Cowpea protein isolates: Functional properties and application in gluten-free rice muffins

- Protein isolates were prepared from two different types of cowpeas.
- The isolates differed for physicochemical and functional properties.
- These isolates were also explored for application in rice muffins.
- Addition of protein isolates improved muffin-making properties of rice flour.
- This improvement depended on the level of addition and source of proteins.

The present work was undertaken to explore application of cowpea protein isolates in gluten-free rice muffins. Protein isolates from large-white and small-red cowpeas were evaluated for physicochemical and functional properties. These were incorporated at three levels (4, 8 and 12 g/100 g) in rice flour to see their effect on muffin-making properties. Chromatographic analysis revealed that proteins of 133-137 kDa (vicilins) contributed to 53-60 g/100 g of the isolates. Protein isolate from white cowpea (WCPI) showed higher solubility, foaming and emulsification but lower water absorption than that from red cowpea (RCPI). Incorporation of protein isolates decreased flour paste viscosities (peak, breakdown and final) and increased batter viscoelasticity (above 8 g/100 g incorporation level), wherein WCPI exerted greater effect than RCPI. WCPI influenced crumb colour parameters (L*, a* and b*) marginally whereas RCPI increased a* while decreased L* and b* significantly. Firmness, springiness, cohesiveness and chewiness of the muffins increased above 8 g/100 g incorporation levels for both the protein isolates. WCPI increased muffin volume whereas RCPI decreased. The results suggested that not only the level of proteins but also their properties influence characteristics of gluten-free muffins.