Emulsifying Capacity of Cowpea Protein Isolates: Effect of Thermal and Hydrolytic Treatment

Abstract

In this work, modifications due to the effect of thermal treatments (TT 70 and 90 °C) and partial hydrolysis by digestion with alcalase (LH) on the emulsifying properties of cowpea protein isolates (CPIs) extracted at pH 8 and 10 were analyzed. In addition, the influence of protein concentration [0.1 and 1% (w/v)] was evaluated. Emulsions (O:W) were prepared and particle size, stability, interfacial composition, and microstructure were studied. Fresh emulsions formulated with TT CPIs presented lower values of volume-weighted mean droplet size (D4.3), with the increase in temperature and treatment time, compared to the untreated CPIs. After seven days of storage, D4.3 and the indexes of flocculation (FI) and coalescence (CI) increased, mainly at 90 °C. On the other hand, the emulsions with LH CPIs presented lower D4.3 values compared to all the conditions tested, remaining unchanged during the storage time. The destabilization process in the TT CPIs emulsions revealed coalescence at 0.1% (w/v) and cremated-flocculation at 1% (w/v). The presence of polypeptides of low molecular mass (MM) at the interface would be responsible for the better stability found in emulsions with LH CPIs, compared to those formulated with untreated and TT CPIs. Increasing the protein concentration resulted in a significant improvement of all emulsifying properties.