Note:: Influence of pH on the extraction yield and functional properties of macadamia (Macadamia integrofolia) protein isolates

Three protein isolates from de-fatted macadamia nut kernel flour were prepared by extraction at acidic (pH 2.0), neutral (pH 7.2 with 0.2 M phosphate buffer containing 0.5 M NaCl) and alkaline (pH 12.0) conditions. Extraction at pH 2.0 solubilised nearly 52.0% of the proteins present in defatted macadamia flour, while extraction with buffer (pH 7.2) and alkaline pH (12.0) solubilised about 83.0% of proteins. The yield of isoelectrically precipitated protein from acidic extract (pH 2.0, isolate A) was about 65.2% and from neutral (isolate 13) and alkaline extracts (isolate C) was slightly over 83.0% which accounted for 33.7, 69.1 and 69.4% of the proteins present in defatted flour. The protein content of the isolates was 80.1, 92.1 and 92.0% in A, B and C isolates respectively. The functional properties of these isolates were significantly different. Isolate A presented better solubility at pH below isoelectric pH, isolate C at pH above isoelectric pH and isolate B intermediate solubility at the pH range studied. Isolate B showed best water and oil absorption capacities followed by isolate C and least by isolate A. For each isolate, the emulsifying properties were also significantly different at different pH values.