Effect of Freezing on Soybean Protein Solution.

Area of Science:

• Food Science
• Protein Chemistry
• Biophysics

Background:

• Soybean proteins are vital food components.
• Understanding freezing effects on protein structure is crucial for food processing and storage.
• Soybean isolate (SPI), 7S, and 11S globulins are key soybean protein fractions.

Purpose of the Study:

• To investigate how frozen storage impacts soybean protein physicochemical properties.
• To elucidate the mechanisms behind these changes.

Main Methods:

• Soybean protein solutions (SPI, 7S, 11S) were frozen for 1 and 5 days.
• Assessed protein content, physicochemical properties, secondary structure, sulfhydryl content, and chemical interactions.
• Utilized UV spectrophotometry, Zeta potential, SDS-PAGE, FTIR, and fluorescence spectroscopy.

Main Results:

• Solubility and sulfhydryl content decreased with longer freezing times, with 11S affected most.
• Freezing increased protein hydrophobicity, aggregation, and particle size, shifting structure towards order.
• Protein microenvironment polarity increased, with red-shifted fluorescence emission spectra.
• Hydrogen bonding contribution increased, while hydrophobic interactions decreased.

Conclusions:

• Frozen storage significantly alters soybean protein structure and properties.
• Ice crystal growth causes protein unfolding, hydrophobic group exposure, and secondary structure modification.
• Changes in chemical forces, including hydrogen bonding and hydrophobic interactions, are key mechanisms.