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1.
Antioxidant effects of d-tocopherols at different concentrations in oils during microwave heating 总被引:1,自引:0,他引:1
Hiromi Yoshida Goro Kajimoto Shiuji Emura 《Journal of the American Oil Chemists' Society》1993,70(10):989-995
The effects of d-tocopherols at different concentrations (50 to 1000 ppm) on the oxidative stability of ethyl linoleate and
tocopherol-stripped oils were investigated under microwave heating conditions. Purified substrate oils were prepared by aluminum
oxide column chromatography. After the addition of tocopherols (α-, β-, γ- or δ-) to the oils, peroxide, carbonyl andp-anisidine values were measured in the samples after heating in a microwave oven. Further, the residual amount of tocopherol
homologues in the oils after heating was determined by high-performance liquid chromatography for evaluation of their effects
at different concentrations on oxidative deterioration. Microwave heating resulted in some acceleration in the oxidation of
the purified substrate oils. Optimum concentrations of tocopherols required to increase oxidative stability were 100 ppm for
α-, 150–200 ppm for β- or γ- and 500 ppm for δ-tocopherol, respectively. The antioxidant effect of tocopherols decreased in
the order α>β ≒ γ>δ at each level, in all substrates. Therefore, α-tocopherol was consumed first, followed by β- or γ-tocopherol,
and δ-tocopherol was consumed more slowly. The tocopherols had no further significant antioxidant activity (P>0.05) at concentrations higher than 500 ppm. 相似文献
2.
L. Normand N. A. M. Eskin R. Przybylski 《Journal of the American Oil Chemists' Society》2001,78(4):369-373
A study was conducted to compare the relationship between frying stability and levels and degradation rates of tocopherols
in regular and three modified canola oils. Oils were heated at 175 ± 2°C for a total of 72 h, with french fries fried intermittently.
Frying stability was compared based on the rates of formation of free fatty acids (FFA) and total polar compounds (TPC). Significant
differences (P<0.05) were identified between oils using analysis of covariance and t-tests for multiple comparisons. No significant differences were observed in the rates of FFA formation among the canola oils
during frying. Nevertheless, regular canola (RCO) and high-oleic, low-linolenic acid canola (HOLLCO) oils produced less FFA
compared to higholeic LLCO and HOCO both had significantly (P<0.05) faster rates of TPC formation compared to HOLLCO or RCO. HOLLCO with the highest level of tocopherols (893 mg/kg) exhibited
a slow rate of degradation which accounted for a halflife of 48–60 h of frying. RCO, with a lower level of tocopherols (565
mg/kg), however, had the slowest degradation rate with a half-liofe of >72 h. In contrast, HOCO and LLCO with 601 and 468
mg/kg tocopherols, respectively, both exhibited a half-life for tocopherols of 3–6 h of frying. An inverse relatioship was
observed between TPC formation and the reduction of tocopherol. Thus, the greater frying stability of RCO and HOLLCO appears
to be affected far more by the rate of tocopherol degradation than by any changes in fatty acid composition. 相似文献
3.
Hiromi Yoshida Mikiko Tatsumi Goro Kajimoto 《Journal of the American Oil Chemists' Society》1992,69(2):119-125
Effects of 0, 0.05, 0.25, 0.50 and 1.0% levels of fatty acids (caproic, caprylic, capric and lauric) or hydrocarbons (decane
and dodecane) on tocopherol stability in vegetable oils during microwave heating were determined by measuring tocopherol losses
and carbonyl and anisidine values. The fatty acids showed similar prooxidant activities toward tocopherols in purified vegetable,
oils when heated in a microwave oven. However, decane or dodecane, which had the same number of carbons as capric or lauric
acid but no carboxylic group, did not show prooxidant activity. The shorter the chainlength and the higher the level of fatty
acids, the greater was the reduction of tocopherols in the oils. The addition of low-molecular weight fatty acids resulted
in greater acceleration in the oxidation of to pay attention to these free fatty acids produced in the oils when heated in
a microwave oven. 相似文献
4.
