Effect of denaturation during extraction on the conformational and functional properties of peanut protein isolate

Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation. Industrial relevance: Peanut is an important oilseed crop and a well-accepted food. After oil production through thermal treatment, the defatted peanut flour is the main byproduct, which possesses a large amount of proteins. However, due to the low extraction yield and poor functional properties of these proteins, they are not well utilised in industry till now. In this work, peanut proteins were extracted by two techniques. The results indicated that extraction technique could significantly modify the functional properties of peanut proteins. Therefore, this work is helpful for industrial utilisation of peanut proteins. (C) 2011 Elsevier Ltd. All rights reserved.