Fig. 4From: Development of optimal steam explosion pretreatment and highly effective cell factory for bioconversion of grain vinegar residue to butanolThe ultrastructure images of vinegar residue before and after steam explosion treatment. a The control (untreated vinegar residue); b–d the treated VR from 1.5 MPa to 2 min, 2 MPa–2 min and 2.5 MPa–2 min respectivelyBack to article page