EFFECT OF MIXING ON ENZYMATIC LIQUEFACTION OF SAGE STARCH

The effect of mixing as a function of agitation speed and impeller dia meter on the rate and degree of enzymatic liquefaction of sage starch was carried out using a stirred tank reactor with a single Rushton tur bine impeller. The performance of the reactor as a mixing device was f irst examined using different concentrations of carboxymethylcellulose , which exhibited pseudoplastic behaviour similar to that of the solut ion during the sage starch liquefaction process. A correlation between mixing time (t(m)) and Reynolds number (Re) in the form of t(m) = bRe (c) is presented; the constants for the correlation depended on viscos ity of the fluid. For the two ratios of impeller diameter (D-i) to tan k diameter (D-t) used, 0.407 and 0.542, agitation speed gave significa nt influence on both overall rate and degree of liquefaction of sage s tarch. Mixing time (t(m)) was independent of impeller diameter used, a nd correlated well with the overall rate of liquefaction (P) (calculat ed as the reducing sugar produced divided by time of liquefaction) and expressed as P=1.95t(m)(-0.362). (C) 1997 Elsevier Science Ltd.