2.2. Physiological assessment
Lots of 15 fruit were divided into 3 samples and cut into 4
longitudinal parts. Two opposite parts were sliced and frozen at
−20 ◦C to determine soluble tannins. The other opposite parts of
the fruit were placed in an electric juice extractor and the filtered
juice was then used to determine acetaldehyde production.
Soluble tannins were evaluated using the Folin–Denis method
(Taira, 1995), as described by Arnal and Del R´ıo (2004); the
results were expressed in % of fresh weight.
To determine TI (Gorini and Testoni, 1988), five fruit were
evaluated from each treatment. The soluble tannins responsible
for persimmon astringency are compounds that react with
ferric chloride to form tannin–Fe ion complexes, which are
blue–black. The degree of astringency can be estimated by evaluating
colour development during the reaction. Persimmon fruit
were cut equatorially, and after 15 min the freshly cut surface
was immersed in a 5% FeCl3 solution for 3 min. After another
3 min out of the solution, the colour of the freshly cut surface was
scored visually on a scale from 1 (less colour development or
minimum tannin content, no astringency) to 5 (maximum colour
development or maximum tannin content, high astringency).
A sensory evaluation of astringency was also performed on
composite samples of five (peeled and sliced) fruit from each
replicate.