How do temperature and ethylene affect the quality of Hass avocados during ripening?

Avocados have high respiration rates and produce large amounts of ethylene, carbon dioxide, and heat during the ripening process. These factors make management of the ripening process critical in the commercial postharvest environment. The following article presents the results of a study that investigated the effects of short-term exposure to temperatures between 20?35?C on the ripening process and quality of Hass avocado. Introduction Farmers must ripen avocados after they are harvested, rather than allowing them to ripen on the tree before consumers can eat them. Similarly, retailers often ripen avocados before selling them because consumers generally prefer to buy avocados that are almost ready to eat. Food service companies also prefer to receive ripe fruit, which reduces the amount of labor required to process the fruit. All of this means that the ripening process must be managed in the commercial post-harvest environment. Avocados present unique challenges because they have high respiration rates and produce large amounts of ethylene, carbon dioxide, and heat. During the ripening process, these factors must be controlled. As with other fruits, the temperature during ripening affects the time it takes for avocados to soften and the quality of the fruit. Researchers have found that the optimal temperature range for ripening avocados is between 21?C and 27?C. Temperatures above 30?C resulted in uneven ripening and darkening of the flesh. They also found that high temperatures above 25?C inhibited ethylene production and reduced respiration at 40?C, resulting in poor fruit quality. Ripening at 35?C and above caused the fruit to become internally discolored, with rubbery flesh that could not ripen. Besides, they observed that avocados did not ripen at 30?C and that even ripening at 25?C affected fruit quality, causing an increase in storage disorders often associated with postharvest decay. Short-term postharvest heat exposure, such as hot water or hot air treatment, had long-lasting physiological effects on avocados, providing resistance to next exposure to both high and low temperatures. However, excessive short-term heat exposure damaged fruit quality and increased decay. Avocado fruit exposed to the sun while still on the tree can also experience high flesh temperatures, resulting in delayed ripening and increased tolerance to high or low temperatures after harvest compared to fruit that develops in the shade. The avocado industry uses a technique called ?triggering? or preconditioning, which uses ethylene to synchronize and regulate ripening. This method is used in global markets to promote consumption and market penetration. However, pulp temperatures are often unregulated during this process, resulting in temperatures above 21?C. Previous research has demonstrated the negative impact of high temperatures on final ripening, but either lacked thorough quality assessment or used fruit grown in environmental conditions different from California, which may have different postharvest quality issues. In 2018, the journal Postharvest Biology and Technology published a study that was conducted by the University of California. In the first two seasons of their research, they examined the effects of brief temperature increases on the Hass avocado quality that can occur after harvest but before ripening. In the third season, they studied the effect of temperature on the final ripening of avocados, including its effect on the sensory characteristics and flavor components of the fruit. The following is a summary of the discussion of the results and the conclusion of the study. Discussion The purpose of this?study was to investigate the effects of short-term exposure to temperatures between 20?35?C on the ripening process and quality of avocado fruit. This research revealed that exposure to such temperatures for only 24?48 hours resulted in longer final ripening times and loss of fruit quality. In addition, delayed ripening increased the incidence of stem end rot and body rot, especially at higher temperatures of 30?C and 35?C. The availability of ethylene was not enough to cut the inhibitory effect of high temperatures on ripening. Besides, cold storage after heat treatment reduced the temperature-induced delay in ripening. What was also observed during the analysis was that ethylene exposure prior to cold storage was beneficial when the fruit ripened immediately. However, it was detrimental if there was a prolonged period of cold storage because the fruit was at a higher stage of ripeness during this time and was more susceptible to rot development than fruit not treated with ethylene. In the third year of the study, the influence of temperature on sensory quality was evaluated. The results showed that avocados ripened at temperatures above 20?C had more pink flesh, a disorder caused by an accumulation of anthocyanin pigments in the mesocarp. The evaluation concluded that short-term exposure to temperatures above 20?C delayed ripening, increased the incidence of spoilage, and reduced the sensory quality of avocados. Cold storage after heat treatment reduced the temperature-induced ripening delay, and avocados that ripened at temperatures above 20?C had greater amounts of pink flesh. Conclusions The results of this research show that it is important to keep Hass avocados at temperatures below 25?C after harvest and before full ripening. Even short contact with temperatures above this limit, as little as 24 hours, can delay the ripening process and cause more postharvest problems. This is especially true in the California avocado industry, where such temperature peaks can happen during both the field and fruit pre-conditioning phases. The use of ethylene treatment during pretreatment does not solve this problem, especially when temperatures reach 30?C or higher. The study also showed the impact of temperature control during the final ripening phase, as the fruit ripened at temperatures above 20?C had a higher rate of Pink Flesh Disorder. However, the research found that flavor sensitivity to curing temperatures in the 15?C to 25?C interval was not relevant. Author:?Jorge Luis?Alonso G. (with ChatGPT)?Maximizing Agribusiness Profits with Expert Postharvest Storage Strategies | Horticultural Writing Specialist.?This article was written exclusively for the business platform Postharvest. Cover photo: Pixabay