Stability Of Α-tocopherol Research Articles

Double interface formulation for improved α‐tocopherol stabilisation in dehydration of emulsions

Encapsulation of hydrophobic nutrients can be achieved by freezing and freeze-drying of oil-in-water emulsions containing glass-forming materials. The addition of a polyelectrolyte layer on the protein-stabilised oil droplets may provide better protection to the oil phase against external stresses. Soy protein-trehalose and whey protein-trehalose emulsions with (layer-by-layer, LBL) and without (single-layer, SL) ι-carrageenan were used as the delivery systems for olive oil with dissolved α-tocopherol. Emulsions containing 0.125 g kg(-1) protein, 0.42 g kg(-1) oil and 150 g kg(-1) trehalose with (LBL) or without (SL) 0.25 g kg(-1) ι-carrageenan at pH 3 were frozen and freeze-dried and their state transitions were studied. The stability of α-tocopherol in freeze-dried systems at 0 and 0.33 water activity (aw ) during storage at 55 °C was followed. Loss of α-tocopherol was found in soy protein-stabilised SL systems at 0.33 aw , and this loss coincided with trehalose crystallisation. The stability of α-tocopherol was retained in soy protein-stabilised LBL and whey protein-stabilised LBL and SL systems at all conditions. Trehalose crystallisation-induced loss of structure was confirmed from changes in emulsion properties and visual appearance. Component sugar crystallisation contributed to the loss of sensitive compounds, but the stability of these compounds can be improved by the use of LBL formulations.

Stability of α-Tocopherol in Freeze-Dried Sugar–Protein–Oil Emulsion Solids as Affected by Water Plasticization and Sugar Crystallization

Water plasticization of sugar-protein encapsulants may cause structural changes and decrease the stability of encapsulated compounds during storage. The retention of α-tocopherol in freeze-dried lactose-milk protein-oil, lactose-soy protein-oil, trehalose-milk protein-oil, and trehalose-soy protein-oil systems at various water activities (a(w)) and in the presence of sugar crystallization was studied. Water sorption was determined gravimetrically. Glass transition and sugar crystallization were studied using differential scanning calorimetry and the retention of α-tocopherol spectrophotometrically. The loss of α-tocopherol followed lipid oxidation, but the greatest stability was found at 0 a(w) presumably because of α-tocopherol immobilization at interfaces and consequent reduction in antioxidant activity. A considerable loss of α-tocopherol coincided with sugar crystallization. The results showed that glassy matrices may protect encapsulated α-tocopherol; however, its role as an antioxidant at increasing aw accelerated its loss. Sugar crystallization excluded the oil-containing α-tocopherol from the protecting matrices and exposed it to surroundings, which decreased the stability of α-tocopherol.

Characterisation of the β-lactoglobulin/α-tocopherol complex and its impact on α-tocopherol stability

β-Lactoglobulin (β-LG), the major whey protein in the milk of ruminants, has a high affinity for small hydrophobic molecules. In the present study, its interaction with lipophilic α-tocopherol, the most abundant and biologically active form of vitamin E, was investigated using circular dichroism, fluorescence, high performance liquid chromatography and turbidity analysis. The interaction did not disrupt the secondary or tertiary structures of β-LG. It was dependent on the aggregation of α-tocopherol and on β-LG/α-tocopherol ratios, with one binding site appearing to be the protein internal cavity and the other in the hydrophobic surface pocket at protein concentrations 1/10 that of the vitamin. Formation of complexes with β-LG increased the solubility of α-tocopherol. The protein also protected α-tocopherol somewhat against decomposition, which depended on the protein concentration and was most effective at a β-LG concentration of one-tenth the α-tocopherol concentration. Protein–nutrient complexes might therefore be useful in the development of functional foods.

