Effects of β-carotene on light stability of soybean oil

β-Carotene was added to soybean salad oils to study its effect in inhibiting flavor deterioration due to light exposure. Flavor evaluations indicated that (a) when oils treated with citric acid were exposed to light (7535 lux) for 8 to 16 hr, oils containing 5 to 10 ppm β-carotene showed improved flavor stability compared to oils containing 0 to 1 ppm β-carotene; and (b) when oils were not treated with citric acid, only oils containing 20 ppm β-carotene were more stable to light. Capillary gas chromatographic analysis showed that the addition of 1 to 20 ppm of β-carotene significantly decreased formation of 2-heptenal and 2,4-decadienal in the absence or presence of citric acid. Determination of peroxide values showed the same trends as gas chromatographic analyses of volatiles. In the presence of 15 and 20 ppm β-carotene, some off-flavors, as well as poor ratings for color quality, were reported by panelists. Therefore, flavor deterioration initiated by light can be inhibited effectively in soybean oil, without affecting color quality, by addition of β-carotene at concentrations from 5 to 10 ppm to oils treated with citric acid.     

Insight into β-Carotene Thermal Degradation in Oils with Multiresponse Modeling

The aim of this study was to gain further insight into β-carotene thermal degradation in oils. Multiresponse modeling was applied to experimental high-performance liquid chromatography–diode array detection (HPLC–DAD) data (trans-, 13-cis-, and 9-cis-β-carotene concentrations) during the heat treatments (120–180 °C) of two β-carotene-enriched oils, i.e., palm olein and copra. The test of different reaction schemes showed that β-carotene isomerization reactions were dominant and reversible. The resulting cis isomers and trans-β-carotene simultaneously underwent oxidation and cleavage reactions at the same rate constant. From the kinetic analysis, it appeared that—contrary to oxidation and cleavage reactions—isomerization rate constants did not follow the Arrhenius law. However, the isomerization equilibrium constant increased with temperature, favoring isomer production, particularly 9-cis-β-carotene. Its production was shown to be concomitant with oxidation and cleavage reactions, indicating that 9-cis-β-carotene could be a good degradation indicator during oil storage or processing.     

Role of minor constituents in the photooxidation of virgin olive oil

Virgin olive oil was photooxidized at 2 and 40°C and at fluorescent light intensities of 0, 620, 2710, and 5340 lux. As expected, higher fluorescent light intensities induced higher peroxide formation in the oil. The thiobarbituric acid reactive substances (TBARS) were found to be good indicators of photooxidation during the early stage of the reaction. Pheophytin A and β-carotene were light- and temperature-sensitive, whereas α-tocopherol and total polyphenols were mostly affected by light. Pheophytin A functioned as a photosensitizer, resulting in rapid oxidation of the oil. β-Carotene was a strong natural inhibitor of photooxidation for all light intensities at 2°C, suggesting quenching properties for singlet oxygen. However, β-carotene antioxidant activity was reduced at 40°C because of its rapid destruction.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.     

Obtaining Butter Oil Triacylglycerols Free from β-Carotene and α-Tocopherol via Activated Carbon Adsorption and Alumina-Column Chromatography Treatments

It is difficult to remove β-carotene from oils with alumina-column chromatography, because β-carotene is even less-polar than triacylglycerols (TAGs) are. The objective of this study was to obtain butter oil TAGs free from β-carotene and antioxidants via sequential treatments with activated carbon (AC) adsorption and alumina column chromatography. The AC used was prepared from waste apricots. The effects of AC dosages, temperatures and time courses on β-carotene adsorption were studied. The Langmuir and Freundlich isotherms were used to describe the adsorption of β-carotene onto AC, and it was found to be more consistent with the Freundlich isotherm with a higher R ² value (0.9784). Adsorption kinetics of β-carotene was analyzed by pseudo-first order and pseudo-second order models. The pseudo-second order model was found to explain the kinetics of β-carotene adsorption more effectively (R ² = 0.9882). The highest β-carotene reduction was achieved (from 31.9 to 1.84 mg/kg) at an AC dosage of 10 wt%, temperature of 50 °C, and adsorption time of 240 min. A considerable amount of α-tocopherol was also adsorbed during the AC treatment. Remaining portions of α-tocopherol were completely removed with alumina adsorption chromatography. The method described may be used for purification of vegetable oil TAGs, which will be used as model compounds in model oxidation studies.     

