Functional Properties of Sweet Lupin Protein Isolated and Tested at Various pH Levels

Lupin has the potential to be a new source of vegetable protein due to its similar protein content to soy, the common source of vegetable protein used in the food industry. Investigation of its functional properties is essential to validate the potential application in the food industry. Lupin protein isolates were prepared by alkaline extraction at pH 9.0 followed by acidic precipitation at eight different pH levels i.e. 4.0, 4.2, 4.4, 4.5, 4.6, 4.8, 5.0 and 5.5. The range of pH employed here covered the isoelectric points of major legume proteins. The emulsifying and foaming properties of lupin protein isolate (LPI) samples were evaluated and compared with those of soy protein isolate (SPI). Lupin protein isolates prepared by precipitating at a pH range of 4.4 to 5.0 had no significant difference in their emulsifying and foaming properties. Emulsifying activity and emulsion stability of LPI samples were comparable to those of SPI. All LPI samples exhibited greater emulsifying activity and emulsion stability than SPI at pH 4.0. Foaming capacity and foam stability of LPI tested at a range of pH levels was also higher than that of SPI. The study provides a base for more flexible and economical process for making LPI at commercial level.