Structural Behaviour of Lipid Droplets in Protein-stabilized Nano-emulsions and Stability of α-Tocopherol

A stearin-rich milk fraction was used, alone or in combination with α-tocopherol, for the preparation of oil-in-water sodium caseinate-stabilized nano-emulsions. Fat droplets in these two emulsions were characterized for their size distribution and physical stability against aggregation–coalescence, for their heat-induced structural behaviour, and for their ability to protect α-tocopherol during oxidation. Inclusion of α-tocopherol led to changes in the particle size distributions of fat droplets: in the presence of α-tocopherol, approximately 75% of fat droplets were lower than 1 μm, instead of 100% in the absence of α-tocopherol. On the other hand, thermal transitions observed by differential scanning calorimetry showed that supercooling (the increase in differences between temperature of initial crystallization and melting completion) was higher in the emulsified milk fat samples containing α-tocopherol. In addition to a decrease in the temperature of fat crystallization leading this change in the supercooling effect of α-tocopherol, small- and wide-angle X-ray diffraction patterns (SAXS and WAXS, respectively) observed under cooling and re-heating cycles showed that heat-induced polymorphic transitions from\({\text{2L}}_{\text{ $ \alpha $ }} \to {\text{2L}}_{{\text{ $ \beta $ }}\prime } \) forms were more impeded in the emulsion containing α-tocopherol. Immobilisation of α-tocopherol in fat droplets composed by high melting temperature milk fat triglycerides seemed to lead to its protection against degradation.

Tocopherol Fate in Plasma and Liver of Streptozotocin-Treated Rats that Orally Received Antioxidants and Spirulina Extracts

Streptozotocin-induced diabetic rats constitute a model of oxidative stress, and vitamin E continues to be a topic of speculation in this area. On the other hand, marine extracts, particularly microalgae extracts obtained with environmentally clean technologies and which demonstrate antioxidant activity in vitro, are a potential source of in vivo antioxidant defense. We have studied the alpha-tocopherol content in the plasma and liver of diabetic rats after 7 and 14 days under the condition, and before and after the treatment with vitamin E and C, as well as with different Spirulina extracts, as compared with the corresponding controls. The improvement of analytical methodology related to the determination of alpha-tocopherol in the plasma and liver of rats was also considered. To do this, a method previously developed for plasma, employing a single extraction step, was adapted and validated for liver after minor modifications. Moreover, stability of alpha-tocopherol in plasma of diabetic and control animals was compared in different storage conditions. Results showed that diabetic plasma strongly influences stability of alpha-tocopherol, even at -20 degrees C, but samples are stable for at least one year at -80 degrees C. Finally, regarding supplementation, results indicate that supplementation with alpha-tocopherol increases stored alpha-tocopherol in liver, but not in plasma, but this availability is strongly dependent on the stage of diabetes of the animal. Extracts of Spirulina platensis, despite showing antioxidant activity in vitro, increased alpha-tocopherol concentration in neither plasma nor liver.

The combined effect of antioxidants and modified atmosphere packaging on protein and lipid oxidation in beef patties during chill storage

Effect of rosemary extract and ascorbate/citrate (1:1) in combination with modified atmosphere packaging (100% N 2, 80% O 2/20% N 2) on protein and lipid oxidation in minced beef patties during storage in the dark for up to 6 days at 4 °C was investigated. A high level of oxygen in the packaging atmosphere was found to increase both lipid and protein oxidation during storage as evaluated by TBARS analysis of secondary lipid oxidation products and by 2,4-dinitrophenylhydrazine derivatization of protein carbonyls. Both antioxidant systems tested were found to inhibit lipid oxidation but not protein oxidation. In contrast, ascorbate/citrate was found to promote protein oxidation. Rosemary extract was found to regenerate or protect α-tocopherol whereas the packaging atmospheres had no effect on α-tocopherol stability. In high oxygen atmospheres both antioxidants protected the fresh red meat colour with ascorbate/citrate being more efficient than the rosemary extract, whereas no effect of antioxidant on meat colour was found in beef patties stored in 100% nitrogen.

Migration stability of α-tocopherol in irradiated UHMWPE

The oxidation resistance of irradiated ultra-high molecular weight polyethylene (UHMWPE) components used in total joint arthroplasty can be improved by adding α-tocopherol (vitamin E) through diffusion. To ensure long-term oxidative stability, a minimum α-tocopherol concentration needs to be maintained throughout these components. Migration of α-tocopherol out of the components is one mechanism that could compromise long-term oxidative stability. We hypothesized that α-tocopherol could elute out during standard implant fabrication steps such as cleaning as well as during in vivo use. We doped 85 kGy irradiated UHMWPE with α-tocopherol at 120 °C and homogenized at 120 °C. We determined the extent of elution of α-tocopherol or its effect on oxidative stability following cleaning in isopropyl alcohol (IPA) and following 5 million cycles (MC) of simulated normal gait in bovine serum. There was no significant elution of α-tocopherol in repeated and prolonged cleaning in IPA as measured by average surface and bulk α-tocopherol concentrations. There was no change in the oxidative stability following 5 MC of hip simulator testing, indicating minimal elution during simulated normal gait.

