Changes in the protein secondary structure of hen's egg yolk determined by Fourier transform infrared spectroscopy during the first eight days of incubation.

In this study, incubation-induced alterations in the protein secondary structures of egg yolk and its major fractions (granules, plasma, and low-density lipoproteins [LDL]) were monitored during the first 8 d of embryogenesis using Fourier transform infrared spectroscopy (FTIR) and isoelectric focusing (IEF). Two factors potentially connected with egg yolk protein secondary structure changes were evaluated, i.e., the pH value of incubated egg yolk, and phosvitin, an important egg yolk protein assumed to play an important role in hematopoiesis as the iron carrier during early embryogenesis. However, neither the significant increase in pH value (6.07 to 6.92) of egg yolk during incubation of fertilized eggs, nor the release of iron from phosvitin were found to be directly related to the changes in protein secondary structure in egg yolk and its fractions. FTIR showed that the protein conformation in whole egg yolk, granules, and LDL was stable during incubation, but separate evaluation of the plasma fraction revealed considerable changes in secondary structure. However, it is unlikely that these changes were provoked by structure changes of the proteins originally present in plasma; instead, the physiological influx of albumen into the yolk sac was expected to play an important role in the protein modifications of egg yolk, as was shown both by FTIR and IEF of the water-soluble egg yolk proteins. Moreover, FTIR was used to determine the naturally occurring proportions (%) of the secondary structure elements in egg yolk and its 3 fractions on d 0 of incubation. The granules fraction mainly consisted of a mixture of inter- and intramolecular ß-sheets (57.04%±0.39%). The plasma fraction was found to consist mainly of α-helices (43.23%±0.27%), whereas LDL was composed almost exclusively of intramolecular ß-sheets (67.36%±0.56%) or ß-turns, or both. On the other hand, whole egg yolk was mainly composed of intermolecular ß-sheets (39.77%±0.48%), potentially indicating molecular interchanges between the individual fractions.

Comparison of dietary tocotrienols from barley and palm oils in hen's egg yolk: transfer efficiency, influence of emulsification, and effect on egg cholesterol.

BACKGROUND: The main component in tocotrienols (T3) from barley (Hordeum vulgare L.) is α-T3, the vitamer with the highest bioavailability, while palm oil T3 is particularly rich in γ-T3. Unlike tocopherols, T3 are known for their cholesterogenesis-inhibiting, neuroprotective and anticarcinogenic properties. In this study the oral bioavailabilities of T3 from barley oil (3.98 mg day⁻¹) and T3 from palm oil (3.36 mg day⁻¹) in nanoemulsified formulations (NE) and self-emulsifying systems (SES) were compared using hen's eggs as a bioindicator. In addition, the transfer efficiencies of barley oil T3 and palm oil T3 into egg yolk were compared, as well as their effects on egg cholesterol levels. RESULTS: Nanoemulsification led to T3 levels (132.9 µg per egg) higher than with non-emulsified barley oil (112.8 µg per egg) and barley oil SES (116.7 µg per egg) owing to the high proportions of α-T3 (99-117 µg per egg), which has a particularly high transfer efficiency (4.32-6.75%). T3 contents of eggs from hens fed barley oil supplements (112-132 µg per egg) were significantly higher than those of eggs from hens fed palm oil supplements (70-78 µg per egg). Addition of barley and palm oils to laying hen feed decreased egg yolk cholesterol by 4 and 6% respectively. CONCLUSION: Results from this animal study may help to establish T3 from barley as a dietary supplement and to develop nutritionally improved hen's eggs.

Determination of heat-induced changes in the protein secondary structure of reconstituted livetins (water-soluble proteins from hen's egg yolk) by FTIR.

This study characterized the impact of technological treatments on the protein secondary structure of a newly developed egg yolk livetin formulation and its components α-livetin, which is identical with chicken serum albumin, and γ-livetin, the bioactive antibody immunoglobulin Y. Fourier transform infrared (FTIR) spectroscopy at 25 °C revealed that the largest proportion of conformal elements comprised intramolecular (native) ß-sheets (60-80%) in γ-livetin, and α-helices/random coils (60.59%) in α-livetin. In reconstituted freeze-dried livetins, the main protein conformations were also intramolecular (native) ß-sheets (55.08%) and α-helices/random coils (30.51%), but upon heating from 25 to 95 °C, the former decreased sigmoidally at the onset-of-denaturation temperature (TOD (FTIR)) of 69.5 °C, concomitant with a sigmoidal increase in intermolecular (denatured) ß-sheets at a TOD (FTIR) of 72.4 °C and a sigmoidal decrease in IgY activity at TOD (ELISA) of 67.5 °C. Reconstituted spray-dried livetins showed less native ß-sheets and significantly lower TOD (FTIR) values than freeze-dried livetins.

HPLC Separation of Vitamin E and Its Oxidation Products and Effects of Oxidized Tocotrienols on the Viability of MCF-7 Breast Cancer Cells in Vitro.

Tocotrienols, a vitamin E subgroup, exert potent anticancer effects, but easily degrade due to oxidation. Eight vitamin E reference compounds, α-, ß-, γ-, or δ-tocopherols or -tocotrienols, were thermally oxidized in n-hexane. The corresponding predominantly dimeric oxidation products were separated from the parent compounds by diol-modified normal-phase HPLC-UV and characterized by mass spectroscopy. The composition of test compounds, that is, α-tocotrienol, γ-tocotrienol, or palm tocotrienol-rich fraction (TRF), before and after thermal oxidation was determined by HPLC-DAD, and MCF-7 cells were treated with both nonoxidized and oxidized test compounds for 72 h. Whereas all nonoxidized test compounds (0-100 µM) led to dose-dependent decreases in cell viability, equimolar oxidized α-tocotrienol had a weaker effect, and oxidized TRF had no such effect. However, the IC50 value of oxidized γ-tocotrienol was lower (85 µM) than that of nonoxidized γ-tocotrienol (134 µM), thereby suggesting that γ-tocotrienol oxidation products are able to reduce tumor cell viability in vitro.

Identification of α-tocotrienolquinone epoxides and development of an efficient molecular distillation procedure for quantitation of α-tocotrienol oxidation products in food matrices by high-performance liquid chromatography with diode array and fluorescence detection.

The aim of this study was to investigate the most important oxidation products of α-tocotrienol (α-T3) along with other tocochromanols in lipid matrices and tocotrienol-rich foods. For this purpose, an efficient molecular distillation procedure was developed for the extraction of analytes, and α-T3-spiked and thermally oxidized natural lipids (lard and wheat germ oil) and α-T3-rich foods (wholemeal rye bread and oil from dried brewer's spent grain) were investigated through HPLC-DAD-F. The following α-T3 oxidation products were extractable from lipid matrices along with tocochromanols: α-tocotrienolquinone (α-T3Q), α-tocotrienolquinone-4a,5-epoxide (α-T3Q-4a,5-E), α-tocotrienolquinone-7,8-epoxide (α-T3Q-7,8-E), 7-formyl-ß-tocotrienol (7-FßT3), and 5-formyl-γ-tocotrienol (5-FγT3). Recovery rates were as high as 88% and enrichment factors up to 124. The proposed method allows the investigation of α-T3Q, α-T3Q-4a,5-E, α-T3Q-7,8-E, 7-FßT3, and 5-FγT3 in small quantities (<0.78 µg/g) in lipid matrices, which is necessary for the investigation and analysis of the formation kinetics of these oxidation products in fat, oils, and tocotrienol-rich foods.