CHEMISTRY OF OILS AND FATS. Albert J. Dijkstra

Transcription

1 CHEMISTRY F ILS AND FATS Albert J. Dijkstra

2 Production vegetable oil (m tonnes) Seven oil seeds 2008/ / / /12 total Soya bean ther Nine plant oils Total Palm oil Soya bean oil Rapeseed oil Sunflower seed oil Lauric oils ther (CS,GN,)

3 Topics to be discussed Composition of oils and fats Triglycerides, fatty acids, phosphatides, tocopherols, tocotrienols, phytosterols, colouring compounds Properties of oils and fats Physical, melting point Chemical, oxidation Sources of oils and fats Processing of oils and fats: Refining/modifying Degumming, neutralisation,bleaching, deodorisation Hydrogenation, interesterification, fractionation 3

4 Saponifiable fraction of oils and fats Amount of saponifiable fraction is around 98% Reacts with alkali under formation of soaps (alkali salts of FA) Triglycerides: esters of glycerol with 3 fatty acids (FA) Mono- and diglycerides (partial glycerides) Free fatty acids (FFA) Waxes: esters of fatty acids with fatty alcohols Phospholipids (phosphatides, sphingomyelins) Glycolipids H Sterol esters 2 C CH R 2 C H 2 C C R 1 C R 3 4

5 Unsaponifiable fraction Amount: around 2% : Tocopherols Free (non-esterified) sterols Hydrocarbons, carotenoïds, squalene, chlorophyll Vitamins Polyphenols: in olive oil xidation products 5

6 Nutritional aspects of oils and fats Source of energy (9 kcal/g or 37 kj/g) Source of essential fatty acids (ω-3, ω-6) Fat soluble vitamins (A, D, E) Functional minor components: tocopherols, sterols oryzanol (rice bran oil) polyphenols (olive oil) Sensorial and rheological appreciation Just imagine a salad without dressing or mayonnaise 6

7 Quality aspects of oils and fats Gourmet oils (olive oil, walnut oil, pumpkin seed oil etc.) are appreciated for their characteristic taste, smell and colour Refined oils should have: Bland taste (deodorisation) Low acidity (neutralisation) Low colour (bleaching and thermal breakdown of colouring compounds during deodorisation) Transparency (filtration) Low cloud point (winterisation/dewaxing) 7

8 Structure of fatty acids 18 Linoleic acid (18:2) C H For nearly all naturally occurring fatty acids holds: Straight chains with Even number of carbon atoms Unsaturation has cis configuration Methylene interruption in polyunsaturated fatty acids Elongation at carboxyl end so position of double bond does not shift with respect to methyl end (ω-6 remains ω-6) 8

9 Nomenclature of fatty acids C H -CH 2 -CH=CH-CH 2 -CH=CH-CH 2 -CH=CH-(CH 2 ) 7 -CH -(CH 2 -CH=CH) 3 (CH 2 ) 7 CH Systematic name: (9Z,12Z,15Z)-ctadeca-9,12,15-trienoic acid Trivial name: α-linolenic acid First shorthand: 9c12c15c-18:3 Second shorthand:18:3 ω3 or 18:3 n-3 See also: 9

10 Nomenclature of fatty acids Systematic name Trivial name Notation ctanoic Caprylic (PK, CN) 8:0 Decanoic Capric (PK, CN) 10:0 Dodecanoic Lauric (PK, CN) 12:0 Tetradecanoic Myristic (PK, CN) 14:0 Hexadecanoic Palmitic (P, PK, CN) 16:0 ctadecanoic Stearic (P, PK, CN) 18:0 9-cis-octadecenoic acid leic (P, PK, CN) 18:1ω9 9-trans-octadecenoic acid Elaidic (hydrogenation) 18:1ω9 9c,12c-octadecadienoic Linoleic (P, PK, CN) 18:2ω6 6c,9c,12c-octadecatrienoic γ-llinolenic 18:3ω6 5c,8c,11c,14c-eicosatetraenoic Arachidonic (meat) 20:4ω6 9c,12c,15c-octadecatrienoic α-linolenic (soya, Canola) 18:3ω3 6c,9c,12c,15c-octadecatetraenoic Stearidonic (GM soya) 18:4ω3 5c,8c,11c,14c,17c-eicosapentaenoic EPA (fish oil) 20:5ω3 4c,7c,10c,13c,16c,19c-docosahexaenoic DHA (fish oil) 22:6ω3 10

