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Spoilage in dried Shrimps
nymphs sticking on to the hairs on the append-
ages and body. Such flies carrying the eggs and
larvæ infect fresh consignments during their
visits to the latter. This mode of infection takes
place during the later stages of the curing process.
The curing sheds and drying yards are always in-
fested with flies and the possibility of infection is
ever present in these places. In the laboratory,
though under artificial conditions, infection
through flies was found to take place. These
observations corroborate the view held by many
authors that nymphal stages of mites are trans-
ported to new surroundings on the legs of flies
and other allied agents.
Another probable method of infection is that
which takes place through the agency of the wind,
in which case the brown powder containing the
eggs, larvæ and adults is blown to fresh consign-
ments of cured material. Such infection can only
take place when shrimp meat in an advanced state
of infection is stored in open windy places along
side freshly cured material. Since this is not a
common method of storage, chances of this type
of infection are rare, though Patton [1930] men-
tions the possibility of this type of infection, es-
pecially in the case of other household Tyrog-
lyphoids.
SPOILAGE IN RELATION TO METHODS OF CURING
In Appendix II is given the progress of spoilage
in the different samples cured under various
methods of preservation. An analysis of these
results and a comparison of the respective keeping
values mainly indicate the following.
Unshelled shrimps are more susceptible to
infection and they retain freshness for a much
shorter period than the shelled variety. Whether
they be sun dried or salt cured, infection sets in
at an earlier date and even the progress of spoilage
is comparatively vigorous. Probably the presence
of shells and certain amount of moisture retained
within them create the optimum conditions
favourable for the multiplication and development
of the parasites.
Commercially cured product is much inferior
in quality and it is easily susceptible to infection.
The maximum period during which commercially
cured shrimps remain devoid of any trace of
infection is found to be 9 weeks. This low keeping
quality is attributable to the low standard of
preservation adopted by the ordinary curers.
The keeping quality of cured shrimps is highly
enhanced by three days' drying in the open sun.
In the unshelled variety of shrimps dried for three
full days, infection commenced by the 10th week,
while in the shelled variety it set in by the 12th
week. Three days' drying made the shrimps
sufficiently dry and crisp, while four days' drying
made them too brittle and rendered perfect packing
difficult.
Treatment of shrimps in a 5 per cent solution
of sodium chloride is very effective in increasing
the keeping value of the cured product. In the
unshelled samples cured in 5 per cent brine, in-
fection set in by the 13th week, while in the shelled
variety infection started only by the 15th week.
This was the maximum period during which any of
the present series of samples was found to remain
devoid of any trace of infection. Samples cured
in brines varying from 6 to 8 percent, were found
to be in no way superior to sample cured in 5
per cent, since in all the former samples infection
commenced by the 15th week. Excess of salt on
the shrimp is found to have no action either in
inhibiting or preventing the infection by the
parsites.
GENERAL OBSERVATIONS
Investigation on the relative action of mites
to conditions of humidity showed the following;
when cured shrimps in which infection was vigo-
rous and number of parasites numerous were
placed inside a desiccator from which moisture
had been removed by means of anhydrous calcium
chloride, it was observed that the activity of the
parasites was slowly suspended. After four days,
most of the organisms were found to be either
inert or dead. When shrimps which were freshly
cured and infected were placed inside the desic-
cator, no spoilage took place and development of
the parasites was very slow. It was noticed that
even constant exposure to dry atmosphere was
detrimental to the mites.
Thus it is seen that certain degree of moisture
in the atmosphere is essential for the successful
development of the parasites. This is fully
supported by the fact that it is only during mon-
soon seasons, when humidity of the atmosphere
is rather high that spoilage of shrimps due to the
attack of mites is very vigorous. Unfortunately,
the monsoon season coincides with the season of
maximum abundance of shrimps in the back-
waters and so infection is inevitable under the
existing conditions.
Storage of cured shrimps in air tight containers
was attempted with satisfactory results. Con-
tainers were devised out of ordinary cigarette tins
and cured shrimps introduced into these were
sealed in partial vacuum. The material thus
kept was found to be in perfect condition and
devoid of any trace of infection. In Madras and
Sind, ' semi-dried ' prawns are packed in con-
tainers sealed in an atmosphere of carbon dioxide.
A somewhat similar process is adopted in this
country for packing cashew nuts. But the
present investigations indicate that the presence
of carbon dioxide is not always necessary for