Subject: Re: Q: Hydrogenation and trans fat formation

From: "Peter J. Barnes" <[email-masked]>
Date: Mon, 2 Dec 1996 13:00:51 +0000

In article <[email-masked]>, David Leonard
<[email-masked]> writes
>Does trans fat formation increase lineraly with hydrogenation?  The CSPI 
>Newsletter's article on trans says that heavily hydrogenated oil has more 
>trans fat than partially hydrogenated oil.   However, another source says that 
>fully hydrogenated oil is basically converted to stearic acid and is still 
>in the cis-form.    That's why you're supposedly better off buying a 
>margarine that's made from fully hydrogenated oil mixed with liquid 
>vegetable oil.  Who's right??

Unsaturated fatty acids have double bonds between some of the pairs of
carbon atoms in the chain. These bonds can be in the cis form or the
trans form, depending whether the bond bends one way or the other. Most
plant and animal unsaturated fatty acids have the cis form. The single
bonds between other carbon atoms (called saturated bonds) are fixed and
do not have cis and trans forms

During hydrogenation (whether in edible oil processing or in the gut of
a cow) some of the double bonds have hydogen atoms added to make them
saturated. If this were a simple process, then cis bonds would disappear
and only saturated bonds would be left. But some of the cis bonds are
flipped to trans to give a byproduct of trans fatty acids. If you keep
on hydrogenating, then the trans bonds will themselves also become
saturated by addition of hudrogen. The typical polyunsaturated fatty
acid, linoleic acid, would become the saturated acid stearic acid. This
has neither cis nor trans bonds, because it has no double bonds.

In general, it is right that "heavy" hydrogenation by conventional
methods will give more trans than will "light" hydrogenation. But if you
continue hydrogenating, the level of trans will decrease beause there
are no more double bonds left.

So why don't the processors simply hydrogenate fully so that there are
no trans acids present at all? The answer is that the resulting fat
would be very hard, greasy and not suitable for most of the typical
applications. And it would be highly saturated which would upset the
nutritionists.

What is the answer? Hydrogenation conditions can be optimised to yield
the minimum level of trans acids: things like catalyst, temperature,
pressure etc. Or an oil can be fully hydrogenated then combined with an
unsaturated oil by a process called interesterification. This give a
suitable hardened product without the trans acids.

Further information about how to produce low-trans fats is given in:-

1. an article by Dr L.H. Wesdorp of Unilever in the November issue of
*Lipid Technology*, pages 129-135 ("Current trends in oil processing").
Published by PJ Barnes & Associates;

2. the book "Lipids & Nutrition -- Current Hot Topics" (to be published
in December 1996 by PJ Barnes & Associates; ISBN 0-9526542-6-1) in
chapters by Dr R. Ariaansz of Engelhard De Meern BV ("Hydrogenation with
minimum trans acids"), and by Dr D.A. Allen of Partnership Solutions
("Food technology problems of replacing trans acids");

3. and by Prof. N.-H. Schoon of Chalmers University of Technology, in
Oils-Fats-Lipids 1995: Proceedings of the 21st World Congress of the
Int. Soc. for Fat Research (Published by PJ Barnes & Associates, ISBN 0-
9526542-4-5), pages 155-159 ("Is a low trans content attainable by a
conventional hydrogenation of vegetable oils").

Hope this helps!

Peter J. Barnes

-- 
Dr Peter J. Barnes
PJ Barnes & Associates, PO Box 200
Bridgwater TA7 0YZ, England.
Tel: +44-1823-698973
Fax: +44-1823-698971
E-mail: editor(a)pbarnes.demon.co.uk