‘Hass’ avocado quality as influenced by temperature and ethylene prior to and during final ripening

Abstract

Avocados (Persea americana Mill.) are often held for short periods after harvest at relatively high temperatures both in the field, in storage during preconditioning (ethylene ripening), or prior to ripening with unknown effects on subsequent quality. To better understand the quality effects of short-term high temperature exposure, avocados were harvested at five different times during the first commercial season and held at 20, 25, 30 or 35 °C for 24 h or 48 h, with and without ethylene. During the subsequent season (2) the experiment was repeated, but without the 30 and 35 °C treatments. In both seasons, following the short-term temperature treatment, fruit were either immediately ripened at 20 °C or stored for 14 d at 5 °C and then ripened to determine the influence of storage. After final ripening to eating firmness (4.4–6.7 N) the fruit were evaluated for quality parameters. Results from the first two seasons showed that even a 24 h exposure to 25 °C and above was sufficient to inhibit subsequent ripening and enhance the occurrence of postharvest disorders such as stem end rot and body rot. Application of ethylene during the short-term temperature exposure was ineffective in preventing the disorders. In the third season of the study the effect of prolonged temperature exposure on final ripening was examined. Although there had been research done in the past on this subject, prior work had not examined the effect of different ripening temperatures on flavor. Avocados were harvested at seven harvest dates, stored for either 4 d or 14 d at 5 °C and then ripened to eating firmness at temperatures ranging from 15 to 25 °C. Increasing temperatures up to 20 °C decreased ripening time, beyond which there was no further change. Avocados ripened at temperatures above 20 °C had an increased incidence of the development of pink discoloration in the mesocarp. Ripening temperature had no effect on overall likeability, or ratings of grassy or rich flavor. This correlated with a lack of clear effect of ripening temperature on aroma volatile content of the fruit. Panelists found fruit ripened at 15 °C to have a different texture that those ripened at 20 °C but this had no influence on likeability. This study strongly indicated the importance of maintaining the ripening temperature of avocados at or near 20 °C both when the fruit is ripened soon after harvest or after storage to optimize postharvest quality.