11 Fatty acid composition of various oils oil 8:0 10:0 12:0 14:0 16:0 18:0 18:1 18:2 18:3 22:1 coconut oil palm kernel oil palm oil palm superolein palm stearin cocoa butter olive oil soya bean oil rapeseed oil canola oil sunflower seed oil linseed oil N.B. Totals 100% because minor fatty acids have not been listed 11

12 Fatty acid distribution in triglycerides Vegetable oils (mostly 1,3-random, 2-random) 16:0 and 18:0 mainly on 1,3-positions Lauric acid (12:0) has some preference for 2-position Linoleic acid (18:2) has preference for 2-position leic acid (18:1) fills in vacancies For cocoa butter this is mainly the 2-position Animal fats (1-position differs from 3 position) Palmitic acid (16:0) has preference for 2-position Stearic acid (18:0) has some preference for 1-position Unsaturated acids on outer, especially 3-position 12

13 Examples of fatty acid distributions il pos 12:0 14:0 16:0 16:1 18:0 18:1 18:2 18:3 Palm oil 1, Palm kernel 1, Coconut oil Soya bean 1, Lard

14 Sources and types of oils and fats Animal oils and fats Lard Beef and mutton tallow Fish oil (microbial oil in future?) Vegetable oils and fats Fruit oils (olive oil, palm oil) Seed oils (soya bean oil, rapeseed oil, sunflower seed oil, lauric oils, cottonseed oil, etc.) Specialty fats and gourmet oils Technical applications (castor oil) Confectionery fats (cocoa, shea, illipe butter) Niche products (nut oils, grape seed oil, avocado oil..) 14

15 Sole product, co-product, by-product Sole product and major source of income (byproducts are not important or even useless) Palm oil, olive oil, sunflower seed oil, rapeseed oil, castor oil, jatropha, wild fats, nut oils Microbial oils? Co-product (important by-product) Soya bean oil is a co-product of soya bean meal Palm kernel oil is co-product oil palm oil By-product in true sense. Raw material is harvested or farmed/grown for other reasons Animal fats, fish oil, cotton seed oil, corn germ oil, grape seed oil 15

16 Chemical structure of phosphatides A1 C R 1 A2 H 2 C D CH R 2 C H2 C P X C X = choline (phosphatidyl choline or PC) H H 2 C H H 2 C choline H 2 C N H 2 C NH 2 ethanolamine H H X = ethanolamine (phosphatidyl ethanolamine, PE) H X = inositol (phosphatidyl inositol or PI) H H X = hydrogen (phosphatidic acid or PA) inositol, link in 1-position 16

17 Chemical structure of tocopherols H R 2 6 R 1 R ' 8' Trivial name R 1 R 2 R 3 α-tocopherol β-tocopherol H γ-tocopherol H δ-tocopherol H H 17

18 Chemical structure of tocotrienols R 1 H R 2 R 3 Tocopherols occurs in vegetable oils (α-tocopherol is vitamin E); soya bean oil (900 ppm), corn germ oil (1 100 ppm), sesame seed oil (2 900 ppm) Tocotrienols occur mainly in palm oil (530 ppm), rice bran oil (580 ppm) and wheat bran (650 ppm) 18

19 ccurrence of tocols (ppm) il tocopherol tocotrienol α β γ δ α β Palm Rapeseed Soya bean oil Sunflower oil Walnut oil Wheatgerm oil

20 Chemical structure of plant sterols H Shown is β-sitosterol ther plant sterols (campesterol, stigmasterol, brassicasterol, Δ 5 -avena-sterol, etc) differ with respect side chains, number and position of double bonds The free hydroxyl group can be esterified with a fatty acid or ferulic acid, or form an ether with glucose 20

21 Free and esterified phytosterols Red palm olein (crude) Palm oil (crude) Coconut (crude) live oil (cold pressed) Palm oil (refined) Walnut (refined) soybean (crude) live oil (cold pressed) Peanut (refined) Soya (refined) Cotton (refined) Cotton (crude) Sunflower (refined) Frituur (sunflower) Corn oil (crude) Corn (refined) Rapeseed (crude) Rapeseed (refined) sterol content (mg/100g) esterified free 21

