Protease-Induced Aggregation and Gelation of Whey Proteins

Aggregation and gelation of whey proteins induced by a specific protease from Bacillus licheniformis was revealed by turbidimetry, size exclusion chromatography, dynamic light scattering and rheology. The microstructure of the gel was examined by transmission electron microscopy. During incubation of 12% whey protein isolate solutions at 40°C and pH 7, the major whey proteins were partly hydrolyzed and the solution gradually became turbid due to formation of aggregates of increasing size. The viscosity of the hydrolysate simultaneously increased and eventually a gel formed. The gel had a particulate type of microstructure. We hypothesized that the aggregates forming the gel were held together by noncovalent interactions.     

Gelation and Emulsification Properties of Partially Insolubilized Whey Protein Concentrates

Ultrafiltered retentate of whey was heat-processed to prepare whey protein concentrates (WPC) with protein solubilities ranging from 27.5% to 98.1% in 0.1M NaCl, pH 7.0. Proximate and protein compositions of each WPC were determined. Properties of 20% (w/w) protein WPC gels in 0.1M and 0.6 M NaCl, pH 7.0, on heating to 60, 70, 80, and 90°C and emulsification properties of WPC (0.5% (w/w) protein) in 0.1M NaCl at pH 6.0, 7.0 and 8.0 were analyzed. Gel apparent stress and strain at failure decreased and expressible moisture increased as solubility decreased from 98.1% to 41.0% at all heating temperatures. Emulsification Activity Index was highest at pH 7.0, emulsions were most stable at pH 8.0.     

Gelation Properties of Lipid-Reduced, and Calcium-Reduced Whey Protein Concentrates

Gels made from six experimental whey protein concentrate (WPC) processes using chemical pretreatment, ultrafiltration and microfiltration (MF) of Swiss cheese whey, and three commercial WPC, were compared for rheological, microstructural and sensory properties. Based on relations between shear stress (ST) and total sulfhydryl levels, we contirmed that disulfide bonding is important in gelation. Other components, i.e., lipids, lactose, calcium and sodium, interacting simultaneously, affected gel formation. Gel water holding capacity (WHC) was related to microstructure but not to ST. WHC was useful to characterize the 3-dimensional gel structure formations. Light microscopy showed the strongest gel had a fine-stranded, solvent-retaining structure.     

Factors Affecting the Functional Properties of Whey Protein Products: A Review

Numerous why protein products (WPP) have been developed as excellent food ingredients with unique functional properties. However, the functional properties of WPP are affected by several compositional and processing factors. Recently, novel processing technologies such as high hydrostatic pressure, ultrasound, extrusion and tribomechanical activation have been used to modify the functional properties of WPP. Also, WPP have been used as delivery systems for functional ingredients and in edible films. The present paper reviews the latest developments in the role of different factors on the functional properties of WPP with emphasis on novel processing technologies, and interaction with other food ingredients     

Protein and Salt Effects on Ca2+-Induced Cold Gelation of Whey Protein Isolate

Increasing whey protein concentration (from 6 to 10% w/v) decreased gel opacity but increased gel strength and water-holding capacity (WHC). Increasing CaCl₂, concentration (from 5 to 150 mM) increased gel opacity and gel strength at the high protein concentration (i.e., 10%). However, it lowered gel strength at protein concentration > 10%. Young's modulus and distance to fracture values indicated that gels were most rigid at 30 mM CaCl₂, at which point the extent of aggregation (measured by turbidity) was the highest. Increasing CaCl₂ concentration from 5 to 150 mM slightly affected the WHC of Ca²⁺-induced gels. Protein concentration was the major factor in determining fracture properties and WHC.     

Factors Affecting the Gelation Properties of Hydrolyzed Sunflower Proteins

The effects of temperature and several chemicals on gelation time and strength of gels formed by heating (pH 8) 5% solutions of trypsin hydrolyzed sunflower proteins were studied by dynamic rheological methods. The storage modulus reached a maximum at 80°C. Ca₂Cl (and NaCl at > 0.2M) accelerated gelation and weakened the gel. NaCOCH₃Na₂SO₄ and NaSCN decreased the storage modulus. Urea decreased gelstrength and at high concentrations slowed gelation. Time for gelation diminished and gel strength increased with increasing mercaptoethanol concentration up to 0.1M. Propylene glycol at 5–20% concentrations accelerated gelation and at 5% also increased gel strength. Trypsin hydrolyzed sunflower proteins could be useful in products requiring strong gels at high temperatures.     

Gelation of Commercial Whey Protein Concentrates: Effect of Removal of Low-Molecular-Weight Components

Low-molecular-weight solutes were removed from reconstituted, commercial whey protein concentrate (WPC) and isolate (WPI) by centrifugal gel filtration. Effects on gelation properties were investigated as a function of pH, protein concentration, and mineral ion addition by least concentration endpoint (LCE) and uniaxial compression testing. Partial removal of low-molecular-weight solutes had little effect on WPC and WPI gelation. Lowest LCE values were obtained at pH 6, 0.2M ion addition, and with KC1 and CaCl₂ addition. Highest gel firmness (shear stress and strain) values were at pH 6 and 7.5, and at 0.1M ion addition. WPI functioned better than WPC by both test procedures.     

