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Prof. Di Renzo - Università della Basilicata

Notes on tannin removal to eliminate persimmon astringency

The astringency phenomenon, which makes persimmons inedible, is due to the action of procyanidins, a class of phenolic compounds better known as condensed tannins. They interact with salivary proteins and form those complexes responsible for the astringent feel. 

There are numerous methods to remove astringency, all of which are based on the conversion of tannins from soluble to insoluble (Bellini et al., 2010).

Among the most common post-harvest treatments, CO2 is used alone or in combination with other gases (ethylene or nitrogen) with different concentrations, percentages, and administration methods and times.

The treatment consists in keeping persimmons in special units with a high concentration of CO2 for more than 20 hours. The units are equipped with plants for the dosing and measurement of CO2 as well as isolating and safety systems.

Produce in units for the treatment to eliminate atringency
Prodotto in cella per l'esecuzione del trattamento di rimozione dell'astringenza.

Many authors proved how variable treatment times (from 20 to 48 hours) with high percentages of CO2 (85-95%) at room temperature (20-25°C) do eliminate astringency and extend shelf-life, thus improving the characteristics of the fruit without affecting weight or compactness.

Instrument to control CO2 concentration in the treatment unit.

The method is efficient and eliminates astringency after approximately 1 day of CO2 treatment.

Quick test to determine the level of astringency before (testimone) and after the treatment. A few drops of ferric chloride are distributed on the fruit. The intensity of black spots is proportional to the level of astringency. In fact, the testimone (not treated) is dark, whereas the other fruits are not.

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