Abdalbasit Mariod Bertrand Matthus Karl Eichner Ismail H. Hussein 《European Journal of Lipid Science and Technology》2006,108(4):298-308
In a refining experiment, on a laboratory scale, crude oils from Sclerocarya birrea (SCO), sorghum bugs (SBO), water‐extracted melon bugs (MBO H2O) and solvent‐extracted melon bugs (MBO SOL) were processed by alkali refining. Quality changes were characterized by the determination of free fatty acids (FFA), peroxide value, tocopherols, sterols, phosphatides and stability against oxidation (Rancimat test). In addition, the fatty acid composition was determined. It is clear that the contents of phosphatides, peroxides, tocopherols, sterols as well as oxidative stability were reduced during processing, while FFA were nearly totally removed. The content of phosphorus was reduced in SCO, SBO, MBO H2O and MBO SOL by 26, 19, 12, and 78%, respectively, while complete oil processing removed 95, 99, 96 and 99% of the FFA in crude oils, respectively. The level of total tocopherols decreased during processing by 38.7, 83.8, 100, and 33.3%, respectively. The color decreased through the processing steps up to bleaching; then, in the deodorization step, it darkened sharply in all samples. No change in the fatty acid composition was observed. The order of oxidation stability was crude > degummed > deodorized > neutralized > bleached, in SCO; and crude > degummed > neutralized > bleached = deodorized, in MBO H2O; and crude > degummed > deodorized > neutralized > bleached in MBO SOL; while in SBO, the order of oxidative stability was deodorized > crude > degummed > neutralized = bleached. Total sterols decreased by 42–92% in the processed oils, compared with crude oils. 相似文献
5.
Supercritical fluid extraction of oil from millet bran 总被引:4,自引:0,他引:4
C. Devittori D. Gumy A. Kusy L. Colarow C. Bertoli P. Lambelet 《Journal of the American Oil Chemists' Society》2000,77(6):573-579
Proso millet bran [Panicum miliaceum (L.)], variety Dakota White, was extracted with supercritical carbon dioxide (SC-CO2) to yield crude oil. The effects of operating parameters (pressure, temperature, and specific solvent flow) and of features
of the raw material (moisture content and particle size) on oil extraction were investigated. Complete de-oiling of ground
millet bran pellets was achieved under 300 bar at 40°C with a specific solvent flow of 2–10 h−1 within 200 to 500 min. Solvent requirements were 20–30 kg CO2/kg raw material. Composition of crude SC-CO2 oil extracted under optimal conditions, i.e., fatty acid profile, amount of unsaponifiables, tocopherols, free fatty acids,
sterols, sterol esters, waxes, hydrocarbons, and phospholipids, was compared to that of crude oil obtained by petroleum ether
extraction. These two oils were similar in terms of fatty acid profile and amount of free fatty acids, unsaponifiables, peroxides,
and tocopherols. They differed in respect to phospholipids (present in petroleum etherextracted oil and absent in SC-CO2 extracted oil), metals, and waxes (lower levels in SC-CO2 extracted oil). The effects of extraction procedures on oxidative stability of crude SC-CO2 oil were studied. Ensuring that all pieces of the extractor in contact with the oil were in stainless steel; cleaning the
separator, i.e., washing with KOH, rinsing, purging with N2 and CO2, and heating; performing a couple of extractions before the main extraction; and achieving the extraction without interruption
all positively influenced the oxidative stability of the oil. Conversely, increasing CO2 purity above 99.5% had no effect. Oxidative stability of the SC-CO2 oil extracted under these conditions was only slightly lower than that of the oil extracted with petroleum ether. 相似文献
6.
