98 Handbook of herbs and spices
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5.9 Microbiological safety of herbs and spices...................................
The microbiological risks associated with herbs and spices vary dramatically according
to the plant type and the process to which it is subjected. The main factors are:
∑ Growth habit. Herbs with curly or hairy leaves and stems are more likely to
collect and retain bird droppings, dust and moisture than flat-leafed varieties, as
are those with low growing habits. Root and bulb crops are obviously closely
associated with the soil and are prone to contamination by poor irrigation techniques.
All these factors are potential contributors to contamination with Enterobacteriaceae
(including Salmonella and E. coli), yeasts and moulds.∑ Harvesting and storage. Many herbs and spices are gathered from the wild and
then stored in uncontrolled conditions. Ingress of insect and rodent pests can
present major problems.∑ Processing. High moisture content products are often air dried, open to the sun
or under minimal cover.
Spices are used all over the world as flavouring agents in staple food items. The
harvest of these crops predominately occurs in the warm, humid areas of the world
where large numbers of micro-organisms are readily viable. The microbiological
quality, load of total heterotrophs or Enterobacteriaceae in particular, often acts as an
indicator of the hygienic conditions. Spices are exposed to a wide range of environmental
contamination during collection and processing by dust, waste water and animal and
even human excreta. Contaminated spices may cause a microbiological problem,
depending on the end use. Cuisines that incorporate spices may pose a risk to public
health because they are often added to foods that undergo no further processing or are
eaten raw. Spices are the principal source of spore-forming bacteria in large volumes
of foods such as soups, casseroles, stews and gravies. Under favourable conditions
they germinate and multiply to infective and toxic levels. The key micro-organisms
responsible for these are Bacillus cereus, Clostridium perfringens, Escherichia coli,
Salmonella and toxigenic moulds.
The number of microbes on spices varies considerably according to the particular
spice. Black pepper, capsicum spices, turmeric and allspice contained the highest
microbial levels whilst cloves, nutmeg and cinnamon tend to be less contaminated. In
many spices the microflora consists mainly of mesophilic spore formers that originate
from the soil. Levels vary considerably but average counts in untreated products are
in the region of 100,000 colony-forming units per gram. Spores may comprise more
than 50% of the bacterial count. Spore formers capable of causing food poisoning
when ingested in large numbers, such as B. cereus, B. subtilis and C. perfringens, are
found in spices in low levels. Non-spore formers also form part of the microflora of
spices. Studies show they are present in approximately 50% of untreated spices at
levels between 10 to 100,000 CFU per gram.