Compositional differences of acid whey (AW) in comparison with other whey types limit its process... more Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.
Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20... more Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20 kHz to investigate the effect of ultrasonication. For fresh skim milk, the average size of the remaining fat globules was reduced by approximately 10 nm after 60 min of sonication; however, the size of the casein micelles was determined to be unchanged. A small increase in soluble whey protein and a corresponding decrease in viscosity also occurred within the first few minutes of sonication, which could be attributed to the breakup of casein-whey protein aggregates. No measurable changes in free casein content could be detected in ultracentrifuged skim milk samples sonicated for up to 60 min. A small, temporary decrease in pH resulted from sonication; however, no measurable change in soluble calcium concentration was observed. Therefore, casein micelles in fresh skim milk were stable during the exposure to ultrasonication. Similar results were obtained for reconstituted micellar casein,...
The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat ha... more The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem. The use of preheating treatments to induce whey protein aggregate formation in whey products is well known in the field. However, we show that the application of ultrasound for a very short duration after such a heating step breaks down these aggregates and prevents their reformation on subsequent heating, thereby reducing the viscosity increase that is usually associated with this process. This novel technique has the potential to provide significant economic benefit to the dairy manufacturing industry.
Low-fat Mozzarella cheeses containing 6% fat were made by preacidification of milk, preacidificat... more Low-fat Mozzarella cheeses containing 6% fat were made by preacidification of milk, preacidification combined with exopolysaccharide- (EPS-) producing starter, used independently or as a coculture with non-EPS starter, and preacidification combined with whey protein concentrate (WPC) and EPS. The impact of these treatments on moisture retention, changes in texture profile analysis, cheese melt, stretch, and on pizza bake performance were investigated over 45 d of storage at 4 degrees C. Preacidified cheeses without EPS (control) had the lowest moisture content (53.75%). These cheeses were hardest and exhibited greatest springiness and chewiness. The meltability and stretchability of these cheeses increased most during the first 28 d of storage. The moisture content in cheeses increased to 55.08, 54.79, and 55.82% with EPS starter (containing 41.18 mg/g of EPS), coculturing (containing 28.61 mg/g of EPS), and WPC (containing 44.23 mg/g of EPS), respectively. Exopolysaccharide reduced...
Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS cult... more Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS culture on the exopolysaccharide (EPS) production by Streptococcus thermophilus 1275 were studied. The organism was grown in 10% reconstituted skim milk (RSM) in a Biostat B fermenter for 24 h at various pH (4.5, 5.5 and 6.5) and temperatures (30, 37, 40, and 42 degrees C), and supplementation with WPC 392, and non-EPS producing S. thermophilus 1303 and the amount of EPS produced were determined. Bacterial counts were enumerated and the concentrations of lactic acid, lactose, glucose, and galactose were also determined. A maximum of 406 mg/L of EPS was produced in RSM at 37 degrees C after 24 h of fermentation at pH 4.08 when the pH was not controlled. A pH of 5.5 and temperature of 40 degrees C were found to be optimal for EPS production by S. thermophilus 1275, yielding 458 mg/L. The EPS production increased when RSM was supplemented with WPC 392. At optimum pH and at 37 degrees C with WPC...
Gelation is a significant operation in dairy processing. Protein gelation can be affected by seve... more Gelation is a significant operation in dairy processing. Protein gelation can be affected by several factors such as temperature, pH, or enzyme addition. Recently, the use of ultrasonication has been shown to have a significant impact on the formation of whey protein gels. In this work, the effect of ultrasonication on the gelation of casein systems was investigated. Gels were formed by the addition of 7.6 mm Tetra Sodium Pyro Phosphate (TSPP) to 5 wt% micellar casein (MC) solutions. Sonication at 20 KHz and 31 W for up to 30 min changed the surface hydrophobicity of the proteins, whereas surface charge was unaltered. Sonication before the addition of TSPP formed a firm gel with a fine protein network and low syneresis. Conversely, sonication after TSPP addition led to an inconsistent weak-gel-like structure with high syneresis. Gel strength in both cases increased significantly after short sonication times, while the viscoelastic properties were less affected. Overall, the results showed that ultrasonication can have a significant effect on the final gel properties of casein systems.
