Kinetics and Mechanism of the Primary Steps of Degradation of Carotenoids by Acid in Homogeneous Solution

Abstract

The kinetics of reaction between trifluoroacetic acid as an acid of medium strength and the carotenoids beta-carotene, zeaxanthin, canthaxanthin, and astaxanthin has been examined in detail including the effects of dioxygen, acid concentration, and carotenoid structure. Reaction between acid and carotenoid leads to species absorbing in the red and near-infrared (NIR) spectral regions, intermediates that subsequently disappear. ESR experiments clearly show that these species are not carotenoid radicals, although their NIR absorption is similar to the absorption of carotenoid radical cations. Under most reaction conditions, the disappearance of carotenoids follows pseudo-zero-order kinetics, whereas the reaction order is >1 with respect to acid, and the long-lived (hours) intermediates are suggested to be mono- (700 nm) and diprotonated carotenoid ( approximately 950 nm). Acid induces cis/trans-isomerization via the protonated intermediates, which also decay to nonradical species with shorter conjugated systems-most probably carotenoid esters. Slow protonization of the methine carbon is the primary step in the degradation, but dioxygen increases the rate as a result of formation of a charge-transfer complex with the carotenoids as indicated by a red-shift of the NIR absorption bands. Carotenoids with carbonyl groups (astaxanthin and canthaxanthin) have slower rates of degradation than beta-carotene and zeaxanthin, indicating preferential nondegradative protonation of the carbonyl groups.

Feeding Forage in Poultry: A Promising Alternative for the Future of Production Systems

“…Antioxidant supplementation of feed is an efficient method for increasing poultry meat oxidative stability [74]. Moreover, β-carotene, a pro-vitamin A compound abundant in forages, is the predominant carotenoid in meat and meat products [75]. Feeding of dehydrated leguminous-based forage vitamin E homologs and β-carotene for broiler meat oxidative stability remains, however, to be established [73].…”

Degradation of β-carotene during fruit and vegetable processing or storage: reaction mechanisms and kinetic aspects: a review

“…Mortensen et al studied degradation of carotenoids with nitric acid and moderately strong acids, such as trichloroacetic and trifluoroacetic acids [72]. The intermediary reactions were mono-and di-protonated carotenoids, which exhibited a long lifetime (hours) in the experimental conditions of the study.…”

Overview of carotenoid bioavailability determinants: From dietary factors to host genetic variations

“…The fraction of cis isomers present in our diet 303 is usually produced by technological treatments, in particular elevated temperatures 304 (Milanowska & Gruszecki, 2005;Rodriguez-Amaya, 1999;Updike & Schwartz, 2003). A 305 "trans to cis" conversion in the acidic environment of the stomach has also been proposed 306 (Mortensen & Skibsted, 2000), although it has not been observed in vivo (Richelle, et al, 307 2010;Tyssandier, et al, 2003). However, Richelle et al reported lycopene conversion to 308 occur within the enterocyte (Richelle, et al, 2010).…”