Method for extracting protein, starch and fiber from buckwheat

A process for extracting buckwheat proteins, buckwheat starch and buckwheat fibers from a buckwheat flour or from a buckwheat groat, said buckwheat being common buckwheat (Fagopyrum esculentum), the process being free of organic solvents and organic reactants and comprising the steps of:

• a) preparing an aqueous suspension from the buckwheat flour or from the buckwheat groat with a pH between 7 and 9, wherein the preparation of the aqueous suspension comprises a step of adding water to the buckwheat flour or to buckwheat groat in proportion of 4:1 (w/w) at a temperature comprised between room temperature and 50° C.,
• b) fractionating the aqueous suspension by density, so as to obtain a light fraction (supernatant) comprising proteins, soluble carbohydrates and salts, and a heavy fraction (precipitate) comprising starch and fibers;
• c) treating the light fraction (supernatant), so as to isolate the proteins;
• and
• d) treating the heavy fraction (precipitate), so as to separate starch from fibers;
• wherein when the process starts from buckwheat groat the step a) of preparation of the aqueous suspension comprises a step of wet grinding to obtain the buckwheat aqueous suspension with the buckwheat particles in said suspension having an average particle size of 100 μm, wherein when the process starts from buckwheat groat, the treating step of the light fraction c) comprises the following steps:
• c1) adjusting the pH of the light fraction to the isoelectric pH of proteins, corresponding to a pH comprised in the range of 4 to 5, at a temperature comprised between room temperature and 50° C., so as to precipitate proteins;
• c2) fractionating the light fraction by density, so as to separate the protein precipitate from a supernatant comprising soluble carbohydrates and salts;
• c3) treating the protein precipitate at pH in the range of 6.5 to 7.5 at a temperature comprised between room temperature and 50° C., so as to neutralized and resolubilize proteins;
• and
• c4) drying said proteins
• wherein, when the process starts from buckwheat flour, the treating step of the light fraction c) comprises the following steps:
• c′1) adjusting the pH of the light fraction to the isoelectric pH of proteins, corresponding to a pH comprised in the range of 4 to 5, at a temperature comprised between room temperature and 50° C., so as to precipitate proteins;
• c′2) fractionating the light fraction by density, so as to obtain a protein precipitate and a supernatant comprising soluble carbohydrates and salts;
• c′3) treating the protein precipitate at pH in the range of 6.5 to 7.5 at a temperature comprised between room temperature and 50° C., so as to neutralize and partially resolubilize the proteins to obtain an insoluble protein fraction and a soluble protein fraction;
• c′4) separating by filtration the insoluble protein fraction from the soluble protein fraction;
• c′5) drying the insoluble proteins;
• and
• c′6) drying the soluble proteins,
• wherein yield of buckwheat protein from said process is 2 to 10%, yield of buckwheat starch from said process is 45 to 60% and yield of buckwheat fiber from said process is less than 35%.