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University of Ghent, Faculty of Agricultural and Applied Biological Sciences
Department of Organic Chemistry
Influence of processing on minor components in vegetable oils
Prof. dr. ir. Roland Verhé
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General introduction
Composition crude oilNutritional importance
Oils and fats
• delivering energy (9 kcal/g)
• essential fatty acids (ω3, ω6)
• fat soluble vitamins (Vitamine A, D, E, K)
• sensorial and rheological appreciation of foods
• Triglycerides (>98%) and partial acylglycerides, free fatty acids
• Tocopherols, phytosterols, phospholipids, waxes, metals, colouring pigments
• Odour, flavour components
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Overview vegetable oil refining
Chemical refiningChemical refining Physical refiningPhysical refining
Degumming
Bleaching
Steam refining Deodorization
Degumming
Neutralisation
Bleaching
Deodorization
Refined OilRefined Oil
SOAPS
GUMS
FFA
Crude OilCrude Oil
FFA
distillate
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Vegetable oil quality characteristics
Currently : minor componentsTraditional parameters
bland taste
light colour
good oxidative stability
+ : Functional minor components
tocopherols, phytosterols,
oryzanol, coenzyme Q10
→ application in functional foods
- : Harmful contaminantspesticides, PAH’s, PCB’s
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Tocopherols
O
HO
R1
R2R3
CH3CH3
CH3 CH3 CH3
LOO
Chemical structureName R1 R2 R3
α-toco CH3 CH3 CH3
γ-toco H CH3 CH3
δ-toco H H CH3
Non-polar and polar oxidation products
Natural source : vegetable oils, corn oil 1100 ppm, soya oil 900 ppm
Nutritional importance : → Vitamin E, prevention of free radical damage in vivo e.g. cardiovascular diseases, cancers, neurological disorders (Alzheimer,...)
Application : dietary supplements
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Phytosterols
Chemical structure : – flexible side chain at C17
(sitosterol, campesterol, stigmasterol,…)– sterols versus stanols
HO
β-sitosterol
Nutritional importance : phytosterols lower plasma cholesterol and LDL cholesterol
Natural source : vegetable oils and cereals
Function : Essential component of the membranes
Application : in functional foods (e.g. margarine's,…)
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Objective study
Refining process
Phytosterols & Tocopherols
Crude oil
Technology AnalysisChemistry
Observations → chemical modification → explanations
Naturallypresent
0.02-0.9%
modification
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Occurrence of tocopherolsand phytosterols in vegetable
oils : free or bounded
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Natural occurrence
OCH3
C16H33
HOFreeData available
Tocopherols
OCH3
C16H33
O
O
Esterified
Confuse data
→ synthesis of tocopheryl esters
→ development of analytical procedure (HPLC - UV)
→ tocopheryl esters are absent in crude vegetable oils
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Natural occurrence
HO
β-sitosterol
• Tocopherols
→ only free tocopherols occur naturally in vegetable oil
• Phytosterols occur
• free
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Natural occurrence
β-sitosteryl-oleate
C O
O
O
β-sitosteryl ferulate (γ-oryzanol)HO
H3CO
O
• Tocopherols
→ only free tocopherols occur naturally in vegetable oil
• Phytosterols occur
• free
•esterified to fatty acid
•esterified to phenolic acids•e.g. rice bran oil
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Natural occurrence
O
β-sitosteryl-D-glucoside
O
OH
OH
CH2OH
• Tocopherols
→ only free tocopherols occur naturally in vegetable oil
• Phytosterols occur
• free
• esterified to fatty acid
• esterified to phenolic acid
• linked to sugar
O
β-sitosteryl-(6'O-oleoyl)-D-glucoside
O
OH
OH
CH2C
O
O
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Total sterol analysis• Has been widely studied• Involves a saponification
• Little data is available on level of free and esterified phytosterols
