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.