Effects of extraction and precipitation conditions on efficiency and functional properties of rapeseed protein isolates

High protein content and well-balanced essential amino acids in rapeseed meal have increased importance of this oil seed in recent years. The presence of complex protein compounds of rapeseed meal caused the extraction and precipitation of proteins depend on pH, which can also affect the efficiency and functional properties of protein. In this study, response surface and face central composite design were used to evaluate the effect of independent variables. i.e. alkaline protein extraction pH, (10-12) and acid protein precipitation pH (4.5-6.5) on the efficiency and functional properties of rapeseed (cv.Hyola) protein isolates. The determination coefficients of the fitted regression models were 0.98, 0.94, 0.91, 0.92, 0.90 and 0.93 for efficiency, water absorption, fat absorption, solubility index, emulsifying capacity and foaming capacity, respectively. The results showed that the effect of protein extraction and precipitation pH on efficiency, and water and fat absorptions was significant and the index of solubility, foaming and emulsifying properties were only affected by extraction pH. The optimum conditions for extraction and precipitation with maximum yield and functional properties of protein isolate at pH of 11.93 and 5.57 for extraction and precipitation, respectively. Under these conditions, yield, water absorption, fat absorption, solubility index, emulsifying capacity and foaming capacity were 89, 225, 185, 41, 64 and 165 percent, respectively.