Lupin proteins: Structure, isolation and application

The interest in plant-based protein sources has risen in the last few decades due to their benefits to human health, the environment and sustainable farming. Lupins are a protein-rich legume crop, popular as fodder but limited for human consumption due to the presence of alkaloids. The sweet lupin varieties (free of/reduced alkaloid) developed through intensive plant breeding have widened the scope of lupin applications in food.This review firstly compares the composition of the major globular proteins of Australian Sweet Lupin (Lupinus angustifolius) with soybean (Glycine max) followed by a review of the underlying principles of three well-established extraction methods: alkaline extraction-isoelectric precipitation; micellization; and selective fractionation, used for the preparation of lupin protein isolates (LPI). We have also discussed the functional properties of isolated proteins concerning the extraction methods.The extraction conditions, which mainly rely on pH change or salt concentrations, can be modified to achieve isolation of the desired protein fraction. We conclude that extraction conditions have a direct influence on various functional properties. LPI resulting from alkaline extraction-isoelectric precipitation led to protein denaturation due to acid treatment, while micellization produces LPI in a less denatured form resulting in better protein solubility, emulsifying and foaming properties. LPI from selective fractionation has the advantage of recovering γ-conglutin exhibiting good foaming capacity, whereas, alkaline extraction-dialysis/ultrafiltration recovered albumin along with globulin exhibiting excellent gelling behaviour. This review is timely for driving future research and applications in lupin seed as a sustainable, plant-based protein source for human foods.