Amino Acid Composition
The determination of total amino acids of the walnut kernel flours (WKF)
was performed by high performance liquid chromatography (HPLC, Agilent
1260, Agilent Technologies Co., Ltd., Palo Alto, CA, USA, USA) according
to the described previously method of Trigui et al [17]. The HPLC
system was equipped with two columns (Styragel HMW7 and HMW6; Styragel,
Waters, Milford, MA, USA). Two hundred milligrams of samples were
hydrolyzed by 15 mL 6 M HCl for 24 h at 120 ºC. Then, the hydrolyzed
samples were mixed with 40 mL of 0.2 M citrate buffer (pH 2.2).
Norleucine was added as the standard solution with the amount of 1mL.
The mixture solution was diluted to 100 mL by citrate buffer. After the
samples were filtered by a 0.2 μm nylon filter, which was detected by
HPLC. The amino acid contents were expressed as g 100g-1 protein. Amino Acid Score (AAS) of amino acid
composition in samples was expressed as following the equation [18].
\(\text{AAS\ }\left(\%\right)=\frac{mg\ of\ amino\ acid\ in\ 1\ g\ of\ test\ protein}{\text{mg\ of\ amino\ acid\ in\ requirement\ pattern}}\times 100\)(1)