Microstructural changes while persimmon fruits mature and ripen. Comparison between astringent and non-astringent cultivars

• New information on natural astringency loss process in persimmon fruit is provided.
• Natural astringency loss is linked to a process of tannin insolubilization.
• Microstructural techniques allowed visualizing the process of astringency loss.
• Tannin insolubilization during maturation was slower in astringent fruit.

Persimmon cultivars are classified into two categories, those that bear astringent fruit at harvest and those that bear non-astringent fruit. Causes of natural astringency loss that fruits of non-astringent cultivars undergo on tree are yet to be clarified. A physicochemical and microstructural study of the maturity process of two astringent cultivars (‘Rojo Brillante’ and ‘Giombo’), and two non-astringent ones (‘Fuyu’ and ‘Hana Fuyu’) has been carried out. Light microscopy (LM) analysis allowed visualizing the higher soluble tannins content in astringent cultivars compared to non-astringent ones in early maturity stages as well as the natural tannin insolubilization that took place in both the astringent and non-astringent cultivars during maturation and ripening. In astringent cultivars this tannin insolubilization process was gradual and led to a progressive decline in soluble tannins. In non-astringent cultivars this insolubilization was much faster than in astringent cultivars. The present study also revealed that both colour evolution and fruit softening during maturation are characteristic for each cultivar, although in all of them a strong negative correlation was observed between these two parameters. Fruit softening was associated with a gradual parenchyma structure loss due to a cell wall and membrane degradation process. The total soluble solids content was found to be a good indicator of the sugars level in non-astringent cultivars, but should be ruled out in astringent varieties.