W. S. Choo E. J. Birch J. P. Dufour 《Journal of the American Oil Chemists' Society》2007,84(8):735-740
Flaxseed oils are used in stir-frying in parts of China. In this study, flaxseed oils were heated at approximately 150 °C
as a thin film in a frying pan for 3 and 6 min, respectively. Pan-heating caused loss of tocopherols, plastochromanol-8, phenolic
acids and chlorophyll pigments. There was a significant decrease in the linolenic acid resulting in a concomitant relative
increase in palmitic, stearic, oleic and linoleic acids in the oils after pan heating. Positive CIELAB “b*” color value, which indicates yellowness and levels of β-carotene and lutein in these oils showed a 42–56% and 8–53% decrease,
respectively. Peroxide values, p-anisidine values, percentage of conjugated dienoic acid, specific extinction at 232 and 270 nm and food oil sensor readings
of these oils showed significant increases to levels exceeding good oil quality indices. Acid values only showed one to twofold
increase from fresh oil values of 0.65–2.23 mg KOH/g of sample. These results indicate that significant levels of oxidation
products would be present in flaxseed oils after pan heating. The flaxseed oil with a lower amount of PUFA appeared to be
more degraded suggesting that the major factor affecting the oxidative stability of the flaxseed oils during pan-heating was
not the degree of unsaturation but was dependent on the complex interaction between the fatty acids and minor constituents
in the oils.
Presented at the American Oil Chemists’ Society 97th Annual Meeting & Expo, St. Louis, MO, 30 April–3 May, 2006. 相似文献
7.
Minor constituents of vegetable oils during industrial processing 总被引:6,自引:10,他引:6
R. Ap. Ferrari E. Schulte W. Esteves L. Brühl K. D. Mukherjee 《Journal of the American Oil Chemists' Society》1996,73(5):587-592
We report the effects of individual steps of industrial refining, carried out in Brazil, on the alteration of selected minor
constituents of oils, such as corn, soybean, and rapeseed oils. Total sterols, determined by capillary gas chromatography
(GC), decreased by 18–36% in the fully refined oils, compared with the crude oils. The total steradienes, dehydration products
of sterols, were determinedvia a simple clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with ultraviolet
detection. The level of steradienes, normally not present in crude oils, increased after each refining step, especially after
deodorization. Thus, the content of steradienes increased after deodorization by about 15- to 20-fold in corn and soybean
oils, and by about 2-fold in rapeseed oil. The total steryl esters were also determinedvia clean-up on a short silica gel column, followed by HPLC with evaporative light scattering mass detection. A minor decrease
in the level of steryl esters was observed after complete refining. The individual tocopherols and tocotrienols were determined
by HPLC with a fluorescence detector. The level of total tocopherols and tocotrienols decreased by about 2-fold after complete
refining of corn oil and by about 1.5-fold in soybean and rapeseed oils. In all three cases, maximum reduction of tocopherols
was observed after the deodorization step. The level of polymeric glycerides, determinedvia clean-up on a short silica gel column followed by size-exclusion HPLC, increased to some extent (0.4–1%) during refining.
The level oftrans fatty acids, determined by capillary GC, also increased to a substantial extent (1–4%) after refining.
Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas,
Campinas, Brazil. 相似文献
8.
Microwave roasting effects on the physico-chemical composition and oxidative stability of sunflower seed oil 总被引:1,自引:0,他引:1
Fozia Anjum Farooq Anwar Amer Jamil M. Iqbal 《Journal of the American Oil Chemists' Society》2006,83(9):777-784
The purpose of the present study was to explore the influences of microwave heating on the composition of sunflower seeds
and to extend our knowledge concerning the changes in oxidative stability, distribution of FA, and contents of tocopherols
of sunflower seed oil. Microwaved sunflower seeds (Helianthus annuus L.) of two varieties, KL-39 and FH-330, were extracted using n-hexane. Roasting decreased the oil content of the seeds significantly (P<0.05). The oilseed residue analysis revealed no changes in the contents of fiber, ash, and protein that were attributable
to the roasting. Analysis of the extracted oils demonstrated a significant increase in FFA, p-anisidine, saponification, conjugated diene, conjugated triene, density, and color values for roasting periods of 10 and
15 min. The iodine values of the oils were remarkably decreased. A significant (P<0.05) decrease in the amounts of tocopherol constituents of the microwaved sunflower oils also was found. However, after
15 min of roasting, the amount of α-tocopherol homologs was still over 76 and 81% of the original levels for the KL-39 and
FH-330 varieties, respectively. In the same time period, the level of σ-tocopherol fell to zero. Regarding the FA composition
of the extracted oils, microwave heating increased oleic acid 16–42% and decreased linoleic acid 17–19%, but palmitic and
stearic acid contents were not affected significantly (P<0.05). 相似文献
9.
