3.2. Total phenolics and PPOThe mar

3.2. Total phenolics and PPO
The marked colour change that occurred during the processing
of tubers suggested the presence of polyphenolics and PPO. It was
previously reported that Jerusalem artichokes contain phenolic
compounds as bioactive constituents (Pan et al., 2009). Colour value
of the dried chip extract as shown in Table 1 revealed the existence
of water-soluble polyphenolics. Consistent with the results
reported by Seljåsen and Slimestad (2007), our results of the total
polyphenolics’ content in a raw tuber revealed that peels were the
main source of polyphenolics; the peel fraction contained 82.3 ±
30.6 mg GAE/100 g whereas whole tubers contained 37.0 ±
8.2 mg GAE/100 g. When the tubers were peeled, the content
markedly decreased to 8.0 ± 0.5 mg GAE/100 g, which is 10 times
less than that in the peel fraction. However, only a small amount
of phenolics was detected in dried chips; (A), (B), and (C) contained
0.57, 0.38, and 0.61 mg GAE/g dry matter, respectively. It was
hypothesised that the drying temperature was not high enough
to inactivate PPO, and therefore some phenolic compounds were
not quantified properly. Tchoné et al. (2005) have reported that
PPO of Jerusalem artichoke had been heat-inactivated and only
30% remained after incubation for 5 min at 70 C. Thus the enzymatic
characteristics of the PPO were re-examined. First, a crude
extract was prepared as an enzyme source and then the activity
remaining after heat treatment of the extract was determined. As