Improved photosynthesis of previtamin D by wavelengths of 280–300 nm

Effect of UV-B irradiated vitamin D enriched yeast supplementation on milk performance and blood chemical profiles in dairy cows

OBJECTIVE

The objective was to evaluate the effects of UV-B irradiated vitamin D-enriched yeast supplementation on milk yield, milk composition, vitamin D in milk, milk fatty acids, blood chemistry, and 25(OH)D status in dairy cows.

METHODS

Six Thai Friesian cows (milk production, 11.2±2.0 kg/d; body weight, 415.0±20.0 kg; and days in milk, 90.0±6.0) were allocated to each treatment in a 3×3 Latin square design, with three treatments and three periods. Each period of the Latin square lasted 49 days consisting of 14 days for diet adaptation and 35 days for sample collection. Dairy cows were randomly assigned to one of three treatments: i) feeding a basal diet without yeast (CON); ii) basal diet + 5 g of live yeast (75 IU/head/d of vitamin D2; LY); and iii) basal diet + 5 g of UV-B irradiated vitamin D enriched yeast (150,000 IU/head/d of vitamin D2; VDY). Feed intake and milk production were recorded daily, milk sample collection occurred on days 14 and 35 of each collection period, and blood plasma was collected on days 0, 7, 14, 21, 28, and 35 of each collection period.

RESULTS

The results show that after a trial period of 14 and 35 days, the VDY group had significantly higher vitamin D content in milk than the LY and CON groups (376.41 vs 305.15, 302.14 ng/L and 413.46 vs 306.76, 301.12 ng/L, respectively). At days 7, 14, 21, 28, and 35 of the experiment, cows fed the VDY group had significantly higher 25(OH)D2 status in blood than the CON and LY groups (51.07 vs 47.16, 48.05 ng/mL; 54.96 vs 45.43, 46.91 ng/mL; 56.16 vs 46.87, 47.16 ng/mL; 60.67 vs 44.39, 46.17 ng/mL and 63.91 vs 45.88, 46.88 ng/mL), respectively.

CONCLUSION

In conclusion, UV-B irradiated vitamin D-enriched yeast supplementation could improve vitamin D content in the milk and 25(OH)D status in dairy cows during the lactation period.

Characterization of various isomeric photoproducts of ergosterol and vitamin D2 generated by UV irradiation

Vitamin D2 is produced from its precursor ergosterol under the impact of ultraviolet (UV) light which is also commercially carried out to increase vitamin D2 contents in mushrooms (‘Novel Food’). However, this process is accompanied by the formation of various isomers that partly co-elute with the target compound and are currently difficult to analyze. For this reason, vitamin D2 and ergosterol were irradiated with the goal to generate and characterize various isomeric photoproducts with three analytical methods. High-performance liquid chromatography with ultraviolet detection (HPLC–UV) was accompanied by using a chiral detector (CD) which was serially linked with the UV detector. Applied for the first time in this research area, HPLC-CD chromatograms provided complementary information which was crucial for the identification of several co-elutions that would have been overlooked without this approach. Additional information was derived from gas chromatography with mass spectrometry analysis. Diagnostic fragment ions in the GC/MS spectra allowed to distinguish four classes of tri- (n = 2), tetra-, and pentacyclic isomer groups. Despite several drawbacks of each of the applied methods, the shared evaluation allowed to characterize more than ten isomeric photoproducts of vitamin D2 including previtamin D2, lumisterol2, tachysterol2,trans-vitamin D2 isomers, and two pentacyclic isomers (suprasterols2 I and II), which were isolated and characterized by proton magnetic resonance spectroscopy (1H NMR).

Safety Assessment of Vitamin D and Its Photo-Isomers in UV-Irradiated Baker's Yeast

Vitamin D deficiency due to, e.g., nutritional and life style reasons is a health concern that is gaining increasing attention over the last two decades. Vitamin D₃, the most common isoform of vitamin D, is only available in food derived from animal sources. However, mushrooms and yeast are rich in ergosterol. This compound can be converted into vitamin D₂ by UV-light, and therefore act as a precursor for vitamin D. Vitamin D₂ from UV-irradiated mushrooms has become an alternative source of vitamin D, especially for persons pursuing a vegan diet. UV-irradiated baker’s yeast (Saccharomyces cerevisiae) for the production of fortified yeast-leavened bread and baked goods was approved as a Novel Food Ingredient in the European Union, according to Regulation (EC) No. 258/97. The Scientific Opinion provided by the European Food Safety Authority Panel on Dietetic Products, Nutrition, and Allergies has assessed this Novel Food Ingredient as safe under the intended nutritional use. However, recent findings on the formation of side products during UV-irradiation, e.g., the photoproducts tachysterol and lumisterol which are compounds with no adequate risk assessment performed, have only been marginally considered for this EFSA opinion. Furthermore, proceedings in analytics can provide additional insights, which might open up new perspectives, also regarding the bioavailability and potential health benefits of vitamin D-fortified mushrooms and yeast. Therefore, this review is intended to give an overview on the current status of UV irradiation in mushrooms and yeast in general and provide a detailed assessment on the potential health effects of UV-irradiated baker’s yeast.

