15 May 2015

Segregation is good… sometimes

Cold chain operators are usually counselled that they must segregate goods in the cold-chain.

The need to segregate stems from the fact that fresh farm produce is frequently incompatible with one another, and is good practice to mitigate risk of damage & food loss.

Segregation is important in the cold-chain

Cold-chain is not only about cooling alone but must look at various compatibility aspects between different species of the goods involved. This is in particular the case when handling fresh fruits and vegetables. Unlike aseptically sealed foods, the packaging of fresh produce has to allow access to the surrounding air and therefore makes it susceptible to tainting, moisture loss and biological triggers.

The primary level of care is about individual temperature tolerance levels - the chart on the bottom will show that Apple is stored optimally close to 0°C and Avocado is best kept at air temperature of 7°C. If kept at the same temperature as apples, the avocado crop would be subject to chill injury and eventually die and suffer rot.

Other tactful segregation relates to other differing living parameters and tolerances and the possibility of incongruous effects between species.

Tainting is easy to understand, in relation to odours. It is common know-how that when stored in an enclosure alongside garlic, banana will begin to taste of garlic. This cross-transfer of odour occurs due to air exchange in a common environment. Citrus items are known to contribute an “off-taste” in eggs or to open dairy products & meats.

Cross contamination occurs when ethylene sensitive produce is stored alongside those that produce large amount of this gas. Poor planning can set of biological triggers and spoilage in some cases. For example, brinjal will turn pity and bitter when stored with banana or mango. This is because the latter crop types are high ethylene producers and brinjal will brown and mature faster when exposed to even mild levels of ethylene.

Similarly, storing apple or kiwi with cauliflower or lettuce will negatively impact upon the quality and saleability of the latter.

The compatibility is not limited only to tainting through odours and the cross-contaminating exchange of physiological triggers; Humidity levels also require matching. While most fruits and vegetables are 80% to 90% water, some will catch rot if stored at high moisture content.

For example, pumpkins, winter squash and peppers need low humidity conditions, whereas leafy greens and most fruits maintain best quality when held at above 95% RH levels.

Other produce types like melon, sweet potatoes, tomatoes and citrus will tend to grow mould if kept for long with leafy greens, asparagus and others that require very high humidity levels.

Fresh air needs are also different between the various species of fruits and vegetables. This means that air replenishment patterns in the holding space needs to suit the goods being stored. In case of inanimate products, there is no breathing mechanism and in such cases there is little concern on this aspect (except about keeping the enclosed space safe for human entry).

Produce Compatibility must be understood by all cold-chain users. Luckily, cross contamination takes a while to effect and for short volume & duration storage, like in home refrigerators, the last mile consumer need not be overly concerned (if storing for a day or so at most). Nevertheless, it is best to open the fridge door, at least once every two days to keep the air oxygenated for the vegetables and fruits inside.

Segregate fresh produce in storage and transport.

by Pawanexh Kohli, published in NCCD Journal - Edn 11

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