Comparing the activation energy obtained for HMF=HMF0 to A420=A0 420 it was observed that the activation energy found for HMF formation was lower than that of brown pigment formation. The results implied that HMF occurred at a higher rate than the latter substance. After heating, HMF retained in the juice would change to a brown pigment during storage. Therefore, HMF was proposed as a useful indicator to determine the change of color in the pineapple juice (Table 4).