R. Ap. Ferrari W. Esteves K. D. Mukherjee 《Journal of the American Oil Chemists' Society》1997,74(2):93-96
Steryl ester content of refined and interesterified corn, soybean, and rapeseed oils has been measured via clean-up on a short silica gel column, followed by high performance liquid chromatography with evaporative light-scattering
mass detector. Chemical interesterification, catalyzed by sodium methoxide, led to random positional distribution of fatty
acids in triacylglycerols and some increase in the steryl ester content of all three oils. Enzymatic interesterification,
catalyzed by the immobilized lipase from Rhizomucor miehei (Lipozyme), resulted in a distinct reduction in steryl ester content, but essentially no alteration in positional distribution
of fatty acids in triacylglycerols occurred. Formation of steryl esters during chemical and enzymatic interesterification
was also examined by radioactive tracer technique with [4-14C]β-sitosterol added as marker to refined rapeseed oil and measurement of the radioactive steryl esters formed. Chemical interesterification
of rapeseed oil resulted in moderate formation (10% of total radioactivity) of radioactive β-sitosteryl esters. Enzymatic
interesterification of the oil, catalyzed by Lipozyme, led to little formation of radioactive β-sitosteryl esters, whereas
with the lipase from Candida cylindracea high proportions (>90% of total radioactivity) of 14C-labeled β-sitosteryl esters were formed.
Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas,
Campinas, Brazil. 相似文献
10.
Anita Rani Vineet Kumar Sandeep K. Verma Arvind K. Shakya G. S. Chauhan 《Journal of the American Oil Chemists' Society》2007,84(4):377-383
Plant seed oils, including soybean seed oil, represent the major source of naturally derived tocopherols, the antioxidant
molecules that act as free radical quenchers preventing lipid peroxidation in biological systems and vegetable oil products.
All four isomers of tocopherols, i.e. α, β, γ, δ tocopherols that exist in nature are found in soybean seeds. The biological
activity and the contribution of these isomers in improving the oxidative stability of vegetable oil are in reverse order.
Because of the nutritive value and the importance for oil stability, enhancement of tocopherol content, through breeding programs,
in soybean seeds has become a new and an important objective. Genotypic variability, which is the basis of every breeding
program, is scarcely reported for tocopherol content and profile in soybean seeds. In the present investigation, the tocopherol
content and profile in seed samples of 66 genotypes of Indian soybean were determined. The ratios observed between the lowest
and the highest values for α, β, γ, δ, total tocopherol content were 1:13.6, 1:10.4, 1:7.5, 1:9.1, 1:7.9, respectively. The
mean contents for α, β, γ, δ and total tocopherols were 269, 40, 855, 241 and 1,405 μg/g of oil, respectively. Total tocopherol
content was the highest in ‘Co Soya2’ followed by ‘Ankur’. Concentration of α-tocopherol was the highest (27%) in ‘Ankur’
followed by ‘MACS124’ (26%) whereas gamma tocopherol concentration was the highest (69%) in ‘VLS1’ and ‘PK327’ followed by
‘MACS13’ (67%). In view of the fact that levels of unsaturated fatty acids, apart from tocopherols, also determine the oxidative
stability of vegetable oils, the relationship of four isomers of tocopherols with each other as well as with different unsaturated
fatty acids and oil content was also investigated in the present study. All the four isomers of tocopherols exhibited highly
significant correlations with each other (p < 0.001) whereas γ-tocopherol and total tocopherol content showed a significant relationship with linoleic acid (p < 0.05). 相似文献
11.
