Dietary methanol can arise in large part from fresh fruits and
vegetables where it occurs as the free alcohol, methyl esters of fatty
acids or methoxy group on polysaccharides such as pectin (Kirchner &
Miller, 1957; Casey et al., 1963; Self et al., 1963; Lund et al.,
1981; Stegink et al., 1981; Monte, 1984).</p>
<pre><code> The methanol content of fresh and canned fruit juices
(principally orange and grapefruit juices) varies considerably and may
range from 1-43 mg/litre (Kirchner & Miller, 1957), 10-80 mg/litre
(Lund et al., 1981; Monte, 1984) and 12-640 mg/litre with an average
of 140 mg/litre (Francot & Geoffroy, 1956; Monte, 1984). Methanol
evolved during the cooking of high pectin foods (Casey et al., 1963)
has been accounted for in the volatile fraction during boiling and is
quickly lost to the atmosphere (Self et al., 1963). However entrapment
of the volatiles during canning is possible and probably accounts for
the elevated methanol levels of certain fruits and vegetables during
this process (Lund et al., 1981).
Fermented distilled beverages can contain high levels of
methanol, with some neutral spirits having as much as 1.5 g/litre
(Francot & Geoffroy, 1956). Methanol was found at levels of
6-27 mg/litre in beer, 96-321 mg/litre in wines and 10-220 mg/litre
in distilled spirits (Greizerstein, 1981). The methanol content in
representative beverage alcohol varied between 40 and 55 mg/litre
bourbon. This value is comparable with those reported by the
distillers. The concentration of methanol in 50% grain alcohol was
found to be approximately 1 mg/litre (Majchrowicz & Mendelson,
1971).The presence of methanol in distilled spirits is directly linked
to the pectin content of the raw materials. During the process of
making fruit spirits, pectic substances contained in different parts
of the fruit undergo degradation by pectin methylases, which can lead
to the formation of significant quantities of methanol (Bindler et
al., 1988). Concentrations of methanol permitted in brandies in the
USA, Canada and Italy range from 6-7 g/litre ethanol (Bindler et al.,
1988).
Methanol has been identified in the volatile fraction of sherry
wine vinegars (Blanch et al., 1992), lemon, orange and lime extracts,
distilled liquors and cordials (AOAC, 1980, 1990).
Methanol has been identified as a volatile component of dried
legumes with reported levels of 1.5-7.9 mg/kg in beans, 3.6 mg/kg in
split peas and 4.4 mg/kg in lentils (Lovegren et al., 1979). Methanol
has also been reported (no levels stated) in roasted filberts (Kinlin
et al., 1972) and baked potatoes (Coleman et al., 1981). It has been
detected in low-boiling volatile fractions of cooked foods, including
Brussels sprouts, carrots, celery, corn, onion, parsnip, peas and
potatoes (Self et al., 1963).