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Advanced Maturity of "Empire" at Harvest Increases Flesh Browning in Storage

'Empire' apples are very susceptible to flesh browning (a.k.a. internal browning). This usually occurs after mid- to long-term controlled atmosphere (CA) storage and has recently been the cause for substantial fruit losses.

During the past few years, within various projects, research results in Ontario have shown that later harvested 'Empire' fruit are much more prone to developing flesh browning. Harvest maturity was a major factor in the incidence and severity of this disorder.

In one study, the maturity of 'Empire' at harvest was trace internal ethylene (<0.5 ppm), 4.3 starch, 15.7 lb firmness, and 10.8% soluble solids. Similar fruit harvested 7 days later also had trace internal ethylene (<0.5 ppm) and 15.7 lb firmness, but starch was 5.8 and soluble solids 11.6%. After 6 months in CA (2.5% O2 + 2% CO2 at 3oC), 'Empire' apples from the first harvest had 4.5% incidence of flesh browning, whereas those from the later harvest had 17.7%. Treatment with SmartFresh (1-MCP) increased the incidence to 8.0% and 35.7%, respectively. It is important to note the small difference in harvest maturity in relation to the substantial increase in the amount of flesh browning.

In another study, the maturity of 'Empire' at first harvest was trace internal ethylene (<0.5 ppm), 3.7 starch, 16.4 lb firmness, and 12.4% soluble solids, while fruit maturity at second harvest (7 days later) was 0.7 ppm internal ethylene, 4.0 starch, 15.5 lb firmness, and 13.0% soluble solids. After 9 months in standard CA at 1-3oC, fresh-cut apple slices made from fruit from the first harvest exhibited much less browning than those made from the second harvest (72.5% good-excellent ratings vs. 31.2%)

Similar results showing the importance of harvest maturity in relation to flesh browning have been found by Drs. Chris Watkins and Hannah James at Cornell University. The effects of harvest maturity, delayed cooling, stepwise cooling, diphenylamine (DPA) drench, calcium application, Smart Fresh (1-MCP) treatment and timing, delayed CA, CO2 concentration, low humidity storage, and fruit nutrient levels were all studied. Results showed that harvest maturity was the most important factor and that earlier harvested 'Empire' developed less flesh browning during storage.

Based on the above information, it is recommended that harvesting 'Empire' apples destined for mid- to long-term storage occur when the starch index is close to 3 and there is only trace amounts of internal ethylene (<0.5 ppm). Apples harvested later will have a substantial increased risk of developing flesh browning.