Foam and emulsion properties of potato protein isolate and purified fractions

Spray dried potato protein and specific isolated fractions were used for foaming and emulsification studies. The spray dried protein was separated into a patatin and a protease inhibitor (PI) rich fraction by ion exchange chromatography (IEX), respectively, and these two fractions were purified by hydrophobic interaction chromatography into a low (HIC 1) and a high (HIC 2) hydrophobic fraction. Foam overrun for the spray dried powder and all patatin fractions were highest at pH 3, with gradually lower values at pH 5 and 7, while the PI fractions had highest overrun at pH 5 and equally lower values at pH 3 and 7. Relative foam stability varied from 18 to 78% of the initial foam at pH 3 while lower variation of 67–80% was seen at pH 5 and 7. The HIC fractions did generally perform better than the spray dried powder and IEX fractions, with patatin HIC 1 and HIC 2 having superior performance at pH 3 and PI HIC 2 at pH 5 and 7. Emulsions were characterized by emulsion stability and activity, emulsion droplet size and small scale dynamic rheological measurements. The PI, and especially PI HIC 1 showed poor emulsion properties with low stability, large droplet size and less texture. Interestingly, PI HIC 2 had much better emulsion properties on par with the spray dried powder and patatin, while having a more frequency dependent textural response. Overall, the best emulsion properties were obtained with patatin HIC 2, thus showing the importance of hydrophobicity for protein functionality.