REDUCTION OF ASTRINGENCY IN PERSIMMON CAUSED BY ADHESION OF TANNINS TO CELL WALL FRAGMENTS

Removal of astringency in persimmon fruits (Diospyros kaki) subjected to different freezing temperature treatments

The effects of two different freezing temperatures (- 20 °C and - 80 °C) on the astringency trait of persimmon fruits during 15 to 60 days of storage were investigated. The levels of soluble and insoluble tannins, proanthocyanidins and other physicochemical characteristics were evaluated. Storage at - 20 °C and - 80 °C temperatures up to 60 days has been found to be an effective method to remove astringency of persimmon fruits. Proanthocyanidin concentration was negligible at both temperatures during storage. Total soluble solid contents were decreased as 3.34 from 4.59 (mg/g DW) whereas, insoluble tannin contents were increased as 20.30 from 16.45 (mg/g DW) by freezing temperatures treatment during storage. Comparatively, higher soluble tannin content 11.68 (mg/g DW) and lower insoluble tannin content 10.02 (mg/g DW) was observed in control (day 0). Therefore, the astringency of persimmon fruits incubated at - 20 °C and - 80 °C was markedly reduced and after 15 up to 60 days of storage, the astringent taste virtually disappeared. The proanthocyanidin contents were decreased as 0.02 from 0.52 (mg/g DW) at - 20 °C storage and 0.17 from 0.47 (mg/g DW) at - 80 °C storage, in comparison with the control 2.65 (mg/g DW). The moreover, along with the removal of astringency, other physicochemical parameters including color, pH, moisture content, total soluble solid, and sensory attributes were also conserved on freezing at both the temperatures. These findings suggest that freezing temperature treatments aid the removal of astringency from persimmon fruits which could be used in different food preparations or as supplements.

Physico-Chemical and Microstructural Changes during the Drying of Persimmon Fruit cv. Rojo Brillante Harvested in Two Maturity Stages

The physico-chemical and microstructural changes of “Rojo Brillante” persimmons in two maturity stages (S1 and S2) were evaluated during air drying. The maturity stage influences moisture loss. A Moisture level of approximately 50%, a limit at which persimmons are considered semidried, was reached after 21 and 28 days for S1 and S2, respectively. Shrinkage resulting from water removal led to secondary epidermis formation concomitantly to internal flesh gelling, which was related to moisture loss and water activity changes of each fruit part. The thicker epidermis and the lower volume of gelled area inside the S1 fruits led to harder fruit compared to the S2 fruits. The microstructural study revealed parenchyma degradation during drying in both the outermost area (secondary epidermis) and internal flesh, and this process was faster in S1 than in S2. The second peel presented hollows, generated by water outflow, which were bigger in S1 and explained the faster internal dehydration in S1. During drying, slight browning occurred, as reflected in the declining color parameters (L*, h* and C*). Water removal led to soluble solids tannin reduction to non-astringency values on day 28.

Temperature and Ultra Low Oxygen Effects and Involvement of Ethylene in Chilling Injury of ‘Rojo Brillante’ Persimmon Fruit

The effects of storage temperature, inhibition of ethylene action by treatment with 1-methylcyclopropene (1-MCP) and ultra low oxygen (ULO) atmosphere on chilling injury (CI), fruit firmness and ethylene production in the astringent ‘Rojo Brillante’ persimmon fruit were investigated. CI symptoms were manifested as a very dramatic loss of firmness after fruit transfer from cold storage to shelf-life conditions (18 °C). During cold storage, fruit softening appeared more rapidly in fruit stored at the intermediate temperature of 10 °C than at 1°C or 14.5 °C. Ethylene production increased with storage time at the chilling temperature (1 °C) but a sharp increase took place upon fruit transfer from 1 °C to ambient temperature. This ethylene increase was accompanied by a loss of fruit firmness associated with chilling damage development. A pre-treatment with the competitive inhibitor of ethylene action 1-MCP, at 1 μL/L, reduced firmness loss and mitigated CI damage but considerably increased ethylene production in fruit transferred to shelf-life conditions after a prolonged cold storage period. Collectively, these results suggest a role of ethylene in the reduction of flesh firmness and consequently in the induction of CI in persimmon fruit. Moreover, ethylene exerts a negative feedback regulation of cold-induced ethylene biosynthesis. Storage of ‘Rojo Brillante’ persimmon fruit under ULO (1.3—1.8% O2, v/v) atmosphere did not affect the incidence of CI but reduced fruit astringency, suggesting that ULO may be an alternative postharvest storage system for ‘Rojo Brillante’ persimmon fruit.