2.3. Ripening and storage treatments (Tests 1A and 1B)
To examine the effect of ripening prior to cold storage on subsequent fruit quality (part A) avocados were placed into cold storage either immediately after harvest (average firmness = 200 N) or following treatment with 25 μL L−1 ethylene and ripening at 20 °C until the fruit were either partially ripe (average firmness = 80 N) or near ripe (average firmness = 19 N). In each case firmness was determined by use of a penetrometer (U.C. firmness tester, 8 mm tip). Fruit were stored at either 5 °C or 12 °C at 95% RH for either 4 d or 14 d. The storage times were selected to represent common avocado commercial handling practices in the United States, with 4 d or 14 d being typical short- or long-term storage durations, respectively. A temperature of 5 °C is used by the industry to slow ripening and maintain quality for as long as possible while 12 °C might be used to accelerate softening for the purpose of delivering ripened fruit at a specific time. After cold storage the fruit were held at 20 °C and 90–95% RH until the average flesh firmness was ≤6.7 N, at which time the fruit were considered to be fully ripe and at optimal eating firmness. In a separate experiment to assess the impact of prior cold storage on ripening time and quality (part B), avocados were placed in storage at 5 °C for 0 d, 7 d, 14 d, and 28 d the day after harvest and then ripened with 50 μL L−1 ethylene at 20 °C for 0 h, 24 h or 48 h following storage. The fruit were then ripened to eating firmness and assessed for fruit quality parameters. The impact of the various treatments on the timing of ripening was assessed by measurement of firmness and recording the number of days from when the treatments left cold storage until full ripeness was reached.