ABSTRACT Concentrated skim milk was treated with high intensity low frequency ultrasound (20 kHz)... more ABSTRACT Concentrated skim milk was treated with high intensity low frequency ultrasound (20 kHz) to lower viscosity through a process of acoustic cavitation. Batch sonication for 1 min at 40–80 W, and continuous treatment delivering an applied energy density of 4–7 J mL−1, reduced the viscosity of medium-heat skim milk concentrates containing 50–60% solids. Viscosity was reduced by approximately 10%, but this improved to >17% in highly viscous age thickened material. Sonication also changed the shear thinning behaviour at shear rates below 150 s−1. Although ultrasound lowered the viscosity of skim milk concentrated to ≥50% solids, the treatment could only delay the rate of thickening once the ageing process was established. It was only when ultrasound was activated during concentration that sonication prevented the viscosity of skim milk concentrates from increasing rapidly.
ABSTRACT In this study, the structural and functional changes of pure and 3:1 mixtures of β-Lacto... more ABSTRACT In this study, the structural and functional changes of pure and 3:1 mixtures of β-Lactoglobulin (β-LG) and α-Lactalbumin (α-LA), the most abundant whey proteins in milk were studied after sonication at 20 kHz (31 W) for up to 60 min. The reactive thiol content and surface hydrophobicity of pure β-LG increased continuously during sonication, suggesting an unfolding of the dimer structure. Minor secondary and tertiary structural changes were also observed by circular dichroism. The α-LA protein appeared to be more strongly affected by sonication, with significant increases in surface hydrophobicity. The results suggest that sonication has a greater effect on α-LA than on β-LG, which means that the properties of their mixture differ substantially from that of either protein in isolation.
Compositional differences of acid whey (AW) in comparison with other whey types limit its process... more Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.
Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20... more Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20 kHz to investigate the effect of ultrasonication. For fresh skim milk, the average size of the remaining fat globules was reduced by approximately 10 nm after 60 min of sonication; however, the size of the casein micelles was determined to be unchanged. A small increase in soluble whey protein and a corresponding decrease in viscosity also occurred within the first few minutes of sonication, which could be attributed to the breakup of casein-whey protein aggregates. No measurable changes in free casein content could be detected in ultracentrifuged skim milk samples sonicated for up to 60 min. A small, temporary decrease in pH resulted from sonication; however, no measurable change in soluble calcium concentration was observed. Therefore, casein micelles in fresh skim milk were stable during the exposure to ultrasonication. Similar results were obtained for reconstituted micellar casein,...
The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat ha... more The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem. The use of preheating treatments to induce whey protein aggregate formation in whey products is well known in the field. However, we show that the application of ultrasound for a very short duration after such a heating step breaks down these aggregates and prevents their reformation on subsequent heating, thereby reducing the viscosity increase that is usually associated with this process. This novel technique has the potential to provide significant economic benefit to the dairy manufacturing industry.
Low-fat Mozzarella cheeses containing 6% fat were made by preacidification of milk, preacidificat... more Low-fat Mozzarella cheeses containing 6% fat were made by preacidification of milk, preacidification combined with exopolysaccharide- (EPS-) producing starter, used independently or as a coculture with non-EPS starter, and preacidification combined with whey protein concentrate (WPC) and EPS. The impact of these treatments on moisture retention, changes in texture profile analysis, cheese melt, stretch, and on pizza bake performance were investigated over 45 d of storage at 4 degrees C. Preacidified cheeses without EPS (control) had the lowest moisture content (53.75%). These cheeses were hardest and exhibited greatest springiness and chewiness. The meltability and stretchability of these cheeses increased most during the first 28 d of storage. The moisture content in cheeses increased to 55.08, 54.79, and 55.82% with EPS starter (containing 41.18 mg/g of EPS), coculturing (containing 28.61 mg/g of EPS), and WPC (containing 44.23 mg/g of EPS), respectively. Exopolysaccharide reduced...
Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS cult... more Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS culture on the exopolysaccharide (EPS) production by Streptococcus thermophilus 1275 were studied. The organism was grown in 10% reconstituted skim milk (RSM) in a Biostat B fermenter for 24 h at various pH (4.5, 5.5 and 6.5) and temperatures (30, 37, 40, and 42 degrees C), and supplementation with WPC 392, and non-EPS producing S. thermophilus 1303 and the amount of EPS produced were determined. Bacterial counts were enumerated and the concentrations of lactic acid, lactose, glucose, and galactose were also determined. A maximum of 406 mg/L of EPS was produced in RSM at 37 degrees C after 24 h of fermentation at pH 4.08 when the pH was not controlled. A pH of 5.5 and temperature of 40 degrees C were found to be optimal for EPS production by S. thermophilus 1275, yielding 458 mg/L. The EPS production increased when RSM was supplemented with WPC 392. At optimum pH and at 37 degrees C with WPC...
Gelation is a significant operation in dairy processing. Protein gelation can be affected by seve... more Gelation is a significant operation in dairy processing. Protein gelation can be affected by several factors such as temperature, pH, or enzyme addition. Recently, the use of ultrasonication has been shown to have a significant impact on the formation of whey protein gels. In this work, the effect of ultrasonication on the gelation of casein systems was investigated. Gels were formed by the addition of 7.6 mm Tetra Sodium Pyro Phosphate (TSPP) to 5 wt% micellar casein (MC) solutions. Sonication at 20 KHz and 31 W for up to 30 min changed the surface hydrophobicity of the proteins, whereas surface charge was unaltered. Sonication before the addition of TSPP formed a firm gel with a fine protein network and low syneresis. Conversely, sonication after TSPP addition led to an inconsistent weak-gel-like structure with high syneresis. Gel strength in both cases increased significantly after short sonication times, while the viscoelastic properties were less affected. Overall, the results showed that ultrasonication can have a significant effect on the final gel properties of casein systems.
ABSTRACT Concentrated skim milk was treated with high intensity low frequency ultrasound (20 kHz)... more ABSTRACT Concentrated skim milk was treated with high intensity low frequency ultrasound (20 kHz) to lower viscosity through a process of acoustic cavitation. Batch sonication for 1 min at 40–80 W, and continuous treatment delivering an applied energy density of 4–7 J mL−1, reduced the viscosity of medium-heat skim milk concentrates containing 50–60% solids. Viscosity was reduced by approximately 10%, but this improved to >17% in highly viscous age thickened material. Sonication also changed the shear thinning behaviour at shear rates below 150 s−1. Although ultrasound lowered the viscosity of skim milk concentrated to ≥50% solids, the treatment could only delay the rate of thickening once the ageing process was established. It was only when ultrasound was activated during concentration that sonication prevented the viscosity of skim milk concentrates from increasing rapidly.
ABSTRACT In this study, the structural and functional changes of pure and 3:1 mixtures of β-Lacto... more ABSTRACT In this study, the structural and functional changes of pure and 3:1 mixtures of β-Lactoglobulin (β-LG) and α-Lactalbumin (α-LA), the most abundant whey proteins in milk were studied after sonication at 20 kHz (31 W) for up to 60 min. The reactive thiol content and surface hydrophobicity of pure β-LG increased continuously during sonication, suggesting an unfolding of the dimer structure. Minor secondary and tertiary structural changes were also observed by circular dichroism. The α-LA protein appeared to be more strongly affected by sonication, with significant increases in surface hydrophobicity. The results suggest that sonication has a greater effect on α-LA than on β-LG, which means that the properties of their mixture differ substantially from that of either protein in isolation.
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