| dc.description.abstract | The concentration of tin and lead in canned foodstuffs including vegetables, fruit juices,
meat products and fish and baby foods (Nan, S-26
and Cerelac) are determined by spectrophotometric
methods. The amounts of the two metals have also
been determined in bottled and fresh foods for
comparison.
The analysis for tin has been done using two
methods, that is, quercetin (3, 3', 4', 5, 7-
pentahydroxyflavone reagent and catechol violet
(Pyrocatechol Sulphonphthalein) reagent. The
absorbance of the orage quercetin-tin complex
in 96% ethanol was measure~1rat 437nm while the
red-orange catechol-violet complex was measured
at 555nm in aqueous solution. The catecholviolet
method was found to be more sensitive than
the quercetin method at concentrations below 1.0 mg
kg-l but the two methods gave comparable results
for the concentrations normally found in canned
foods.
Lead has been determined using dithizone
(diphenylthiocarbazone) reagent and the absorbance
of the red lead dithizonate complex dissolved in
chloroform was measured at 516nm. Lead has also
been determined using the atomic-absorption method
and the two methods gave comparable results.
Tomato products contained the highest
concentration of tin ranging from 20 - 300 mg kg-1
while fruit juices, vegetables and fish contained
40.0 - 110.0, 7.0 - 55.0, 4.0 - 7.4 mg kg
respectively. Comparison with fresh foods showed
more than ten fold increase for the canned
foodstuffs except fish which had a two-fold
increase. The amount; of tin in each can indicates
the extent of corrosion and this depends on the
type of can (plain o lacquered), whether the food
contains corrosion accelerators such as nitrate
(NO-3) ion and also the shelf-life.
In the lead determination, canned fish
contained the highest concentration ranging from
0.70 - 1.42 mg kg-1 while tomato products, fruit juices
-1
and vegetables contained 0.30 - 1.03, 0.20 - 0.60 mg kg
respectively. No lead was detected in baby foods
that is Nan, 8-26 and Cerelac. Comparison with
fresh foods showed a four to six-fold increase for
canned foods. The amount of lead in each category
of food may be accounted for by the amount originally
present and that introduced from the solder.
Total lead in Kenyan tea was found to be
6.0 mg kg and the amount dissolving in an
equivalent of one cup of tea (125 cm3) was found
to be 0.02 mg.
The estimated daily tin intake is 0.2- 17mg
and tin poisoning has been observed with samples
-1 containing 250 mg kg tin. For lead, the daily
intake is estimated at 0.2 - 0.3 mg and levels in
excess of 0.8mg per litre in blood give rise to
lead poisoning. The World Health Organization
-1 has recommended a limit of 250 mg kg of tin
in canned foods and a statutory 2.0 mg kg for lead.
Although the amount of tin in most of the foods
analysed was found to be below, this can be dangerous
occasionally if an old sample, is consumed. The
nitrate in the foods can also be converted to
nitrosoamines which are known to have carcinogenic
effects. Again, although most of the foods were
found to contain low quantities of lead, that is,
below the recommended level, there should however
be concern about canned fish and beverages such
as tea whose lead content is high. | en |
