Abstract
In this study, the influence of defined extrusion-like treatment conditions on the denaturation behavior and kinetics of single- and multi-component protein model systems at a protein concentration of 70% (w/w) was investigated. α-Lactalbumin (αLA) and β-Lactoglobulin (βLG), and whey protein isolate (WPI) were selected as single- and multi-component protein model systems, respectively. To apply defined extrusion-like conditions, treatment temperatures in the range of 60 and 100 °C, shear rates from 0.06 to 50 s⁻1, and treatment times up to 90 s were chosen. While an aggregation onset temperature was determined at approximately 73 °C for WPI systems at a shear rate of 0.06 s⁻1, two significantly different onset temperatures were determined when the shear rate was increased to 25 and 50 s⁻1. These two different onset temperatures could be related to the main fractions present in whey protein (βLG and αLA), suggesting shear-induced phase separation. Application of additional mechanical treatment resulted in an increase in reaction rates for all the investigated systems. Denaturation was found to follow 2.262 and 1.865 order kinetics for αLA and WPI, respectively. The reaction order of WPI might have resulted from a combination of a lower reaction order in the unsheared system (i.e., fractional first order) and higher reaction order for sheared systems, probably due to phase separation, leading to isolated behavior of each fraction at the local level (i.e., fractional second order).
Highlights
Due to their nutritional and functional properties, proteins are often used to produce protein-based products such as sports beverages, meat substitutes, baked products and dairy infant formulae
A distinct change in the slope happened at approximately 73 ◦ C, which is defined as the aggregation onset temperature [9,10]
It seems at high protein concentrations, the renaturation of αLA after thermal and mechanical treatment might decrease due to high reaction rates
Summary
Due to their nutritional and functional properties, proteins are often used to produce protein-based products such as sports beverages, meat substitutes, baked products and dairy infant formulae. Thermal, chemical, or mechanical treatment may lead to changes in the molecular structure of proteins, and on their functionality. Processes such as extrusion have been used to produce protein-based emulsifiers and thickeners [3,4]. Heat, and pressure to change the structure of food components, including proteins [5]. Different unit operations such as transport, mixing, shearing, and heating are possible within the extruder, making it a continuous flow reactor. This leads to a Polymers 2020, 12, 2145; doi:10.3390/polym12092145 www.mdpi.com/journal/polymers
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