties and the lowest foaming capacity. This could be due to a higher ratio of phospholipids to protein in whey buttermilk compared with cultured or sweet buttermilk. Whey buttermilk appears to be a promising and unique ingredient in the formulation of low pH foods.     

Comparative Study on Heat Stability and Functionality of Camel and Bovine Milk Whey Proteins

Heat stability, emulsifying, and foaming properties of camel whey have been investigated and compared with that of bovine whey. Camel whey is similar to bovine whey in composition, but is deficient in β-lactoglubulin (β-LG), a major component of bovine whey. Whether the deficiency in β-LG will affect stability and functional properties is not yet known. Substantial information on the functional properties of bovine milk whey proteins is available; however, there is little research done on functional properties of camel whey proteins. Therefore, the objective of this study was to investigate the heat stability, emulsifying, and foaming characteristics of camel whey proteins. Calorimetric studies showed no significant difference in heat stability between bovine and camel whey proteins in liquid form. Upon drying, thermograms indicated that the 2 proteins are different in composition and thermal stability. The difference is represented in the absence of β-LG and the occurrence of protein denaturation peak at a lesser temperature in camel whey. The first marginal thermal transition in bovine whey appeared at 81°C, followed by 2 other transitions at 146 and 198°C. For camel whey, the transitions appeared at 139, 180, and 207°C respectively. The first marginal denaturation peak in bovine whey is due to β-LG, which is essentially absent in camel whey, while the second peak is due to the mixture of α-lactalbumin, serum albumin, and possibly part of the partially stabilized β-LG structure during the denaturation process. Because camel whey is deficient in β-LG, the denaturation peak at 139 must be due to the mixture of α-lactalbumin and camel serum albumin. In both proteins, the highest thermal transition is due to sugars such as lactose. The solubility study has shown that camel whey is more sensitive to pH than bovine milk whey and that heat stability is lowest near the isoelectric point of the proteins at pH 4.5. The sensitivity to pH resulted in partial denaturation and increased tendency to aggregate, which caused poor and unstable emulsion at pH 5. Both bovine and camel whey proteins have demonstrated good foaming properties; however, the magnitudes of these properties were considerably greater in bovine milk for all of the conditions studied.     

Insulin in bovine colostrum and milk: evolution throughout lactation and binding to caseins.

The changes in insulin concentration in bovine milk in the first period of lactation and its association with other milk proteins were studied. Highest concentration was found in the first milking (327 ng/ml). This concentration fell within the first 24 h postpartum to about 50% of its initial value. By d 3, the level was about 25%, and, on d 7, a stable concentration was reached at approximately 46 ng/ml (about 14% of its initial value). This concentration is about 100 times higher than that in serum, which suggests a specific mechanism of transfer from blood to milk. Colostral whey obtained by ultrafiltration or ultracentrifugation contains much less insulin than colostrum. When colostrum or milk was incubated with [125I]insulin and whey and casein fractions were separated by precipitation, it was observed that most insulin remained with the casein. However, when colostrum was incubated with [125I]insulin and subjected to gel filtration, most of the radioactivity corresponded to free insulin, indicating that insulin is associated with the precipitated casein but not with the casein micelles in solution.     

Effect of heat treatment on milk protein functionality at emulsion interfaces. A review

Heat treatment affects the molecular structure of milk proteins at the interfaces of oil-in-water emulsions and in aqueous media. Experimental evidence of the impact of thermal processing on milk protein structure is presented and the contribution of whey proteins and caseins at film formation during emulsification is discussed. Recent advances in understanding the effect of heat treatment in milk protein functionality at emulsion interfaces are reviewed with particular emphasis on the emulsifying ability of whey proteins with or without the presence of the casein fraction. The major findings regarding the destabilizing mechanisms of oil-in-water emulsions brought about by heat-induced denaturation of milk proteins are presented. This paper aims to combine recent knowledge on how thermal processing of milk proteins affects their molecular configurations in bulk and particularly at interfaces, which in turn appear to be important with respect to the physico-chemical properties of milk protein-stabilized emulsions.     

