Surface Rheology of Solutions From Redissolved Protein Powders

Abstract

Spray-dried milk serum protein concentrate powders could be applied either as ingredients in dairy applications or delivery materials in pharmaceutical and biotechnology industry. Yet, one of the critical challenges is that lumps are easily to form when the powders is added into water. Surface rheology of solutions from redissolved protein powders is suggested to be an important part in increasing the systematic knowledge about this phenomenon. The objective of this thesis is to compare milk SPC aggregates with unheated milk SPC on the adsorption behaviors to the given air-water interface. Surface rheology (surface tension, surface pressure and dilational rheology) of solutions from redissolved protein powders were measured and the spray drying parameters were fixed. The total solids, that is the total weight percentage of proteins and lactose, is with constant value 22.5%. The ratio of milk SPC aggregates to unheated milk SPC is 1, 4/1, 9/1, 19/1 and 0 of the system before the spray drying. Bulk protein concentrations, with designed values of 10%, 7%, 2%, 1% and 0.2%, on the surface rheology of solutions from redissolving protein powders are also under investigation.

It is found that ratios of milk SPC aggregates to unheated milk SPC do not significantly influence static surface tensions statistically. While, the bulk protein concentrations significantly influence static surface tensions. Despite this, through dynamic surface tension measurements, the lowest surface tension value is given by protein powders with unheated milk SPC only. The induction regime of solutions with unheated milk SPC is shorter than that with milk SPC aggregates. Yet, the adsorption rate show that protein aggregates could decrease the surface tension more constantly.

Regarding the elasticity of adsorbed protein films, the formation of a gel-like protein film is shown at the bulk protein concentration 6.15% and above while unheated milk SPC is mixed with milk SPC aggregates. Milk SPC aggregates from protein powders may be the main contributor to a stiff adsorbed protein films. And unheated milk SPC could play as the blocking polymer during the interfacial polymerization. This is based on the result that an increase in modulus of elasticity with the measurement time shows at the bulk protein concentration as low as 1.76% of solutions from protein powders with milk SPC aggregates only. While, if proteins of solutions from redissolved protein powders were the mixing of unheated milk SPC with milk SPC aggregates, similar trends requires the bulk protein concentration as high as 9.5%.

Popular Abstract

Milk Serum protein concentrate, namely milk SPC, is produced by filtering milk without fat. It does not contain caseins after the filtration. The application of protein powders from milk SPC is widespread, cause proteins included in milk SPC are similar as byproducts from cheese manufacturing. Spray drying is a method to dry milk SPC and produce milk SPC powders. Through spray drying, the milk SPC liquid is fed into the chamber filled with hot air. The liquid is atomized into a lot of small droplets. The water of the liquid evaporates quickly by contacting with the hot air. Powders are collected afterwards. Properties of protein powders depend on powder compositions and spray drying parameters, such as inlet air volume, inlet and outlet temperatures. For instance, lumps are easily form when powders are added into the water.

This thesis studies this type of system, including milk SPC and denatured milk SPC, as well as lactose. Heating milk SPC under 85 °C for 20min, milk SPC is denatured. Different from natural milk SPC state, sub-structures of denatured milk SPC change, and render different properties, such as solubility. One example of protein denaturation is heating egg proteins during cooking. This thesis is to compare denatured milk SPC and unheated milk SPC on the diffusion of proteins to the droplet surface. The diffusion is connected to the surface activity of proteins. The surface activity is the ability of milk SPC and denatured milk SPC to lower surface tensions at phases. Surface tension is the force to hold the shape of a droplet. One typical example is the water droplet and the water surface tension is the force to give its sphere shape. Surface elasticity is also studied. Surface elasticity is the ability of the droplet to stretch the original shape and recover from deformation, that is, the stiffness of the droplet surface.

The aim of the thesis was to look at the surface rheology values of diluted solutions from redissolved protein powders. How the surface rheology was influenced by diluting the system with lactose in different ratios and the addition of denatured milk SPC was studied.

The method to measure the surface rheology is Pendant drop method. For the surface tension values, the droplet forms automatically and the surface tension was calculated by the software based on the droplet image. The surface elasticity value was given by oscillating pendant drop method. The droplet is under regular compression and expansion and the area of the droplet is changing within the measurement.

Results show that unheated milk SPC from solutions is more surface active than denatured milk SPC. However, the ratio of unheated milk SPC to denatured milk SPC does not affect surface tensions of diluted solutions with lactose from redissolved protein powders significantly. Regarding the layer on the droplet surface, its stiffness depends on how much proteins in the solution and whether proteins are unheated SPC or denatured SPC. The formation of gel-like layer happened with the existence of denatured milk SPC at a lower protein concentration than that of the industrial scale. And the fraction of hollowed protein particles could be related to a stiff protein film as a result. However, no decisive conclusion is available about the impact of the lactose in the system on the surface rheology.

• author: Wenjia, Gao
• supervisor: Björn Bergenståhl; Ida-Marie Andersson
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences; Chemistry
• keywords: Food technology, Livsmedelsteknologi
• language: English
• id: 8997448
• date added to LUP: 2019-12-20 13:53:14
• date last changed: 2019-12-20 14:05:39