The problem of food spoilage has plagued humans throughout history. As early humans evolved from a gathering and hunting life style to raising crops and keeping animals, they were forced to store their own food. Early attempts to preserve foods involved use of sugars, spices, salts, and wood smoke. Today, however, preservation has used such factors as temperature, water activity, pH, gases, organic acids, salts, antibiotics, irradiation, packaging, and various combinations of these factors. No matter which factors are selected, use of the proper antimicrobial is dependant on the chemical properties of the antimicrobial; properties and composition of the food product; type of preservation system, other than the chemical, used in the food; type, characteristics, and number of microorganism; safety of the antimicrobial and cost effectiveness of the antimicrobial (Ray 2001).
Fungi are among the most challenging organisms to inhibit in foods given their ability to grow under a diverse range of environmental conditions. Environmental conditions such as water activity (aw), pH, temperature, and atmosphere can be manipulated to control fungal growth. However, these conditions often need to be taken to extremes to control fungi, since subgroups exist that have become adapted to extreme environmental conditions. Using water activity as an example, most molds are inhibited by an aw of 0.80 or lower, although some xerophilic molds can grow at aw values as low as 0.65. Most yeast are inhibited by aw values of 0.87, but some osmophilic yeasts can grow at aw values as low as 0.60 (Farkas 1997; ICMSF 1980).
Most fungi are little affected by pH over broad range, commonly 3-8. Some molds can grow at pH 2.0, and yeasts at pH 1.5 (ICMSF 1980; Rahman and Labuza 1999). However, as pH moves away from an organism's optimum growth range, typically about 5.0 for fungi, the effect of other growth-limiting factors becomes more apparent.
Fungi are generally easily inactivated by heat treatments such as pasteurization, although some heat-resistant molds associated with fruits and fruit products can survive rather severe heat treatments and spoil products such as pasteurized juices and canned fruits. In addition, molds can grow over a wide range of temperature. Some mold can grow at temperatures less than 0°C while other can grow at 50-55°C.
Molds have an absolute requirement for oxygen. Many species, however, are efficient oxygen scavengers and can grow in atmospheres containing less that 1.0% O2 (Cerny 1979). From a practical standpoint, it can be difficult to inhibit mold growth in foods solely by exclusion of oxygen from the package. Foods often contain dissolved oxygen, which slowly equilibrates with the package headspace, and oxygen can leach through all but the most impermeable packages. While mold growth can be delayed, it is not inhibited over long-term storage. Yeast have no requirement for oxygen and can grow in its complete absence.
Antifungal food additives are an efficient, cost-effective, and often the only successful way to control fungal growth in foods. Antifungal food additives are basically chemicals that prevent or interfere with mold growth. These chemicals may be found naturally occurring in certain foods, such as some organic acids and essential oils, or may be added to food during processing (Naidiu 2000; Thompkin and Singh 2000). The various antifungal food additives are briefly overviewed in this chapter.
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