Combined effect of extraction and purification conditions on yield, composition, functional and structural properties of lupin proteins

Abstract

The growing global population combined with the socio-economic changes leads to the increase of the demand of plant proteins for human nutrition. In recent years, many studies has been aimed at developing new high-quality and functional plant-based protein food. Lupin being a widely cultivated legume crop is one of the most promising alternative source of proteins for human nutrition. However, the scientific knowledge of the production process of proteins from lupin meal is still very scarce.In this work, different conditions of extraction and purification were evaluated for production of lupin protein isolates. The results showed that the extraction yield was comparable between acidic and alkaline pH (37% vs 40-45%) and the extracted proteins were principally composed of globulins. This finding was astonishing regarding the selective extraction of albumins in acidic pH previously reported for other plant protein sources. The ionic strength negatively impacted the protein extractability at pH 2, whereas no significant differences were observed between extraction at 20 to 50°C.The selected extraction conditions (pH 2 and 7) combined with purification by isoelectric precipitation or ultrafiltration process generated the isolate grade products. Further structural characterization of isolates revealed a partial denaturation of lupin proteins extracted under acidic pH resulting in low protein solubility at pH 6-7 (10-50%), loss in secondary structure, low thermal stability, and formation of aggregates. However, these modifications did not significantly impact the foaming and emulsifying properties of proteins. The obtained results highlighted the original and previously not described behaviors of lupin proteins observed during the isolation process. For the first time the combined effect of extraction and purification conditions on the process performances and the quality of producing proteins was shown. The presented conclusions may help to better characterize lupin proteins and valorize lupin meal as a source of plant proteins in food industry.