Abstract: In this study, lupin proteins were extracted from lupin seeds by two different methods, namely, micellization and alkali dissolution followed by acid precipitation, and their physicochemical properties were evaluated. The molecular mass distribution of lupin proteins was mainly in the range of 18–90 kDa and consisted of proteins with various molecular masses. The total amino acid content of lupin proteins extracted by sequential alkali dissolution and acid precipitation (66.2%) was significantly higher (P < 0.05) than that obtained by micellization (27.8%). The isoelectric point (pI) of lupin proteins extracted by the two extraction methods was close to 5.0. The water-holding capacity of lupin protein extracted by micellization was significantly higher (P < 0.05) than that obtained by alkali dissolution followed by acid precipitation, but there was no significant difference (P > 0.05) in oil-holding capacity between the two methods. The foaming capacity of lupin protein extracted by sequential alkali dissolution and acid precipitation decreased significantly at pH 2.0–6.0, and was the lowest at pH 6.0, and the trend of foam stability was similar to that of foaming capacity. However, pH had no significant effect (P > 0.05) on the foaming ability of lupin protein extracted by micellization. The emulsifying capacity of lupin protein extracted by micellization was the lowest at pH 4.0, and then increased with the increase of pH. The emulsifying capacity of lupin proteins extracted by the two extraction methods was the highest at pH 10.0. The solubility of lupin protein extracted by alkali dissolution followed by acid precipitation was the lowest at pH 4.0, and increased rapidly with the increase of pH from 4.0 to 10.0. The solubility of lupin protein extracted by micellization increased with the increase of pH from 2.0 to 10.0. The results of this study can provide theoretical and technical support for the development and application of lupin proteins in the food industry.

Key words: micellization; alkali solution followed by acid precipitation; lupin; protein; extraction; physicochemical properties