Dietary Fibre - ILSI Argentina

16 Concise Monograph Series
BOX 3
Resistant starch (RS)
RS1 – starch that is physically inaccessible e.g. enclosed within
intact cell structures in foods such as leguminous seeds and
partly milled cereal grains and seeds.
RS2 – native starch granules (of B-type X-ray spectrum),
e.g. in maize rich in amylose, raw potatoes, green bananas.
RS3 – retrograded amylose (and to a lesser extent, amylopectin)
in processed foods. Food starches may be rendered
partially indigestible by physical or chemical processes and
by cooling, e.g. in bread, cornflakes and cooled cooked potato
or rice.
RS4 – chemically modified starch (including pyrolised,
pyrodextrinated starch).
The resistant starch content of a food may change
during storage, depending on temperature and water
content, and during food preparation. Consequently, an
exact quantification of resistant starch in a food item at
the time of consumption is impossible. One person may
digest a greater proportion of starch in the small
intestine, while in another individual this would behave
as resistant starch.
Non-digestible oligosaccharides
Non-digestible oligosaccharides with degree of
polymerisation ranging from 3-10 occur naturally in
plant foods, mainly vegetables, cereals and fruits. They
can also be synthesised either chemically or
enzymatically from monosaccharides and disaccharides,
or by enzymatic hydrolysis of polysaccharides. They are
included in the definition of dietary fibre because, as a
result of their non-digestibility, they exhibit similar
physiological effects as their larger polysaccharide
counterparts. They are generally highly fermentable and
some have so-called prebiotic properties. The most well
known prebiotics are the fructans, which include the
fructo-oligosaccharides or oligofructoses, obtained from
the enzymatic hydrolysis of naturally occurring inulins
(with degree of polymerisation 3-60) and their synthetic
analogues obtained through enzymatic synthesis from
sucrose. Onions, chicory and Jerusalem artichokes are the
major dietary sources of naturally occurring fructans,
from which inulin and fructo-oligosaccharides are
obtained.
Large numbers of processed and synthetic nondigestible
oligosaccharides have been described.
Physiological properties have been confirmed for some
of these. Primarily these are effects mediated by changes
in the activity and/or composition of the human colonic
microflora. Therefore, these may be seen to represent
new sources of dietary fibre in that they conform to the
criteria laid down by recent definitions of dietary fibre.
However, not all non-digestible oligosaccharides are
universally permitted for food use. Currently, fructooligosaccharides
and certain galacto-oligosaccharides
are permitted within most European countries, USA and
Canada. Japan permits a wider range of non-digestible
oligosaccharides for food use.
Other synthetic carbohydrate
compounds
Like cellulose itself, synthetic derivatives of cellulose,
such as methylcellulose and hydroxypropylmethylcellulose,
are non-digestible. Unlike their parent
molecule they are soluble, but are hardly fermented by
the colonic microflora.