Carotenoids from red palm methyl esters by nanofiltration

Palm oil contains high concentrations of carotenoids and tocopherols that can be recovered by first converting them to methyl esters and then applying membrane technology to separate the carotenoids from the methyl esters. Several solvent-stable nanofiltration membranes were investigated for this application. Flux with a model red palm methyl ester solution ranged from 0.5 to 10 Lm⁻²h⁻¹, and rejection of β-carotene was 60–80% at a transmembrane pressure of 2.76 MPa and 40°C. A multistage membrane process was designed for continuous production of palm carotene concentrate and decolorized methyl esters. With a feed rate of 10 tons per hour of red palm methyl esters containing 0.5 gL⁻¹ β-carotene, the process could produce 3611 L·h⁻¹ of carotene concentrate containing 1.19 gL⁻¹ carotene and 7500 Lh⁻¹ of decolorized methyl esters containing less than 0.1 gL⁻¹ β-carotene. The economics of this process is promising.     

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.     

Chia seeds as a source of natural lipid antioxidants

Chia (Salvia sp) seeds were investigated as a source of natural lipid antioxidants. Methanolic and aqueous extracts of defatted chia seeds possessed potent antioxidant activity. Analysis of 2 batches of chia-seed oils demonstrated marked difference in the fatty acid composition of the oils. In both batches, the oils had high concentrations of polyunsaturated fatty acids. The major antioxidant activity in the nonhydrolyzed extract was caused by flavonol glycosides, chlorogenic acid (7.1 × 10⁻⁴ mol/kg of seed) and caffeic acid (6.6 × 10⁻³ m/kg). Major antioxidants of the hydrolyzed extracts were flavonol aglycones/kaempferol (1.1 × 10⁻³ m/kg), quercetin (2.0 × 10⁻⁴ m/kg) and myricetin (3.1 × 10⁻³ m/kg); and caffeic acid (1.35 × 10⁻² m/kg). Two methods were used to measure antioxidant activities. Both were based on measuring bleaching ofβ-carotene in the coupled oxidation ofβ-carotene and linoleic acid in the presence of added antioxidants.     

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α-tocopherol in liposomes

The ¹O₂ quenching rate constants (k _Q ) of α-tocopherol (α-Toc) and carotenoids such as β-carotene, astaxanthin, canthaxanthin, and lycopene in liposomes were determined in light of the localization of their active sites in membranes and the micropolarity of the membrane regions, and compared with those in ethanol solution. The activities of α-Toc and carotenoids in inhibiting ¹O₂-dependent lipid peroxidation (reciprocal of the concentration required for 50% inhibition of lipid peroxidation: [IC₅₀]⁻¹) were also measured in liposomes and ethanol solution and compared with their k _Q values. The k _Q and [IC₅₀]⁻¹ values were also compared in two photosensitizing systems containing Rose bengal (RB) and pyrenedodecanoic acid (PDA), respectively, which generate ¹O₂ at different sites in membranes. The k _Q values of α-Toc were 2.9×10⁸M⁻¹s⁻¹ in ethanol solution and 1.4×10⁷ M⁻¹s⁻¹ (RB system) or 2.5×10⁶ M⁻¹s⁻¹ (PDA system) in liposomes. The relative [IC₅₀]⁻¹ value of α-Toc in liposomes was also five times higher in the RB system than in the PDA-system. In consideration of the local concentration of the OH-group of α-Toc in membranes, the k _Q value of α-Toc in liposomes was recalculated as 3.3×10⁶ M⁻¹s⁻¹ in both the RB and PDA systems. The k _Q values of all the carotenoids tested in two photosensitizing systems were almost the same. The k _Q value of α-Toc in liposomes was 88 times less than in ethanol solution, but those of carotenoids in liposomes were 600–1200 times less than those in ethanol solution. The [IC₅₀]⁻¹ value of α-Toc in liposomes was 19 times less than that in ethanol solution, whereas those of carotenoids in liposomes were 60–170 times less those in ethanol solution. There were no great differences (less than twice) in the k _q and [IC₅₀]⁻¹ values of any carotenoids. The k _Q values of all carotenoids were 40–80 times higher than that of α-Toc in ethanol solution but only six times higher that of α-Toc in liposomes. The [IC₅₀]⁻¹ values of carotenoid were also higher than that of α-Toc in ethanol solution than in liposomes, and these correlated well with the k _Q values.     

