1. CHM2962 and BND1022 FOOD CHEMISTRY Lect 9 – 12 2002

2. LIPIDS Organic chemicals of living systems insoluble in water soluble in non polar solvents *Oils (liquid) *Fats (solid) *Phospho-lipids (in cell membranes) food lipids *generally esters of long chain fatty acids (triglycerides) *cholesterol (a steroid) *terpenes, other steroids – see Peter Junk lectures later

3. Foods - “total fat” content Milk chocolate30.3 shortbread26.1

4. Fats in nutrition Role much more complicated than previously thought. Fat is an essential macro-nutrient. High levels of saturated fats are bad. - Leads to high serum cholesterol - High triglycerides - High VLDL - High ratio of VLDL/HDL Mono-unsaturated fats now being recommended in lieu of carbohydrate

5. The ratio of  3/  6 fats is important The role of polyunsaturated fats is now not clear excess  6 linoleic promotes oxidation of cholesterol - leads to atherosclerotic plaque Trans polyunsaturated fatty acids appear to be bad

6. Fatty Acids monocarboxylic, aliphatic major components of food lipids properties of food lipids depend on those of fatty acids even number of carbon atoms, unbranched chain Eg. Capric acid n-decanoic acid A saturated fatty acid (SFA)

7. Unsaturated fatty acids Mono-unsaturated (MUFA) Almost always cis in natural fatty acids Palmitoleic

8. Unsaturated fatty acids poly-unsaturated (PUFA) Almost always cis in natural fatty acids Never conjugated linoleic Naming: Systematic + trivial + shorthand

10. 20:4 18:3 18:2 18:1 16:1 20:0 18:0 16:0 14:0 12:0 Carbon Atoms/ Double Bonds mp (°C) Common Name -49 -11 -5 16 32 77 70 63 58 44 arachidonic acid linolenic acid linoleic acid oleic acid palmitoleic acid arachidic acid stearic acid palmitic acid myristic acid lauric acid Saturated Unsaturated 8:0 17 caprylic acid Oils : low melting - high in polyunsaturated and short chain saturated Fats : high melting - high in saturated fats

11. Organisms achieve the physical properties required by using a mixture of different molecules “Designer Lipids”

12. Mol% of fatty acids in fats and oils

13. Rapeseed oil (for margarine) originally contained 20-25% erucic acid cis 13-docosenoic acid 22:1  13 Erucic acid thought to be toxic to humans now bred out of some rapeseed oil.

14. Triglycerides form major energy source + adipose layers Linoleic acid (18:2  9,12) - adult requires 2 -10 g per day Arachidonic acid (20:4) Precursors of the prostaglandins Mammals cannot synthesize linoleic Only unsaturation in position 9 is possible (1st double bond between C 9 - C 10 ) eg. oleic Humans can synthesize arachidonic from linoleic The Essential Fatty Acids

15. 6 7 18:2delta 9,12 Linoleic -2H +2C 18:3delta 6, 9,12 20:3delta 8, 11,14 20:4delta 5, 8, 11,14 Arachidonic 6 7 Human Biochemical pathway to Arachidonic Cats NB. All  -6 polyunsaturated fatty acids

16.  -3 fatty acids Synthesized by algae from  -linolenic Fish consume algae Humans consume fish to obtain  -3 polyunsaturated fatty acids Eicosapentaenoic Acid; 20:5,  5,8,11,14,17 3 4 Example of  -3 UFA

17.  -6 UFA’s lead to prostaglandins - potent promoters of blood clot formation  -3 UFA’s lead to prostaglandins - less potent promoters of blood clot formation Conclusion: Eat more herring, mackeral, trout  -9 UFA eg oleic not essential fatty acid but “good for general health”

18. Polyunsaturate rich margarines lower the risk of CHD? Trans Fatty Acids (TFA) TFA associated with increased Coronary Heart Disease (CHD) in a number of studies. - Suspected that TFA acts as though saturated Trans forms are essentially linear like SFA - Studies range from TFA suspected to be bad TFA worse than saturated fats http://www.ifst.org/hottop9.htm http://www.mayohealth.org/mayo/9806/htm/trans.htm

19. Where do TFA’s come from? Very small number of natural acids most produced during hydrogenation in processing Degree of unsaturation controlled to yield desired physical properties. Trans form is energetically favoured 5% - 40% of cooking oil content Liquid PUFA Ni (catalyst) H 2 (2-10atm, 160-220ºC) Solid PUFA