The influence of carotenoids and tocopherols on the stability of safflower seed oil during heat-catalyzed oxidation

The stability and antioxidant effects of carotenoids and tocopherols in safflower seed oil were evaluated under thermal (75°C) and oxidative conditions and the oxidative stability index (OSI) determined. The antioxidant capability of butylated hydroxytoluene (BHT) was also compared with that of β-carotene in a model system. Lycopene and β-carotene (1 to 2000 ppm) were heated (75°C) and exposed to air (2.5 psi) in an oxidative stability instrument. β-Carotene had no antioxidant effect at concentrations below 500 ppm, because it did not alter the induction time. Lycopene increased the induction time only slightly at low concentrations. However, at concentrations greater than 500 ppm, both β-carotene and lycopene acted as prooxidants, significantly decreasing the induction period. At the highest concentration, 2000 ppm, lycopene was more prooxidative than β-carotene. α- and γ-Tocopherol (concentration, 1000 ppm) delayed the induction time by 16 and 26 h, respectively. There was no cooperative interaction between α-tocopherol and β-carotene in delaying the onset of oxidation. Furthermore, BHT was significantly more antioxidative than β-carotene. Thus, under thermal and oxidative conditions, β-carotene could not delay the onset of oxidation. The tocopherols and BHT were effective in suppressing the onset of oxidation, as determined by the oxidative stability measurement.     

Antioxidant activity of β-carotene-related carotenoids in solution

The effect of the antioxidant activity of β-carotene and related carotenoids on the free radical-oxidation of methyl linoleate in solution was examined by measuring the production of methyl linoleate hydroperoxides. Canthaxanthin and astaxanthin which possess oxo groups at the 4 and 4′-positions in the β-inonone ring retarded the hydroperoxide formation more efficiently than β-carotene and zeaxanthin which possess no oxo groups. The rates of autocatalytic oxidation of canthaxanthin and astaxanthin were also slower than those of β-carotene and zeaxanthin. These results suggest that canthaxanthin and astaxanthin are more effective antioxidants than β-carotene by stabilizing the trapped radicals.     

Oxidation kinetics of β-carotene in oleic acid solvent with addition of an antioxidant, α-tocopherol

Oxidation experiments with β-carotene were performed in oleic acid solvent with addition of an antioxidant, α-tocopherol. A kinetic model was proposed based on a reaction mechanism consisting of the oxidation of β-carotene, oleic acid, and α-tocopherol; the antioxidation reactions of β-carotene and oleic acid by α-tocopherol; the cross-reaction of β-carotene and oleic acid; and the radical-exchange reaction of β-carotene and α-tocopherol. The model quantitatively described the oxidation behavior of β-carotene over a wide range of temperatures, oxygen compositions, and initial antioxidant concentrations. The model simulated well the time over which β-carotene was almost totally consumed under practical storage conditions at room temperature in air.     

Kinetics of all-trans-β-carotene degradation on heating with and without phenylalanine

All-trans-β-carotene was heated in liquid paraffin at 210°C for 15 min in the presence and the absence of phenylalanine to assess the effect of the amino acid on the rate of degradation of all-trans-β-carotene. The curve that represents all-trans-β-carotene degradation in both model systems is formed of two distinct parts that correspond, respectively, to the propagation and termination phases of an autocatalytic reaction. The reaction over 1–15 min followed first-order reaction kinetics in both systems, and the rate constant obtained was 2.8 times lower in the presence of phenylalanine. The kinetic behavior and the rate constant for color loss were similar to those for all-trans-β-carotene degradation for each model system.     

