The intelligent application of hurdle technology for a mild but efficient food preservation is advancing worldwide in industrialized as well as in developing countries. Some examples and trends are presented next.
Deliberate and intelligent hurdle technology for food preservation started about 20 years ago in Germany with meat products. First it was used for the gentle preservation of mildly heated, freshlike meats storable without refrigeration (4). In the meantime, several categories of these shelf-stable meat products have evolved, which are in large quantities on the German market and have caused no problems related to spoilage or food poisoning. In the manufacturing plants, processing these shelf-stable meats requires no microbiological tests to be carried out; however, other process parameters have to be strictly controlled; these are time, temperature, pH, and aw (15). Furthermore, a better understanding of the sequence of hurdles that leads to microbial stability of fermented sausages (salami) has improved the safety and quality of these products (16). In fermented sausages, the microstructure of the products, which was studied by electron microscopy, also turned out to be an important hurdle related to the behavior of pathogens as well as starter cultures in salami (17).
More recent is the application of hurdle technology for microbial stabilization of novel healthful foods derived from meat, poultry, or fish, which contain less fat and/or salt and therefore are more prone to spoil or cause food poisoning. The reduction of salt and fat as well as the substitutes and replacers of these traditional ingredients for muscle foods diminish the microbial stability, since several hurdles (aw, pH, preservatives, and possibly Eh and microstructure) will change. Compensation could be achieved by an intelligent application of hurdle technology (18). The advantages of hurdle technology are most obvious in high-moisture foods, which are shelf stable at ambient temperature due to an intelligent application of combined methods for preservation. However, the use of hurdle technology is appropriate for chilled foods, too, because in the case of temperature abuse, which can easily happen during food distribution, the stability and safety of chilled foods could break down, especially if low-temperature storage is the only hurdle. Therefore, it is advisable to incorporate into chilled foods (eg, sous vide dishes, salads, fresh-cut vegetables) some additional hurdles (eg, modified atmosphere packaging) that will act as a backup in case of temperature abuse. This type of safety precaution for chilled foods is called invisible technology, implying that additional hurdles act as safeguards in chilled foods, ensuring that they remain microbiologically stable and safe during storage in retail outlets as well as in the home (19).
Packaging is an important hurdle for most foods, since it supports the microbial stability and safety as well as the sensory quality of food products. Industrialized countries have the tendency to overpackage foods. This is especially true for Japan, where "active" packaging (using scavengers, absorbers, emmiters, antimicrobial or antioxidative packaging materials, etc.) has been developed to perfection. These "smart" packaging systems are very sophisticated, but wasteful, too. Therefore, Japanese experts are aiming now for less packaging of foods (20). Future packaging shall provide only necessary information and some convenience to the consumer; however, the required shelf life of the products should not come from the packaging but should be based (1) on superclean packaging combined with just-in-time delivery or (2) on the development of hurdle-technology foods that are stable and safe in spite of minimal packaging.
Finally, it also should be mentioned that novel emerging technologies for food preservation, that is, nonthermal preservation methods (high hydrostatic pressure, pulsed electric fields, oscillating magnetic fields, light pulses, etc), are often most efficient in combination with traditional food preservation methods. Thus, even for the application of futuristic food preservation methods, hurdle technology is essential (21).
Most of the food in developing countries, which preferably must be storable without refrigeration since electricity is expensive and not continuously available, are based on empiric use of hurdle technology. However, recently such foods have been optimized by the intentional application of hurdles. Relevant examples are optimized meat products of China and Taiwan as well as dairy and meat products of India. Moreover, in several countries of Latin America (ie, Argentina, Mexico, Venezuela), by the application of hurdle technology, high-moisture fruit products (HMFPs)have been developed. In spite of a high water activity (aw 0.98 to 0.93), HMFPs are storable in freshlike condition for several months at ambient temperatures and even become sterile during storage due to metabolic exhaustion of the bacteria, yeasts, and molds originally present in these products. There is a general trend in developing countries to move gradually away from the traditional intermediate-moisture foods because they are often too salty or too sweet and have a less appealing texture and appearance than high-moisture foods; this goal is achieved by the application of intentional hurdle technology. The progress made in the application of intelligent hurdle technology in developing countries of Latin America, China, India, and Africa has recently been reviewed (22).
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