Functional and technological aspects of whey powder and whey protein products

Commercial whey powder, whey protein concentrates and whey protein isolates (WPIs) were evaluated for certain functional properties and for their application in full‐fat and nonfat yoghurts. The functional properties of whey products varied, and the highest functionality was recorded in samples with high protein levels. Whey powder had the lowest foaming performance and emulsifying capacity, while WPIs possessed the best functional properties of all the other samples. Curd tension (CT), viscosity and syneresis were improved in yoghurts made using fortified cow's milk or reconstituted skim milk with any whey products, while whey powder had no impact on CT.     

蛋白含量对牦牛乳清蛋白浓缩物功能特性的影响

通过不同截留分子质量的再生纤维素膜过滤纯化牦牛原乳清液和牦牛甜乳清液,分别制取牦牛原乳清蛋白浓缩物（native whey protein concentrate,NWPC）和牦牛甜乳清蛋白浓缩物（sweet whey protein concentrate,SWPC）,研究蛋白含量不同的乳清蛋白浓缩物（whey protein concentrate,WPC）主要成分（乳糖含量、pH值和总蛋白质含量）和功能特性（溶解性、持水性、持油性、起泡性、乳化性及热稳定性）的特征。结果表明：10 000 Da再生纤维素膜透析得到的牦牛WPC中总蛋白含量达到80%以上,不含乳糖,功能特性（溶解性、持水性、持油性、起泡性、乳化性及热稳定性）均显著高于经3 500 Da卷式膜、5 000 Da再生纤维素膜透析得牦牛WPC,WPC蛋白含量越高,其功能特性越好;不同蛋白含量的牦牛SWPC起泡能力、泡沫稳定性、乳化活性和乳化稳定性均显著（P＜0.05）高于牦牛NWPC。牦牛乳WPC最不稳定温度为85 ℃,高于荷斯坦牛乳WPC的80 ℃,热处理会适当改善牦牛WPC的起泡性能、乳化性能和热稳定性。通过膜牦牛处理获取的高蛋白含量的WPC,功能特性较好,应用广泛,对解决牦牛乳清资源的利用问题、保护环境、提高企业的经济效益起到关键性作用。     

A comparison of the buttermilk solids functional properties to nonfat dried milk,soy protein isolate,dried egg white,and egg yolk powders

Physicochemical (i.e., sulfhydryl group, protein, and total solubility) as well as functional properties (i.e., water-holding and fat-absorption capacity, foaming and emulsification capacity, and stability) of commercial buttermilk solids (BMS) were compared to nonfat dried milk, soy protein isolate, and dried egg yolk and egg white powders on an equivalent protein basis. BMS showed limited functional properties in water-holding capacity (0.75 g water/g protein) and fat-absorption capacity (1.2 g of oil/g of protein), and foaming capacity (0.5 ml of foam/ml of solution) and stability. However, emulsifying capacity and stability of BMS was not significantly different from other dried protein powders. Results indicated that 0.9 g of protein (approximately 0.45%, wt/vol, concentration) from BMS was needed to emulsify a maximum oil concentration of 50% in water at temperatures up to 50 degrees C. Denaturation of protein, quantified by free sulfhydryl groups, was a critical factor affecting the functionality of BMS and all other protein powders tested. The milk fat globule membrane present in BMS did not enhance either emulsifying capacity or stability.     

pH treatment as an effective tool to select the functional and structural properties of yak milk caseins