Storage stability evaluation of some packed vegetable oil blends

The physicochemical characteristics and minor component contents of blended oils packed in pouches in relation to starting oils used for blending were studied over a period of 6 mon at two storage temperatures and humidity conditions: 27°C/65% RH and 40°C/30–40% RH. Color, PV, FFA value, β-carotene content, tocopherol content, and oryzanol content of the oils were monitored at regular intervals. The color, PV (0.6–20.7 meq O₂/kg, FFA value (0.08–2.1%), tocopherol content (360–1700 ppm%), oryzanol content (460–2,000 mg%), and sesame oil antioxidants (400–2,000 mg%) were not changed in either the starting oils or their blends. Oils and oil blends containing a higher initial PV (18.9–20.7 meq O₂/kg) showed a slight reduction in value at 40°C, whereas oils having lesser PV of 5–10 showed a slight increase during the storage period. Among the minor components studied, only β-carotene showed a reduction, 8.9–60.2% at 27°C and 48–71% at 40°C, for the different oil blends studied. The observed results indicated that the packed oil blends studied were stable under the conditions of the study, and the minor components, other than β-carotene, remained unaltered in the package even at the end of 6 mon of storage.     

In vivo determination of triglyceride secretion using radioactive glycerol in rats fed different dietary saturated fats

Our objective was to determine the relative rates ofin vivo triglyceride (TG) secretion and the composition of very low density lipoproteins (VLDL) in rats fed different dietary saturated fats. Male Sprague-Dawley rats (150–200 g) were fed diets containing 16% corn oil, or 14% butterfat, 14% beef tallow, 14% olive oil, or 14% coconut oil plus 2% corn oil for 5 wk. Changes in plasma TG specific radioactivity were determined in individual, unanesthetized fasted rats after injection of 100 μCi [2-³H]glycerol. Nonlinear regression analysis using a 2-compartment model was used to determine the fractional rate constant for TG turnover in plasma. The plasma TG pool was 33–40% larger with beef tallow than with corn, olive or coconut oil feeding (p<0.05), and 20% larger with beef tallow than with butterfat feeding. The rate of TG secretion into plasma (mg/min/100 g body weight) was 60% higher in animals fed beef tallow than corn or coconut oil (p<0.05) and 26–33% higher in animals fed beef tallow than olive oil or butterfat. Differences in VLDL composition (% wt) were also noted. Our data suggest that greater TG secretion is the primary factor contributing to the larger TG pool with ingestion of beef tallow relative to butterfat, corn or coconut oil. These results suggest that different dietary saturated fats have unique effects on TG metabolism in rats. Presented in part at the 1990 meeting of the Federation of American Societies for Experimental Biology in Washington, D.C. (see ref. 1).     

Studies in photooxidation of olive oil

Photooxidation of olive oil, bleached to remove most non-triglyceride components, was studied to elucidate the role of added chlorophyll a, pheophytin a and b,α- andβ-carotene, d-α-tocopherol and nickel dibutyldithiocarbamate. Chlorophyll functioned as a photosensitizer resulting in rapid oxidation of the oil and the added components and loss of color.α- andβ-carotene acted essentially equally as singlet oxygen quenchers.α-tocopherol had little apparent effect on the oxidation rate. Carotenes and tocopherols apparently were destroyed more rapidly when chlorophyll was present. The ratio of peroxide value to conjugated dienoic acids formed developed greater values when chlorophyll was present, thus suggesting a singlet oxygen effect in the system. Pheophytin also proved to be an oxidation promoter.     

