Carotenoids temperature

Liprd Carotenoid Temperature m Solubility threshold [mol%] Reference... 

Canthaxanthin crystallines from various solvents as brownish violet, shiny leaves that melt with decomposition at 210°C. As is the case with carotenoids in general, the crystals are sensitive to light and oxygen and, when heated in solution or exposed to ultraviolet light or iodine, form a mixture of cis and trans stereoisomers. Consequentiy, crystalline canthaxanthin should be stored under inert gas at low temperatures. Unlike the carotenoid colorants P-carotene and P-apo-8 -carotenal, canthaxanthin has no vitamin A activity. It is chemically stable at pH 2—8 (the range normally encountered in foods) and unaffected by heat in systems with a minimal oxygen content. 

Stndies of the antoxidation of carotenoids in liposomal suspensions have also been performed since liposomes can mimic the environment of carotenoids in vivo. Kim et al. stndied the antoxidation of lycopene," P-carotene," and phytofluene" " in liposomal snspensions and identified oxidative cleavage compounds. Stabilities to oxidation at room temperature of various carotenoids incorporated in pig liver microsomes have also been studied." The model took into account membrane dynamics. After 3 hr of reactions, P-carotene and lycopene had completely degraded, whereas xanthophylls tested were shown to be more stable. 

Lisiewska, Z., Kmiecik, W., and Shnpski, J., Contents of chlorophylls and carotenoids in frozen dill effect of nsahle part and pre-treatment on the content of chlorophylls and carotenoids in frozen diU (Anethum graveolens L.), depending on the time and temperature of storage. Food Chem., 84, 511, 2004. 

The effects of temperature on carotenoid content can be considered from three perspectives (1) evaluation of stability or retention of carotenoids, (2) study of the chemical changes (isomerization, oxidation, epoxy-furanoid rearrangement), and (3) their effects on the nutritional value and other carotenoid actions in humans. The first two topics are discussed in the following sections. The third is presented in Section 3.2.4.1 of Section 3.2. 

Since values reported in different studies for the same carotenoid at the same temperature showed differences of at least one order of magnitude, it is imperative to conhrm the kinetic reaction order model by conducting experiments with different carotenoid concentrations and at different temperatures. 

In dark conditions, the spontaneous isomerization of carotenoids occurs in solution the rate is dependent on temperature, solvent, and carotenoid structure. In the case of P-carotene, 13-di-P-carotene was formed approximately three times faster than the 9-cis- isomer at room temperature and at 150°C. ... 

Plant extracts rich in carotenoids, hydrolyzed with acetic and propionic aldehydes under controlled temperature and pressure... 

High temperature must be avoided temperatures below 35°C should be used for evaporation of a large amount of solvent in a rotary evaporator or evaporation of small volumes directly under an N2 or Ar stream. Avoid acid in ambient air where carotenoids are handled. 

When the aim is isolation for identification by direct probe insertion mass spectrometry (MS), plastic materials, filter papers, and blenders should be avoided to prevent contamination during extraction and chromatography. It is also very important to avoid the cis-trans isomerization of carotenoids in solution, which is accelerated by heat, light, acids, and active surfaces. Therefore, a pure carotenoid or even a crude extract should never be stored in solution it should be kept completely dry in an inert atmosphere at low temperature. 

On the other hand, quantitative extraction requires complete and exhaustive extraction and no material can be lost. To assure complete extraction when a food is analyzed for the first time in a laboratory, it is useful to carry out two or three extractions, pool the solvents, and keep separate the next extracts to verify the presence of carotenoids. Usually four to six extractions are enough to remove the carotenoids completely from a sample. The extraction can be carried out in a blender, vortex, or with a mortar and pestle. Accelerated solvent extraction (ASE), an important extraction technique in residue analysis, currently attracts interest due to its short duration, low level of solvent use, and high extraction yield. The average recoveries for all carotenoids with the exception of norbixin ranged from 88.7 to 103.3% using manual extraction and from 91.0 to 99.6% by ASE (70 bar and temperature of 40°C) both extractions were carried out with a mixture of MeOH, EtOAc, and petroleum ether (1 1 1). ... 

A general procedure that our laboratory generally employs is the addition of an equal amount of methanolic 10% potassium hydroxyde (KOH) to an ethereal carotenoid extract. This solution is bubbled with N2 and allowed to stand overnight at room temperature. Other conditions that shorten time at room temperature have also been used, such as saponification of the dichloromethane (CH2CI2) extract with the same amount of 10% KOH in MeOH for 1 hr (peppers and fruits ) and ethereal extract treated with 30% methanolic KOH under N2 for 3 hr (green leaves, vegetables and fruits ). 

