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The annual imports of tomato puree into U.K. from Italy alone have been estimated at 35,000
tons,5 and whilst no quantitative conclusions are justified the results summarised in Table I
appear to support the inference that prior to 1964 substantial quantities of tomato puree of a
quality illegal in other countries were being dumped in the Port of London.
Samples taken under the Food and Drugs Act.
A short survey of tomato purees as sold by retail in the London area may be of interest.
Table II shows the Howard Mould Count of ordinary random samples purchased by inspectors in
1965-67. To ascertain if any material difference occurred in the quality of puree filled into
different sized cans and tubes the results have been classified according to size of container.

As may be seen from the tables the counts on retail samples show much the same proportion
of mould as in samples taken on importation; and although the best quality purees were formerly
found in the 5 Kg. cans imported by the large manufacturers, the results show that small cans
and tubes are now also filled with purees of equally low mould counts.
Only two of the samples, an informal and a formal of the same brand, in 61/3 oz. tubes in 1966,
exceeded 50% positive. These gave 80% positive and 75% positive respectively and were the
subject of the Lewisham prosecution mentioned earlier.
The Howard Technique
The counts are carried out precisely as directed in the A.O.A.C., 10th Edn, No. 36.069.
Fuller information about the test, including descriptions of the kinds of rot that affect tomatoes,
is given in a booklet entitled "Mould Counting of Tomato Products".6 Howard cells are available
from Watson & Sons Ltd.,Barnet, Herts or from Hawksley&Sons Ltd. of 17 New Cavendish Street,
W.l.
In U.S.A. special courses of instruction in mould counting are given at Technical Schools
sponsored by State Canners Associations. No experienced microscopist should have much difficulty
in carrying out the prescribed method, but in the absence of such instruction some minor
points have arisen which call for special mention.
(1) If a binocular microscope is used, or if it is not found possible to adjust the diameter of
field to exactly 1.382 mm. diameter by means of the draw tube, a circular diaphragm can be cut
from a piece of black card with a cork borer and file to give an ocular aperture corresponding to
the specified width as measured on a ruled slide. This diaphragm can then be left in the microscope
and saves repeated adjustments provided the same ocular and objective are always used.
(2) Some moulds, particularly Colletotrichum. which causes Anthracnose rot, have extremely
fine hyphae. Short lengths are easy to miss, sometimes resembling a crease in a cell wall, and
it is essential to focus up and down carefully, on four quarters of each field, to make sure hyphae
are not missed out; and to turn to a higher power when in doubt. Several workers add stains to
facilitate recognition of hyphae and methylene blue, cotton blue and crystal violet have been used
but since they also stain tomato tissue their value is questionable.
(3) When a field is "borderline" the viewer will be in doubt whether to record it as positive or
negative, and the question will arise whether to follow the traditional tendency to give the benefit
of the doubt to the product or to ignore the field altogether and pass on to the next one. Both
practices are open to criticism, but in the writer's view the latter is to be preferred, because if a
degree of tolerance is introduced into the actual counting variations will occur between laboratories
and it is better to have only one, known, tolerance to apply for experimental error. On the
other hand, at least when a count is near the critical 50% positive, the result will not be much
affected by ignoring a few borderline fields.
(4) Occasionally one may find a small colony of compact, short branched, mycelium, measuring
in width less than a sixth of the diameter of the field. No directions are prescribed in the official
method but it is suggested that the field should be regarded as positive, because if the hyphae
were disentangled and straightened out they would measure more than the specified sixth.
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