Oxidative stabilities of soybean oils that lack lipoxygenases

Lipoxygenase (LOX)-null soybean lines that lack LOX 2, or LOX 2 and 3, and contain normal (8.0–8.6%) or low (2.0–2.8%) linolenate (18∶3) amounts were evaluated for their oil qualities and storage stabilities. Soybean oils of six genotypes were extracted by both laboratory-scale and pilot-plant systems and were refined, bleached, and deodorized in the laboratory. Citric acid was added to oils during the cool-down stage of deodorization. Two replications, separated at the point of conditioning, were evaluated for each genotype. Under storage conditions of 55–60°C in the dark, soybean oils with low 18∶3 contents were significantly (P<-0.05) more stable as measured by peroxide values than were oils with normal 18∶3 contents, regardless of the LOX content of the beans. The volatile analysis showed few differences between oils with low and high 18∶3 contents or among oils from beans that lack different LOX enzymes. After 16 d of storage, the amount of 1-octen-3-ol was significantly greater in oils with low 18∶3 content, and soybean oils from beans with normal LOX content had a significantly (P<-0.05) lower amount of 1-octen-3-ol than did the oils that lacked LOX enzymes. Storage at 35°C under light showed no differences in volatile amounts or sensory evaluations after 14 d of storage. During storage, peroxide values tended to be lower in oils from beans with normal 18∶3 content and in oils from beans with normal LOX content. Generally, the abscence of LOX 2 or LOX 2 and 3, although having a small effect on lipid oxidation, was not as important to oil quality as was the 18∶3 content.     

Analysis of autoxidized fats by gas chromatography-mass spectrometry: V. Photosensitized oxidation

The role of singlet oxygen in oxidation was studied by analyzing hydroperoxide isomers in unsaturated fats and esters by gas chromatography-mass spectrometry (GC-MS). On oxidation photosensitized with methylene blue at 0 C, methyl oleate produced a 50–50% mixture of 9- and 10-hydroperoxides, linoleate a mixture of 66% conjugated (9+13) and 34% unconjugated (10+12) hydroperoxides, and linolenate a mixture of 75% conjugated (9+12+13+16) and 25% unconjugated (10+15) hydroperoxides. Cottonseed, safflower, and corn oil esters showed, as in soybean esters, the presence of varying amounts of 12-hydroxy esters derived from the corresponding hydroperoxide at low peroxide values. Since these oils do not contain linolenic acid, a likely source of the 12-hydroperoxide is linoleic acid by photosensitized oxidation. Several lines of evidence support the conclusion that singlet oxygen may contribute to the unique hydroperoxide composition of vegetable oil esters at low levels of oxidation. In the presence of photosensitizers such as methylene blue and chlorophyll, the unique hydroperoxide composition (high levels of 10- and 12-hydroperoxides) obtained in soybean esters was similar to that produced by oxidation at low peroxide values. In contrast, a normal hydroperoxide composition was produced, as expected from the fatty acid composition of soybean oil esters, when singlet oxygen quenchers such as β-carotene and α-tocopherol were used and when the esters were treated with carbon black to remove natural photosensitizers. GC-MS analyses of the derived unsaturated alcohols provided indirect evidence for 12-hydroperoxy-9,13-diene in soybean esters as expected by photosensitized oxidation of linoleate. Presented at the AOCS Meeting, San Francisco, California, April 29–May 3, 1979. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Inhibition of tubulin guanosine-5′-triphosphatase by lipid peroxides: Protective effects of vitamin A derivatives

Lipid peroxidation of cellular proteins has been postulated to be involved in cellular aging. Given the importance of the cytoskeleton in cellular function, it is a prime candidate as a potential target for the deleterious effects of lipid peroxides. In this study, the effects of lipid peroxides on microtubule assembly have been studied in an in vitro assay system, as have the protective effects of the vitamin A group (β-carotene, retinal, and retinol). The assay was based on tubulin guanosine-5′-triphosphatase (GTPase) activity, which is associated with all steps of microtubule assembly. Soybean lecithin was utilized as the starting point to generate lipid peroxides. Its selection was based on the high proportion of phospholipids in the cellular membrane. Lipid peroxides were generated by photooxidation of lecithin, dissolved in methanol, in the presence of 0.004% methylene blue at 4°C for 8 h. Lipid peroxides (1.0 mg/mL) inhibited tubulin GTPase by 49%, relative to the control. Vitamin A derivatives (retinol, retinal, and β-carotene) all had the ability to protect against the inhibitory effects of lipid peroxides, presumably owing to their antioxidant activities. This protective effect was more pronounced when utilizing a 30-min, as opposed to a 15-min, reaction time. This suggests a relatively slow rate of reaction between the peroxide and vitamin A group. These studies present a mechanism for the ability of vitamin A to inhibit aging of the cell.     

