Zn, Cu, and Fe Concentrations in Dehydrated Herbs (Thyme, Rosemary, Cloves, Oregano, and Basil) and the Correlation with the Microbial Counts of Listeria monocytogenes and Other Foodborne Pathogens

Abstract

Zn, Cu, and Fe concentrations were measured in dehydrated herbs (thyme, rosemary, cloves, oregano, and basil) marketed in bulk or packaged in glass or polyethylene terephthalate (PET). Microbial counts of Listeria monocytogenes and other five foodborne pathogens were also checked when herbs were previously added to the growing media. The highest mean concentrations were found in basil for Zn and Cu, and in thyme and basil for Fe; the lowest ones for these minerals were in cloves (p < 0.05). Basil had significantly higher microbial counts in five of the six foodborne pathogens studied (p < 0.05). Cloves have the best hygienic quality as there is no microbial growth of L. monocytogenes, Clostridium perfringens, and Bacillus cereus; they therefore could be used as a natural preservative in food. Aromatic herbs marketed in bulk showed a significantly higher microbial count (p < 0.05). Zn, Cu, and Fe concentrations were positively correlated with microbial growth for L. monocytogenes, C. perfringens, B. cereus, and psychrophilic microorganisms (p < 0.05), so they could act as a growing factor for the foodborne pathogens.

Ca and Mg Concentrations in Spices and Growth of Commonly Sporulated and Non-Sporulated Food-Borne Microorganisms According to Marketing Systems

“…As noted in a previous study [ 3 ], basil is the spice that presented higher microbial counts for most of the studied microorganisms.…”

“…The samples were analyzed microbiologically on the collection day. Full information on the characteristic of sampling of dried spices considered in this study has been previously reported elsewhere [ 3 ].…”

“…Sample preparation (for the microbial count, 1.5 g of each of the dehydrated spices were diluted in 9 mL of sterile buffered peptone water solution and from these, decimal dilutions were made) and counting procedures for sporulated microorganisms were described in detail in another study [ 3 ] and were performed with official techniques, namely ISO 7932:2005 standard [ 29 ] for B. cereus , ISO 7937: 2005 standard for C. perfringens [ 30 ], ISO 4833:2003 standard for aerobic mesophilic and psychrophilic bacteria [ 31 ], ISO 21527-2: 2008 for molds and yeasts [ 32 ] and ISO 11290: 2017 for L. monocytogenes [ 33 ].…”

“…This fact has lead to an increase in possible industrial and home sources of sporulated and non-sporulated microorganisms in spices in recent years, due to the monitoring of inadequate hygienic-sanitary conditions during their cultivation (which are specifically affected by the hygienic-sanitary quality of the irrigation water, the fertilisers used, the specific climatic and edaphic conditions of the area, etc. ), harvesting, technological treatment, storage, marketing system and final handling by consumers, which can finally lead to food-borne infections and intoxications [ 2 , 3 ]. For this reason, it has been indicated that it is necessary to implement good hygienic and sanitary practices throughout the supply chain of dehydrated spices, in addition to the application of validated lethal processes before distribution and retail, to ensure the necessary food safety standards [ 4 ].…”

“…However, in recent years, consumers have been interested in finding more natural alternatives to control the development of pathogenic microorganisms in foods, such as spices, based on their content of essential oils [ 9 ], as opposed to the commonly used chemical preservatives [ 10 ]. In this sense, consumers are asking for less processed, safer and more stable foods, preferring to use natural ingredients [ 11 , 12 ], such as certain spices like cloves [ 3 ], especially to control the growth of non-sporulated anaerobic microorganisms such as Listeria monocytogenes , and of sporulated microorganisms such as Bacillus cereus and Clostridium perfringens . Other authors [ 13 ] have indicated that the addition of aqueous or alcoholic thyme extracts to yoghurt inhibited the development of moulds and yeasts.…”