The present work was carried out to investigate the secondary structure of Speckled sugar bean protein isolates (SSBPI) as a new source for the formation of oil in water emulsions. For this purpose the structure and emulsifying properties of SSBPI were compared with other common bean protein isolates namely, Red mexican bean protein isolates (RMBPI) and Great northern bean protein isolates (GNBPI). Results showed that all proteins were rich in globulin with Phaseolin being the major protein fraction. These bean proteins had high acidic amino acids contents of glutamic and aspartic acids. The major building fractions for the secondary structure of all bean protein isolates were beta form structures (turn and sheet) and SSBPI had the highest and GNBPI possessed the lowest turn substructure. Comparison between different bean proteins exhibited that RMBPI had more fluorescence intensity yield followed by SSBPI and GNBPI. Among bean proteins, SSBPI had less surface hydrophobicity while GNBPI had the highest hydrophobic surface at pH 3 and 7. Surface tension was influenced by protein sources and RMBPI was more effective in the reduction of water surface tension compared to other bean proteins. Although SSBPI had better surface activity at oil-water interface no significant differences were observed between bean proteins. Among bean proteins, SSBPI had the highest electrical charge on the surface which promoted enough repulsion between emulsions oil droplets. Emulsions prepared with SSBPI had lower droplet size with narrow distribution compared to other bean proteins. Results revealed that SSBPI has a great potential to be used as a new source of food emulsifier.

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