Effect of protein extraction on antinutritional factors composition and protein quality of three quinoa varieties (Chenopodium quinoa Wild.)

Quinoa (Chenopodium quinoa Wild.), a pseudocereal, is renowned for its high protein content and complete profile of essential amino acids necessary for human growth, making it an excellent candidate for protein extraction. However, protein extraction techniques, may impact the properties of the extracted protein. Additionally, variances in amino acid content and anti-nutritional factors (ANFs) among different quinoa varieties can lead to changes in digestibility and protein quality. Consequently, this study aimed to evaluate in-vitro protein digestibility (IVPD), protein quality, and ANFs (anthocyanins, saponins, oxalates, phytic acid, lectins, and tannins) in three quinoa protein isolates/concentrates (black, yellow, and red).

The protein content in black, yellow, and red quinoa was found to be 94.03, 86.01, and 87.23 g/100g, respectively. The IVPD of the three quinoa isolates ranged between 82.16 – 86.41%, which is higher compared to quinoa flours (76.90 – 77.69%). The IVPDCAAS indicated that the limiting amino acid in black quinoa protein isolate (PiBQ) was Met and Cys, while for yellow quinoa protein isolate (PcYQ) and red quinoa isolate (PiRQ), it was Trp. In contrast, quinoa flours (black, yellow, and red) shared the same limiting amino acids, Met and Cys. 
The study also revealed that quinoa protein isolates/concentrates contained higher levels of some ANFs compared to quinoa flours. For instance, phytic acid was higher in PcRQ (2.0 g/100g) compared to PiBQ (1.65 g/100g) and PcYQ (1.15 g/100g), yet lower than in quinoa flours. Similarly, saponin levels were higher in PcRQ (162.2 mg/100g) compared to PiBQ (84.0 mg/100g) and PcYQ (103.8 mg/100g). Notably, hemagglutination assays detected activity only in the three quinoa flours. 

In summary, the extraction method increased the presence of certain ANFs such as trypsin inhibitors, saponins, tannins, and oxalates in quinoa isolates/concentrates. However, the digestibility of quinoa protein isolates was not adversely affected by the presence of ANFs.