Abdalbasit Mariod Bertrand Matthäus Ismail H. Hussein 《Journal of the American Oil Chemists' Society》2011,88(5):603-609
Stripped and non-stripped oils from Sclerocarya birrea [marula oil (SCO)], Aspongopus viduatus [melon bug oil (MBO)] and Agonoscelis pubescens [sorghum bug oil (SBO)], traditionally used for nutritional applications in Sudan, were investigated for their fatty acid
and tocopherol composition, and their oxidative stability. Three stripping methods were used, phenolic compounds extraction,
silicic acid column, and aluminum oxide column. The stripping methods did not affect the fatty acid composition. Non-stripped
SCO, MBO and SBO contained oleic, palmitic, stearic and linoleic acids, which were not significantly (P < 0.05) different than stripped SCO, MBO and SBO. The stripping methods’ effect on the tocopherol composition of the studied
oils, the total amount of tocopherol in non-stripped oils decreased by extraction of phenolic compounds, mean that part of
the tocopherols was extracted with the phenolic compounds. No traces of tocopherols were found in oils stripped using silicic
and aluminum columns and the tocopherols were eliminated during the stripping processes. The stability of SCO, MBO and SBO
oils was 43, 38 and 5.1 h, respectively, this stability decreased by 22.0, 37.6 and 23.5%, respectively after extraction of
phenolic compounds. This stability decreased by 96.9, 98.2 and 90.2% respectively, when stripped using the aluminium column
and decreased by 92.6, 96.1 and 86.3% when stripped by the silicic column. It is possible to assume that the tocopherols and
phenolic compounds play a more active role in the oxidative stability of the oils than the fatty acid composition and phytosterols. 相似文献
12.
Methyl and ethyl monoalkyl esters of various vegetable oils were produced for determining the effects of type of alcohol and
fatty acid profile of the vegetable oil on the lubricity of the ester. Four methyl esters and six ethyl esters were analyzed
for wear properties using the American Society for Testing and Materials method D 6079, Evaluating Lubricity of Diesel Fuels
by the High-Frequency Reciprocating Rig. Ethyl esters showed noticeable improvement compared to methyl esters in the wear
properties of each ester tested. No correlation was found between lubricity improvement and fatty acid profile of the ester,
except that esters of castor oil had improved lubricity over other oils with similar carbon chain-length (C18) fatty acids. 相似文献
13.
Bleaching of alkali-refined vegetable oils with clay minerals 总被引:5,自引:0,他引:5
Keito Boki Moriaki Kubo Tetsuyuki Wada Takamichi Tamura 《Journal of the American Oil Chemists' Society》1992,69(3):232-236
Bleaching efficiencies of bentonites, montmorillonites and sepiolites for alkali-refined rapesseed, soybean, wheatgerm, safflower,
corn, cottonseed and sunflower oils were investigated by a batch method at 110°C. The sepiolites with more acid sites at −5.6
< Ho ≥ −3.0 were the most effective in bleaching of each alkali-refined oil. Surface area and acidity at −5.6>Ho ≥ −3.0 were highly significant with bleaching efficiency. The sepiolites (numbers 2 and 3) were more suitable than standard
activated clay because they were more effective both in retaining tocopherols and in reducing free fatty acids after bleaching. 相似文献
14.
The absorption of tocopherols (α, γ, and σ) and fatty acids from rapeseed (RO), soybean (SOO), and sunflower (SUO) oil, both
from the natural oils and from the oils following moderate heating (180°C for 15 min), was measured in lymphcannulated rats.
Oils were administered as emulsions through a gastrostomy tube, and lymph samples were collected for 24 h. The composition
of tocopherols in oils and lymph fractions was measured by high-performance liquid chromatography, and fatty acids were measured
by gas-liquid chromatography. The highest accumulated transport of α-tocopherol was observed after SUO administration, the
lowest after SOO, with RO in between, corresponding to their relative contents (41.6±8.8, 32.7±5.0, and 24.9±4.3 μg at 24
h after administration of SUO, RO, and SOO, respectively). The calculated recoveries (in %) 24 h after oil administration
were 21.4±4.5, 45.7±7.0, and 78.8±13.5 for SUO, RO, and SOO, respectively, suggesting that the absorption efficiency decreased
when the α-tocopherol concentration increased. The recovery of α-tocopherol was higher than the recoveries of γ-and σ-tocopherol,
indicating that the different tocopherols were not absorbed to the same extent or with similar rates. No differences between
unheated and heated oils were observed in the absorption of tocopherols, whereas heating led to lower absorption of fatty
acids, thus showing no direct association between absorption of tocopherols and fatty acids. 相似文献
15.
