Isolation and evaluation of quinoa (Chenopodium quinoa Willd.) protein fractions. A nutritional and bio-functional approach to the globulin fraction.

This study evaluated the solubility profiles of quinoa grain proteins and applied a complete process for the isolation of its main protein fractions, namely: albumins, globulins, prolamins and glutelins, which corresponded to 26.96%, 41.3%, 1.7% and 23.16% of the total protein content, respectively. When these fractions were digested with pepsin followed by pancreatin, the degrees of hydrolysis achieved varied between 26.62% (for unheated globulin fraction) and 38.97% (for unheated glutelin), with casein reached 33.73% hydrolysis. After heating, the globulin hydrolysis degree increased to 34.7%, not significantly differing from casein. These results reflect its good susceptibility to hydrolysis by digestive enzymes, and this observation is reinforced with assays with pepsin, trypsin and chymotrypsin tested separately. Globulins, the largest protein fraction, showed promising results in additional assays regarding the amino acid profile, with limitation only for lysine in relation to the FAO standard, and the potential for releasing bioactive peptides after digestion. Although pepsin-digested globulin inhibited only 5% of ACE activity under the conditions tested, after 24h with the addition of pancreatin, the inhibition was 100%. Antioxidant activity (DPPH assay) also indicated very similar results, when hydrolysis with pepsin was inefficient in releasing antioxidant peptides, while hydrolysis by pancreatin led to 35 times greater results.