Structural and functional properties of Moringa stenopetala seed meal protein isolates obtained from solvent-assisted protein extraction

Abstract

Moringa stenopetala (MS) is a stress-resilient, multipurpose African tree known for its valuable leaves as well as the protein and oil rich seeds. This study evaluated the effects of acetone (AMSPI), hexane (HMSPI), methanol (MMSPI), 100% ethanol (EMSPI), 70% ethanol (7EMSPI), 50% ethanol (5EMSPI), and water (WMSPI) pretreatments of MS seed meal on the physicochemical and functional properties of protein isolates obtained via alkaline isoelectric precipitation (ISO). These protein isolates were compared with the isolate produced from the untreated moringa seed meal (UMSPI). The protein content ranged from 85.34% for 5EMSPI to 96.95% for MMSPI. Protein isolates obtained from solvent-treated meals had higher contents of hydrophobic, positively charged, negatively charged, and sulfur containing amino acids than the UMSPI. Bitterness scores of the protein isolates obtained from solvent extracted MS meals ranged from 23.3 to 28.3 when compared to the 23.8 for the UMSPI while AMSPI and 7EMSPI had the highest scores of 28.3 ± 0.2 and 27.9 ± 0.1, respectively, as determined by electronic tongue. AMSPI demonstrated superior (p < 0.05) solubility (25–75% across pH 3–9), foaming capacity (~ 80%), and thermal stability (Td = 88.77 °C) while MMSPI displayed the highest fluorescence intensity at pH 3. The UMSPI had the highest (p < 0.05) total phenolic content of 1.45 mg gallic acid equivalent (GAE)/g, while WMSPI (0.86 mg GAE/mg) had the lowest value. These findings highlight the significant influence of solvent extraction methods, with AMSPI and 7EMSPI emerging as optimal choices for food applications requiring high solubility, stability, and foaming properties.