Hiromi Yoshida Yuki Hirakawa Sayaka Abe Yoshiyuki Mizushina 《European Journal of Lipid Science and Technology》2002,104(2):116-122
Sunflower seeds ((Helianthus annuus were roasted for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a domestic microwave oven. After the kernels were separated from the sunflower seeds, the quality characteristics and the compositions of the oils were investigated in relation to their tocopherol distributions, and they were further evaluated as compared with an unroasted oil sample. Only minor increases (p < 0.05) in chemical and physical changes of the oils, such as the carbonyl value, the p‐anisidine value and the color development, occurred at a prolonged roasting period. Significant decrease (p < 0.05) was observed in the amounts of phospholipids in the oils after microwave roasting. Nevertheless, compared to the original level, more than 92 wt‐% tocopherols still remained after 30 min of roasting. With a few exceptions, these results indicate that the exposure of sunflower seeds to microwaves for 12 min caused no significant (p < 0.05) loss or change in the content of tocopherols and polyunsaturated fatty acids in the kernels. 相似文献
16.
Fatty Acid Composition,Oxidative Stability,and Radical Scavenging Activity of Vegetable Oil Blends with Coconut Oil 总被引:1,自引:1,他引:0
A. S. Bhatnagar P. K. Prasanth Kumar J. Hemavathy A. G. Gopala Krishna 《Journal of the American Oil Chemists' Society》2009,86(10):991-999
Coconut (Cocos nucifera) contains 55–65% oil, having C12:0 as the major fatty acid. Coconut oil has >90% saturates and is deficient in monounsaturates
(6%), polyunsaturates (1%), and total tocopherols (29 mg/kg). However, coconut oil contains medium chain fatty acids (58%),
which are easily absorbed into the body. Therefore, blends of coconut oil (20–80% incorporation of coconut oil) with other
vegetable oils (i.e. palm, rice bran, sesame, mustard, sunflower, groundnut, safflower, and soybean) were prepared. Consequently,
seven blends prepared for coconut oil consumers contained improved amounts of monounsaturates (8–36%, p < 0.03), polyunsaturates (4–35%, p < 0.03), total tocopherols (111–582 mg/kg, p < 0.02), and 5–33% (p < 0.02) of DPPH (2,2-diphenyl-1-picrylhydrazyl free radicals) scavenging activity. In addition, seven blends prepared for
non-coconut oil consumers contained 11–13% of medium chain fatty acids. Coconut oil + sunflower oil and coconut oil + rice
bran oil blends also exhibited 36.7–89.7% (p < 0.0005) and 66.4–80.5% (p < 0.0313) reductions in peroxide formation in comparison to the individual sunflower oil and rice bran oil, respectively.
It was concluded that blending coconut oil with other vegetable oils provides medium chain fatty acids and oxidative stability
to the blends, while coconut oil will be enriched with polyunsaturates, monounsaturates, natural antioxidants, and a greater
radical scavenging activity. 相似文献
17.
Arnar Halldorsson Bjorn Kristinsson Gudmundur G. Haraldsson 《European Journal of Lipid Science and Technology》2004,106(2):79-87
The main objective of this study was to compare the fatty acid selectivity of numerous commercially available lipases toward the most ubiquitous fatty acids present in fish oils in form of their corresponding ethyl esters. Special interest was taken in their ability to separate the n‐3 long‐chain polyunsaturated fatty acids (PUFA), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), from the more saturated fatty acids as well as exploiting the putative discrimination between these highly valuable n‐3 PUFA. Hydrolysis of sardine oil ethyl esters in a Tris buffer solution by 12 microbial lipases is described. The results reveal that all of the lipases strongly discriminate against the n‐3 PUFA and prefer the more saturated fatty acids as substrates. Most of the lipases discriminate between EPA and DHA in favor of EPA, however, 2 bacterial lipases from Pseudomonas were observed to prefer DHA to EPA. Digestive lipolytic enzymes isolated from salmon and rainbow trout intestines displayed reversed fatty acid selectivity when their fish oil triacylglycerol hydrolysis was studied. Thus, the n‐3 PUFA including EPA and DHA were observed to be hydrolyzed at a considerably higher rate than the more saturated fatty acids. 相似文献
18.
