2.7. Organic acid assay
Organic acids were extracted according to Li et al. (2014). Different
degrees of dried samples were weighed, ground sufficiently,
and extracted with 10 mL of 0.01 M KH2PO4 (pH = 5.6) solution at
45 C for 1 h. Then the suspension was centrifuged at 4500g for
15 min, the supernatant filtered using a 0.45-lm micro-pore filter
membrane before analysing.