82 Handbook of herbs and spices
the chute separates the spice seeds at the side of the chute from the foreign materials
in the centre of the chute. Spiral separators do not require a motor or blower, as
gravitational forces are sufficient to achieve the separating effect (Tainter and Grenis
2001).
4.6 Sterilization of herbs and spices....................................................
Herbs and spices often have a high microbial population when they are harvested. A
number of factors lead to an increase in the microbial population, including delays in
drying, incomplete drying, contact with infested surfaces, re-absorption of moisture
during storage, faulty packing, etc. Hence it is not unusual to find total plate counts
in the range of about ten million or more colonies per gram in certain spices, such as
black pepper. A high microbial load can reduce shelf-life, as well as lead to the risk
of phytotoxins being produced by harmful species. Thus herbs and spices should be
subjected to sterilization or microbial treatment.
Food sterilization treatments that can be used effectively to combat moulds and
other microorganisms in herbs and spices are essentially sterilization by heat, steam
or chemicals, use of low temperature, dehydration, desiccation, lyophilization,
modification of acidity, application of chemical preservatives or irradiation (Bourgeois
and Leveau 1995). Steam sterilization or chemical fumigation appears to be better for
processed or ground herbs and spices, as these processes are easy and cheap to carry
out, especially compared to irradiation, which requires highly sophisticated and
expensive equipment. The chemicals permitted for sterilization in herbs and spices
are ethylene oxide (ETO) and propylene oxide (POP). The subject of irradiation is
dealt with in Chapter 3.
4.6.1 Ethylene oxide (ETO)
This chemical has been used to reduce microbial population in herbs and spices for
many years. It is very effective for reducing the microbial population significantly.
However, the process itself is not easy to carry out because of potential health
hazards to workers and pollution risks. ETO is reported to be carcinogenic by inhalation,
but not when herbs and spices treated with it are consumed. Regulations in the USA
permit an ETO residue of not more than 50 ppm after treatment. However, European
countries do not permit the use of ETO because of the possible health hazards.
Treatment with ETO is also effective for killing insects at various instars, particularly
in seed spices, such as coriander, cumin, fennel, fenugreek and celery, which carry
insect eggs laid inside or on them while reaching full maturity in the field. Treating
these spices with ETO destroys the eggs and prevents them from hatching. The
material to be treated is placed in a sealed chamber, the air inside is evacuated and
pure ETO or a mixture of ETO with other gases is passed through the chamber. After
a specified time, the remaining ETO in the chamber is carefully removed by evacuation
until the residual level of ETO is brought down to desired levels. Blends of herbs and
spices can also be treated with ETO, but they must contain no traces of common salt,
which will react with ETO and form toxic chlorohydrins.
By carefully selecting time, temperature and concentration of ETO, it is possible
to achieve a significant reduction in microbial population. The material may then
have a plate count as low as 50,000 colonies, yeasts and moulds 500 colonies and