Participation of singlet oxygen in photosensitized oxidation of 1,4-dienoic systems and photooxidation of soybean oil

Sensitized photooxidation of a model 1,4-diene, 4cis, 7cis-undecadiene, was shown to yield 4-hydroperoxy-5trans,7cis-undecadiene and 5-hydroperoxy-3trans,7cis-undecadiene as initial products. Further irradiation (in the presence of the sensitizer) caused the isomerization of 4-hydroperoxy-5trans,7cis-undecadiene to 4-hydroperoxy-5trans,7trans-undecadiene. Oxidation of 4cis,7cis-undecadiene with chemically formed singlet oxygen gave the same initial products as the photosensitized oxidation. 5-Hydroperoxy-3trans,7cis-undecadiene is, however, not formed in the radical autoxidation of the diene. It is concluded that singlet oxygen is the reactive intermediate in the photooxidation. Comparison with this model reaction suggests that the photooxidation of refined soybean oil in propanol also proceeds via singlet oxygen: the photooxidations of both 4,7-undecadiene and soybean oil are inhibited by β-carotene and by triethylamine, but unlike radical chain autoxidation, they are not inhibited by 2,6-di-t-butyl-4-methylphenol. Also soybean oil can act as a sensitizer for the photooxidation of 4,7-undecadiene. Chlorophyl-like sensitizers are probably unimportant in the well refined soybean oil used in this work. The observed photooxidation of the skipped dienoic components of soybean oil, which is probably due to some other, unidentified sensitizer(s), absorbing below 500 nm, can be avoided by using a yellow filter. Presented in part in the symposium “Oxidation Chemistry,” New Chemical Society Meeting, Manchester, April 1972.     

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.     

Raman studies of structural rearrangements induced in human plasma lipoprotein carotenoids by malondialdehyde

Raman and resonance Raman spectra of plasma lipoproteins ± malondialdehyde were studied at concentrations which block the normal receptor-mediated uptake by cells. The strong resonance Raman bands at about 1010, 1162 and 1530 cm⁻¹, due to the presence of carotenoids in the lipoproteins, are envisaged as structural probes. High resolution resonance Raman spectra of the 1500–1600 cm⁻¹ region reveal multiple features suggesting the coexistence of several structural populations of β-carotene whose precise assignment is complex. When plasma lipoproteins are reacted with malondialdehyde, a complex change occurs in the resonance Raman banding of β-carotene in the 1500–1600 cm⁻¹ region. Malonaldehyde (MDA) also modifies the acoustical region (70–200 cm⁻¹ of low density lipoprotein (LDL) lipids. We suggest that malondialdehyde association with plasma lipoproteins alters the lipid structure via apoprotein or apoprotein/lipid associations.     

Quenching mechanism and kinetics of ascorbyl palmitate for the reduction of the photosensitized oxidation of oils

Effects of 0, 500, 1000, and 1500 ppm (wt/vol) ascorbyl palmitate (AP) on the methylene-blue- and the chlorophyll-sensitized photooxidations of linoleic acid or soybean oil, either in methanol or in a solvent mixture (benzene/methanol, 4:1, vol/vol), were studied during storage under 3300 lux fluorescent light for 5 h. Steady-state kinetic approximation was used to determine a quenching mechanism and quenching rate constant of AP in the chlorophyll-sensitized photooxidation of methyl linoleate in a solvent mixture (benzene/methanol, 4:1, vol/vol). Both methylene blue and chlorophyll greatly increased the photooxidation of linoleic acid and soybean oil, as was expected. AP was extremely effective at minimizing both methylene-blue-and chlorophyll-sensitized photooxidations of linoleic acid and soybean oil, and its effectiveness was concentration-dependent. The addition of 500, 1000, and 1500 ppm AP resulted in 69.3, 83.6, and 94.6% inhibition of methyleneblue-sensitized photooxidation of linoleic acid, respectively, after 5-h storage under fluorescent light. AP showed significantly greater antiphotooxidative activity than α-tocopherol for the reduction of methylene blue-sensitized photooxidation of linoleic acid (P < 0.05). The steady-state kinetic studies indicated that AP quenched singlet oxygen only to minimize the chlorophyll-sensitized photooxidation of oils. The calculated total quenching rate of AP was 1.0 × 10⁸ M⁻¹s⁻¹. The present results clearly showed, for the first time, the effective singlet oxygen quenching ability of AP for the reduction of photosensitized oxidation of oils.     

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.     

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.     

