Studies on the characterization, biosynthesis and isolation of starch and protein from quinoa (Chenopodium quinoa Willd.)

Abstract

Starches isolated from sixteen quinoa lines ranged in amylose content from 3 to 20%. With the exception of pasting temperature, large variations in pasting characteristics were found among starches and were correlated with amylose content. The gelatinization onset (44.7-53.7 ºC) and peak (50.5-61.7 ºC) temperatures and retrogradation tendencies (19.6-40.8%) were positively correlated with amylose content. No significant variation in gelatinization enthalpy was observed. Swelling, solubility, freeze-thaw stability and water-binding capacity also differed among starches and were correlated with amylose content. The wide variation in amylose content and physicochemical characteristics among quinoa starches suggests applications in a variety of food and non-food products. Two major polypeptides with apparent molecular masses of 56 and 62 kDa were present in quinoa starch and were identified as isoforms of Granule Bound Starch Synthase I (GBSSI). The content of the two isoforms was positively correlated with the concentration of amylose in starch. Starch synthase activity in developing seed was positively correlated with the amylose concentration in starch during seed development. An integrated process was developed for the fractionation of quinoa into starch, protein, oil and saponins. Seed was first roller milled, yielding a coarse bran fraction (48% of the seed weight) that was high in protein (22.9%, db), oil (8.8%, db), and saponins (7.4%, db), and a fine, starch-rich fraction [52% of the seed weight containing 77.2% (db) starch]. Protein, oil and saponins were extracted from the bran under optimized conditions. The protein extracts were concentrated and purified using isoelectric precipitation or ultrafiltration. The means of concentration as well as the presence of saponins strongly affected protein recovery and functionality. Starch was recovered using aqueous alkali (pH 9) to solubilize the protein followed by centrifugation, after which the starch-rich pellet was washed and the sediment which accumulated on top of the pellet was removed. The end-products of the integrated extraction process were a crude saponin extract, a crude oil product, and several protein and starch products. Forty-one percent of the protein present in the seed was recovered as a protein product that contained over 77% (db) protein. Sixty-eight percent of the starch was recovered as a starch product that contained 97% (db) starch and 1.2% (db) protein.