vitamin c data

nigel Robinson said:

Does anyone have some data for the rate of vitamin c decomposition at
different temperatures. I would be grateful for some
Thanks

Go to pubmed:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed

and do a search on:

"vitamin c losses"

TC

"nigel Robinson" <[email hidden]> schrieb im Newsbeitrag
news:[email hidden]...

Quoted message said:

Does anyone have some data for the rate of vitamin c decomposition at
different temperatures. I would be grateful for some
Thanks

it heavily depends on the environment you measure in (are you searching for
in vivo or in vitro data.. or data in food items?). if you could be a little
more precise at what you want to know I could probably give you some
estimates- we do a lot of ascorbate resarch here.

I do not know about the temperatuire factor but this is good to know.

1: Clin Pharmacokinet. 2003;42(5):437-59.

Clinical pharmacokinetics of antioxidants and their impact on systemic
oxidative stress.

Schwedhelm E, Maas R, Troost R, Boger R.
Institute of Experimental and Clinical Pharmacology, Clinical Pharmacology
Unit, University Hospital of Hamburg-Eppendorf, Hamburg, Germany.

Dietary antioxidants play a major role in maintaining the homeostasis of the
oxidative balance. They are believed to protect humans from disease and
aging. Vitamin C (ascorbic acid), vitamin E (tocopherol), beta-carotene and
other micronutrients such as carotenoids, polyphenols and selenium have been
evaluated as antioxidant constituents in the human diet. This article
addresses data provided from clinical trials, highlighting the clinical
pharmacokinetics of vitamin C, vitamin E, beta-carotene, lycopene, lutein,
quercetin, rutin, catechins and selenium.

The bioavailability of vitamin C is dose-dependent. Saturation of transport
occurs with dosages of 200-400 mg/day. Vitamin C is not protein-bound and is
eliminated with an elimination half-life (t((1/2))) of 10 hours. In Western
populations plasma vitamin C concentrations range from 54-91 micro mol/L.
Serum alpha- and gamma-tocopherol range from 21 micro mol/L (North America)
to 27 micro mol/L (Europe) and from 3.1 micro mol/L to 1.5 micro mol/L,
respectively. alpha-Tocopherol is the most abundant tocopherol in human
tissue. The bioavailability of all-rac-alpha-tocopherol is estimated to be
50% of R,R,R-alpha-tocopherol. The hepatic alpha-tocopherol transfer protein
(alpha-TTP) together with the tocopherol-associated proteins (TAP) are
responsbile for the endogenous accumulation of natural alpha-tocopherol.
Elimination of alpha-tocopherol takes several days with a t((1/2)) of 81 and
73 hours for R,R,R-alpha-tocopherol and all-rac-alpha-tocopherol,
respectively. The t((1/2)) of tocotrienols is short, ranging from 3.8-4.4
hours for gamma- and alpha-tocotrienol, respectively. gamma-Tocopherol is
degraded to 2, 7, 8-trimethyl-2-(beta-carboxyl)-6-hyrdoxychroman by the
liver prior to renal elimination. Blood serum carotenoids in Western
populations range from 0.28-0.52 micro mol/L for beta-carotene, from
0.2-0.28 for lutein, and from 0.29-0.60 for lycopene. All-trans-carotenoids
have a better bioavailability than the 9-cis-forms. Elimination of
carotenoids takes several days with a t((1/2)) of 5-7 and 2-3 days for
beta-carotene and lycopene, respectively. The bioconversion of beta-carotene
to retinal is dose-dependent, and ranges between 27% and 2% for a 6 and
126mg dose, respectively. Several oxidised metabolites of carotenoids are
known. Flavonols such as quercetin glycosides and rutin are predominantly
absorbed as aglycones, bound to plasma proteins and subsequently conjugated
to glucuronide, sulfate, and methyl moieties. The t((1/2)) ranges from 12-19
hours. The bioavailabillity of catechins is low and they are eliminated
with a t((1/2)) of 2-4 hours. Catechins are degraded to several
gamma-valerolactone derivatives and phase II conjugates have also been
identified. Only limited clinical pharmacokinetic data for other polyphenols
such as resveratrol have been reported to date.
PMID: 12739983 [PubMed - in process]