summarised in Table 3, most PPO activity remained after heating at
60 C for 10 min, and 74% of the activity remained at 70 C. Blanching
for 30 s did not inactivate the PPO, but inactivation occurred
time-dependently during further blanching. Microwave treatment
almost completely abolished the activity in a short time. The sample
temperatures after 10 and 30 s treatment were 70 and 88 C, respectively.
Thus, it was concluded that microwave treatment effectively
inactivated PPO at a relatively low temperature. Blanching for 120 s
did not completely inactivate the PPO, but the remaining heat was
enough tomaintain a pale sample colour according to the extract colour
of 120 s-blanched chips above as shown in Table 1. It is noteworthy
that the extract colour became significantly redder during the
homogenisation of tubers, especially in peel-containing samples.
This fact is consistent with the above results: the peel contained
more polyphenolics than the tuber body, and blackening proceeded
from the rim of tuber slices. Therefore, for direct consumption, peeling
will be preferred and mixing in a juicer should be avoided in order
to improve the appearance.
3.3. Water- and oil-holding capacity
It was found that tuber samples absorbed moisture while extracts
were being prepared and that a considerable volume of pellet
remained after filtration. Therefore, it was anticipated that the
tubers would have a high water-holding capacity, and the waterholding
capacity was measured using dried artichoke tuber powder.
Potato starch is widely used as moisture absorbent in the food
industry, but it is only active at high temperatures. In our study,
Jerusalem artichoke tubers revealed having capacity to absorb at
least 6 ml of water/g dry matter at 40 C (Fig. 1A). Interestingly,
dried Jerusalem artichoke absorbed almost the same volume of
water at either 40 or 80 C. Unblanched samples absorbed less
water compared to blanched samples. It was hypothesised that
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