Comparison between isoelectric precipitation and ultrafiltration processes to obtain Amaranth mantegazzianus protein concentrates at pilot plant scale

► Alternative processes to obtain amaranth protein concentrates were studied. ► Electrophoresis, HPLC, amino acid determination of protein fractions were carried out. ► Alternative processes resulted in higher protein concentration and low protein yield. ► Ultrafiltration protein concentrate presented high phenylalanine and lysine content. The aim of this study was to compare protein yield, protein concentration and physicochemical characteristics of Amaranth mantegazzianus protein concentrates (APC) obtained at pilot-scale by a conventional process (CP) (alkaline extraction and isoelectric precipitation) and two alternative processes (AP): (1) acid pre-treatment process combined with isoelectric precipitation and (2) acid pre-treatment process combined with ultrafiltration. Although AP resulted in higher protein concentration, protein yield was lower than in CP. SDS–PAGE and size-exclusion chromatography showed high molecular weight fractions only for isoelectric precipitation concentrates (obtained by CP and AP). The amino acids concentration, especially phenylalanine, isoleucine and methionine, increased in all protein concentrates respect to the amaranth flour. Particularly, the product obtained by ultrafiltration was rich in phenylalanine and lysine, and presented no limiting amino acid with respect to the recommendation of the Food and Agriculture Organization of the United Nations (FAO). In conclusion, process (2) improved protein concentration and nutritional quality (balanced amino acid composition) of A. mantegazzianus protein concentrates respect to CP and process (1), suggesting that the ultrafiltration process is a viable alternative to conventional process and a promising method for obtaining protein concentrates.