Surface and emulsifying properties of raw ethanolic extracts from legumes containing soyasaponins and proteins

The development of new amphiphilic compounds of natural origin is a challenging field of research in surfactant science. In this scenario, surfactants obtained from renewable organic sources is a valuable option to be exploited. The present work proposes raw ethanolic extracts containing soyasaponins, proteins and polysaccharides from legumes as surface active mixtures and stabilizers for emulsified systems. These extracts are produced by a green extraction process using an hydroalcoholic mixture (70:30 w/w) as solvent and six different legumes soybean, lentils, peas, beans, chickpeas, wild peas as starting materials. After freeze-drying, extracts were characterized in terms of total soyasoponin (from 1377 to 7354 mg/100 g), soyasaponin I (from 15 to 1459 mg/kg), soyasaponin VI (from 13 to 1076 mg/kg) and protein (16–28 g/100 g) contents. All extracts aqueous solutions show good surface active properties, being able to reduce the air-water surface tension to values comparable to those of the commonly employed surfactants (28–33 mN/m). Differences are observed in terms of emulsifying ability, since only lentils and soybeans extracts, thanks to their high soyasaponins and protein content, can act as stabilizers for emulsions containing up to 10% w/w of ethyl oleate (as oil phase) over six months of storage at 4 ◦C. These extracts are promising amphiphilic natural mixtures, potentially employable for food or pharmaceutical applications. Their relevance is also related to the possibility of using legumes derived from industrial wastes of food manufacturing, thereby giving valorization of by-products and residues in the context of a “circular economy” model.