Qula is made from yak milk after defatting, acidifying, and drying. Yak milk caseins are purified from Qula by dissolving in alkali solution. The effects of different pH treatments on the functional and structural properties of yak milk caseins were investigated. Over a broad range of pH (from 6.0 to 12.0), functional properties of yak milk caseins, including solubility, emulsifying activities, and thermal characteristics, and the structural properties, including 1-anilino-8-naphthalene-sulfonate fluorescence, turbidity and particle diameter, were evaluated. The results showed that the yak milk casein yield increased as the pH increased from 6.0 to 12.0. The solubility dramatically increased as the pH increased from 6.0 to 8.0, and decreased as the pH increased from 9.0 to 12.0. The changes in emulsifying activity were not significant. Caseins were remarkably heat stable at pH 9.0. The turbidity of the casein solution decreased rapidly as the pH increased from 6.0 to 12.0, and the results suggested that reassembled casein micelles were more compact at low pH than high pH. At pH values higher than 8.0, the yield of yak milk caseins reached more than 80%. The highest solubility was at pH 8.0, the best emulsification was at pH 10.0 and the greatest thermal stability was at pH 9.0. According to the functional characteristics of yak milk caseins, alkali conditions (pH 8.0–10.0) should be selected for optimum production. These results suggested that pH-dependent treatment could be used to modify the properties of yak milk caseins by appropriate selection of the pH level.     

鳙鱼鱼肉蛋白的酶解及其对功能性质的影响

为了改善鳙鱼鱼肉蛋白(BCMP)的功能性质以扩大其在食品工业中的应用,以鳙鱼为原料制备了鳙鱼鱼肉蛋白,并利用碱性蛋白酶Alcalase2.4L对其进行水解,得到了3种不同水解度(DH4.5%、DH9.0%、DH13.5%)的酶解物。研究了BCMP及其酶解物的功能性质,包括溶解性、持水性、持油性、乳化性、起泡性。结果表明,与原鳙鱼鱼肉蛋白相比,酶解物的功能性质除持油性以外均有不同程度的提高。此外,DH4.5%的酶解物乳化性和起泡性最高,过度水解(DH9.0%、DH13.5%)反而造成乳化性和起泡性下降。     

Colostral constituents including immunoglobulins in the first three milkings postpartum

Colostral changes in immunoglobulin (IgG), dry matter, ash, total protein, and whey protein were studied over the first three milkings postpartum. Immunoglobulin IgG concentration in colostrum from Holstein cows beginning their first, second, or third lactation was similar. However, older animals had more IgG in colostrum. Its rate of disappearance from colostrum was greater in younger animals. Dry matter, ash, total protein, and whey protein concentrations decreased from the first to the third milking (24 h) postpartum. Protein was the most variable constituent between cows at the same postpartum time.     

Relationship between physicochemical and functional properties of amaranth (Amaranthus hypochondriacus) protein isolates

Protein isolates from six amaranth lines/cultivars (APIs) were evaluated to study their physicochemical (hunter colour, protein content and zeta potential), structural (thermal and conformational) and functional (emulsification, foaming, water and fat absorption) properties. APIs had protein content, whiteness index and gel temperature in range of 79.4–85.4%, 41.17–54.26 and 87.8–91.8 °C, respectively. The Fourier‐transform infrared spectra of APIs revealed α‐helix, β‐sheets and random coil conformations in the secondary structure. APIs with higher relative proportion of β‐sheets had higher Differential Scanning Calorimeter denaturation temperature and gel temperature. Minimum protein solubility (PS) was observed at pH 5.0, indicating isoelectric point (pI) of amaranth proteins. The PS, emulsifying activity index (EAI), emulsifying stability index (ESI), foaming capacity (FC) and foam stability (FS) of APIs at neutral pH were related to their zeta potential (ζ). The emulsifying and foaming properties were also determined at different pHs (between 2.0 and 9.0). The EAI‐pH profile of APIs confirmed close relationship between the emulsifying ability and PS.     

