Relationship between Endogenous Ethylene Production and Firmness during the Ripening and Cold Storage of Raspberry (Rubus idaeus ‘Heritage’) Fruit

The raspberry (Rubus idaeus) is an important fruit crop; however, its accelerated softening is a critical postharvest problem, even at low temperatures. Its softening has been partially associated with the endogenous production of ethylene from the receptacle during ripening. To understand the relationship between ethylene production and fruit quality at the beginning of the ripening process, the physiological and quality parameters were evaluated during the ripening of the ‘Heritage’ cultivar. Two storage assays, at 0^◦ C and 10^◦ C, were carried out with independent groups of fruits attached to their receptacle at the white stage of fruit development. The treatments included fruit treated with ethylene (1000 ppb) and ethylene perception inhibitor 1-methyl cyclopropene (1-MCP, 1600 ppb) and a control treatment. During ripening, the endogenous production of ethylene in whole fruit was negatively correlated with the loss of firmness. During storage at 0^◦ C, firmness and ethylene production only decreased by the effect of storage time, with a firmness near 1.5 Newtons at 16 days. On the other hand, the storage at 10^◦ C showed a delay in the firmness loss and lower ethylene production of the fruit treated with 1-MCP, compared to the control and ethylene-treated fruit. In addition, these two last assays showed a firmness close to 1 Newton at 5 days. No significant differences were observed in the total soluble solids content and titratable acidity between the three treatments at the two storage temperatures. The results during ripening and storage at 10^◦ C indicate that the loss of the fruit’s firmness is positively related to the endogenous ethylene production of the whole fruit from 1 to 5 days of storage. Future assays should be performed to determine the role of ethylene in raspberry ripening.