6 replies to this topic

[Anthony_Loera]

I just wondered if there are any studies regarding cis -> Trans isomerization for Resveratrol that you all can help shed some light on. I ran into this study here regarding Lycopene that got me thinking about it:

http://www.lycopene....df/CIS2003-.pdf

This is from page 2:

Moraru C, Lee TC.
Department of Food Science, Center for Advanced Food Technology, Rutgers, The
State University of New Jersey, New Brunswick, New Jersey 08901, USA.
Kinetic studies of lycopene isomerization in a tributyrin model system at
gastric pH. J Agric Food Chem. 2005 Nov 16;53(23):8997-9004.

A semi-preparative HPLC method was developed in order to isolate and purify the
13-cis-lycopene isomer in tomato-based materials. The result was compared with
the naturally predominant all-trans-lycopene isomer, in terms of stability to
gastric pH at physiological temperature in a tributyrin model system. Kinetic
experiments confirmed that lycopene isomerization is a reversible reaction, and
under these conditions the all-trans isomer is more stable than the 13-cis
isomer. In addition, it was found that at gastric pH 13-cis-lycopene would
predominantly isomerize to the all-trans form rather than undergo
oxidation/breakdown. A simulation based on the rate constants calculated in the
kinetic study indicated that at gastric pH the lycopene isomeric distribution
aimed toward an equilibrium characterized by approx 16% 13-cis-, 16% 9-cis-, and
68% all-trans-lycopene. This study suggests that pH-driven isomerization in the
stomach is at least partially responsible for the relatively high cis-lycopene
proportion found in vivo.

This is the part I found interesting:

"In addition, it was found that at gastric pH 13-cis-lycopene would
predominantly isomerize to the all-trans form rather than undergo
oxidation/breakdown."

thanks
Anthony Loera

[maxwatt]

The B. Trela paper on stability of resveratrol addressed the issue. Any pH under 11 favored the conversion of cis to trans-resveratrol, if I recall. If the medium was acidic, the conversion would go all the way to trans-resveratrol. Someone more knowledgeable than I doubted that gastric pH would convert sufficiently during the time it remained inthe stomach when ingested.

The full paper isno longer available on-line AFAIK, but I can send you a copy if you need to see it.

[Anthony_Loera]

Can you? I would like our consultant to look at it for me and get his opinion, thanks.

[dannov]

If I am to get this right, the implication is that Cis can be converted to Trans-res? If this is true, this would make Res50 into something higher than 50 and allow for more value for the dollar.

[krillin]

Here's some related information on beta-carotene.

A group at Cornell University [PMID: 8694017] gave three healthy adults a 1 mg (1666 IU) single dose of 99-percent cis beta-carotene labeled with a radioactive tracer (13C) and found over 95 percent of the cis isomers had been isomerized to trans beta-carotene or transformed into retinol prior to entering the bloodstream. Using calculations the authors admit “may be underestimates” they speculated that 14-52 percent of the cis beta-carotene had been isomerized to the all-trans form.

So natural beta-carotene could be just as bad for you as the synthetic all-trans.

[niner]

The B. Trela paper on stability of resveratrol addressed the issue. Any pH under 11 favored the conversion of cis to trans-resveratrol, if I recall. If the medium was acidic, the conversion would go all the way to trans-resveratrol. Someone more knowledgeable than I doubted that gastric pH would convert sufficiently during the time it remained inthe stomach when ingested.

The trans form is more stable than cis in general, on steric considerations alone. If any pH under 11 favors the conversion, then that should include the gut, blood, etc. This would suggest that we don't need to worry all that much about trans to cis isomerization of resveratrol. In the solid form, which is the way most people store it, the isomerization is also disfavored. In solution it's more likely. As I recall, the stability studies that led to concerns about isomerization were done in solution.

If I am to get this right, the implication is that Cis can be converted to Trans-res? If this is true, this would make Res50 into something higher than 50 and allow for more value for the dollar.

Maybe 50.5 or something like that. My impression is that the cis content of typical extracts is already pretty low. Anthony, or others that have had analyses done, what do you usually see as the cis content? Is it even quantitated?

[maxwatt]

[quote][quote]The B. Trela paper on stability of resveratrol addressed the issue. Any pH under 11 favored the conversion of cis to trans-resveratrol, if I recall. If the medium was acidic, the conversion would go all the way to trans-resveratrol. Someone more knowledgeable than I doubted that gastric pH would convert sufficiently during the time it remained inthe stomach when ingested.[/quote]
The trans form is more stable than cis in general, on steric considerations alone. If any pH under 11 favors the conversion, then that should include the gut, blood, etc. This would suggest that we don't need to worry all that much about trans to cis isomerization of resveratrol. In the solid form, which is the way most people store it, the isomerization is also disfavored. In solution it's more likely. As I recall, the stability studies that led to concerns about isomerization were done in solution.

[quote]If I am to get this right, the implication is that Cis can be converted to Trans-res? If this is true, this would make Res50 into something higher than 50 and allow for more value for the dollar.[/quote]
Maybe 50.5 or something like that. My impression is that the cis content of typical extracts is already pretty low. Anthony, or others that have had analyses done, what do you usually see as the cis content? Is it even quantitated?[/QUOTE

Not only does low pH favor cis to trans conversion, but so do most frequencies of light. One particular frequency of UV from fluorescent lights converts tran to cis, but I think window glass blocks the frequency from sunlight, so sunlight through a window should then convert cis to trans.

The lots I've had tested have all had less than 1% cis resveratrol, usually much less. Typical for 98% powder is 0.15 to 0.25%.

The paper is copyrighted; I wouldn't upload it here without the authors permission. If you're affiliated with a school, you should be able to get it free. You can see the abstract HERE and download it from the ACS link at the bottom of the page.