Effect of Hofmeister Series Anions on the Formation of Mung Bean Protein Amyloid Fibrils

Plant proteins, including those from wheat, soy, and mung beans, have been shown to form amyloid fibrils under specific conditions. Factors such as pH, temperature, ionic strength, and the presence of certain ions can influence the aggregation of these proteins into fibrils by inducing conformational changes. This study investigates the impact of various Hofmeister anions on fibril formation, focusing on the resulting fibril structure and its associated techno-functional properties.

Mung beans were milled into flour and extracted using an alkaline-acid method to obtain mung bean protein isolate. These isolates were then subjected to acid hydrolysis and heat treatment to facilitate amyloid fibril formation. Thioflavin T (ThT) fluorescence spectroscopy revealed the kinetics of fibril formation, showing an initial exponential increase in ThT intensity over the first 4 hours, followed by a decrease after 6-7 hours. Iodide ions led to the highest increase in ThT intensity, while sulfate ions inhibited fibril formation. Atomic force microscopy (AFM) analysis revealed fibrils of 500-600 nm in size with periodic helical structures in all samples. Chloride ions caused increased agglomeration of fibrils into large clumps, while citrate and iodide ions reduced this agglomeration, and sulfate ions hindered fibril formation altogether. Particle size analysis indicated a decrease in particle size during the first 2 hours of heat treatment, followed by an increase, with the largest particles observed in the presence of citrate ions. Zeta potential analysis showed minimal effect from fibril formation. Rheological testing indicated the strongest gel formation in citrate-treated samples and the weakest gel in the sample without salts.

In conclusion, the addition of Hofmeister salts did not significantly alter the structure of the fibrils but had notable effects on the techno-functional properties of the samples. This study provides a foundation for understanding the mechanism of fibril formation and the influence of various additives.