β-Carotene adsorption on acid-activated montmorillonite

The adsorption of β-carotene from solution in benzene on acid-activated Canakkale montmorillonite of Turkey has been investigated. The adsorption isotherm had two steps. The first step was of the Langmuir type, and the isosteric heat of adsorption corresponding to this step was equal to −193.514 kJ/mol. The decrease in the total number of acid sites of the clay surface was determined to be 0.45×10⁻⁴ mol/g clay by nonaqueous titration with diethylamine. The phenomenon seems to be mainly a chemisorption stemming from the interaction of β-carotene with acid sites. Also, the activated clay acts as an oxidation catalyst on the β-carotene left in the solution.     

Effect of selected oat sterols on the deterioration of heated soybean oil

Two sterol fractions of different purity, each containing both Δ⁵-avenasterol and β-sitosterol, were separated from oat oil, and their antioxidant effects studied in soybean oil at 180 C. Oil samples with added pure β-sitosterol and control samples (no added sterol) also were studied. Fatty acid changes, conjugated diene formation and polymerization were monitored in all samples. All heated oils with added oat-sterol fractions containing Δ⁵-avenasterol deteriorated more slowly than did the controls. Oil with added pure β-sitosterol was altered at a rate similar to that of the controls.     

Sensory Thresholds of Selected Phenolic Constituents from Thyme and their Antioxidant Potential in Sunflower Oil

The odor detection thresholds of carvacrol (5-isopropyl-2-methyl-phenol), thymol (2-isopropyl-5-methyl-phenol) and p-cymene 2,3-diol (2,3-dihydroxy-4-isopropyl-1-methyl-benzene) in sunflower oil, determined by the three-alternative, forced-choice procedure, were 30.97, 124 and 794.33 mg kg⁻¹, respectively. Sunflower oil containing 13, 70, or 335 mg kg⁻¹ of carvacrol, thymol or p-cymene 2,3-diol, respectively, was judged to be similar (P < 0.01) in taste and odor to its antioxidant-free counterpart. The rate constant of sunflower oil oxidation, measured from the increase in peroxide value during storage at 25 °C, was 9.2 × 10⁻⁹ mol kg⁻¹ s⁻¹ while the rate constants were 9.3 × 10⁻⁹, 9.8 × 10⁻⁹, and 4.3 × 10⁻⁹ mol kg⁻¹ s⁻¹ in the presence of 13 mg kg⁻¹ carvacrol, 70 mg kg⁻¹ thymol, and 335 mg kg⁻¹ p-cymene 2,3-diol, respectively. At a level of 335 mg kg⁻¹, p-cymene 2,3-diol did not impart flavor taints and effected a 46.7% reduction in the rate of oxidation of sunflower oil. These findings indicate that the diphenolic p-cymene 2,3-diol could potentially replace synthetic antioxidants and is a valuable addition to the antioxidants used by the food industry in its quest to meet consumer demands for synthetic-additives-free and ‘natural’ foods.     

Ultrasonic attenuation of edible oils

The frequency dependence (1–60 MHz) of the ultrasonic attenuation coefficient of canola oil, corn oil, olive oil, peanut oil, safflower oil, soybean oil, and sunflower oil was measured at 25°C. The attenuation coefficient of all the oils could be described by the relation: α ∼ Af ⁿ(with A between 6 and 40 × 10⁻¹², and n between 1.74 and 1.86).     

Kinetics of geometrical isomerization of unsaturated FA in soybean oil

Laboratory treatment of soybean oil were carried out at the following conditions: atmospheric pressure in the presence of air or nitrogen at different temperatures ranging from 160 to 250°C for 12 to 72 h. These conditions were used to study geometric isomerization of cis,cis-linoleic and cis,cis,cis-linolenic acid in the presence or in the absence of oxidative degradation reactions. Based on these experiments, a model of consecutive, parallel reactions was developed to describe the reaction steps occurring in the soybean oil during heating at constant temperature. For both cis,cis-linoleic and cis,cis,cis-linolenic acid, the reaction of formation isomers followed a first-order reaction, and the rate constant of isomerization varied according to the Arrhenius law. The isomerization rate constant for linoleic acid was 9.57×10⁻³±0.50 h⁻¹ in the presence of oxygen and 7.39×10⁻³±0.39 h⁻¹ in its absence, and the isomerization rate constant for linolenic acid was 1.18×10⁻¹±0.10 h⁻¹ in the presence of oxygen and 0.87×10⁻¹±0.07 h⁻¹ in its absence (all obtained at 250°C).     