20. Fatty acid intake: UK - based on a 1994 seven day survey of 8000 households http://www.ifst.org/hottop9.htm 99 representative foods were purchased in June 1995 to April 1996, representing 95 % of total mean fat intake, and analysed. Mean total fat intake =77g/day ( 35.7% of energy intake) Mean TFA consumption was 2.8g/day (= 1.3% of energy) and 28.5g/day (= 13.2% of energy) was as SFA NB. 5 -12g TFA per day quoted in some literature

21. Which foods contribute to the TFA intake? In the UK survey the contributions (%) of various foods to TFA intake was :

22. USA Nov 1999 FDA proposed the inclusion of TFA content on food labels (easy to analyse) http://www.hsph.harvard.edu/reviews/transfats.html Europe: Development of TFA free margarines Fast foods are the primary source of TFA in Europe, USA, Australia

23. Go to 2 nd year servery to get a copy of prac 5 if necessary

24. Rancidity Deterioration of fats and oils Dairy fats micro-organisms hydrolyse triglycerides odorous short chain fatty acids produced Other( meat, fish) autoxidation of unsaturated fatty acids Oxidative rancidity initiation propagation termination

25. CH=CH-CH-CH=CH H Reactive pentadiene unit in fatty acid chain

26. CH=CH-CH-CH=CH H Reactive pentadiene unit in fatty acid chain Reactive allylic bond

27. Initiation Involves singlet oxygen 1 O 2 3O23O2 + Pigment (haem, chorophyll, riboflavin) 1O21O2 h The light energy is transferred to the oxygen molecule And it ends up in a high energy quantum state

28. CH=CH-CH-CH=CH H Heat, light, temperature cause bond cleavage Initiation

29. CH=CH-CH-CH=CH H Bond begins to break Initiation

30. CH=CH-CH-CH=CH. H. Bond is completely broken Free radical is formed 1 O 2 3 O 2 Initiation

31. CH=CH-CH-CH=CH. O-O Reaction with atmospheric oxygen Propagation

32. CH=CH-CH-CH=CH. O-O

33. CH=CH-CH-CH=CH O-O. Bond begins to form

34. CH=CH-CH-CH=CH O-O. Unstable hydroperoxy radical

35. CH=CH-CH-CH=CH O-O. HR Hydroperoxyl radical reacts with a molecule of the original lipid, removing a reactive allylic hydrogen (this is a propagation step)

36. CH=CH-CH-CH=CH O-O-H.R Returns to propagation Hydroperoxide (unstable, will decompose to form odor compounds)

37. CH=CH-CH-CH=CH O-O-H Bonds begin to break These reactions are catalysed by transition metal ions

38. CH=CH-CH..CH=CH O..O-H Return to propagation Bonds are broken, electrons pair up to form a carbon-oxygen double bond

39. CH=CH-CH O These aldehydes are the source of the rancid smell in lipid oxidation. The alkoxy radicals (R-CHO ) also give ketones, alcohols and supply of free radicals

40. Termination when free radicals react with each other. Testing for rancidity smell (too late) quantification of total carbonyl content reaction with 2,4 - dinitrophenylhydrazine (coloured product) determination of hydroperoxide content with I 2 (titration) UV spectrum of conjugated dienes.

41. Cooking oils With high heat final stage of oxidation is polymerization. discarded cooking oils are ca 25% polymerized Are lipid oxidation products toxic to humans? Bulk quantities of oxidized fats fed to animals Vitamin E deficiency (used up as anti-oxidant) Carcinogenic? Some are mutagenic but little evidence for cancer in humans Http:

42. Rancidity and shelf life Include anti-oxidants to increase shelf life Butylated hydroxyanisole Butylated hydroxytoluene n-Propyl Gallate Vitamin E

43. Rancidity and shelf life Minimize transition metal content Peroxidation of blood lipids and CHD Antioxidant vitamins (A,E and C) reduce peroxidation reduce CHD eat more fruit and Veg.

44. Triglycerides n Major component of Fats/oils n In nature, triglycerides are formed from glycerol and three molecules of fatty acids. n The 3 fatty acids can be the same (i.e. R=R 1 =R 2 ) or different ( R ≠ R 1 ≠ R 2 ).

