# Nutritional and Functional Properties of Gluten-Free Flours
## 3 Results
### Amino Acid Compositions  
The amino acid composition of the GF flours studied is presented in Table 3 (expressed as g/100 g protein) and Table S3 (as g/100 g d.m. flour). There was a great variability in the amino acid content between the flours analyzed. Glutamic acid, aspartic acid, and arginine had the highest non-essential amino acids in GF flours, while leucine was the highest essential amino acid. Overall, tiger nut and plantain flours had the lower content in amino acid.  
It is well known that lysine is a nutritionally limiting amino acid in cereals. Regarding its content, chickpea (8.5%) and gram (6.6%) flours, followed by the pseudo-creals (quinoa, buckwheat, and amaranth, between 5.2-5.9%) and oat (5.2%) flours were found to be high in lysine. [PERSON] et al. [55] also confirmed that the pseudo-cereals amaranth and quinoa contained higher amount of lysine than cereals. It was showed that high levels of globulins and albumins was responsible for high lysine content [56]. Maize and millet flours showed a high content of leucine (12.3% and 11.8%, respectively), while the lowest content was for plantain and amaranth flours (5.9% and 5.6%, respectively). The percentage of methionine in the GF flours was significantly much higher in millet and teff flours (3.4-3.7%) than the others flours.  
Glutamic acid was the most abundant amino acid, ranging from 12.9 to 23.3 g/100 g protein, except for plantain flour with significantly lower value (9.8%). In general, plantain flour had lower level of amino acids, except for threonine and histidine.  
The higher arginine content (12%; \(p<0.05\)) in chickpea and tiger nut will lead to a higher contribution of these flours to the Maillard reaction [57].  
According to Table 4, gram, chickpea, quinoa, buckwheat, and oat flours did not contain any limiting amino acids as AAS value were higher than 1. Millet flour showed a lack of lysine. In addition, maize, teff, rice, brown rice, and plantain flours were lacking in lysine. Conversely, chickpea and gram flours recorded the highest scores for lysine. PDCAAS ranged between 0.27 and 0.97 (Table 4). A value of 1 is considered an optimum value. Accordingly, chickpea followed by oat, quinoa, gram, and buckwheat flours can be considered as GF sources with a good protein quality compared to the other flours investigated.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Flows** & **Leu** & **Lys** & **Phe** & **Val** & **Ile** & **Thr** & **Met** & **His** \\ \hline Rice & 8.10 \(\pm\)0.14\({}^{\rm\,d}\) & 3.31 \(\pm\) 0.08\({}^{\rm\,d}\) & 4.61 \(\pm\  
Other indexes which are used to estimate the protein quality are presented in Table 5. The protein score indicates the chemical score of the most limiting EAA that is present in the sample. The greater the EAAI, the more balanced amino acid composition and the higher quality and efficiency of the protein. EAAI, an indicator of the ratio of essential amino acids of the sample compared to the reference (hen's egg) and BV (which estimates the nitrogen potentially retained by the human body after consumption) were the highest for chickpea flour, followed by oat, brown rice, maize, and gram flours. The PER index, which describes the ability of a protein to support the body weight increase, was higher for maize and millet flours. Among all the indexes calculated, NI is the only one which considers both qualitative and quantitative factors and it is a global predictor of the quality of a protein source. Accordingly, gram and chickpea flours showed the higher nutritional index, followed by the pseudo-cereals flours, while plantain flour had the lowest NI.