Whey protein concentrates and isolates: Processing and functional properties

Substantial progress has been made in understanding the basic chemical and structural properties of the principal whey proteins, that is, β‐lactoglobulin β‐Lg), α‐lactalbumin (α‐La), bovine serum albumin (BSA), and immunoglobulin (Ig). This knowledge has been acquired in terms of: (1) procedures for isolation, purification, and characterization of the individual whey proteins in buffer solutions; and (2) whey fractionation technologies for manufacturing whey protein concentrates (WPC) with improved chemical and functional properties in food systems. This article is a critical review of selected publications related to (1) whey fractionation technology for manufacturing WPC and WPI; (2) fundamental properties of whey proteins; and (3) factors that affect protein functionality, that is, composition, protein structure, and processing.     

Gelation of Calcium-Reduced and Lipid-Reduced Whey Protein Concentrates as Affected by Total and Ionic Mineral Concentrations

Rheological and microstructural properties of five dialyzed whey protein concentrate (WPC) gels were investigated. Maximum WPC gel hardness as determined by shear stress (ST) was observed at 2.7–4.5 mM Ca and 0.6–1.1 mM Ca²⁺ concentrations with a Ca ionization of 20–25%. Gel cohesiveness by shear strain (SN) correlated with total lipid and phospholipid (PLP) concentrations and percent of lipid unsaturation. Microstructural characteristics of the gels, as determined by light microscopy (LM), confirmed their water holding capacity (WHC) and rheological properties.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

Chemical Pretreatment and Microfiltration for Making Delipidized Whey Protein Concentrate

Chemical pretreatment, microfiltration (MF) and ultrafiltration (UF) were applied to produce delipidized whey protein concentrates (WPC). Processes including both chemical pretreatment and MF resulted in WPC with <0.5% lipids. Low-pH UF and isoelectric point (PI) precipitation were more effective for lipid removal than chemical pretreatment by thermocalcic aggregation. Protein permeation ratios in MF processes were improved by UF preconcentration of whey. Protein permeation and flux were different between the two MF membranes used. Isoelectric point precipitation increased β-Lg contents, but not α-La, in the resulting WPC (B). Minor proteins exhibited lower concentrations in WPC B and MF WPC products.     

乳清浓缩蛋白可食用包装膜的研制

以乳清浓缩蛋白为基质,通过加入成膜剂、增塑剂制得可食用包装膜。研究了不同成膜剂添加量、不同增塑剂添加量、不同转谷氨酰胺酶添加量对成膜的影响。通过响应面分析表明,制备乳清浓缩蛋白可食用膜的最佳条件是：乳清浓缩蛋白浓度10%、添加山梨醇5%、无水氯化钙1.2166%、转谷氨酰胺酶0.018%,在60~65℃的温度范围成膜。     

Foaming Properties of Lipid-Reduced and Calcium-Reduced Whey Protein Concentrates

The ability of whey protein concentrates (WPC) to form highly expanded and stable foams is critical for food applications such as whipped toppings and meringue-type products. The foaming properties were studied on six experimental and three commercial WPC, manufactured by membrane fractionation processes to contain reduced lipids and calcium. Lipid-reduced WPC had excellent foaming properties. Experimental delipidized WPC MF 0.45 and commercial delipidized WPC E had higher (P < 0.05) foam expansion than egg white protein (EWP). However. WPC B made bv low-pH UF and isoelectric orecinitation did not form a foam. Lipids and ash were the main factors affecting foaming properties.     

Hydrolysates from Proteolysis of Heat-denatured Whey Proteins

Whey protein isolate was denatured at 85°C, pH 4.6 for 30 min to produce heat denatured whey protein isolate (HDWPI) which was hydrolyzed with trypsin, chymotrypsin, Alcalase or Neutrase to 2.8, 4.3, 6.0 or 8.0% degree of hydrolysis (DH). Analysis of freeze-dried fractions revealed a linear increase in primary amino groups, non-protein nitrogen and ash contents. Polyacrylamide gel electrophoresis showed that high and intermediate molecular weight peptides were converted to lower molecular weights with progress of hydrolysis. Differences in proteolysis patterns were observed with different enzymes. The time required to achieve equivalent hydrolysis at 1, 2, 3 or 4% enzyme/substrate ratio varied with the type of enzyme and DH.     

