Subject: Re: mashing oats (HBD 924)
Date: 1992-07-16 12:27:00 GMT
Mike McNally writes:
> Oats have no diastatic capacity.....
Not true! Steel-cut, rolled or flaked oats have no amylase
because they haven't been malted, ie. the grain hasn't been
germinated and allowed to produce the enzymes - also the heat
generated during rolling would destroy the enzyme anyway. Oats
are quite competent at producing amylase when germinated -
otherwise the seeds would be incapable of mobilising the stored
starch reserves in the endosperm. Granted, the amount of amylase
produced may be less in barley, but I think I'm right in saying
that some (wonderful) German oat beers are made from a high
proportion of malted oat, with maybe some barley.
My partner has been working on alpha amylase gene expression in
cultivated oat (_Avena sativa_ cv. Rhiannon) for the past seven
years, so she should know! As in all cereals, the enzyme is
produced by the aleurone cells (a thin layer of living tissue
just inside the seed coat, surrounding the endosperm) in response
to a hormone (gibberellin) which is produced by the embryo on
hydration. The gibberellin is probably perceived by a receptor
in the aleurone cell membrane, which conveys the signal (via an
unknown pathway, the subject of her research) to factors in the
nucleus which activate transcription of the alpha-amylase genes
(and proteases etc). The mRNA is then translated in the cytoplasm
and the enzyme transported out of the cell, where it diffuses
into the endosperm and hydrolyses the starch.
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