Microstructural Analysis of Whey/Soy Protein Isolate Mixed Gels Using Confocal Raman Microscopy

Area of Science:

• Food science and technology
• Biophysical analysis
• Spectroscopic imaging

Background:

• Understanding the microstructure of mixed protein gels is crucial for controlling their functional properties.
• Whey protein isolate (WPI) and soy protein isolate (SPI) are widely used proteins in food systems.
• Confocal Raman microscopy offers potential for non-destructive analysis of complex food matrices.

Purpose of the Study:

• To investigate the microstructure of mixed WPI and SPI gels using confocal Raman microscopy.
• To evaluate different data analysis approaches for extracting structural and compositional information.
• To identify the distribution of proteins, water, and other components within the gels.

Main Methods:

• Preparation of heat-set protein gels with varying WPI:SPI ratios (100:0, 75:25, 50:50, 25:75, 0:100).
• Analysis using confocal Raman microscopy to acquire spectral data.
• Application of univariate and multivariate analysis methods for spectral data processing.

Main Results:

• Small spectral differences were observed between pure WPI and SPI gels, linked to conformational changes (amide bands).
• SPI gels exhibited significantly higher auto-fluorescence compared to WPI gels.
• Univariate analysis effectively mapped protein and water distribution; higher fluorescence in capsule-like structures suggested enrichment in SPI.
• Multivariate analysis differentiated protein hydration levels and detected non-proteinaceous compounds, including residual lipids.

Conclusions:

• Confocal Raman microscopy is a valuable tool for elucidating the microstructure of mixed protein gels.
• The technique can differentiate between protein types, hydration states, and detect impurities like lipids.
• Soy protein isolate's higher auto-fluorescence aids in identifying its distribution within mixed systems.