Acid gelation properties of fibrillated model milk protein concentrate dispersions

Whey proteins in milk are globular proteins that can be converted into fibrils to enhance functional properties such gelation, emulsification, and foaming. A model fibrillated milk protein concentrate (MPC) was developed by mixing micellar casein concentrate (MCC) with fibrillated milk whey proteins. Similarly, a control model MPC was obtained by mixing MCC with milk whey proteins. The resulting fibrillated model MPC and control model MPC contained 5% protein and a ratio of casein to whey proteins similar to milk. The objective of the current study was to understand the rheological characteristics of fibrillated and control model MPC during acid gelation, using Förster resonance energy transfer (FRET) to assess small amplitude oscillation and casein–whey protein interaction. The results from the FRET index images showed greater interactions between caseins and whey proteins in fibrillated model MPC compared with the moderate and uniform interactions in control model MPC gels. Rheological study showed that the maximum storage modulus of acid gel of fibrillated model MPC was 546.9 ± 15.5 Pa, which was significantly higher than acid gel made from control model MPC (336.9 ± 11.3 Pa), indicating that fibrillated model MPC produced a firmer gel. Therefore, it can be concluded that acid gel produced from fibrillated model MPC was stronger than control model MPC. Selective fibrillation of the whey protein fraction in MPC can be used to improve gelation characteristics of acid gel type products.     

大豆乳清蛋白功能特性的研究

对经过膜分离技术提取的大豆乳清蛋白的功能特性进行研究。主要研究了pH对大豆乳清蛋白的溶解特性、起泡性能及乳化性能的影响,并对大豆乳清蛋白的组成成分进行了电泳分析。结果表明,大豆乳清蛋白具有较好的溶解性及起泡性,但泡沫稳定性及乳化性不如大豆分离蛋白。大豆乳清蛋白主要包含6种成分。     

桃仁清蛋白与大豆分离蛋白功能特性比较研究

为提高桃仁清蛋白(PKA)在食品工业中的应用,将其与大豆分离蛋白(SPI)对照,研究了PKA的溶解性、持水性、持油性、起泡性及泡沫稳定性、乳化性及乳化稳定性和凝胶性等功能特性.结果表明:与SPI相比,PKA具有很好的溶解性、泡沫稳定性、乳化稳定性及较低的凝胶质量浓度,持油性略高于SPI,但起泡性、乳化性及持水性较差;PKA溶解性受溶解条件影响较小.PKA具有良好的功能性质,适合作为食品添加剂或配料.     

Enzymatic and extrusion pretreatments of defatted rice bran to improve functional properties of protein concentrates

This study evaluated effects of enzymatic, extrusion and combined pretreatments on functional and thermal properties of protein concentrates from defatted rice bran to improve their applicability to food formulations. After the pretreatments, protein concentrates were recovered by alkaline solubilisation and isoelectric point precipitation. Water absorption capacity, oil absorption capacity, emulsifying and foaming properties, and thermal stability were determined in protein concentrates. Yields of each pretreatment were above 62% protein. Enzymatic hydrolysis increased all functional properties studied, mainly for emulsifying activity index (an increase of 71.1%) and foaming capacity (an increase of 60.3%). The extrusion affected positively the oil absorption capacity, emulsifying activity index and foaming capacity. The combined process was able to raise the functional properties. The principal component analysis confirmed that 95.5% improvement in functional properties of concentrates had a strong positive correlation with the pretreatments. However, the pretreatments affected thermal stability and the enthalpy of denaturation negatively.     

Changes in physical properties of bovine milk from the colostrum period to early lactation

The aim of this study was to analyze individual cows’ samples from the colostrum, postcolostrum, and early lactation periods to investigate how milk composition, physical properties, stability, and suitability for processing change throughout this period. Attention was paid to the first week postpartum in which the composition of bovine mammary secretion can change markedly. Properties including pH, titratable acidity, ethanol stability (ES), rennet clotting time, and casein micelle size were analyzed, together with some compositional factors such as fat, total protein, lactose, total and ionic calcium, magnesium, citrate, phosphorus, sodium, and potassium. Total Ca (36.2 mM) and free ionic Ca (2.58 mM), Mg (5.9 mM), P (32.2 mM), and Na (24.1 mM) appeared to be high on d 5 postpartum, having decreased substantially over the first 5 d; they gradually decreased thereafter. The average pH on d 5 was only 6.49, compared with 6.64 at 1 mo postpartum. Stability measurements showed that the average ES on d 5 was 70% and the rennet clotting time was 12.2 min, which were significantly lower than values at later stages. A number of milk properties including ES, pH, protein content, and Ca²⁺ concentration could be useful for identifying the point of transition from colostrum to the early lactation period. Knowing the composition and physical properties of colostrum and postcolostrum secretions will help establish when such milk is suitable for processing and determine the best use for that milk.     

