Effects of Other Degradation Processes

Moisture Loss

Nearly all fresh produce has very high water content - in excess of 80%. The rate at which
moisture is lost from fresh produce varies with produce type. However, for extended storage
periods, it is essential to suppress the natural rate of moisture loss.

Moisture is lost from fresh produce due to transpiration. The moisture leaves the produce as water vapour. It is possible to prevent water vapour from leaving produce by placing the produce in an atmosphere with 100% relative humidity. At 100% RH, the atmosphere is saturated with water
vapour, and it will not accept further water vapour. Hence the produce is unable to release water vapour and moisture loss ceases.

Plastic film can have low water vapour transmission rates and thus sealed packaging made from such films acts as a substantial barrier to prevent loss of water vapour from the internal MA. In turn, this then suppresses the moisture loss from the produce. The produce will release an initial small amount of water vapour to create the 100% RH, but thereafter the rate of transpiration cannot exceed the leakage of water vapour through the packaging walls.

External and Internal Quality

There is little value in using MAP to slow the ripening and senescence of fresh produce, unless the MAP also prevents other causes of quality deterioration. In particular, MAP must ensure the
produce appearance is fresh after storage. For instance, bananas with bright yellow skins appear
to be at optimum eating quality. If MAP has stopped the internal tissue from ripening, but the skin has coloured fully, then consumers will be dissatisfied with this fruit. They will be expecting a banana that is soft and sweet, but will taste a banana that is firm and acidic. It is important that when MAP suppresses changes to internal tissue, changes to external tissue are also suppressed to an equivalent extent. All LifeSpan product designs take account of the need to balance both external appearance and internal (flesh) quality changes during extended storage.

As well as skin colour changes, there are numerous physiological disorders that can detract from produce appearance. Some of these occur independently of MAP, but they appear more obvious after storage in MAP simply because of the extended storage time. Fresh produce always attempts to heal wounds. The coarse tissue that grows over wounds is often unsightly. Its growth is progressive and hence can appear worse after extended storage periods. Similarly, rub marks,
sunburn, frost damage, etc. can become more apparent with longer storage of the produce. There
are no specific procedures to eliminate these effects with the use of MAP. The important issue is to be aware of the potential for such defects during grading of produce to be packed in MAP.

Chilling Injury

Some physiological disorders are due to chilling injury. In general, optimum MA will reduce the
susceptibility of produce to chilling injury, but only to a limited extent. For instance, stone fruit stored in air at 0°C may suffer chilling injury (internal flesh discolouration, mealy texture, and flesh breakdown) after storage periods in excess of 4 weeks. However, this is not a commercial problem if such fruit will be sold within 4 weeks of harvest. After 4 weeks storage in air, the fruit will be overripe, and thus air storage is limited to a maximum of 4 weeks.

Use of LifeSpan can suppress the ripening of stone fruit and stop it reaching full ripeness for at least 8 weeks. However, often this full potential cannot be utilised commercially because chilling injury becomes apparent upon ripening after storage periods in excess of 6 weeks. MAP has suppressed chilling injury for a further period of 2 weeks, but has introduced chilling injury as a commercial issue for the first time with stone fruit. It is important to understand which mechanism for quality degradation is the limiting factor for each application of LifeSpan. LifeSpan staff and sales agents will always provide advice on the proven limitations of LifeSpan and assist in proving LifeSpan for specific customer applications.

Rots and Mould

Pathogen growths (rots) need to be suppressed for the extended period of storage offered by
LifeSpan. In some situations, MA can help to suppress pathogen growth, but the effects are far
from universal and it is unwise to depend on MAP to prevent pathogen growths. Storage
temperatures near 0°C (32°F) are quite effective in suppressing most pathogen growths. However,
when produce is stored above 5°C (41°F), temperature will suppress very few pathogens. It is
always essential that fresh produce is given the best possible sanitation and fungicide treatments (both preharvest and postharvest) when the produce is stored for extended periods in MAP. As well as the longer period during which pathogens might grow, MAP creates a high humidity
environment that can favour pathogen growths. In applications where rots are a serious concern,
LifeSpan offers packaging formats that can minimize the impact of rot growths.