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Other Tomato Products
For tomato sauce it has been the practice in this laboratory to examine a portion of the sample
direct in a Howard cell. Occasionally difficulty is encountered in identifying all the mould filaments,
particularly in products containing gelatinised starch as a thickening or stabilizing agent,
and in such cases it may be advantageous to hydrolise the starch before counting, e.g. by adding
1 ml. 1/1 NaOH (w/w) to 10 ml. sauce.
In the 1965 Changes in Official Methods of Analysis of the A.O.A.C., to facilitate identification
of hyphae, the catsup is directed to be mixed with an equal volume of sodium carboxymethyl
cellulose solution before being mounted in the Howard cell. For predicting mould counts at various
dilutions the Poisson distribution equation has been found to apply, using a graph to find the relation
between the mould count and the number of countable elements per field14, but no directions
are given in the official method for calculating the result back to the undiluted catsup, nor for relating
it to the tomato content; and it is not clear what limit would be applicable.
Tomato Juice is examined as received, without dilution or concentration. It will be noted
that in this case the count will be based upon an average soluble tomato solids of 5.5%, as compared
with 8.4% for purees, and that the U.S.A. limit is considerably lower than for purees.
Dehydrated tomato powder may be diluted with water to give a refractive index of 1.34471.3460,
or with a stabilizing solution to 8.4% tomato solids, and then counted. If difficulty arises
with other products such as tomato soup, or beans, spaghetti or fish with tomato sauce, the
operator may be referred to A.O.A.C. 36.075, duly noting that in such products the count is expressed
on the original volume of the soup or sauce.
Mycotoxins
In view of the large number of highly toxic metabolites recently identified from fungi of
relatively common genera it is evident that the occurrence of moulds in foods and feeding stuffs
requires a new and much more serious appraisal.
Instead of any question of poisoning being restricted to a few notorious fungi such as the
Amanitas and Claviceps, many common saprophytes are now incriminated and the decomposition
of food can no longer be regarded merely as a nuisance, unhygienic but basically harmless. It
consequently becomes necessary to consider whether a mould count of less than 50% positive can
be regarded as unimportant if the fungal species are unknown.
Of the fifty odd species of fungi that thrive on cereals and other foods of vegetable origin
and are known to produce toxins the following call for prior consideration. In most instances the
mycotoxins have now been identified; they show wide differences of chemical constitution and
physiological action, and in some instances their toxicity to animals far exceeds that of the
traditional chemical poisons.
The known pathogenic metabolites include Hepatotoxins (Ochratoxin from A. ochraceus;
Islanditoxin and Luteoskyrin from P. islandicum; Rubratoxin from P. rubrum; Xanthocillin from
P. notatum and A. chevalieri); Nephrotoxins (Citrinin and Citreomycetin from P. citrinum and other
Penicillia); Neurotoxins (Patulin from P. urticae and other species of Penicillium and Aspergillus;
Maltoryzine from A. oryzae microsporus; Citreoviridin from P. toxicarium and P. citreoviride);
Haemotoxins (Fusariogenin and the Cladosporic acids from F. sporotrichioides and other
species of Fusaria, and a toxin from Stachybotrys atra); Dermatoxins (Methoxy and Trimethylpsoralen
from Sclerotinia sclerotiorum); Oestrogens (Zearalenone from Gibberella zeae, or Fusarium
roseum; and a metabolite from Monascus papulospora); Carcinogens (Aflatoxin from A. flavus,
Sterigmatocystin from A. versicolor and possibly Ochratoxin).
Many of the mycotoxins mentioned above do not appear to be affected by boiling. Since the
species of fungi present in a sterilised product cannot usually be identified any attempt to ascertain
by analysis whether a puree containing fungus has become injurious to health (Section I of
the Act) must depend upon identification of the mycotoxins.
With recent advances this problem is not quite so intractable as might be thought. Most of
the toxigenic fungi are highly coloured and many of the mycotoxins are intensely fluorescent under
U-V light, including Aflatoxin B & G, Ochratoxin A, Xanthocillin, Zearalenone, Citreoviridin and
Sterigmatocystin. Patulin gives a fluorescent compound if the lactone ring is ruptured, e.g. by
exposing the chromatoplate to ammonia, and it is probable that the anthraquinone derivatives and
some other toxins could also be recognised by U-V fluorescence after separation by chromatography.
Screening methods for mycotoxins are at present under trial in U.S.A. and a method for the
detection of aflatoxin, ochratoxin and zearalenone in various commodities has recently been published.
The mycotoxins are extracted with chloroform and the extracts passed through a sillica
gel column; after cleaning up with hexane and benzene the absorbed zearalenone is eluted with
acetone: benzene, the aflatoxine with methanol: chloroform and the ochratoxins with acetic acid:
benzene. Aliquots of each eluate are developed against standards on TLC plates and compared
under U-V.
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