Functional properties and molecular structure of quinoa starch

Abstract

Quinoa has gained popularity worldwide due to the attractive nutritional profile, and has much potential for world food security. Starch is the main component of quinoa seed and makes up to 70% of the dry matter, which plays a crucial role in the functional properties of quinoa and related food products. The aims of this study were to fill the gaps in the current knowledge of properties, structure, and modification of quinoa starch as well as to explore the structure-function relationships. Quinoa starch granules are rather small (1−3 μm) with relatively low amylose contents. Great diversities in physicochemical properties of 26 quinoa samples were observed. Principal component analysis was applied to identify the samples with characteristic properties. The selected 7 quinoa sample were then tested for their flour properties which have been found in close relationship with starch properties. The molecular structure including amylose, amylopectin and its internal part of 9 quinoa starches were characterised by chromatographic techniques. Quinoa amylopectin showed a high ratio of short chain to long chains (14.6) and a high percentage of fingerprint A-chains (Afp) (10.4%). The average chain length (16.6 glucosyl residues), external chain length (10.6), and internal chain length (5.00) were calculated. Although quinoa starch had a high amount of short chains, the presence of super-long chains was also observed. The structure of amylopectin and amylose content affected the starch properties which were revealed by Pearson correlation analysis. For example, the molar amount of Afp was negatively correlated with peak temperature estimated by DSC (r = −0.815, p < 0.01) and pasting temperature (r = −0.743, p < 0.05). The steady shear and dynamic oscillatory properties of the same quinoa starch samples were tested. The rheological properties were found correlated with the starch composition and amylopectin structure. The long chains in amylopectin have significant impact on the rheological properties of quinoa starch (e.g., the long chains in amylopectin positively correlated with G' at 0.1 Hz). Quinoa starch was more susceptible to high hydrostatic pressure treatment than maize starch, which could due to the difference in chemical composition, granular and chemical structures of starch molecules. The unique properties of high pressure treated quinoa starch have potentials in food industry. This work could fill the gaps in the present knowledge of quinoa starch and provides a basis for better understanding and utilization of this unique starch.