Throughout the years numerous investigations concerning the inhibition of microorganisms by spices, herbs, their extracts, essential oils and various constituents have been reported. Many of these materials possess significant antimicrobial activity, which in many cases is due primarily to a particular constituent. Interpretation and comparison of results of various studies is complicated by variations in the methodology used for the determination of antimicrobial activity. The antimicrobial activity varies depending on the microorganism, the spice or herb and the test medium. These and other factors are examined in the light of their effect on the outcome of the test method.

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We have attempted to review the literature dealing with compounds that have been tested for their ability to inhibit growth and/or aflatoxin production by Aspergillus flavus and A. parasiticus. Although the list presented is by no means exhaustive, it serves as an indication of the type of research that has been carried out to date. A number of compounds and substances have been found that effectively inhibit fungal growth and aflatoxin production, while others have stimulatory properties. Unfortunately, most of these assessments have only dealt with fungal growth and/or aflatoxin production, and relatively few studies have attempted to identify possible mechanisms of action. Further research into the means by which other compounds influence aflatoxin synthesis is warranted and potentially could be highly beneficial to expand our understanding of mycotoxigenesis. Such studies are likely to yield knowledge that would lead to isolation of additional intermediate compounds of the pathway leading to aflatoxins, identification of key bioregulatory loci controlling aflatoxin synthesis and development of basic knowledge that would provide insights into new strategies for controlling aflatoxin formation in foods and feeds.

Increasing concentrations (0.5-8g/liter) of oregano, rosemary, sage, and thyme progressively delayed growth and acid production by Lactobacillus plantarum and Pediococcus acidilactici in a liquid medium. After the bacteriostatic activity was overcome, all four herbs strongly stimulated acid production. The relative inhibitory effect of the herbs toward both microorganisms was oregano >> rosemary = sage > thyme. L. plantarum was more resistant than P. acidilactici to the toxic effect of the herbs. Organisms from cultures exhibiting delayed fermentation in the presence of sublethal concentrations of an herb, when subcultured into fresh media containing identical herb concentrations, initiated fermentation without delay, indicating development of resistance to the herb's effect. Moreover, bacteria which had acquired a resistance to one herb were also resistant to the other three herbs.