Fig. 6

a Extraction performance of the three extraction procedures. BE: boiling ethanol, 75% (v/v) ethanol boiling in 95 °C for 4 min; TF: thawing–freezing in liquid nitrogen and cryostat at − 30 °C in 50% (v/v) methanol for three cycles; G: grinding in liquid nitrogen in 50% (v/v) methanol. Metabolites were divided in four parts, which were: AA amino acids, OA organic acids, PS phosphate sugars, SA sugar alcohols. All means the summation of these four parts. b Intracellular metabolites in Streptomyces ZYJ-6. Based on IsoaB and Meth60 as the quenching solution, and thawing–freezing (TF) in liquid nitrogen and cryostat at − 30 °C within 50% (v/v) methanol for three cycles as the extraction procedure. IsoaB: isoamylol with base solution 5:1 (v/v) at − 30 °C; and Meth60: 60% methanol at − 30 °C, respectively. Base solution consisted of acetone:ethanol = 1:1 (mol/mol). The red polygon represents intracellular metabolites from Meth60 quenching and the black square represents intracellular metabolites from IsoaB. Data were averages ± standard deviation of the three replicate samples, each of which was analyzed in triplicate