Effect of power ultrasound pre-treatment on the physical and functional properties of reconstituted milk protein concentrate
Introduction
Milk protein products are widely used valuable ingredients in the food and dairy industries; these products made a major contribution in the development of new food products. Traditional milk protein products are produced by acid or rennet precipitation, which involves the application of high heat or pH adjustments that denature the whey protein. Milk protein concentrate (MPC) powders are manufactured through ultrafiltration (UF), diafiltration (DF), and optional evaporation of the retentate prior to spray drying. These processes are relatively moderate without heat treatment and pH adjustment; hence, MPC contains undenatured casein and whey proteins. Compared with skim milk powders, MPCs have less lactose and higher amounts of protein. The casein/whey protein ratio of MPC is similar to that of skim milk powder. MPCs are crucial in the production of cheese, confectionary, yoghurt, and other food products. Generally, the protein powder needs to be dispersed and fully dissolved before it can be utilized. Therefore, prior dissolution of MPC in water must be as rapid as possible at room temperature with moderate agitation to minimize operating costs. However, MPC powders are poorly soluble because of their high protein content (40–90%), which restricts their applications. Several researchers have focused on different ways to improve the solubility of MPC powders in cold water. Examples include the addition of monovalent ions prior to spray drying (Carr et al., 2002), removal of calcium ions using a cation exchanger (Bhaskar et al., 2003, Dybing et al., 2003), acidification to lower pH followed by UF/DF or addition of a calcium chelating agent (Schuck et al., 2002, Bhaskar et al., 2003), and high shear treatment of the milk concentrates prior to spray drying (Augustin et al., 2012).
In contrast to low-intensity ultrasound (typically less than 1 W cm−2, with a frequency range of 5–10 MHz), high-intensity ultrasound (HIUS), which uses much higher power levels (typically in the range of 10–1000 W cm−2, with a frequency range of 20–1000 kHz), causes physical disruption of the material and promotes certain chemical reactions (Mason, 1998). HIUS has been applied in many processes, including homogenization, cutting, drying, and extraction, inactivation of microbes and enzymes, degassing of liquid foods, nucleation, and even preparation of submicron emulsions (Bhaskaracharya et al., 2009, Camino et al., 2009, Knorr et al., 2004).
Several studies have focused on the effect of HIUS treatment on whey proteins (Wang et al., 2008, Jambrak et al., 2008, Guzey et al., 2006) and soy proteins (Jambrak et al., 2009). Augustin et al. (2012) examined the effect of various shear treatments (homogenization, microfluidization, or ultrasonication) of UF/DF concentrates on the solubility of MPC. Their work demonstrated that the solubility of MPC powder can be improved by ultrasonication.
To date, systematic studies on the effects of ultrasonication treatment on the functionality of MPCs are lacking. In the present work, skim milk retentate was treated with power ultrasound (PUS) at different durations to evaluate the influence of PUS pre-treatment on the solubility, emulsification, and other functional characteristics of MPC powder.
Section snippets
Materials
Raw cow’s milk was obtained from the dairy farm of the China Agriculture University. The raw milk was composed of 3.4% (w/w) protein, 4.5% (w/w) lactose, and 4.0% (w/w) fat (data collected from Beijing Dairy Cattle Center). The raw milk was kept at 4 °C until use.
Sample preparation
The fat content of the raw milk was removed by a disc bowl centrifuge (FT15, Armfield Company, UK). MPC was manufactured through UF of skim milk with DF. Pasteurized skim milk (60 kg) was heated to 50 °C and ultrafiltered to approximately
pH and conductivity
The pH and conductivity of the samples did not change significantly (p > 0.05) upon PUS pre-treatment with probe (Table 1).
Jambrak et al. (2008) observed no significant changes (p > 0.05) between the pH of the control and sonicated samples at 20 kHz. However, some researchers found that milk shows lower values of pH after ultrasound treatment (Bermudez et al., 2008). The decrease in pH in milk after sonication can be attributed to several reasons. Walstra et al. (2006) mentioned that a decrease in
Conclusions
The present study showed that PUS pre-treatment (20 kHz, 12.50 ± 0.31 W and 50% amplitude) can significantly improve the functional properties of MPC, such as solubility, emulsification, and gelation. The pH and conductivity of all samples did not change significantly (p > 0.05). The retentates presented shear-thinning behavior when the shear rate was in the range of 1–100 s−1, which assisted in the optimization of spray drying. These changes were closely related to the increase in surface
References (40)
- et al.
Comparative study of high intensity ultrasound effects on food proteins functionality
Journal of Food Engineering
(2012) - et al.
Molecular and functional modification of hydroxypropylmethylcellulose by high-intensity ultrasound
Food Hydrocolloids
(2009) - et al.
Effects of ultrasound on the thermal and structural characteristics of proteins in reconstituted whey protein concentrate
Ultrasonics Sonochemistry
(2011) Adsorption of protein and the stability of emulsions
Trends in Food Science and Technology
(1997)Properties of emulsions stabilized with milk proteins: overview of some recent developments
Journal of Dairy Science
(1997)- et al.
Emulsion stabilization by ionic and covalent complexes of β-lactoglobulin with polysaccharides
Food Hydrocolloids
(1991) - et al.
Influence of a thermal treatment on the functionality of hens egg yolk in mayonnaise
Journal of Food Engineering
(2007) - et al.
Structural and functional changes in ultrasonicated bovine serum albumin solutions
Ultrasonics Sonochemistry
(2007) - et al.
High-speed observation of the effect of ultrasound on liquid mixing and agglomerate crystal breakage processes
Powder Technology
(2007) - et al.
Interfacial properties and structural conformation of thermosonicated bovine serum albumin
Food Hydrocolloids
(2006)
Effect of ultrasound treatment on solubility and foaming properties of whey protein suspensions
Journal of Food Engineering
Physical properties of ultrasound treated soy proteins
Journal of Food Engineering
Applications and potential of ultrasonics in food processing
Trends in Food Science and Technology
Structure and Functional Properties of Modified Threadfin Bream Sarcoplasmic Protein
Food Chemistry
Influence of novel food processing technologies on the rheological and thermophysical properties of whey proteins
Journal of Food Engineering
Sonolysis of synthetic sediment particles: particle characteristics affecting particle dissolution and size reduction
Ultrasonics Sonochemistry
Recent advances in the understanding of egg white protein functionality
Trends in Food Science and Technology
Coalescence of O/W emulsions stabilized by whey and isolate soybean proteins. Influence of thermal denaturation, salt addition and competitive interfacial adsorption
Food Research International
Emulsifying and foaming properties of acidic caseins and sodium caseinate
Food Chemistry
Influence of different factors on the output power transferred into medium by ultrasound
Ultrasonics Sonochemistry
Cited by (273)
A comprehensive review on donkey milk and its products: Composition, functionality and processing aspects
2024, Food Chemistry AdvancesHigh-energy ultrasound improves culture activity, polyunsaturated fatty acids and in-vitro protein digestibility in probiotic yogurt
2024, Innovative Food Science and Emerging Technologies