Other decontamination techniques for herbs and spices 83
coliforms 10 colonies per gram. The nature of the material will determine what level
of microbial load will be present after treatment. For instance, ETO-treated coarse
ground black pepper will have lower counts than fine-ground black pepper. This is
because the ETO gas penetrates more effectively among the coarse ground black
pepper particles than among the fine particles. Raw materials with lower initial
counts can achieve much lower levels after treatment than those with higher initial
counts.
The type of container used for the raw material during ETO treatment also influences
the reduction in microbial load. For example, if the raw material is contained in
burlap bags, ETO gas penetration is excellent and the reduction of the microbial
population is very good. If the same raw materials are packed in heavy polythene
bags and placed in corrugated boxes, which can withstand the evacuation of air, ETO
will not have free access to the materials and microbial destruction will be limited.
4.6.2 Propylene oxide (PPO)
This chemical occurs in the form of a liquid with a low boiling point of 34.5 oC. It
has been used as a food sterilizing agent since 1958, but it is not as effective as ETO.
However, it has been approved for the microbiological treatment of herbs and spices.
Many spice processors in California had switched over to PPO for paprika and chili
peppers because of the problems associated with ETO. PPO also has insecticidal
properties.
The basic equipment for fumigation is a vacuum chamber and a volatilizer, similar
to that used for ETO treatment. The raw materials are loaded into the chamber at a
vacuum of 26 inches of Mercury and vaporized PPO is released. After four hours, the
gas is removed by air washing. Use of PPO for food fumigation is governed by CFR
40 Part 185.15 of the US FDA and US EPA regulations. The residue tolerance for
PPO in herbs and spices is 300 ppm. Though this chemical does not yet face the same
threat from the US Environmental Protection Agency (EPA) regarding treatment of
herbs and spices as ETO, it is likely that it will also eventually be phased out once the
use of ETO is banned.
4.6.3 Steam sterilization
Steam sterilization is ideal for herbs and spices because no chemical residue is left on
account of this treatment. Steam sterilization can be applied to both whole and
ground herbs and spices. However, special equipment is required because steam must
be applied under pressure if the treatment is to be effective, and the treatment requires
high precision. The pressure must be kept at the required level as otherwise the
temperature of the product will rise and essential oil will be lost. The moisture
brought in by the steam should be removed fully as soon as treatment is over, to
prevent clogging and mould growth (Anon. 1991 and 1999). Steam sterilization
equipment is expensive and only a few processing factories use it.
4.7 Detoxification.................................................................................
Herbs and spices can be infected by different fungi, some of which produce toxins
that are harmful to health. The most common and dangerous mycotoxin found in