Composition and secondary structure of proteins isolated from six different quinoa varieties from China

Due to its high nutritional value, quinoa has recently been attracting worldwide attention. The composition and secondary structure of proteins isolated from quinoa varieties from other countries have been determined, but proteins from Chinese quinoa varieties have not been described. The aim of this research was to determine the composition and secondary structure of proteins isolated from six different quinoa varieties from China. In all varieties, the protein content was 69.62–73.14%. The fat content and ash content were all less than 2%. The starch content was 20.67–23.12%. The amino acid composition and secondary structures of quinoa protein isolates (QPIs) purified from six Chinese quinoa varieties were investigated by using a combination of amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and Fourier transform infrared spectroscopy (FTIR). The results revealed that QPIs, with molecular weights ranging from 10.0 kDa to 50.0 kDa, were rich in essential amino acids. In addition, glutamic acid was the most abundant amino acid found in the quinoa protein isolates. The remaining amino acid contents were balanced, except for tryptophan. The secondary structures of QPIs have been quantified by the deconvolution of the amide I band of the FTIR spectrum of QPIs. The main secondary structure in quinoa isolate protein was the β-sheet (from 30.86% to 36.88%). These results will be promising guides for the use of QPIs in food processing and additives.