Traditional intermediate moisture foods (IMF) can be regarded as one of the oldest foods preserved by man. The mixing of ingredients to achieve a given aw, that allowed safe storage while maintaining enough water for palatability, was only done, however, on an empirical basis. The work done by food scientists approximately three decades ago, in the search for convenient stable products through removal of water, resulted in the so-called modern intermediate moisture foods. These foods rely heavily on the addition of humectants and preservatives to prevent or reduce the growth of microorganisms. Since then, this category of products has been subjected to continuous revision and discussion.
Definitions of IMF in terms of aw values and moisture content vary within wide limits (0.6-0.90 aw, 10-50% moisture), and the addition of preservatives provides the margin of safety against spoilage organisms tolerant to low aw. Of the food poisoning bacteria, Staphylococcus aureus is one of the organisms of high concern since it has been reported to tolerate aw as low as 0.83-0.86 under aerobic conditions. Many of the considerations on the significance of microorganisms in IMF are made in terms of awlimits for growth. However, microbial control in IMF does not only depend on aw but on pH, Eh, F and T values preservatives, competitive microflora, etc., which also exert an important effect on colonizing flora.
Advantages and disadvantages of IMF preservation
Advantages:
Intermediate moisture foods have an aw range of 0.65-0.90, and thus water activity is their primary hurdle to achieving microbial stability and safety. IMF foods are easy to prepare and store without refrigeration. They are energy efficient and relatively cheap. They are not readily subject to spoilage, even if packages have been damaged prior to opening, as with thermostabilized foods, because of low aw. This is a plus for many developing countries, especially those in tropical climates with inadequate infrastructure for processing and storage, and offers marketing advantages for consumers all over the world.
Disadvantages:
Some IMF foods contain high levels of additives (i.e., nitrites sulphites, humectants, etc.) that may cause health concerns and possible legal problems. High sugar content is also a concern because of the high calorific intake. Therefore, efforts are been made to improve the quality of such foods by decreasing sugar and salt addition, as well as by increasing the moisture content and aw, but without sacrificing the microbial stability and safety of products if stored without refrigeration. This may be achieved by an intelligent application of hurdles (Leistner, 1994).
Fruit products from intermediate moisture foods (IMF) appear to have potential markets. However, application of this technology to produce stable products at ambient temperature is limited by the high concentration of solutes required to reduce water activities to safe levels. This usually affects the sensory properties of the food.
Definitions of IMF in terms of aw values and moisture content vary within wide limits (0.6-0.90 aw, 10-50% moisture), and the addition of preservatives provides the margin of safety against spoilage organisms tolerant to low aw. Of the food poisoning bacteria, Staphylococcus aureus is one of the organisms of high concern since it has been reported to tolerate aw as low as 0.83-0.86 under aerobic conditions. Many of the considerations on the significance of microorganisms in IMF are made in terms of awlimits for growth. However, microbial control in IMF does not only depend on aw but on pH, Eh, F and T values preservatives, competitive microflora, etc., which also exert an important effect on colonizing flora.
Advantages and disadvantages of IMF preservation
Advantages:
Intermediate moisture foods have an aw range of 0.65-0.90, and thus water activity is their primary hurdle to achieving microbial stability and safety. IMF foods are easy to prepare and store without refrigeration. They are energy efficient and relatively cheap. They are not readily subject to spoilage, even if packages have been damaged prior to opening, as with thermostabilized foods, because of low aw. This is a plus for many developing countries, especially those in tropical climates with inadequate infrastructure for processing and storage, and offers marketing advantages for consumers all over the world.
Disadvantages:
Some IMF foods contain high levels of additives (i.e., nitrites sulphites, humectants, etc.) that may cause health concerns and possible legal problems. High sugar content is also a concern because of the high calorific intake. Therefore, efforts are been made to improve the quality of such foods by decreasing sugar and salt addition, as well as by increasing the moisture content and aw, but without sacrificing the microbial stability and safety of products if stored without refrigeration. This may be achieved by an intelligent application of hurdles (Leistner, 1994).
Fruit products from intermediate moisture foods (IMF) appear to have potential markets. However, application of this technology to produce stable products at ambient temperature is limited by the high concentration of solutes required to reduce water activities to safe levels. This usually affects the sensory properties of the food.