Low Molecular Weight Sunflower Protein Hydrolysate with Low Concentration in Aromatic Amino Acids

A method to obtain low molecular weight hydrolysates with a high Fischer ratio (molar ratio of Val + Leu + Ile to Tyr + Phe) is described. Sunflower protein concentrate, with a low concentration in polyphenols, was hydrolyzed with kerase in a pH-stat to a 16.5% degree of hydrolysis. The hydrolysate was fractionated by ultrafiltration using membranes with cutoffs of 30 000 and 5000. The obtained fractions, UC-30, UC-5, and UF-5, were characterized for molecular weight distribution and amino acid composition. From a quantitative point of view, the two main fractions were UC-5 and UF-5. Fraction UC-5 contained a high percentage of proteins and peptides with molecular weights above 5000 and below 30 000 (61.9%), with a considerable content of peptides and free amino acids (37.2%). Fraction UF-5 was composed only of peptides having molecular weights below 5000 and free amino acids (99.8%). The main difference in total amino acid composition of the fractions UC-5 and UF-5 was a higher value of Fischer ratio for fraction UF-5. The treatment of this fraction with actinase followed by Sephadex G-15 chromatography (fraction A) led to a marked reduction in the content of aromatic amino acid, the Fischer ratio increasing from a value of 5.52 in UF-5 to 20.47 in fraction A.