Structural dynamics of photochemical reactions probed by time-resolved photoelectron spectroscopy using high harmonic pulses

Femtosecond ring-opening dynamics of 1,3-cyclohexadiene (CHD) in gas phase upon two-photon excitation at 400 nm (=3.1 eV) was investigated by time-resolved photoelectron spectroscopy using 42 nm (=29.5 eV) high harmonic photons probing the dynamics of the lower-lying occupied molecular orbitals (MOs), which are the fingerprints of the molecular structure. After 500 fs, the photoelectron intensity of the MO constituting the C[double bond, length as m-dash]C sigma bond (σ_{C[double bond, length as m-dash]C}) of CHD was enhanced, while that of the MO forming the C-C sigma bond (σ_CC) of CHD was decreased. The changes in the photoelectron spectra suggest that the ring of CHD opens to form a 1,3,5-hexatriene (HT) after 500 fs. The dynamics of the σ_{C[double bond, length as m-dash]C} and σ_CC bands between 200 and 500 fs reflects the ring deformation to a conical intersection between the 2¹A and 1¹A potential energy surfaces prior to the ring-opening reaction.

Dose-Response Effect of Sunlight on Vitamin D2 Production in Agaricus bisporus Mushrooms

The dose response effect of UV-B irradiation from sunlight on vitamin D2 content of sliced Agaricus bisporus (white button mushroom) during the process of sun-drying was investigated.Real-time UV-B and UV-A data were obtained using a high-performance spectroradiometer. During the first hour of sunlight exposure, the vitamin D2 content of the mushrooms increased in a linear manner, with concentrations increasing from 0.1 μg/g up to 3.9 ± 0.8 μg/g dry weight (DW). At the subsequent two measurements one and 3 h later, respectively, a plateau was reached. Two hours of additional exposure triggered a significant decline in vitamin D2 content. After just 15 min of sun exposure and an UV-B dose of 0.13 J/cm(2), the vitamin D2 content increased significantly to 2.2 ± 0.5 μg/g DW (P < 0.0001), which is equivalent to 17.6 μg (704 IU) vitamin D2 per 100 g of fresh mushrooms and comparable to levels found in fatty fish like the Atlantic salmon.

Safety assessment of the post-harvest treatment of button mushrooms (Agaricus bisporus) using ultraviolet light

Wild mushrooms are an excellent source of vitamin D. The presence of vitamin D in mushrooms is attributed to sunlight exposure, which catalyzes the conversion of fungal ergosterol to vitamin D2 via a series of photochemical/thermal reactions. Mushroom growers now incorporate UV light treatments during processing to produce mushrooms with levels of vitamin D that compare to those in wild mushrooms. Presented herein is a comprehensive review of information relevant to the safety of introducing vitamin D mushrooms, produced using UV light technologies, to the food supply. Historical reference to the use of UV light for production of vitamin D is discussed, and studies evaluating the nutritional value and safety of vitamin D mushrooms are reviewed. Traditional safety evaluation practices for food additives are not applicable to whole foods; therefore, the application of substantial equivalence and history-of-safe-use is presented. It was demonstrated that vitamin D in mushrooms, produced using UV light technologies, are equivalent to vitamin D in mushrooms exposed to sunlight, and that UV light has a long-history of safe use for production of vitamin D in food. Vitamin D mushrooms produced using UV light technologies were therefore considered safe and suitable for introduction to the marketplace.