45. Tripalmitin, a saturated triglyceride. Three straight hydrocarbon chains derived from palmitic acid. Compare the shape of the triglyceride to the fatty acid components. The triglycerides are named with a code showing the 1,2 and 3 substituents Tripalmitin is PPP

46. Polyunsaturated triglyceride. The ‘kinks’ in the hydrocarbon chains are due to the cis-C=C double bonds present in the fatty acids (stearic, oleic and linolenic acids) making up the triglyceride. Code : SOL NB. SOL and SLO are different and there are many possible isomers. Natural fats are all mixtures of triglycerides Eg. Lard consists of >35 triglycerides

47. Physical properties of fats Depend on their constituent triglycerides Lard melts over 30 degree range (many components) Cocoa butter melts over a few degrees! (few components with similar MP’s) Triglycerides are polymorphic crystallize out in different forms 3 principal forms

48. Eg. Tripalmitin has  form MP = 44ºC  form MP = 56ºC  ’ form MP = 66ºC rapid cooling produces the less stable lowest melting point, solid  form Slow re-warming produces solid  ’ form. Repetition produces most stable solid  form Each form has unique IR spectrum X-ray crystal pattern

49. http://www.cals.wisc.edu/media/news/01_97/milkfat_chocolate.html Chocolate: Cocoa butter has 6 polymorphic states. MP 17.3 - 36.4ºC Polymorph with MP 33.8 ºC has desired properties but is not the most stable form Chocolate making skill involves crystallization of the correct polymorph by tempering Faulty chocolate has crystals of the most stable form embedded. This “bloom” can also appear on old chocolate Milk fat is included as a bloom inhibitor

51. A Digression - Why do we eat and drink Chocolate "Theobroma Cacao" - "food of the gods.” flavour : balance of bitter/sweet Dark depends on cocoa bean blend Milk depends on beans + sugar + dairy 380 flavour components found Eg. vanillin 2-phenyl-4-methyl-pent-2-enal

52. Why do we eat and drink Chocolate cntd. effect: caffeine, theobromine stimulant alkaloids - stimulant alkaloids natural cannabinoids Anandamide. N-oleoylethanolamine and N- lineoeoylethanolamine - natural cannabinoids

53. Why do we eat and drink Chocolate cntd: Texture: physical chemistry fat crystallized in a controlled fashion melting point at mouth temperature Aroma: aromatic oils - benzoic esters, vanillin Aphrodisiac?Aphrodisiac? http://www.choclat.com/perfume.htm Energy:Energy: sugars ( carbohydrates) protein fat

54. Why do we eat and drink Chocolate cntd: Vitamins: Biotin dermatitis if lacking in biotin Minerals: Minerals: calcium, phosphorus... Trace elements Trace elements: Iron,Selenium ++

55. Polar lipids eg.Phospholipids Important in biological function Phosphate group gives polarity Constituent of some food foods Polar lipids have the ability to stabilize emulsions see later lectures

56. Cholesterol esterified in blood non esterified in membranes and egg yolk

57. Cholesterol: 93% within cells (brain is 33% cholesterol) structural support biochemical reactions precursor of vitamin D, sex hormones 7% in blood insoluble in water solubilized with phospholipid protein coat lipoprotein - HDL LDL (cholesterol carrier) LDL carries cholesterol into cell <LDL and you have problems

58. Analysis of lipids Near IR spectroscopy for total lipids Fatty Acids Addition of halogens to double bonds Iodine number to quantify UFA Derivatization to methylated volatile esters GC Deterioration of fats measurement of carbonyl content reaction with 2,4 dinitrophenylhydrazine

59. Analysis of lipids measurement of hydroperoxide content reaction with iodine Triglycerides Thin layer chromatography silica gel impregnated with silver nitrate Enzyme analysis of purified triglycerides

60. The company line: http://www.olean.com/indepth/indepth.shtml not digested or absorbed by the body not metabolized by microorganisms in the gut. Adds no fat or calories. Olestra - fat substitute triglyceride sucrose with six to eight fatty acids attached Olestra

61. FDA approved 1996 Olean used initially to replace up to 100% of the added fat used in making fried or extruded snacks, such as potato, corn and tortilla chips, cheese puffs, cheese curls, and savory crackers. Some reports of stomach cramps, discomfort etc The opposition line: http://www.cspinet.org/olestra/pbg.html

62. http://www.ag.uiuc.edu/~food-lab/nat/mainnat.html Chemical and nutritional content of foods Check out