Iodine number determination of milk fat and vegetable fats by refractometry

A refractometric method for the estimation of iodine number of milk fat has been suggested. About 0.2 ml of milk fat was iodinated with ca. 10 ml Wijs iodine reagent for 3 min using mercuric acetate as catalyst. The iodinated fat showed a higher refractive index than the original fat. The changes in refractive indices showed a very high correlation with the iodine values of the fats (T=0.9993). The average of the ratios of change in refractive index to iodine number was 50.7×10⁻⁵, from which the iodine number of milk fat can be calculated. The method can also be applied to vegetable fats. The ratios of change in refractive index to iodine number for the oils of peanut, rapeseed, soybean, niger, sesame, and sunflower were similar, and the average was 45.2×10⁻⁵. The ratio for linseed oil was 38.4×10⁻⁵, and for coconut fat it was similar to that of milk fat.     

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.     

Cholesterol oxides II. Measurement of the 5,6-epoxides during cholesterol oxidation in aqueous dispersions

Cholesterol in aqueous dispersion with sodium stearate or Triton surfactants was aerated at various pH values at 50 and 80 C. Analysis of the reaction mixtures by TLC during the oxidation produced qualitatively similar patterns regardless of pH or temperature. Major oxidation products observed were 7-ketocholesterol, the isomeric 7-hydroperoxy- and 7-hydroxycholesterols, the isomeric 5,6-epoxycholestanols and 3β,5α,6β-trihydroxycholestanol. The concentrations of 3β,5α,6β-trihydroxycholestanol and an unknown compound increased greatly at the lower pH values. Recovery of the 5,6-epoxide isomers by preparative TLC followed by capillary GC allowed theα- andβ-epoxide isomers to be quantitated. Oxidations at pH 8 and 12 produced increasing amounts of the epoxides with time, without significant changes in theα/β-epoxide ratio. However, oxidations at the acidic pH values of 5.5 and 3 showed large changes in theα/β-epoxide ratio during the oxidation. Measurement of the hydrolysis rates of the 5,6-epoxides at pH 5.5 showed that theβ-epoxide isomer is more labile than theα-isomer by a factor of 2.5. The rate constant for the hydrolysis of theα-epoxide isomer was 5.3 × 10⁻⁷ sec⁻¹ and that of theβ-isomer 13 × 10⁻⁷ sec⁻¹.     

Kinetics of oxirane cleavage in epoxidized soybean oil

The kinetics of oxirane ring cleavage in epoxidized soybean oil have been studied using glacial acetic acid at 60, 70, 80 and 90°C. It was shown that the reaction can be successfully modelled as first order with respect to the epoxide concentration and second order with respect to acetic acid. The reaction velocity constant at 70°C was found to be 2 × 10⁻³ 1⁻³ hr⁻¹ mol⁻², the frequency factor, A, = 2.321 × 10⁷ hr⁻¹ and the energy of activation, E_a = 15.84 k cal mol⁻¹. The effects of the concentration of acetic acid and the temperature on the net yield of epoxides by in situ epoxidation were also studied on the basis of the predicted kinetic parameters of the reaction system.     

Kinetics of photoperoxidation of arachidonic acid: Molecular mechanisms and effects of antioxidants

The kinetics of photoperoxidation of [1⁻¹⁴C]arachidonic acid (20∶4n−6) at 1.32 mM was studied either with the unsaturated fatty acid alone or in the presence of 10μM of antioxidants and/or inhibitors of eicosanoid metabolism. The photosensitizer used wasmeso-tetraphenylporphine. The time-course of the reactions was followed by ultraviolet spectral analysis, thiobarbituric acid reactivity and high-performance liquid chromatographic analysis of aliquots sampled every 15 min during the 4 h of irradiation. The kinetics of photoperoxidation of 20∶4n−6 can be divided into three main successive steps: (i) monohydroperoxidation, characterized by the appearance of conjugated diene patterns and monohydroperoxidized 20∶4n−6; (ii) secondary oxidation characterized by polyoxygenated products such as dihydroperoxidized 20∶4n−6 possessing conjugated triene patterns; and (iii) the disappearance of conjugated patterns and the oxidative cleavage of the products of the two first steps into aldehydic molecules reacting with thiobarbituric acid. During the first 90 min of irradiation, the mechanism of monohydroperoxidation (step one) is purely or predominantly type II photoperoxidation involving only singlet oxygen. This step was inhibited by β-carotene and by BW755C (3-amino-1-[3-trifluoromethylphenyl]2-pyrazoline). In contrast, the reactions involved in the second and third steps were predominantly type I photoperoxidation involving radical mechanisms. These latter steps were inhibited by β-carotene, BW755C, vitamin E and probucol. Indomethacin and 5,8,11,14-eicosatetraynoic acid did not alter 20∶4n−6 photoperoxidation. Thisin vitro model of lipid photoperoxidation allows the screening of antioxidants in accordance with their singlet oxygen quenching and/or free radical scavenging properties.