The role of extraction and purification conditions in flaxseed protein isolate production and its emulsifying properties

The design of experiments varying the pH (6−8), NaCl concentration (0−0.5 M), and temperature (20−50°C) showed that the protein extractability doubled at high pH and NaCl concentration. However, the increase of temperature resulted in lower protein purity in the extract (-10%) probably due to the co-extraction of the mucilage. Concerning protein purification, the most efficient precipitation occurred at pH 4 (about 65%). The losses in proteins were primarily attributed to 2S conlinin. However, although NaCl improved the extraction yield, the presence of salt in the extract reduced the precipitation yield at pH 5−6 by 40%. The functional properties of proteins were also strongly dependent on the applied process conditions. As shown by structural analysis, precipitation at low pH led to partial denaturation of proteins, resulting in reduced solubility, notably at pH 3 (20%). However, the flaxseed isolate produced by extraction at pH 7.5 and precipitation at pH 4 exhibited an exceptionally high emulsifying capacity of 90%. Such excellent emulsification is extremely rare in plant proteins, which typically achieve 30−45% emulsifying capacity. Furthermore, the emulsion of flaxseed proteins exhibited remarkable stability for at least 20 days, and after thermal treatment. • NaCl level is the most significant parameter in extraction of flaxseed proteins • High temperature reduces the protein extractability and purity • NaCl used for extraction decreases the recovery of proteins during precipitation • Extraction and purification process impact the protein functionalities • Partially denatured flaxseed proteins exhibit extraordinary emulsifying properties