Packaging of apples in semi-permeable films has the effect of modifying the atmosphere surrounding the produce with respect to the concentration of oxygen, carbon dioxide, nitrogen and other volatiles such as ethylene.
- The effects of elevated carbon dioxide and lowered oxygen in modified atmosphere (MA) packs in slowing product deterioration are essentially similar to those achieved using CA storage.
- However, atmosphere conditions generated in MA packs are generally less well controlled than in a CA store. Nevertheless, an MA pack appropriately designed to accommodate respiration differences due to cultivar and variable ambient temperature affords worthwhile improvements in post-harvest or post-storage life.
Retail packs for Discovery
- In packs of Discovery apples sealed with low density polyethylene films (LDPE) equilibrated atmospheres containing 3-5% carbon dioxide and 5-6% oxygen developed within 1-2 days at 20oC.
- Softening and yellowing of the fruit was markedly retarded. Subsequent work showed that the benefit of MA packaging for Discovery apples was reduced when the technique was used for late-picked fruit and the risk of adverse effects such as the development of off-flavours was increased.
- Discovery apples that benefit most from MA packaging are those that are just beginning to ripen at the point of harvest. Discovery apples harvested earlier are endowed with a longer shelf-life and may not benefit from MA packaging over the period allowed for marketing.
- Late-picked Discovery fruits are unlikely to benefit from MA technology and may develop off-flavours unless accompanied by cool chain marketing.
- Further work is required to identify markers of respiration rate that would enable growers to select fruit that would be most suited to MA packaging.
Retail packs for Bramley’s Seedling, Cox’s Orange Pippin, Egremont Russet and Spartan
- Beneficial effects on the post-storage quality of Bramley, Egremont Russet and Spartan apples were achieved by sealing fruit in LDPE bags of 30 mm thickness for 2‑4 weeks at 15oC.
- In Cox, the best results over 2 weeks at 15oC were achieved using a 30 mm ethylene vinyl acetate (EVA) film.
- Another development in MA technology was a bulk pack consisting of a 18 kg (40 lb) case of fruit with a sealed permeable liner. LDPE (30 mm) liners produced atmospheres of 7-10% carbon dioxide and 5-7% oxygen for Bramley apples during a 4-week period at ambient (10-20oC) temperatures.
- Micro-perforated LDPE liners were most suitable for Cox apples. Shelf-life improvements with the bulk packs were similar to those achieved using retail (1 kg) packs.