Analysis free - esterified sterols• Free and esterified sterols were separated on polarity by silica gel chromatography, followed saponification and GC quantification
•Development and validation of analytical method
Steryl esters → free sterols
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Free and esterified phytosterols
0 200 400 600 800 1000
Rapeseed (refined)Rapeseed (crude)
Corn (refined)
Corn oil (crude)Frituur (sunflower)
Sunflower (refined)Cotton (crude)
Cotton (refined)
Soya (refined)Peanut (refined)
Olive oil (cold pressed)
soybean (crude)Walnut (refined)
Palm oil (refined)Olive oil (cold pressed)
Coconut (crude)
Palm oil (crude)Red palm olein (crude)
sterol content (mg/100g) esterified free
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Influence of refining on free and esterified
phytosterols in soybean oil
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Influence of refining on soybean
0 50 100 150 200 250 300 350
Sterol concentration (mg/100 g)
Crude
Degummed
Neutralized
Bleached
Deodorized
Chemical refining
Esterified sterols Free sterols
0 50 100 150 200 250 300 350
Sterol concentration (mg/100 g)
Crude
Degummed
Bleached
Deodorized
Physical refining
Esterified sterols Free sterols
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Chemical neutralisation of soybean
Time 30 min, temperature 45°C
0
50
100
150
200
250
300
350
sterol mg/100g
feed 2.5 5 10 12.5 15
strength NaOH (%)
0% excess NaOH
free esterified
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Bleaching of soybean oil
050
100150200250300350400
sterol mg/100g
feed 2.8 3.1 3.1 3.2 3.6 3.6 4.15 6
pH bleaching earth (10% suspension in water)
1% earth, 100°C, 30 min
free esterified
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Steradienes - disteryl ethers
• Steradienes : sterol dehydration productsR
HO
R
phytosterol steradienetemperature
bleaching earth
-H2O
• Disteryl ethers : sterol condensation productsR
O
R
→ ratio dehydration / condensation : 10/1
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Steradienes - bleaching
• Steradiene formation is mainly influence by– bleaching temperature– degree of acid activation of the bleaching earth
0
5
10
15
20
25
2.5 3.5 4.5 5.5
pH suspension bleaching earth / water (10%)
rela
tive
ster
adie
ne in
crea
se
30 min, 80°C, 1% earth30 min, 100°C, 1% earth30 min, 100°C, 2% earth
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Deodorization of soybean oil
0
50
100
150
200
250
300
350
Sterol mg/100g
Feed 220°C 230°C 240°C 250°C 260°C
Deodorization temperature (°C)
Chemical refining (FFA feed=0.1%)
Esterified sterols Free sterols
0
50
100
150
200
250
300
350
Sterol mg/100g
Feed 220°C 230°C 240°C 250°C 260°C
Deodorization temperature (°C)
Physical refining (FFA feed=1.1%)
Esterified sterols Free sterols
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Steradiene - deodorization
• Steradienes are distillated and condensed in the deodoriser distillate ( 90 - 600 ppm steradienes in soya distillate)
• Degree of sterol dehydration is mainly influenced by deodorization temperature
60
100
140
180
220
215 220 225 230 235 240 245
Temperature (°C)
Tota
l ste
radi
ene
(ppm
)
Temperature(°C)
Free sterolDehydration (%)
220 0.05230 0.1240 0.23250 0.4260 1.06
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Influence of processing on tocopherols
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Stability of tocopherolsObjective : assess the stability of tocopherols at high temperature
deodorization
Distillate
Refined oilBleached oil
Tocopherol mass balance during deodorization
Toco bleached oil = toco refined oil + toco distillate + ??
Observation :Tocopherol loss of 20-30% in the tocopherol mass balance
Explanation : analytical - incomplete condensation -thermal breakdown - oxidative degradation
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Stability of tocopherols
• Fundamental study
Reference :
With TBHQ : (1500ppm)
N2 flush :
Tocopherol loss (%)
Conclusion : thermal stability, probably oxidative degradation
⇒ major tocopherol oxidation products?
