Table 2 shows the amount of TA extracted from microwaved
potato using different ultrasound amplitudes and ethanol:water
ratios. Generally, for 50% ethanol, there is an increase in TA
extracted with increase in amplitude but the results here are
not so clear cut. The greatest amount of TA obtained was after
30 min UAE at 70% amplitude whilst other values were significantly
lower than this value. In this case, the purely thermal
extraction led to an increase in TA over time but the UAE
showed an increase up to 30 min but then a decrease for the
next 90 min. With 70% ethanol, there was a great variation in
the results, with the highest amount being obtained after
30 min treatment at 70% amplitude but this was still less than
that obtained with 50% ethanol for the same time and amplitude.
Once more, degradation of TA was apparent after 30 min
but this did not seem to be as striking as the results from the
freeze dried potatoes. In this case, the maximum TA extraction
was obtained with 50% ethanol after 30 min of ultrasound at
70% amplitude. Although extraction under thermal conditions
reached similar values, when compared to UAE (at 70:30 solvent
ratio), it requires longer times (120 min instead of 30 min). It
should be noted that the highest TA extracted was observed
with the lower solvent ratio, meaning that in these extraction
conditions/form of potato it is possible to optimise TA extraction
with UAE and simultaneously reduce the amount of organic solvent
required for the extraction.
The TA extracted from slices of potatoes is much lower than the
amount of TA obtained from the other forms of potatoes (see
Table 3), however the use of UAE on this form of potato proved to
have a greater impact on the amounts extracted (certain conditions
lead to a 3–4-fold increase of the amount of TA extracted compared
to the thermal process). The amount of TA extracted was highest
using 70% ethanol with an ultrasonic amplitude of 70% for
60 min. The thermal treatment was very poor in this case and
resulted in the lowest amounts obtained of all the experiments.