Influence of trace metals, acids and ethanol in food-simulating liquids on the retention of α-tocopherol in low-density polyethylene film

The retention of alpha-tocopherol (vitamin E) in lowdensity polyethylene (LDPE) film was investigated when in contact with different food-simulating liquids. Variations of the aqueous food simulants approved by the EU for testing of interactions between packaging materials and food, and an alternative fatty food simulant (95% aqueous ethanol) were used to study the influence of trace metals and acids, as well as variation in pH and ethanol concentration, on the stability of α-tocopherol in the L DPE film. The presence of trace metals in aqueous media accelerated loss of α-tocopherol from the film, while the addition of citric or ascorbic acid counteracted this loss. In contact with aqueous ethanol at a concentration of 50% or higher, the loss of α-tocopherol from the film was total. However, with solutions containing less than 50% ethanol, the antioxidant was almost completely retained in the film, unless the temperature was increased from 6 to 40°C. For contact with solutions containing ethanol or trace metals, an increase in temperature resulted in a greater loss α-tocopherol from the LDPE film.

Effect of Different Lipid Systems on Antioxidant Activity of Rosemary Constituents Carnosol and Carnosic Acid with and without α-Tocopherol

The effect of oxidizing lipid substrate on the antioxidant activity of carnosol and carnosic acid were evaluated in bulk and emulsified systems. In bulk methyl linoleate, carnosic acid was a better antioxidant than carnosol on the basis of conjugated diene hydroperoxide formation, and both were more active than α-tocopherol. However, in linoleic acid carnosol was more active than carnosic acid. In bulk corn oil triglycerides, α-tocopherol exhibited the most antioxidant activity followed by carnosic acid and carnosol. In all emulsified systems, α-tocopherol consistently exhibited more antioxidant activity than carnosol and carnosic acid. In mixtures, carnosol decreased and carnosic acid increased the oxidative stability of α-tocopherol in corn oil. During oxidation carnosic acid and carnosol are converted to unknown compounds which exhibit antioxidant activity. The type and polarity of the lipid system used as a model substrate significantly affect the antioxidant activity of carnosol and carnosic acid. Ke...

Stability of α-tocopherol in virgin olive oil during microwave heating

The objective of this study has been to analyse the stability of α-tocopherol in virgin olive oil when heated in a microwave oven and a frying pan, as well as the variation of acid value and peroxide value. The samples used in the microwave heating showed a α-tocopherol retention of 51% while the frying-pan heated samples showed 38%.

Effects of Frozen and Other Storage Conditions on α-Tocopherol Content of Cow Milk

The effect of temperature and length of storage on the stability of α-tocopherol in UHT milk was studied by HPLC. The effect of water activity conditions during storage of milk powder on the stability of the same vitamin was also studied. Losses of α-tocopherol occurred in UHT milk after 1 mo of storage at 30°C; losses increased as storage time increased. In general, when the storage temperature changed from 30 to 40°C, decrease in α-tocopherol content was greater. Short periods of frozen storage of the UHT milk (up to 60 d) had no effect on α-tocopherol content. However, frozen storage from 4 to 8 mo produced losses in α-tocopherol. When water activity was increased, the α-tocopherol content in milk powder decreased significantly after 2 mo of storage at 20°C.

Stability of α-Tocopherol in Rumen Liquor of the Sheep

Stability of α-Tocopherol in Rumen Liquor of the Sheep

The distribution and stability of α-tocopherol in subcellular fractions of broad bean leaves

A method is described which enables the preparation of chloroplasts with the minimum enzymic breakdown of α-tocopherol. Using this method, it was shown that α-tocopherol is confined to the chloroplasts of young broad bean leaves. Fifty per cent of this α-tocopherol is removed from the chloroplast lamella by treatment with digitonin. This α-tocopherol is not located in plastoglobuli and is not removed from the lamellae by sonication.