Temperature has an influence on the retention and consequently on the capacity factors of carotenoids in HPLC columns. Usually, as the column temperature increases, the retention decreases however, in a polymeric C30 column, after an initial decrease of the t values of cis isomers of carotenoids, the retention of cis isomers actually increases at temperatures above 35°C. This different behavior can be explained by the increased order and rigidity of the C30 stationary phase at lower temperatures that in turn induce preferential retention of long, narrow solutes as the trans isomer and partial exclusion of bent and bulky cis isomers. The greater chain mobihty and less rigid conformation of the C30 at higher temperatures may increase the contact area available for interaction with the cis isomers and also may lower... 

Perez-Galvez, A., Homero-Mendez, D., and Mmguez-Mosquera, M.I., Dependence of carotenoid content and temperature-time regimes during the traditional slow drying of red pepper for paprika production at La Vera County, Eur. Food Res. Technol., 221, 645, 2005. 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Niedzwiedzki, D., J. F. Koscielecki, H. Cong, J. O. Sullivan, G. N. Gibson, R. R. Birge, and H. A. Frank. 2007. Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. J. Phys. Chem. B 111 5984-5998. 

EPR techniques were used to show (Polyakov et al. 2001a) that one-electron transfer reactions occur between carotenoids and the quinones, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), and tetrachlorobenzoquinone (CA). A charge-transfer complex (CTC) is formed with a -values of 2.0066 and exists in equilibrium with an ion-radical pair (Car Q ). Increasing the temperature from 77 K gave rise to a new five-line signal with g=2.0052 and hyperfine couplings of 0.6 G due to the DDQ radical anions. At room temperature a stable radical with y=2.0049 was detected, its... 

Three-pulse ESEEM spectrum of perdeuterated P-carotene imbedded in Cu-MCM-41 exhibits an echo decay with an echo modulation due to deuterons. The three-pulse ESEEM is plotted as a function of time, and curves are drawn through the maximum and minima. From ratio analysis of these curves, a best nonlinear least-squares lit determines the number of interacting deuterons, the distance (3.3 0.2A), and the isotopic coupling (0.06 0.2MHz). This analysis made it possible to explain the observed reversible forward and backward electron transfer between the carotenoid and Cu2+ as the temperature was cycled (77-300 K). 

CW ENDOR spectrum measurements carried out at 120 K (the optimum temperature for measuring resolved CW ENDOR powder spectra of carotenoid radicals) shows resolved lines from the P-methyl hfc (Piekara-Sady et al. 1991,1995, Wu et al. 1991, Jeevarajan et al. 1993b) (see Figure 9.5). The lines above 19 MHz are due to neutral radicals according to DFT calculations (Gao et al. 2006). 

The 327-670 GHz EPR spectra of canthaxanthin radical cation were resolved into two principal components of the g-tensor (Konovalova et al. 1999). Spectral simulations indicated this to be the result of g-anisotropy where gn=2.0032 and gi=2.0023. This type of g-tensor is consistent with the theory for polyacene rc-radical cations (Stone 1964), which states that the difference gxx gyy decreases with increasing chain length. When gxx-gyy approaches zero, the g-tensor becomes cylindrically symmetrical with gxx=gyy=g and gzz=gn. The cylindrical symmetry for the all-trans carotenoids is not surprising because these molecules are long straight chain polyenes. This also demonstrates that the symmetrical unresolved EPR line at 9 GHz is due to a carotenoid Jt-radical cation with electron density distributed throughout the whole chain of double bonds as predicted by RHF-INDO/SP molecular orbital calculations. The lack of temperature... 

Carotenoids incorporated in metal-substituted MCM-41 represent systems that contain a rapidly relaxing metal ion and a slowly relaxing organic radical. For distance determination, the effect of a rapidly relaxing framework Ti3+ ion on spin-lattice relaxation time,and phase memory time, Tu, of a slowly relaxing carotenoid radical was measured as a function of temperature in both siliceous and Ti-substituted MCM-41. It was found that the TM and 7) are shorter for carotenoids embedded in Ti-MCM-41 than those in siliceous MCM-41. 

To measure distances in the wider temperature range, this procedure was modified. Relaxation of the carotenoid occurs through several different mechanisms including the dipolar-dipolar interaction. Assuming that kAA is the rate constant of the dipolar-dipolar interaction and K=(k,l + k2 + k3 +. ..) is the sum of the rate constants of all other relaxation pathways, we can extract kAA from the following equation ... 

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