Antioxidant activity of some spice essential oils on linoleic acid oxidation in aqueous media

Some spice essential oils (caraway, clove, cumin, rosemary, sage and thyme) and their major constituents were added to emulsified linoleic acid in aqueous media to examine their antioxidant activity. The methods used for measuring linoleic acid oxidation were coupled oxidation ofβ-carotene, conjugated diene formation and thiobarbituric acid test. The essential oils under study possess an antioxidant effect and this phenomenon was increased by increasing their concentration. Generally, the effectiveness of the various essential oils on linoleic acid oxidation was in the following descending order: caraway >sage>cumin>rosemary>thyme>clove. It appears that there was a relationship between the antioxidant effect and the chemical composition of the oils.     

Oxidative degradation kinetics of lycopene, lutein, and 9-cis and all-trans β-carotene

The thermal and oxidative degradation of carotenoids was studied in an oil model system to determine their relative stabilities and the major β-carotene isomers formed during the reaction. All-trans β-carotene, 9-cis β-carotene, lycopene, and lutein were heated in safflower seed oil at 75, 85, and 95°C for 24, 12, and 5 h, respectively. The major isomers formed during heating of β-carotene were 13-cis, 9-cis, and an unidentified cis isomer. The degradation kinetics for the carotenoids followed a first-order kinetic model. The rates of degradation were as follows: lycopene>all-trans β-carotene≈9-cis β-carotene>lutein. The values for the thermodynamic parameters indicate that a kinetic compensation effect exists between all of the carotenoids. These data suggest that lycopene was most susceptible to degradation and lutein had the greatest stability in the model system of the carotenoids tested. Furthermore, there was no significant difference in the rates of degradation for 9-cis and all-trans β-carotene under the experimental conditions.     

A Kinetic Model Describing Antioxidation and Prooxidation of β-Carotene in the Presence of α-Tocopherol and Ascorbic Acid

β-Carotene oxidation in the presence of both lipophilic α-tocopherol and hydrophilic ascorbic acid was experimentally studied in a biphasic oil–water system. Ascorbic acid in the water phase had two opposite effects of promoting and suppressing α-tocopherol consumption in the oil phase and indirectly participated in the antioxidation and prooxidation of β-carotene in the oil phase. The drastic antioxidation of β-carotene by stopping the consumption of α-tocopherol was caused by the depletion of oxygen in the system due to the oxidation of ascorbic acid. A kinetic model was constructed by incorporating the oxidation of ascorbic acid itself in the water phase, the regeneration and consumption of α-tocopherol by ascorbic acid at the oil–water interface, and the oxygen mass transfer across the gas–oil interface and the oil–water interface. The model well described the antioxidation and prooxidation behavior of β-carotene in the presence of α-tocopherol and ascorbic acid and the oxygen concentration profiles in each phase. The model was able to effectively determine the appropriate amounts of lipophilic and hydrophilic antioxidants to prevent β-carotene oxidation under various conditions.     

Effects of minor compounds on hydrogenation rate of soybean oil

The poisoning effects of minor compounds in soybean oil on the activity of nickel-based catalysts during hydrogenation was investigated. Several soybean oils prepared by different processes were used as the starting oils for hydrogenation. Soybean oil prepared by combining neutralization with degumming and then followed by bleaching leads to a slower hydrogenation rate than an oil prepared by sequential degumming, neutralization and bleaching with activated clay. The selection of bleaching earth used in the bleaching process affected the hydrogenation rate. Soybean oil bleached with neutral clay showed a slower hydrogenation rate. Higher amounts of phosphorus compounds, oxidation products, β-carotene and iron in these oils accounted for the slower hydrogenation rate. Storage of refined and bleached soybean oil greatly affected the hydrogenation rate. An increase in the oxidation products of RB soybean oil during storage was the major reason for the decrease in the hydrogenation rate.