Aqueous two phase extraction of alkaline fungal xylanase in PEG/phosphate system: Optimization by Box–Behnken design approach

Alkaline xylanase produced under submerged fermentation by Aspergillus candidus was extracted in aqueous two phase system (ATPS) composed of PEG 4000/NaH2PO4 system. A Box–Behnken design was adopted to optimize critical factors like PEG molecular weight, PEG concentration and phosphate salt concentration and to enhance purification fold of xylanase. Enzyme purification factor was found maximum in presence of low molecular weight of PEG (4000), intermediate concentration of PEG (8.66% w/w) and high salt concentration (22.4% w/w). Under optimized condition threefold increase of purification factor with partition coefficient 8.41% and 88.10% enzyme yield at top phase was attained. The extracted enzyme was found to be stable at high alkaline pH and activity was stimulated in presence of Mn2+ ions. The ATPS was emerged as an effective alternative for primary purification of xylanase.