Fructooligosaccharides production by Schedonorus arundinaceus sucrose:sucrose 1-fructosyltransferase constitutively expressed to high levels in Pichia pastoris.

•A new candidate enzyme for industrial short-chain FOS production.•Recombinant Sa1-SST converts sucrose into 1-kestose and nystose in a ratio 9:1.•First report of constitutive high-level expression and secretion of a plant 1-SST in Pichia pastoris.•The increase to nine gene copies enhanced Sa1-SSTrec yield without causing cell toxicity.•N-glycosylation influences the enzyme stability but not substrate recognition or catalysis.•Evolved Sa1-SST traits of biotech relevance are discussed using a constructed 3D structure model.