Solvent Dependent Conformational Relaxation of cis-1,3,5-Hexatriene

Ultrafast transient absorption spectroscopy was used to study the conformational relaxation dynamics of 1,3,5-cis-hexatriene (Z-HT) produced in the photochemical ring-opening reaction of 1,3-cyclohexadiene (CHD) in methanol and n-propanol solvents. The results are compared with earlier investigations performed using cyclohexane and hexadecane solvents [Anderson, N. A.; Pullen, S. H.; Walker II, L. A.; Shiang, J. J.; Sension, R. J.; J. Phys. Chem. A 1998, 102, 10588-10598.]. The conformational relaxation between hot cZc-HT, cZt-HT, and tZt-HT, where the labels c and t designate cis and trans configurations about the single bonds, is much faster in alcohol solvents than in alkane solvents. The hot Z-HT produced in the photochemical ring-opening reaction evolves from the conformationally strained cZc-HT form to the more stable cZt-HT form on a time scale of 2 ps in alcohols compared with 6 ps in alkanes. The overall decay of the internal vibrational temperature of the hot Z-HT is faster in alcohols (5-6 ps) than alkanes (12-20 ps) and is weakly dependent on the specific alcohol or alkane solvent. A small population of cZt-HT (5-10%) is trapped as the solute equilibrates with the surrounding solvent following UV excitation of CHD or direct UV excitation of Z-HT. The influence of solvent on conformational relaxation of Z-HT was investigated further by probing the temperature dependence of the decay of this thermally equilibrated cZt-HT population. The apparent barrier for the cZt --> tZt conformational isomerization is lower in alcohols (17.4 kJ/mol) than in alkanes (23.5 kJ/mol). However the equilibrium Arrhenius prefactor (A(h)) is an order of magnitude smaller for alcohols (ca. 4 x 10(12)) than alkanes (ca. 6 x 10(13)) resulting in an absolute rate of decay that is faster in the alkane than in the alcohol solvents. These results are discussed in the context of transition state theory and Kramers' theory for condensed phase reaction dynamics.

Conformer-specific photoconversion of 25-hydroxytachysterol to 25-hydroxyprevitamin D3: role in the production of vitamin Ds

The photochemical goal in the production of vitamin Ds (Vit Ds) is to maximize the conversion of the provitamins (Pros) to the previtamins (Pres) while minimizing stoichiometric losses to undesirable over-irradiation products. The last step in the syntheses, the [1,7]-sigmatropic rearrangement of the Pres to the Vits, is thermally induced. The competition between cis-trans photoisomerization and photocyclization of the Pres is known to be highly excitation-wavelength specific. It inspired Havinga's nonequilibration of excited rotamers (NEER) principle and more recent alternative explanations. In contrast, the photochemistry of tachysterol has been reported to be relatively unexceptional with Tachy --> Pre quantum yields in the 0.10-0.13 range, independent of lambdaexc. Examination of the spectrum of the 25-hydroxy derivative of tachysterol (HOTachy) reveals vibronic structure between 295 and 260 nm and a broad structureless shoulder between 330 and 295 nm. These features are consistent with absorption by at least two Tachy conformers. We show that these conformers differ dramatically in their trans-to-cis photoisomerization efficiency. The Tachy --> Pre quantum yield at 313 nm (0.42) in degassed methanol solution is substantially higher than at 254 nm (0.12). On the basis of recent theoretical predictions, it is likely that 313 nm selectively excites the cEc HOTachy conformer which gives photoisomerization much more efficiently than do the other expected conformers (cEt, most abundant, and tEt). Efficient conversion of HOPro D3 to HOPre D3 is accomplished by a two-stage 254/313-nm irradiation sequence. Use of 313 nm in the second step is preferable to previously proposed much longer wavelengths that were hardly absorbed by HOTachy.

Near-UV-induced absorbance change and photochemical decomposition of ergosterol in the plasma membrane of the yeast Saccharomyces cerevisiae

When cells of the yeast Saccharomyces cerevisiae were exposed to near-UV (300-400 nm), their absorption spectra changed slightly within the range 220-300 nm with increasing dosage. Difference spectra, calculated by substracting the curve recorded in cells exposed to near-UV from the curve of unexposed cells, decreased with increasing dosage over a broad band with peaks at 272, 282 and 295 nm and a shoulder at 265 nm. These peaks were in agreement with the absorption maxima of ergosterol, which is one of the major components of the plasma membrane of yeast. Near-UV radiation induced a simultaneous decrease in absorption spectra and reduction of ergosterol content in the plasma membrane. Photochemical decomposition of ergosterol by near-UV radiation was revealed in vivo, although ergosterol is generally known to be photoconverted to previtamin D2 industrially by UV radiation in vitro. In order to remove photosensitizers, liposomes were prepared from phospholipids and glycolipids, with or without ergosterol from purified yeast plasma membranes. Liposomal ergosterol in the orientated state was photochemically decomposed by near-UV radiation but ergosterol in the disorientated state in a homogeneous solution was not. Near-UV radiation also induced a decrease in activity of membrane-bound ATPase. Dose-response curves for the reduction of ATPase activity were similar to that for decomposition of ergosterol, suggesting that near-UV caused membrane function damage.