Ap. Torres et Far. Oliveira, Application of the acid hydrolysis of sucrose as a temperature indicator in continuous thermal processes, J FOOD ENG, 40(3), 1999, pp. 181-188
The hydrolysis of sucrose in an acid medium was used as a temperature indic
ator to measure holding temperatures in a continuous thermal-processing uni
t. From a theoretical analysis, target conversion (chi) and errors in both
acid concentration and conversion measurements were found to affect signifi
cantly the accuracy of predicted temperatures, whereas errors in the determ
ination of the fluid mean residence time did not show a significant effect.
For different pasteurisation temperatures (70 degrees C < T < 86 degrees C
) and flow rates (4800 < Re < 11,300), the acid concentration in the medium
was adjusted so that different extents of reaction could be tested, as the
reaction rate was found to increase exponentially with [H+]. Nitric acid s
olutions were circulated through the unit, a sucrose solution was continuou
sly fed to the entrance of the holding tube and sucrose concentration was a
nalysed at the half way part and at the exit of the holding tube. The tempe
rature of the holding section was then estimated from the measured conversi
on. These results compared well with thermocouple measurements, with deviat
ions of less than 4 degrees C for conversions between 0.4 and 0.7, whereas
greater errors were obtained for both low and high conversions. (C) 1999 El
sevier Science Ltd. All rights reserved.