2.6. Measurement of free amino acid contents
UBM and 30 g/L sulphosalicylic acid solution were mixed at a
ratio of 1:1 by volume and refrigerated overnight. The mixture was
centrifuged (5 C, 10,000 g, 10 min) and then filtered through a
0.22 mm filter. Free amino acid contents in the filtrate were
measured using an automated amino-acid analyzer (JLC500-500/
V2, JEOL Ltd., Akishima, Japan). All experiments were performed in
triplicate. Data was presented as the means with standard deviation
of the results from triplicate experiments.
2.7. Statistical analysis
Significant differences were evaluated using the TukeyeKramer
method (p < 0.01) or t-test (p < 0.01).