Effect of CA storage on aroma and flavour
It is difficult to assess the importance of reduction in the aroma quality of apples by the use of prolonged CA storage. A consumer survey of the quality of Cox apples stored in different CA conditions and subsequently held at different temperatures showed them to be equally acceptable, but for different reasons.
It is clear, however, that high aromatic flavour does not compensate for poor texture and CA-stored Cox may be acceptable on the basis of its desirable texture and taste (sugar/acid balance) characteristics despite a much reduced aroma.
Strategies to improve aroma volatile production are therefore limited by the need to retard changes in other important quality attributes. Johnson (1994c) reviewed the prospect of increasing the flavour of Cox apples stored under CA conditions, and the salient points are reported below:
- The lowest of the oxygen concentrations recommended should be used for that proportion of the crop intended for the longest period of storage.
- The method of scrubbing carbon dioxide (activated carbon or hydrated lime scrubbers) from stores maintained at 2% O2 and 0.7% CO2 had no effect on fruit aroma nor other quality attributes such as fruit texture and background colour. Concerns that activated carbon scrubbers encourage the removal of aroma compounds from the fruit were unfounded.
- Conditioning of the fruit prior to sale by raising the oxygen level part-way through the storage period from 1.2 to 2.0% O2 increased ester (important aroma volatiles) content to a level comparable with continuous 2.0% O2. There may be some loss of instrumental firmness by raising oxygen levels; consequently this should be delayed until 4-5 weeks prior to opening the store. Moreover, this technique should not be practised in a year when firmness in store is marginal or where there is an over-riding necessity to store Cox to its maximum potential.
- Atmospheres generated in modified atmosphere (MA) packs retard ripening and changes in quality in a similar way to CA storage conditions. Although MA packaging provides apples that are generally firmer and more acidic than non-MA packs, they may be less sweet and have less aroma. The acceptability of the fruit will depend greatly on the relative importance that consumers attach to the various quality parameters.
- Some of the consignment variation in aromatic flavour relates to the maturity of the fruit at the time of harvest. The concentration of certain flavour compounds in Cox apples after storage increases with later harvest dates. However, it is also known that growing season and the source of fruit influence ester content.