22 Chemical structure of (poly)phenols H H H H H 3 C H H H H gallic acid protocatechuic acid ferulic acid H H H H H H H H H hydroxytyrosol caffeic acid coumaric acid Source: fruits, berry seed oil β-carotene Nutritional role: radical scavenger; antioxidant Application: adjuvant in bakery ingredients; additive to oils 22

23 H 2 C H 3 C H 3 C Chemical structure of colouring N N Mg N N compounds CH H 3 C H 3 C CH 3 ß-carotene H 3 C chlorophyll b 23

24 Melting points of fatty acids The melting point increases with the number of carbon atoms in the chain It decreases with the number of double bonds Fatty acids with trans double bonds have a higher melting point than their cis isomers In polyunsaturated fatty acids, conjugated double bonds lead to a higher melting point than the common, methylene interrupted double bond systems 24

25 Melting points of triglycerides Substituting a fatty acid in a triglyceride by a higher melting one raises its melting point Triglyceride melting points also depend on positional isomerism Triglycerides exhibit polymorphism They are called: α, β and β Different polymorphs exhibit different melting points: α < β < β They are monotropic 25

26 Solubility of lipids ils and fats are miscible with alkanes, ethers and ketones n-hexane is common extraction solvent They dissolve in hot isopropanol but not in cold Isopropanol extraction process cools the miscella ils and fats are insoluble in water Soaps are water-soluble Washing oil with water to remove soaps Phosphatides are not soluble in acetone Lecithin de-oiling by extracting the oil with acetone 26

27 Reactions during storage and Hydrolysis processing Chemical. Catalysed by alkali and acid. Rate depends on temperature and extent also on time Enzymatic in presence of lipase (palm oil, rice bran oil) xidation (to be discussed by Dr Ignace Debruyne) Isomerisation of double bonds Cis/trans isomerisation CH 2 CH 2 CH 2 CH 2 27

28 Reactions (continued) Conjugation C H 2 C H CH 2 H 2 C CH 2 The reaction rates of both reactions Increase with an increase in temperature Are affected by catalysts (alkali, bleaching earth) Linolenic acid is more reactive than linoleic acid Two bis-allylic methylene groups versus only one Linoleic acid is much more reactive than oleic acid ne bis-allylic methylene group versus none 28

29 Further reactions Dimerisation/polymerisation Promoted by high temperature (deep fat frying) xidation and ring opening of tocopherols Dehydration of sterols forming steradienes Condensation of sterols forming disteryl ethers 29

30 Edible oil processing flow sheet Seed Preparation Cleaning / Drying Cracking Dehulling Flaking Extraction Mechanical Extraction Solvent Extraction il Degumming Meal Hydrogenation Neutralising ( Post - refining ) Interesterification Fractionation Modification Bleaching Winterising Deodorising Refining Edible il Margarine Salad / Frying oil Shortening 30

31 Refining routes Crude oil Water degumming or enzymatic PLC degumming il with NHP Acid degumming il with < 30 ppm P Alkali refining Acid refining Enzymatic PLA gum treatment il with < 5 ppm P Dry degumming Bleaching Deodorisation Fully refined oil Physical refining Bleaching 31

32 When to use which process Dry degumming/physical refining (2-steps) Low phosphatide oils (palm oil, lauric oils, tallow) Alkali refining (3 or 4 steps) Low quality oils, speciality oils (batch process) Low acidity oils (soya bean oil) Acid refining/bleaching/physical refining (3 or 4 steps) High FFA oils (rapeseed and sunflower seed oil) (Use of phospholipases can increase oil yield in high phosphatide oils like soya bean oil,but adds another step) 32

33 Purpose of modification processes Change in physical properties, for instance From oil to solid fat by hydrogenation Lowering of melting point by interesterification Lowering cloud point by fractionation Increase shelf life Lowering iodine value by hydrogenation Avoid $-polymorph formation by interesterification Facilitate interchangeability (cost reduction) Partial hydrogenated soya bean oil versus palm oil 33

34 DIXI (I have spoken)