Agriculture Reference
In-Depth Information
Moisture
Fresh herbs loose water rapidly once they are cut, which
results in early wilting. Keeping herbs at low temperatures
limits the rate of water loss. Other techniques involve
placing the cut stems in water, but rapid growth of
micro-organisms is a problem and the method is not
suitable during transport and storage. Delicate herbs such
as basil can be packed in boxes lined with wet newspaper.
Alternatively, and more commonly, fresh herbs are packed
into plastic bags though the packed bags must be kept at
constant temperatures to reduce condensation inside the
bag that encourages growth of microbes. Bags may be
perforated to improve ventilation or made from
semi-permeable membranes that allow water vapour
egress. In all cases the relative humidity of packing areas,
cold rooms and vehicles should be kept above 95%.
One method of getting around the water loss problem is
to market herbs as rooted plants in pots so that they
continue to grow when purchased and can be 'harvested'
by the customer over a period of time, with no loss of
freshness in the interim.
Although herbs and spices are usually dried to about
12% moisture content for safe storage and transport,
individual products may have different requirements. For
example, the maximum moisture content for onion powder
is 6% under the ISO standard. Requirements for garlic
powder (7%), parsley (7.5%) and bay, celery seed, chives,
dill tops and tarragon (all at 8%) are also low. Cinnamon
and cassia have the highest allowable moisture content at
14%, under ESA criteria (Muggeridge & Clay 2001).
a hygiene regime is beneficial. In the absence of such
measures attack by ubiquitous bacterial soft rotting organisms
or fungi such as grey mould or pin mould are likely.
Spices are also subject to microbiological spoilage,
though once dried growth of microbes is largely prevented.
However, allspice, black and chilli peppers, caraway, celery
seed, cumin, paprika and turmeric may carry a heavy micro-
bial load. Other spices and herbs produce antimicrobial
compounds and are less likely to be heavily contaminated,
for example cinnamon, cloves, fennel, garlic powder, mint,
mustard and nutmeg. Several fungi are of concern in spices,
as are the bacteria
Clostridium perfringens
,
Bacillus cereus
and
Salmonella
spp. (Wolf 1995).
Various methods have been used to disinfect herbs and
spices, though all have some drawbacks in terms of
effectiveness or consumer concern. Microbial counts in
spices can be reduced by 90% by treatment with ethylene
oxide, though its use is being phased out because of
residue and health risks. Propylene oxide has also been
used but this gas is less effective. Methyl bromide fumi-
gation of fresh herbs appears to damage the leaves by
reducing their green hue (McGuire 2000), though the gas
has been used successfully on spices (Yokohama 1994).
Another disinfection method is sterilisation by heat
though this method seriously degrades flavours. In addi-
tion, wet heat would exacerbate decay in fresh herbs and
dry heat may be prohibitively expensive (McGuire 2000).
In spices, microwave radiation is not effective in reduc-
ing microbial levels, and ultraviolet radiation does not
have the necessary penetrative power. One of the most
effective disinfestation methods for spices is perhaps
least likely to find favour with consumers at present,
namely, the use of ionising radiation. The FDA permits
low levels of radiation for this purpose (Table 15.6) but
such products must then have 'treated with radiation' on
the label, and the industry is very wary of public reaction
to this, although foodstuffs containing irradiated
ingredients do not need an irradiation label (Wolf 1995).
Few if any spices in retail stores in the United States are
known to be irradiated and less than 1% of spices used in
processed foods are treated in this way. Notwithstanding,
with the banning of many chemical treatments irradiation
use has increased such that about 25 000 t are now treated
this way world-wide (Peter 2001). Newer preservation
technologies to extend shelf lives and limit contamination
include osmotic drying and storage in high-fructose corn
syrup (Peter 2001).
Fresh herbs may be washed and chlorine dipped to
reduce microbial loads. Andress
et al
. (2002) found that
microbial counts from a range of herbs and spices
Mycotoxins
In common with other foods, mycotoxins have been of
concern in recent years within the spice industry
(Muggeridge & Clay 2001). Legislation has resulted such
that the total aflatoxin maximum in the EU was set in
2001 at 10 ppb and 5 ppb for aflatoxin B
1
, for capsicum,
piper, nutmeg, ginger and turmeric. In the United States,
the total aflatoxin maximum is 20 ppb. Documented
evidence of mycotoxins in herbs and spices is scarce,
although in 24 samples from markets in Egypt aflatoxin
was detected at 8-35 ppb, sterigmatocystin at 10-23 ppb,
but neither ochratoxin or zearalenone were found
(El-Kady
et al
. 1995).
Fungal and bacterial pathogens
In fresh herbs, attack by pathogens can be reduced by careful
handling to prevent injury and correct temperature control,
and appropriate choice of packing material to limit
condensation. Using chlorinated water for washing as part of
