Isoelectric point isolation and characterization of proteins from lupine cultivars as influenced by chemical and thermal treatments

Pulses provide a significant nutritional potential for the large proportion of the population in developing countries. Lupine is among the underutilized legume crops for human food in Ethiopia and globally concomitant to its contents of bitter alkaloids. This research was initiated to investigate the effects of soaking lupine seeds of bitter and sweet varieties in water and 2% sodium carbonate (Na2CO3) solutions as grain softener on the protein extraction efficiency and its sensory acceptability. It was hypothesized that the soaking treatment results in the removal of characteristic bitterness when coupled with thermal treatment (roasting). The result showed that soaking in Na2CO3 significantly increased the protein extraction efficiency (both protein yield and quality (purity)) in the two lupine cultivars. The roasting treatment did not help much. The bitter variety of lupine soaked in Na2CO3 with no roasting treatment gave the highest protein yield (39.45%), while the sweet variety soaked in water followed by roasting exhibited the least protein yield (23.25%). The purity of the protein isolates from the lupine samples soaked in 2% Na2CO3 followed by roasting was the highest (92.29%). The non-soaked samples of the sweet variety after roasting resulted in the lowest purity (75.05%). The water holding, and oil absorption capacity, as well as the emulsification activity and foaming capacity of the protein isolates were significantly varied for the lupine varieties, and by the soaking and roasting treatments. Higher (314.38%) WHC was recorded for the protein isolates from sweet variety soaked in Na2CO3, where the bitter variety, when soaked in 2% Na2CO3 without roasting gave protein isolates of higher emulsion and foaming capacities. The research revealed also that soaking of lupine seeds in grain softeners shows a great potential as a pretreatment for enhanced protein extraction and functional desirability (in terms of emulsion and foaming capacities) as well as sensory acceptability and can be recommended for scaling up at industrial level.