The free amino acid composition of the samples were analyzed
using an amino acid analyzer (L-8900, Hitachi, Katsuda, Japan) following
Li et al. (2014) with some modifications. Different dried
samples were ground finely. The powders (0.2 g) were added to
10 mL 75% ethanol and then heated in a 70 C water bath for
30 min. After centrifugation (10,000 rpm, 10 min), the collected
supernatant was evaporated by nitrogen blowing at 50 C. The
residual was dissolved in 4 mL deionized water and diluted 8 mL
lithium citrate solution to reach a final pH value between 2 and
3. Then, the protein was also removed by adding 3 mL 3% trichloroacetic
acid solution and allowed to stand at 4 C for 1 h, and then
centrifuged for 15 min at 10,000 rpm. The collected supernatant
passed through a 0.22 lm membrane filter. Mixed standard amino
acids with taurine standard were analyzed before sampling. The
amino acids were identified and quantified by comparing peak pro-
files of the mushroom samples with standard amino acid profiles.
The results were expressed as the milligrams of amino acid per
gram dry weight (mg/g).
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