Gilding
Cashew
Irradiation
can help reduce insect infestation in cashew, especially now, given
the trend against chemical fumigants, explain Dr Rekha S Singhal and
MG Sajilata
The
cashew nut (Anacardium occidentale), used extensively in the baking
and confectionery industry, is an oilseed with great potential and increasing
commercial value. India is the largest producer, processor and exporter
of cashew kernels. Exports of cashew nuts contribute to about 7 per
cent of the national exchequer and hence it is imperative to maintain
high standards of quality to meet the foreign trade requirements. To
prevent insect infestation of nuts, chemical disinfestation methods
such as insecticide spraying and fumigation with methyl bromide are
widely employed. Of late, the use of fumigants has been banned in many
countries because of health concerns. Alternative methods are therefore
sought, and treatment with ionising radiation has received much attention
as one of the most promising applications in this regard.
Irradiation
technology has been used extensively for food processing, on a worldwide
basis. The risks associated with this technology are extremely low –
both for workers and for people who live in the vicinity. The irradiation
process is relatively simple. The food is placed in containers or packages,
on a conveyer belt, and passed through a shielded chamber. The specific
procedure and the amount of radiation used depends on the type of food.
While it is in the chamber, the food is briefly exposed to a radiation
source. Because the irradiation process does not heat the food, it can
immediately be stored, packaged or shipped. Over the years, the US Department
of Agriculture (USDA) and the US Food and Drug Administration (FDA)
have approved the use of irradiation on a variety of food products,
for a number of different purposes.
Radiation
disinfestation
Irradiation
for insect disinfestation is not aimed to kill the insect pest instantly.
For an outright kill of adult insects, high doses, which could adversely
affect the functional and nutritional quality of the product, are required.
Therefore, an approximate low dose of 0.25-1 KGy, which interferes with
the development of insects and results in sterility in adult species,
is employed. With such level of irradiation the feeding ability of the
larval stages is considerably diminished, thereby reducing product damage
on storage.
According
to a report, insect control can also be achieved by a combination of
irradiation and cold storage. While radiation alone is not sufficiently
effective for nuts irradiated with 0.25 KGy, radiation combined with
a storage temperature of 20oC or less checks infestation for a whole
year without affecting the desired product quality. However, proper
storage management and the use of insect-resistant packaging materials
for the packaged food products is essential to prevent
re-infestation.
Nuts
may be irradiated to induce inactivation of pathogenic bacteria such
as salmonella and molds that produce aflatoxin. Shelled peanuts irradiated
with doses of 1-1.5 KGy remain free of aflatoxin during storage for
10 months. Doses of about 1 KGy are adequate for insect control in almonds,
peanuts and walnuts. Doses in the range of 120-600 KGy inhibit sprouting
of chestnuts when irradiated 2 months after harvest and stored at 18-20oC;
rotting however is not adequately controlled.
It
is often assumed that radiation treatment of nuts might stimulate development
of rancidity in the lipids. However, practical experience has proved
otherwise. For instance, almonds irradiated with a dose of 1 KGy and
stored for up to 12 months could not be distinguished from non-irradiated
controls in flavour tests with both raw and roasted almonds. Similar
conclusions have been drawn with regard to shelled walnuts stored under
different temperature and packaging conditions. Similarly, almonds and
cashew nuts irradiated up to 2 KGy are not significantly different from
the control (non-irradiated sample) with regard to colour, flavour and
consumer acceptability, even after 180 days of
storage.
Insect
infestation in cashew
The
cashew tree is susceptible to attack by a wide variety of insects and
parasites. There are about 30 species of insects infesting the cashew
such as Ephestia cautella, Tribolium castaneum, Carpophilus sp, Plodia
interpunctella, Corcyra cephalonica, Oryzaephilus surinamensis, tea
mosquito, flower thrips, the stem and root borer, fruit and nut borer
which are reported to cause around 30 per cent loss in yield. These
insects feed and multiply in the nuts during storage, producing undesirable
effects.
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