Quality deterioration of apple juice, thermally processed at constant tempe
ratures ranging from 95 to 123 degrees C for 2 to 30 min, was measured by t
hree quality indexes: nonenzymatic browning (NEBI), 5-hydroxymethylfurfural
(HMF) and fluorescence relative inner (FLRI). All three indexes followed a
n apparent zero-order reaction with activation energies of 148.6, 151.1 and
148.6 kJ/mole for NEBI, HMF and FLRI, respectively. FLRI correlated highly
with HMF (R-2 = 0.98). The correlation between HMF and FLRI, obtained unde
r constant temperatures, was verified under continuous process conditions o
f 85 to 135 degrees C and 30 to 180 s. FLRI was found to be a quantitative
criterion, which could be applied for 'on-line' monitoring of the deleterio
us effects of thermal processing of apple juice.