Conditions affecting production of a protein isolate from lupin seed kernels

Abstract

AbstractConditions were investigated to determine the optimum processing parameters for preparation of a protein isolate from the ground, dehulled lupin seeds of Lupinus angustifolius. The extraction variables were: particle size (16–100 mesh); pH (2–11); extraction medium; solvent to lupin ratio (10:1 to 40:1); temperature (20–60oC) and time (15–60 min). The isoelectric point of the lupin protein was found to be pH 4.5 with a protein solubility of greater than 90% above pH 8.0. Using 60–100 mesh ground lupin and extracting at pH 8.5 for 30 min, a protein isolate was obtained on acidification to pH 4.8 which was 89.4% protein compared to 34.0% protein for the original dehulled lupin. This protein isolate represented 19.8% of the starting material and 52% of the starting nitrogen. Similar results were also obtained when hexane defatted lupin was used. In this case the protein isolate had a protein content of 92.5%. The yield of protein isolate could be increased to 25.7% of the starting material if the extraction was repeated. The protein efficiency ratio for the protein isolate was 2.90 when supplemented with methionine.