Enzymatic pretreatment of deodorizer distillate for concentration of sterols and tocopherols 总被引:15,自引:7,他引:15
Separation of sterols and tocopherols from fatty acids in deodorizer distillate was facilitated through lipase-catalyzed modification
of fatty acids in canola, mixed and soya deodorizer distillates. The fatty acid esterification with methanol catalyzed by
SP-382 (an immobilized nonspecific lipase) proceeded rapidly, with conversion of fatty acid to methyl ester in 5 h being 96.5,
83.5 and 89.4%, respectively. A model mixture of pure oleic acid and dl-α-tocopherol was used to study any potential side
reactions that may lower the tocopherol content during the esterification reaction. Under the conditions employed, the loss
of tocopherol was less than 5%. Simple vacuum distillation (1–2 mm Hg) was employed to remove the volatile fraction (methyl
esters of fatty acids, some fatty acids and other volatiles) of the esterified deodorizer distillate, leaving behind sterols,
sterol esters and tocopherols. Sterols and tocopherols were almost completely retained in the residue fraction with recoveries
in the range of 95%. Overall recoveries of sterols and tocopherols after esterification and distillation were over 90% for
all the deodorizer distillate samples. 相似文献
19.
Pilot plant-processed samples of soybean and canola (lowerucic acid rapeseed) oil with fatty acid compositions modified by
mutation breeding and/or hydrogenation were evaluated for frying stability. Linolenic acid contents were 6.2% for standard
soybean oil, 3.7% for low-linolenic soybean oil and 0.4% for the hydrogenated low-linolenic soybean oil. The linolenic acid
contents were 10.1% for standard canola oil, 1.7% for canola modified by breeding and 0.8% and 0.6% for oils modified by breeding
and hydrogenation. All modified oils had significantly (P<0.05) less room odor intensity after initial heating tests at 190°C than the standard oils, as judged by a sensory panel.
Panelists also judged standard oils to have significantly higher intensities for fishy, burnt, rubbery, smoky and acrid odors
than the modified oils. Free fatty acids, polar compounds and foam heights during frying were significantly (P<0.05) less in the low-linolenic soy and canola oils than the corresponding unmodified oils after 5 h of frying. The flavor
quality of french-fried potatoes was significantly (P<0.05) better for potatoes fried in modified oils than those fried in standard oils. The potatoes fried in standard canola
oil were described by the sensory panel as fishy. 相似文献
20.
Afaf Kamal‐Eldin 《European Journal of Lipid Science and Technology》2006,108(12):1051-1061
The oxidative stability of vegetable oils is determined by their fatty acid composition and antioxidants, mainly tocopherols but also other non‐saponifiable constituents. The effect of fatty acids on stability depends mainly on their degree of unsaturation and, to a lesser degree, on the position of the unsaturated functions within the triacylglycerol molecule. Vegetable oils contain tocopherols and tocotrienols, especially α‐ and γ‐tocopherols, as their main antioxidants. The antioxidant behavior of tocopherols represents a complex phenomenon as they are efficient antioxidants at low concentrations but they gradually lose efficacy as their concentrations in the vegetable oils increase. The “loss of efficacy” of tocopherols, sometimes referred to as a “pro‐oxidant effect”, is witnessed by an increase in the rate of oxidation during the induction period, despite elongation of this phase. The phenomenon is much obvious for α‐tocopherol, but is also evident for other tocopherols. In agreement with nature's wisdom, the tocopherol levels in vegetable oils seem to be close to the optimal levels needed for the stabilization of these oils. The presence of other antioxidants in the oils, e.g. carotenoids, phenolic compounds, and Maillard reaction products, may synergize with tocopherols and minimize this loss of efficacy. 相似文献