Abstract
This work explores the potential of confocal Raman microscopy to investigate the microstructure of mixed protein gel systems. Heat-set protein gels were prepared using whey protein isolate (WPI), soy protein isolate (SPI), and mixtures thereof, with a total of five different whey-to-soy protein ratios (100, 75, 50, 25, and 0%). These were analysed using confocal Raman microscopy, and different data analysis approaches were used to maximize the amount of structural and compositional information extracted from the spectral datasets generated, including both univariate and multivariate analysis methods. Small spectral differences were found between pure WPI and SPI gels, mainly attributed to conformational differences (amide bands), but SPI exhibited considerably greater auto-fluorescence than WPI. The univariate analysis method allowed for a rapid microstructural analysis, successfully mapping the distribution of protein and water in the gels. The greater fluorescence of the capsule-like structures found in the mixed gels, compared to other regions rich in proteins, suggested that these may be enriched in soy proteins. Further analysis, using a multivariate approach, allowed us to distinguish proteins with different levels of hydration within the gels and to detect non-proteinaceous compounds. Raman microscopy proved to be particularly useful to detect the presence of residual lipids in protein gels.
Highlights
Proteins play essential roles in food, as macronutrients, and as structural ingredients, which aid in the formation of food gels and contribute to the desired texture and mouth-feel attributes of the final food products [1]
Bearing in mind that reformulation generally results in structural changes in food products, studying the microstructure of mixed protein systems is essential to gain a better understanding of the implications of partially replacing dairy proteins with plant proteins in food formulations
The aim of this work was to explore the use of confocal Raman microscopy to investigate the microstructure of mixed protein gels and maximize the amount of structural and compositional information extracted from the spectral datasets generated by exploring different data analysis approaches, including both univariate and multivariate analysis methods
Summary
Proteins play essential roles in food, as macronutrients, and as structural ingredients, which aid in the formation of food gels and contribute to the desired texture and mouth-feel attributes of the final food products [1]. The aim of this work was to explore the use of confocal Raman microscopy to investigate the microstructure of mixed protein gels and maximize the amount of structural and compositional information extracted from the spectral datasets generated by exploring different data analysis approaches, including both univariate and multivariate analysis methods. For this purpose, whey/soy mixed protein gels were used as a case study due to the industrial relevance of blends made from these proteins. The advantages and limitations of confocal Raman microscopy for the characterization of mixed protein gels are discussed, and the different approaches proposed for data analysis are compared
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