Seasonal variations in composition,properties, and heat-induced changes in bovine milk in a seasonal calving system

We determined seasonal variations in the composition and characteristics of bovine milk, as well as heat-induced changes in the physicochemical properties of the milk, in a typical seasonal-calving New Zealand herd over 2 full milking seasons. Fat, protein, and lactose contents varied consistently during the year in patterns similar to those of the lactation cycle. Seasonality also had significant effects on milk calcium, ionic calcium, fat globule size, buffering capacity, and ethanol stability, but not on casein micelle size. The ratio of casein to total protein did not vary significantly over the season, but late-season milk had the highest content of glycosylated κ-casein (G-κ-CN) and the lowest content of α-lactalbumin in both years. We observed significant between-year effects on protein, total calcium, ionic calcium, pH, and casein:total protein ratio, which might have resulted from different somatic cell counts in the 2 years. Compared with heating at 90°C for 6 min, UHT treatment (140°C for 5 s) induced greater dissociation of κ-casein, a similar extent of whey protein denaturation, a lower extent of whey protein–casein micelle association, and a larger increase in casein micelle size. Indeed, UHT treatment might have triggered significant dissociation of G-κ-CN, resulting in aggregation among the casein micelles and increased apparent mean casein micelle diameter. Seasonality had significant effects on the partitioning of G-κ-CN between the micelle and the serum phase, the extent of whey protein–casein micelle association under both heating conditions, and the casein micelle size of the UHT milk.     

EFFECT OF ENZYMATIC HYDROLYSIS ON SOME FUNCTIONAL PROPERTIES OF WHEY PROTEIN

A study was undertaken to further elucidate the functional properties of whey protein with respect to foaming and emulsifying capacities and to observe the effect of enzymatic hydrolysis on these properties. Emulsion capacity decreased as proteolysis continued suggesting there is an optimum mean molecular size of the proteins involved which is lower than that of casein. Heat treatment of the reconstituted protein concentrate was necessary for foam stability; specific volume and foam stability increased directly with temperature of heating. Re effect of pH on whippability, data indicate that the greater the net charge the greater the tendency to foam. A limited amount of hydrolysis appears desirable to increase foaming but greatly decreases foam stability.     

猪血蛋白肽功能性质的研究

试验测定了猪血蛋白肽的化学成分和等电点,研究了pH、蛋白肽浓度对猪血蛋白肽溶解性、浊度、乳化性、乳化稳定性、起泡性和起泡稳定性的影响。结果表明:本试验所用猪血蛋白肽蛋白含量为85.03%;等电点为pH5,在等电点时,其溶解性、乳化性、乳化稳定性和起泡性最小,而浊度、起泡稳定性在这点最大;温度在50℃时蛋白肽开始变性,高于50℃时蛋白质的溶解性降低,浊度增加。     

Effect of Whey Pretreatment on Composition and Functional Properties of Whey Protein Concentrate

The effect of pretreatment upon the composition and physicochemical and functional properties of whey, ultrafiltration (UF) retentate and freeze-dried and spray-dried whey protein concentrates (WPC) was investigated. Pretreatment was by cooling cheese whey to 0-5°C, adding calcium chloride, adjusting to pH 7.3, warming to 50°C, and removing the insoluble precipitate that formed by centrifugation or decantation. UF permeation flux rate of pretreated whey was about double that for control whey. Pretreated whey was essentially turbidity free, contained 85% less milkfat, 37% more calcium and 40% less phosphorus than whey. Pretreated whey WPC proteins were slightly more soluble at pH 3, but less functional for emulsification than whey WPC proteins. Neither whey WPC proteins nor pretreated whey WPC proteins was functional for foaming at 6% protein concentration.