Conditioning Cox apples stored in ULO conditions by raising store oxygen concentrations 4-5 weeks before opening the store is effective in enhancing flavour. In Gala apples increasing the store oxygen from 1% O2 to ambient (21%) concentrations part way through a 4-month storage period is reported to have increased the emission of some of the volatiles contributing to aroma. No additional losses of firmness, titratable acidity or soluble solids content were detected after storage in ‘dynamic’ conditions.
Recent research has shown potential benefit of enhanced aroma production in CA-stored Fuji and Granny Smith apples by short-term exposure to hypoxic (low oxygen) treatments. The hypoxic treatment (<0.5% O2) applied for 1 day enhanced subsequent ester production possibly by providing ethanol as a precursor for ester synthesis.
1. The effectiveness of improving the aroma profile of fruit esters by storing fruits under low oxygen conditions as favoured by DCA storage have proved inconclusive in Gala apples. Moreover, raising storage oxygen of Gala apples from 2 to 12% O2 (3% CO2) 2 weeks prior to store opening in June, failed to improve flavour profiles. However, keeping fruit in lower CO2 conditions where concentrations have been lowered from 5% to 3% resulted in better tasting fruits (AHDB Project TF 221). For Gala destined for long-term storage, ensuring fruit is picked at 85% starch, followed by rapid cooling and CA establishment (3% CO2, 1% O2) helped to ratain fruit firmness and good ratio of sweetness to acidty ratio.
2. Conditioning (temperature) of fruits at the start of storage has been used in some cultivars such as Honeycrisp (USA) to reduce the risk of low-temperature damage in store. Keeping fruit at 10 oC for 7 days reduced LTB type symptoms but raised the incidence of bitter pit. Where fruits were stored subsequently at 2 oC, bitter pit symptoms were not raised.
3. Temperature modulation has been tested in Cox’s Orange Pippin (AHDB Project TF 192) to reduce the incidence of Neonectria – through introducing periods of lower temperature (1.5 oC) to standard 3.5-4.0 oC (1.2% O2, <1.0% CO2). This was only practical where periods of low-temperatures were introduced later in the storage season otherwise a high incidence of low-temperature breakdown was observed.