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II. FOOD ANTIMICROBIALS AS TARGETS OF NANOENCAPSULATION II.A. Definition of antimicrobials Antimicrobial agents have been defined by the U.S. Food and Drug Administration as ‘chemical compounds that when present in or added to foods, food packaging, food contact surfaces, or food processing environments inhibit the growth of, or inactivate pathogenic or spoilage microorganisms’ (Davidson et al., 2005). These agents may be classified as either traditional or naturally occurring antimicrobials (Brul and Coote, 1999; Branen and Davidson, 2000; Lo´pez-Malo et al., 2000). In recent years consumer demand and preference has shifted towards use of naturally occurring antimicrobials derived from microbial, plant, or animal sources, while products containing traditional antimicrobials have increasingly been rejected by consumers (Menon and Garg, 2001). This has led food manufacturers to either begin replacing traditional with naturally occurring compounds or finding alternative methods that allow for reduced concentrations of traditional antimicrobials, e.g. through the use of additional hurdles such as the combination of antimicrobials with other preservation techniques. The need to develop new single antimicrobial formulations, or combinations of multiple antimicrobials, has spurred renewed research efforts in this area and led to the early adoption of a variety of nanoencapsulation approaches.
II.B. Traditional versus naturally occurring antimicrobials II.B.1. Traditional antimicrobials Traditional or regulatory approved antimicrobials in the U.S. consist of a diverse list of compounds that include well-known preservatives such as benzoic acid and benzoates, acetic acids and acetates, nitrite and nitrate, sorbic acids and sorbates, sulfites, propionic acid and propionates, parabens, dimethyl dicarbonate, and more complex compounds such as lactoferrin, lysozyme, natamycin, and nisin (Davidson et al., 2005). In Europe, the list of approved compounds is quite similar to that in the U.S., but specific salts or organic acids are listed rather than the general class of organic acid salts, e.g. calcium, sodium, or potassium acetate rather than just acetates. The great advantage of existing traditional compounds is that their functionality in a large number of foods is well known and documented and, most importantly, that their use is economical. Additionally, as an in-depth report has recently illustrated, some bacterial pathogens and spoilage organisms may develop a temporary tolerance to traditional antimicrobials, which is