500 Handbook of herbs and spices
30.6 Toxicity...........................................................................................
There have been cases of poisoning among some mammals caused by excessive
consumption. Dogs seem to be particularly susceptible (Cooper and Johnson, 1984).
30.7 Quality.............................................................................................
The quality of the raw material affects demand, both locally and for export. In order
to improve quality, it is essential to understand the nature of the product and its
possible defects. The bulbs of potato onions should be harvested at proper maturity
and kept in windrows to cure. After about a week, when the bulbs and leaves have
dried thoroughly, the bulbs are topped by cutting off the leaves, leaving about 2 cm
of the top, and the roots. Diseased and damaged bulbs should be sorted out in the
field. The bulbs should be thoroughly sorted and graded.
There are various quality guidelines (Anonymous, 2003). These include colour
(should be red to bright pink), and size of bulblets (20–30 mm). The dried outer skin
should be fully intact. This is achieved through proper curing as described above, and
careful handling to avoid removing the skin. Storage diseases are prevented through
appropriate storage conditions and, where necessary, the use of Carbendazim (0.1%)
against basal rot and Steptocycline (0.02%) against bacterial soft rot.
The pungency of the onion is due to the presence of very small quantities (about
0.065%) of sulphur compounds in the volatile oil of the plant juice. Pungency can be
tested in the laboratory, or more simply by cutting the bulbs and noting the effect on
the eyes – if the eyes fill with tears, it is clear that the onions are pungent. Potato
onions have strong pungency. TSS should be about 18 to 19%, and dry matter should
be about 21 to 22%. The TSS and dry matter differs according to variety, growing
season and agricultural practices. Immature bulbs have low TSS/dry matter. Rain-
damaged bulbs also have low TSS/dry matter. It is important to avoid pesticide
residues in the crop. Sprays used against diseases and insects should be diluted and
administered according to the manufacturer’s instructions and at the safest dosage
level. Harmful insecticides, fungicides and other chemicals should not be sprayed on
the onions during the last month before harvesting.
Additional important hygienic practices include:
∑ The onions should not be irrigated with water containing harmful industrial
chemicals.
∑ After harvesting, onions should not be left out in fields where they may be
contaminated by industrial waste.
∑ Chemicals used on the crop should always be administered at levels that are safe
to human health.
∑ Jute bags, bullock carts, trucks, tractor trolleys or any other material used for
handling the crop should not be contaminated with chemicals which are hazardous
to health or which may create pesticide residue problems.∑ Materials and waste products that are unfit for human consumption should be
disposed off in such a manner as to avoid contaminating the good produce.
∑ The onions should be stored and packed in well-ventilated areas free of rotten or
other onion wastes.