乳清浓缩蛋白可食用膜成膜工艺的研究

研究了乳清浓缩蛋白可食用膜的成膜工艺,分析了蛋白质浓度、甘油浓度和加热温度对可食用膜透水性和透氧性的影响,并确定了可食用膜阻隔性能的优化工艺参数。研究结果表明,可食用膜的阻水性随蛋白质浓度和甘油浓度的增大而下降,阻氧性随甘油浓度增大而下降。加热温度为70℃时,膜的阻水性和阻氧性达到最佳。响应面分析表明,当蛋白质浓度为100 g/L,甘油浓度为27 g/L,加热温度为69℃时,乳清浓缩蛋白可食用膜的综合通透性能为最佳,其透湿系数为0.004 35 g·mm/(m~2·h·kPa),透氧系数为0.134 cm~3·mm/(m~2·min·kPa)。     

Heat-induced Gelation Properties of Salt-Soluble Muscle Proteins as Affected by Non-Meat Proteins

Addition of whey protein concentrate (WPC), whey protein isolate (WPI) or soy protein isolate (SPI) to salt-soluble muscle proteins (SSP) decreased the gel strength. WPI:SSP gels had higher water-holding capacity than SSP, SSP:WPC or SSP:SPI gels. Myosin heavy chain was a principal contributor to gel network formation in SSP, SSP:WPC, SSP:WPI and SSP:SPI systems. The characteristic fibrous network formed by SSP was the dominant feature of the microstructure of SSP:WPC and SSP:WPI gels. SSP:SPI gels had a more aggregated appearance due to the occurrence of clusters of SPI throughout the gel matrix.     

转谷氨酰胺酶催化大豆蛋白和乳清蛋白合成耐热性聚合蛋白

用商品级转谷氨酰胺酶(TG-B)聚合大豆蛋白和乳清蛋白形成高耐热、耐酸的蛋白聚合物。蛋白聚合物的合成量由SDS-PAGE电泳结合凝胶成像分析测定;蛋白聚合物的耐热性用差示扫描量热法(DSC)测定;蛋白聚合物的酸溶解性用双缩脲法测定。结果表明TG-B聚合大豆蛋白和乳清蛋白形成的蛋白聚合物的最适条件为pH为6～7;反应温度30℃～45℃,反应时间4h,加酶量为6当量单位/g蛋白,在此条件下蛋白聚合物的转化量可达30%,所合成蛋白聚合物可耐130℃的热处理而不发生变性;并在pH3.2～4.3范围不发生沉淀。     

乳清蛋白-茁霉多糖-阿魏酸复合可食性膜的研制

以乳清浓缩蛋白、茁霉多糖、阿魏酸为成膜材料,制备乳清浓缩蛋白-茁霉多糖-阿魏酸复合膜。分别对复合膜的厚度、刺穿强度、拉伸强度、水蒸气透过系数、含水量和溶解性等性能进行测试,研究成膜材料添加量和成膜条件与复合膜性能的关系。结果表明:乳清浓缩蛋白中添加茁霉多糖和阿魏酸作为增强剂,可明显提高膜的性能。最优工艺条件为成膜温度80℃,pH9.0,阿魏酸添加量200 mg/100 mL,茁霉多糖添加量150 mg/100 mL。     

Flow Properties, Firmness and Stability of Double Cream Cheese Containing Whey Protein Concentrate

As estimated on-line, the viscosity after cooling of double cream cheese curd containing heat-denatured WPC (DCC +) increased from 1.4 Pa.s to 1.7 Pa.s when cooled to the range of 45°C to 24°C, and then decreased from 1.7 Pa.s to 1.0 Pa.s when cooled from 24°C to 15°C. The viscosity of DCC^- (without heat-denatured WPC) increased from 1.5 Pa.s to 2.2 Pa.s at temperature shift from 40°C to 15.5°C. The firmness of stored DCC + and DCC^-, respectively, decreased from 15.1N to 6.5N when cooled to temperatures from 45°C to 15°C, and from 17.9N to 9.9N when cooled from 40°C to 15.5°C, as recorded by cone penetrometry. The structure of DCC+ cooled to 15°C collapsed after penetrometry, and DCC+ cooled to 20°C destabilized during shearing in coaxial cylinder rheometer. A new phase in DCC+ based on milk fat globules liberated by cluster disruption may be the cause of the structural and textural instability.     

Thermally Induced Interactions and Gelation of Combined Myofibrillar Protein from White and Red Broiler Muscles

The gelling properties of broiler myofibrillar protein were studied by determining protein-protein interactions during heating. Breast and leg salt-soluble protein (SSP) showed 1–3 transitions in protein-protein interactions within pH 5.5–6.5. The maximum transition temperatures of leg SSP decreased when leg SSP was mixed with breast SSP. The combined breast/leg myofibrils formed stronger gels than leg myofibrils alone at pH ≥ 6.0, and stronger gels than breast myofibrils alone at pH < 6.0. The results suggest that interactions existed between breast and leg myofibrillar proteins, and the transitions in these interactions were useful for predicting gel strength of the combined breast/ leg myofibrils.