Storage conditions

Chilling is an important preservative hurdle, as is the control of humidity. Storage at 10°C or above allows most bacterial pathogens to grow rapidly on fresh cut vegetables. Storage temperature is also important when MAP or vacuum packaging is used. Toxin production by Clostridium botulinum, or growth of other pathogens such as Listeria monocytogenes, is possible at temperatures above 3°C because of increased oxygen consumption in the package (Francis and O'Beirne, 1997). Processing, transport, display and intermediate storage should all be at the same low temperature (preferably 2-4°C) for produce not vulnerable to chilling injury. Changes in temperature should be avoided. Higher temperatures speed up spoilage and facilitate pathogen growth. Fluctuating temperatures cause in-pack condensation which also accelerates spoilage.

Temperature abuse is a widespread problem in the distribution chain, whether in storage, transportation, retail display and consumer handling. Where this is a significant problem, it may be necessary to restrict shelf-life, for example to 5-7 days at a temperature of 5-7°C, when psychrotrophic pathogens have insufficient time to multiply and produce toxin. If the shelf-life of vacuum or MAP products is greater than 10 days, and there is a risk that the storage temperature will be over 3°C, products should meet one or more of the following controlling factors:

• a minimum heat treatment such as 90°C for 10min

• a pH of 5 or less throughout the food

• a salt level of 3.5% (aqueous) throughout the food

• aw, water activity value of 0.97 or less throughout the food.

• any combination of heat and preservative factors which has been shown to prevent growth of toxin production by C. botulinum.

Practically, if the aim is to keep minimallyprocessedproduce infresh-likestate, the last mentioned factors, and mainly various preservative factors, are the only possibilities to increase shelf-life and assure microbiological safety of MA-or vacuum-packed fresh produce(FAIR,1999).

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