Microbiology of herbs and spices

Imported herbs and spices are widely used to enhance the flavor of foods. As Dr. Roy Betts explains, some herbs and spices are contaminated with potentially harmful microbes, such as bacteria and fungi.¹While this isn’t a widespread problem among herbs and spices derived from developed nations, you might not be aware that your favorite herbs and spices could be adding more than just flavor to foods.

Contamination by microorganisms can occur when fruits, roots, or bark are dried in the sun. While drying, plants are accessible to insects, reptiles and other animals. Once dried, these plant parts are then ground into spices. Similarly, the leafy parts of plants that make up herbs will become contaminated if they are grown in unclean water or soil. This is why washing of herbs and other leafy greens must be undertaken to ensure that foods sold as ready-to-eat items do not harbor microorganisms. Another strategy, heating foods, will kill bacteria, but isn’t always foolproof; spore forming microbes representing the Genera Bacillus and Clostridium, can be resistant to heat and still survive during cooking.

Dr. Betts also describes some of the difficulties involved with applying microbiology testing to herbs and spices. Because they are typically dehydrated, or in powdered form, samples are concentrated and problematic for labs to process. Some contaminants may also be underrepresented because of natural antimicrobial agents within herbs and spices.

In 2013, Van Doran et al. examined foodborne illness outbreaks resulting from herbs and spices occurring between 1973 and 2010.² The authors identified 14 outbreaks reported by countries including Canada, Denmark, England and Wales, France, Germany, New Zealand, Norway, Serbia, and the United States.

From those outbreaks, 1,946 people became sick, 128 were hospitalized and two individuals died. The authors noted that 70% of illnesses occurred from foods in which spices had been added to the food after the final microbial reduction step had been applied, indicating herb and spice contamination resulted in illness. The authors reported that salmonella was identified as the causative agent in 71% (10/14) of outbreaks, accounting for 87% of reported illnesses. Bacillus spp. were identified as the causative agent in 29% (4/14) of outbreaks, accounting for 13% of illnesses.

While this study and others like it highlight a possible risk of contamination, Dr. Betts also states that the likelihood of this is fairly low, and that microbial contamination is much more common with imported and smaller-scale growing operations. He posits that large-scale herb and spice producers have established handling and processing methods that ensure that their products have low levels of contamination.

References

1. Betts, R. “Microbial Update: Herbs and Spices”. International Food Hygiene — Volume 25 Number 1

2. Van Doren, J.M. (2013) “Foodborne illness outbreaks from microbial contaminants in spices.”, Food Microbiology. Dec;36(2): 456-64. doi: 10.1016/j.fm.2013.04.014. Epub 2013 Apr 28., 1973-2010.

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