Saponin and hexanal in pea (Pisum sativum) protein isolates: A comparative study of isoelectric precipitation and ultrafiltration

Yellow pea is considered as a promising source of dietary protein due to its low carbon footprint and adaptability to temperate climates. However, off-flavor compounds such as saponins and hexanal maabsy hinder consumer acceptance. This study investigated how pea protein purification methods influenced saponin and hexanal co-concentration in resulting isolates. High resolution mass spectrometry (MS) identified soyasaponins I and VI as the only saponins in pea flour. Heating saponin extracts at 90 °C converted soyasaponin VI to I, enabling quantification using triple quadrupole MS. Hexanal was extracted by headspace solid phase microextraction and analyzed using gas chromatography-MS. Protein isolates were produced through wet extraction and isoelectric precipitation or ultrafiltration-diafiltration. Isoelectric precipitation (88.03±0.47% protein) concentrated saponins by ∼3-fold, while reducing hexanal by ∼6 times, relative to pea flour. A washing step after isoelectric precipitation (96.92±2.19% protein) further increased saponin concentration by ∼34% but did not affect hexanal. Ultrafiltration-diafiltration using a 30 kDa membrane yielded isolates (78.91±1.90% protein) with saponin and hexanal content similar to pea flour, regardless of salt extraction (79.05±3.30% protein). Although isoelectric precipitation resulted in higher protein purity, gel electrophoresis showed minimal differences in protein profiles. These findings highlight that processing influences off-flavor compounds retention in pea protein ingredients.