Assessment of the microstructural characteristics and the in vitro bioactive properties of sunflower oil-based emulsions stabilized by fava bean (vicia faba) protein

Abstract

Much interest is currently focused on plants such as legumes as an alternative source of protein for human nutrition. In this work a Vicia faba (fava bean, FB) protein concentrate was characterised for its ability to stabilise sunflower oil, oil-in-water (o/w) emulsions at three different pHs (3.0, 5.0 and 8.0). Emulsion microstructure was characterised by droplet size distribution (DSD) and optical microscopy, and resulting rheological properties were assessed. Smaller droplet sizes and better rheological properties (G′ and G″) were obtained at pH 3.0 and 8.0, i.e., at pH values away from the isoelectric point (pH 5.0). The in vitro bioactive properties of the emulsions at pH 3.0, 5.0 and 8.0 were tested using the ferric-reducing antioxidant power (FRAP) and the oxygen radical absorbance capacity (ORAC) antioxidant assays. The angiotensin converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory activities were also determined. The highest antioxidant activity was observed when the emulsions were generated at pH 8.0 with FRAP and ORAC values of 935.7 ± 151.5 and 368.8 ± 2.3 μmol Trolox Eq. · g−1 of emulsion, respectively. Overall, the emulsions were poor inhibitors of ACE and DPP-IV. However, subjection of the emulsions to in vitro simulated gastro-intestinal digestion (SGID) released peptides which increased ACE and DPP-IV inhibitory activity (67.4 ± 2.7% and 11.2 ± 1.1%, respectively, for emulsions generated at pH 8). The emulsions generated at pH 3.0 displayed the lowest extent of lipid oxidation following 15 d storage. These results show the capability of FB protein concentrate to stabilise o/w emulsions while also demonstrating antioxidant along with ACE and DPP-IV inhibitory properties following gastrointestinal digestion.