α-tocopherol (2000ppm)dissolved in triolein andheated to 245°C, 5-6 mbar for 80 min, no steam injection
9
3
0
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Tocopherol oxidation• Previous tocopherol oxidation studies :
• oxidation of α-tocopherol dissolved in a solvent• oxidation initiators : K3FeCN6, FeCl3, tBOOH, AIBN• oxidation at room temperature • formation of several known oxidation products
O
HO
R
α-tocopherol O O
OO
RR
OO
Rα-tocopherol spirotrimeer
R
O
OOO OH
R
α-tocopheroldimer quinone
O
O OH
R
α-tocopherolquinone
RO
HO
R
O
O
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Tocopherols
• Identification of oxidation products in triglycerides
O
O OH
R
O
7,8-epoxy-α-tocopherolquinone
O
O OH
R
α-Tocopherolquinone
O
O OH
O
R
4a,5-Epoxy-α-tocopherolquinone
- synthesis of most important tocopherol oxidation products
- used as standards for the identification of tocopheroloxidation products formed in triolein
Tocopherols are antioxidants → prone to oxidation
Concentration of tocopherol oxidation products?
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Stability of tocopherol during thermoxidation stress
• Objective :- Modeling of α-tocopherol degradation in function of heating time, temperature and triacylglycerol unsaturation
- Quantification of α-tocopherol oxidation products formed
• Experimental :- Statistical central composite design- Addition of α-tocopherol standard (1000 ppm) to
technical grade triolein and tripalmitin- Heating : 5g of oil in OSI tubes, no air bubbling
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Modeling of α-tocopherol oxidation products during thermoxidation in triolein
and tripalmitin
0
10
20
30
175 200 225
Temp (°C),Time=2h,OOO/PPP=50/50
toco
pher
ol (%
)
0
1
2
3
4
5
poly
mer
(%)
α-tocopherol ( ), epoxy-α-tocopherolquinone ( );
α-tocopherolquinone ( ), total triacylglycerol, polymer (•)
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Modeling of α-tocopherol oxidation products during thermoxidation in triolein
and tripalmitin
α-tocopherol ( ), epoxy-α-tocopherolquinone ( );
α-tocopherolquinone ( ), total triacylglycerol, polymer (•)
0
10
20
30
25 50 75
Triolein (%), Time=2h, Temp=200°C
toco
pher
ol (%
)
0
1
2
3
polym
er (%
)
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Deodoriser distillate : characterisation and
technology to improve quality
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Analytical characterisation major componentsfree free fatty acids
physical refining : > 70%chemical refining : < 60%
monoglyceridesdiglyceridestriglyceridessqualenetocopherols and phytosterols
physical refining : 2-5%chemical refining : 10-25%
Characterisation of deodoriser distillate
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Deodorization technology
• Observation :– chemical distillate : high tocopherol and
phytosterol content → high economic value
– physical distillate : high free fatty acid content → low economic value
• Objective :– develop new deodorization technology to improve
the quality of physical deodoriser distillate
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Deodorization technology
• Methodology :– condensation of free fatty acids in a first distillate
fraction– condensation of tocopherols and phytosterols in a
second distillate fraction
→ by optimisation of the temperature profile
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Improved deodorization technology : conclusion
Free fatty
acids
tocopherols phytosterols
Chemical 10-24 10-15 10-17
Physical 76-87 2-5 2-7
Distillate 1 90-96 1-2 1-2
Distillate 2 37-67 8-10 10-15
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General conclusion
The new and fundamental view followed in this research indicates thattocopherols and phytosterols are stable components, however several transformation reactions can take place of which the ratio is influenced by the technological conditions
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Acknowledgement
Jose Miguel MontiagudoStephan reverseauAna PonsAleksandra SzulczewskaUrsulla SosinsksaRevilija MozuraityteJose Ayala Vila
Ana Belen Cano Dries Cauwenbergh Elena CortesMaria ForcadaLucia Guardiola Garcia Tilemachos GoumperisSofia Ioannidou
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Characterisation of deodorizer distillate2. Rheological characterisation
viscosity is determined byChemical distillate : phytosterols
Physical distillate : free fatty acids
01020304050607080
0 1 2 3 4 5
Steryl ester content (%)
Visc
osity
(cP
or 1
.10-3
Pa.
s)
50°C
60°C
70°C
80°C ×
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Characterisation of deodorizer distillate2. Rheological characterisation
viscosity is determined byChemical distillate : phytosterols
Physical distillate : free fatty acids
010203040506070
30 40 50 60 70 80
Free fatty acid content (%)
Visc
osity
(cP
or 1
.10-3
Pa.
s)
50°C
60°C
70°C
80°C ×