Microbiological Control of Spices and Herbs

By: Jvo Siegrist, AnalytiX Volume 10 Article 1

Ivo Siegrist, Product Manager Microbiology ivo.siegrist@sial.com

Cultures around the world rely on herbs and spices to add flavour and zest to food. Many spices, however, contain very high numbers of bacteria, making them a potent source for food spoilage and pathogens.

To study the microbiological status of herbs and spices, E. de Boer et al.1 tested 150 samples collected from 54 different spices, spice mixtures and herbs. They reported at least 1,000 organisms per gram, withmost spices containing 105-106 cells per gram. A high number of psychotropic bacteria, yeasts and Enterobacteriaceae was detected mainly on herbal spices originating in moderate climate areas. The study also reported highmould counts, identifying Aspergillus niger, A. flavus, A. tamarii, Penicillium citrinium, P. chrysogenum, and Absidia corymbifera as the most frequent isolated species. Since A. flavus may produce aflatoxins, one of the most potent naturally occurring toxins, its presence should be a matter of concern and monitored closely by the spice industry. Another serious potential public health risk may involve the presence of pathogenic bacteria ; frequently reported species are Clostridium perfringens, Bacillus cereus and Salmonella.

Several issues present a challenge in the microbiological study of dried herbs and spices. Dryness, inhibiting substances, high osmotic pressure, and other adverse conditions heavily stress the cells. Long stress periods can eventually lead the cells to a “viable but not culturable“ (VNC) state. In a VNC state, the microbes cannot grow on conventional laboratory plating media but may revive in vivo and cause disease. However, with the addition of certain growth factors, traditional media can be upgraded and VNC organisms can be resuscitated.

One of these growth factors is ferrioxamine E, which significantly improves the recovery of Salmonella, Cronobacter spp., Staphylococcus aureus and Yersinia enterocolitica from contaminated foods2-4. A concentration of ferrioxamine E (available from Sigma-Aldrich, see Table 2) in the range of 5-200 ng/ mL supports reproducible growth (see Table 1). Ferrioxamine E provides the essential bio-available form of micronutrient iron (III) to the organisms (see Figure 2). This leads to a reduced lag-phase in the medium and reactivates damaged bacteria, leading to optimal microbial analyses.

Figure 1 Spices of plant origin

Figure 1 Spices of plant origin

Figure 2 Structure of ferrioxamine E

Figure 2 Structure of ferrioxamine E

 

Organisms ng/mL
Salmonella 75
Cronobacter spp. (Enterobacter sakazakii) 150
Yersinia enterocolitica 100

Table 1 Recommended end concentration of ferrioxamine E

 

Product Cat. No.
Ferrioxamine E 38266
NEW Peptone Water, phosphate-buffered with Ferrioxamine E 67331

Table 2 Ferrioxamine E products

 

Specificity Name Cat. No.
B. cereus Cereus Selective Agar 22310
  HiCrome™ Bacillus Agar 92325
B. cereus/Enterobacteriaceae Glucose Bromcresol Purple Agar 16447
C. perfringens Lactose Gelatin Medium (Base) 61348
  Liver Broth 61724
  Motility Nitrate Medium 14305
  TSC Agar 93745
Coliform/E.coli Brilliant Green Bile Lactose Broth 16025
  EC Broth 44653
  Lauryl sulfate Broth 17349
  m-Lauryl Sulfate Broth 07348
  VRB MUG Agar 95273
Enterobacteriaceae China Blue Lactose Agar 22520
  Levine EMB Agar 62087
  Lysine Iron Agar 62915
  Methyl Red Voges Proskauer Saline Broth 69150
  Triple Sugar Iron Agar 44940
  Violet Red Bile Agar 70188
Enterococci Bile Esculin Agar 48300
  KF-Streptococcus Agar 60641
Lactobacilli Rogosa Agar 83920
Salmonella SS-Agar 85640
  Bismuth sulfite Agar 95388
  Tetrathionate Enrichment Broth according to Muller-Kauffmann 88148
S. aureus Baird Parker Agar 11705
Total Count Vogel-Johnson Agar 70195
  Brain Heart Infusion Broth 53286
Yeasts Czapek Dox Agar 70185
  Plate Count Agar 70152
  Plate Count Agar according to Buchbinder et al. 88588
  Plate Count MUG Agar 51413
  Wort Agar 70196

Table 3 Media used for the microbiological control of spices

Figure 3 HiCrome™ Bacillus Agar

Figure 3 HiCrome™ Bacillus Agar

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Materials

Product #

Description

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48300 Bile esculin agar for microbiology
95388 Bismuth sulfite Agar for microbiology
53286 Brain Heart Infusion Broth for microbiology
16025 Brilliant Green Bile Lactose Broth for microbiology
22310 Cereus Selective Agar for microbiology
22520 China Blue Lactose Agar for microbiology
70185 Czapek Dox Agar for microbiology
44653 EC Broth for microbiology
38266 Ferrioxamine E from Streptomyces antibioticus for microbiology, ≥95%
16447 Glucose Bromcresol Purple Agar for microbiology
60641 KF-Streptococcus Agar for microbiology
61348 Lactose Gelatin Medium (Base) for microbiology
17349 Lauryl sulfate Broth for microbiology
07348 m-Lauryl sulfate broth for microbiology
62087 Levine EMB Agar for microbiology
61724 Liver Broth for microbiology
62915 Lysine Iron Agar for microbiology
69150 Methyl Red Voges Proskauer Saline Broth for microbiology
14305 Motility Nitrate Medium for microbiology
67331 Peptone Water, phosphate-buffered for microbiology, phosphate-buffered with Ferrioxamine E
70152 Plate Count Agar for microbiology
88588 Plate-Count-Agar according to Buchbinder et al. for microbiology
51413 Plate Count MUG Agar for microbiology
85640 SS-Agar for microbiology
44940 Triple Sugar Iron Agar for microbiology
70188 Violet Red Bile Agar for microbiology
70195 Vogel-Johnson Agar for microbiology
95273 VRB MUG Agar for microbiology
70196 Wort Agar for microbiology


References

  1. E. de Boer et al., Microbiology of spices and herbs, Antonie van Leeuwenhoek, Volume 51, Number 4, 435–438, Springer Netherlands (1985).
  2. S. Makino, et al., Does Enterohemorrhagic Escherichia coli O157:H7 Enter the Viable but Nonculturable State in Salted Salmon Roe?, Appl. Environ. Microbiol., 66 (12): 5536–5539 (2000).
  3. I. Barcina, P. Lebaron, J. Vives-Rego, Survival of allochthonous bacteria in aquatic systems: a biological approach, FEMS Microbiol. Ecol., 23:1–9 (1997).
  4. J.C. Choa, S.J. Kim, Viable, but non-culturable, state of a green fluorescence protein-tagged environmental isolate of Salmonella typhi in groundwater and pond water, FEMS Microbiol. Lett., 170:257–264 (1999).

 

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