BIOCONVERSION OF STARCHES INTO MALTOTETRAOSE USING PSEUDOMONAS-STUTZERI MALTOTETRAOHYDROLASE IN A MEMBRANE RECYCLE BIOREACTOR - EFFECT OF MULTIPLE ENZYME-SYSTEMS AND MASS-BALANCE STUDY

A simplified single-step method involving simultaneous production and purification of maltotetraose (G(4)) by employing ultrafiltration (UF) membranes was previously proposed. The addition of a pretreatment ste p using pullulanase and then the G(4)-anaylase was expected to increas e the yield of G(4) The single-enzyme system, however, showed 0.42 g h igher total product output than the successive dual-enzyme system thro ughout 6 h reaction. The G(4) yield using the successive dual-enzyme s ystem could be improved after removing the unwanted side product with UF. Experiments were conducted with membranes of larger pore size, but this did not significantly increase the total product output. The mem brane unit with a molecular weight cutoff of 1,000 was the most approp riate membrane pore size for the G(4)-exo-alpha-amylase membrane recyc le bioreactor system. The total amount of substrate fouled in the memb rane during a 6-h reaction was estimated as 69 mg glucose equivalent w hen substrate concentration was 0.25% (w/v). The mass balance equation indicated that the percent conversion of soluble starch to G(4) at st eady state was 65%.