Peter M.A. Toivonen, Senior Research Scientist, Summerland Research and Development Centre, Summerland, British Columbia
Since its commercial release in the mid-1990’s, ‘Sunrise’ apple has been prized as a summer apple with exceptional taste and crunchiness. However, the challenge for this apple is, that if it is stored and handled as other varieties are, it softens at shelf temperatures at a very rapid rate and can become mealy within a few days on the counter (Lane et al., 1996; Lau, 2012). The reason for this is that ‘Sunrise’ is chilling sensitive and should not be stored below 15 °C (Toivonen and Lu, 2005; Qui et al., 2009) much like what is recommended for vine ripe greenhouse tomatoes.
Lau (2012) proposed two general options for handling and storage of ‘Sunrise’; 1) place them in cold storage, display in a refrigerated display and advise the consumer to keep refrigerated until consumption or at least until within two days before they will be consumed, or 2) treat with 1-MCP and store at 20 °C, display in an unrefrigerated display and advise the customer to not refrigerate the apple prior to consumption. In our laboratory experience with ‘Sunrise’ apple, we echo the recommendations made by Dr. Lau. The one comment that I feel needs to made is that successful or consistent adherence to the advice for retailers and consumers under option 1 is not likely to occur in practice. Therefore, my opinion is to recommend that ‘Sunrise’ growers or shippers consider the possibility of treating their fruit with 1-MCP and handling at temperatures ranging from 15-20 °C and recommending that distributors and retailers handle them warm, much like greenhouse tomatoes. Jeffrey Cassidy of AgroFresh has developed a protocol for treatment of ‘Sunrise’ apples at elevated temperatures (personal communication) and so application of this approach could be relatively straightforward for those interested in exploring this option. Our work has also shown that a second application 1-MCP one week after the first application will enhance the quality retention in ‘Sunrise’ apples when held at 20 °C (Toivonen and Lu, 2005).
Lau (2012) made recommendations for a very narrow harvest window for ‘Sunrise’ not treated with 1-MCP and stored at 0 °C before marketing (starch index between 2.3 and 2.9 and having a firmness of between 15.7-16.6 lb). Quality declines faster for fruit picked after the recommended harvest window and storage disorders become significant if the fruit are picked at starch index greater than 4.4. However, if ‘Sunrise’ apples are treated with 1-MCP at elevated temperatures and stored for three weeks at 22 °C, there is good firmness and acidity retention (Figure 1 and 2) despite a wide range of harvest maturities tested over three years. No storage or senescence related disorders were observed in that work. Lau (2012) recommended that one month of holding is possible when apples are treated with 1-MCP and held at room temperature.
The conclusion for ‘Sunrise’ is that it is a very good summer apple, but it needs to be treated like a greenhouse tomato and stored, shipped, displayed and held at between 15-20 °C. In order to achieve a reasonable storage/shelf life, at least one, but optimally two, 1-MCP treatment(s) are recommended to have a shelf life of about 1 month for this apple. The apple should be harvested at a starch index of 2.3-2.9, but if handled at elevated temperatures as recommended and treated with 1-MCP, there may be some forgiveness for later harvested ‘Sunrise’ apples. Firmness at harvest is extremely important with a suggested average firmness of 15 lb being the lowest acceptable target for commercial marketing.
Figure 1. Changes in firmness for ‘Sunrise’ apples held at 22°C in three seasons (2000 to 2002). The first harvest in each of the three years was at the commercially recommended harvest date. The latter two harvests occurred one and two weeks after the initial commercial harvest. Apples for the 1-MCP treatment were treated 14 hours with 0.25 ppm of 1-MCP at 22 °C. Each data point represents four replicates of 10 apples each and the error bars represent standard errors of the means.
Figure 2. Changes in titratable acidity for ‘Sunrise’ apples held at 22°C in three seasons (2000 to 2002). The first harvest in each of the three years was at the commercially recommended harvest date. The latter two harvests occurred one and two weeks after the initial commercial harvest. Apples for the 1-MCP treatment were treated 14 hours with 0.25 ppm of 1-MCP at 22 °C. Each data point represents four replicates of 10 apples each and the error bars represent standard errors of the means.
Lane, W.D., R.A. MacDonald, O.L. Lau and K.O. Lapins. 1996. Sunrise apple. Canada Journal of Plant Science 76: 165-167.
Lau, O.L. 2012. Optimizing Harvest Maturity, Fruit Quality, and Shelf-Life of ‘Sunrise’ apple. ‘Sunrise’ Apple Factsheet (July 2012), British Columbia Fruit Growers’ Association, 21 pp.
Qiu, S., C. Lu, X. Li and P.M.A. Toivonen. 2009. Effect of 1-MCP on quality and antioxidant capacity of in vitro digests from ‘Sunrise’ apples stored at different temperatures. Food Research International 42: 337–342
Toivonen, P.M.A. and C. L. 2005. Studies on elevated temperature, short-term storage of ‘Sunrise’
Summer apples using 1-MCP to maintain quality. Journal of Horticultural Science and Biotechology 80 (4) 439–446.