2.7. Analysis of AAs contents
The procedures to determine individual AAs were conducted
according to the published literature (Xia, Niu, Wu, & Zhou,
2016), with little modification. Prior to AAs analysis, centrifugations
(4400g, 4 C) were performed for 30 min twice. The collected
supernatants were mixed with equal volumes of
sulfosalicylic acid (10%) to precipitate protein, and then centrifuged
for 15 min (10,500g, 4 C). Aliquots (20 ll) of the supernatants
were injected into an L-8900 automated amino acid
analyzer (Hitachi, Tokyo, Japan). The final contents of individual
AAs in the solutions were qualified by calibrating with standard
AAs.