Low Oxygen Storage Reduces Internal Browning in ‘Ambrosia’

‘Ambrosia’ apples harvested at optimum maturity for storage can be held long-term (i.e. ~8 months) with little firmness loss or disorder development. Optimum fruit maturity at harvest generally consists of more green than yellow background color (2 to 3 on the BC color chart), <1 ppm internal ethylene concentration, fruit firmness above ~18 lb, and starch index between 2 to 4 (Cornell starch chart).

‘Ambrosia’ responds well to 1-MCP, with reduced firmness loss and mealiness, lower internal ethylene, higher acidity, and reduced greasiness. Controlled atmosphere (CA) storage also improves ‘Ambrosia’ fruit quality during storage and oxygen levels below 2% are best.

The following CA regimes at 0.5oC were evaluated during 2018-19:

  1. 2.5% O2 + 2.0% CO2
  2. 1.7% O2 + 1.0% CO2
  3. <1% O2 + 0.5% CO
Figure 1. Internal browning in Ambrosia.

The <1% O2 regime was based on fruit respiration measurements using LabPodTM technology (Storage Control Systems Inc., Michigan). There was an initial flush down to 1.7% O2 and then oxygen was decreased gradually to 0.6% over several weeks and to 0.4% after a couple months. Postharvest 1-MCP treatments (SmartFreshTM) before or after storage were also evaluated in this study, but there was no significant difference due to application timing so these data were combined.

After 8 months of CA storage at 0.5oC, apples held in 2.5% O2 were softer (less ~1 lb) and had more internal browning than those held in 1.7% O2 (Table 1, Figure 1).  Apples held in <1% O2 had much less internal browning (<1% incidence) than fruit from the higher O2 regimes. No other storage disorders or fruit splitting were noted.

Table 1. Incidence of internal browning in ‘Ambrosia’ apples after 8 months in CA storage at 0.5oC.

Treatments
Internal Browning (%)
<1% O2 (LabPod)
No SmartFresh
0.7 D
+ SmartFresh
0.4 D
1.7% O2
No SmartFresh
8 C
+ SmartFresh
8 C
2.5% O2
No SmartFresh
24 A
+ SmartFresh
16 B

Acknowledgements

Thanks to the Ontario Apple Growers, Norfolk Fruit Growers’ Association, Apple Marketers’ Association of Ontario, AgroFresh Inc., Pommes Philip Cassidy Inc., GRB Ag. Technologies Inc., Storage Control Systems Inc., Decco US Post-Harvest Inc., and the Canadian Horticultural Council (BC, ON, QC, and NB apple growers) for their continuous support, as well as Sky Lesage, Geoff Lum, and Younes Mostofi for their technical assistance. Recent work was funded in part through the Canadian Horticultural Council’s Canadian Agri-Science Cluster for Horticulture 3.

Dr. Jennifer DeEll
Dr. Jennifer DeEll

Fresh Market Quality Specialist – Horticulture, OMAFRA