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Similaire à Lipids in Foods: Fats and Oils Explained
Similaire à Lipids in Foods: Fats and Oils Explained (20)
Lipids in Foods: Fats and Oils Explained
- 1. Culinology 101 Lipids in Foods
- 2. Fats and Oils • Concentrated source of energy − Fats: 9 kcal/g − Carbohydrates and proteins: 4 kcal/g • Contribute to flavor and mouth feel • Provide heat exchange medium for cooking • Lubricant
- 3. Fats and oils • Plant origin • Animal origin − Soybean − Lard − Peanut − Butter − Corn − Ghee − Olive − Fish oil − Palm − Sunflower − Safflower − Coconut − Grapeseed − Sesame − Canola
- 4. Overview • Chemistry of fats and oils • Manufacturing/processing • Methods of analysis • Trans fat − History − Which foods have it − Potential health impact − Regulations − Solutions
- 5. Chemistry of Fats and Oils
- 6. Fatty acids • Chain of carbon atoms • Acid group at one end (COOH) • Three fatty acids (FA) form the arms of triglyceride • Defines properties of the fat
- 7. Triglycerides • Three FA are joined to glycerol backbone − Ester linkage
- 8. Minor components of fats and oils • Mono & Diglycerides − Found in crude and processed oils − Function as emulsifiers • Phosphatides − Lecithin − Can darken oil under high heat (frying) • Color bodies − Chlorophyll − Carotenoids (xanthophyll, carotene) • Sterols − Similar in structure to cholesterol • Tocols − Tocopherols, tocotrienols − Natural antioxidants − Can form potent red oxidation compounds
- 9. Saturated fatty acids • No double bonds between carbons • Each carbon is attached to two hydrogens and is, therefore, saturated with hydrogen. • Tend to be solid at room temperature Unsaturated fatty acids • At least one carbon-carbon double bond • Tend to be liquid or very soft at room temperature due to lower melting point.
- 10. Saturated vs. Unsaturated FAs The difference is carbon to carbon double bonds (unsaturated).
- 11. Unsaturated FAs • More chemically reactive than saturated FAs − i.e., more likely to react with oxygen at points of unsaturation (C=C) • Monosaturated − Only 1 double bond • Polyunsaturated − More than 1 double bond − As # of double bonds increases • Chemical reactivity increases • Melting point gets lower − Excellent source: vegetable oils
- 12. Typical FA composition of common oils
- 13. Geometric isomers Hydrogen atoms are on the opposite side of the double bond.
- 14. Cis v. Trans Fat • Cis is the natural form in edible oils • Small amount of trans naturally occurs in fat from ruminants (cows, sheep, etc.) • Artificial trans fats are formed during hydrogenation process − Improves stability/functionality of fat − Potential health implications
- 15. Degradation reactions • Oxidation • Hydrolysis • Polymerization
- 16. Degradation - Oxidation • Autoxidation − Exposure to air at room temperature − First step: peroxide formation (no sensory change) − Second step: start to get sensory changes • Peroxides degrade lipid into secondary and tertiary components − Act as pro-oxidants − Hydrocarbons, ketones, epoxides, short chain acids, aldehydes, alcohols • Iron, copper, and zinc can promote autoxidation − Citric acid can chelate metals − Retard or inhibit oxidation • Oxidation at higher temperatures may result in breakdown that follows a different route − Lipid oxidation is complex. − Many oxidation products are possible.
- 17. Degradation - Oxidation • Usually affects polunsaturated fatty acids (PUFAs) • Carbon double bond weakens H- bonds attached to neighboring carbon • Oxygen spontaneously reacts with exposed H Fatty acid Hydroperoxide Rancid odor molecules
- 18. Relative Oxidation Rates of Fatty Acids at 20°C Stearic Saturated 1 C18:0 Oleic Monounsaturated 10 C18:1 Linoleic Polyunsaturated 120 C18:2 Linolenic Polyunsaturated 250 C18:3 Source: Bailey’s Industrial Oil & Fat Products (1964) p. 74
- 19. Antioxidants • Natural antioxidants scavenge oxygen and chelate metals in living things. • Processing also remove naturally occurring compounds that prevent oxidation. • RBD oils have very little odor and flavor. • Antioxidants are reintegrated to improve product stability (prevent rancidity). − Donates H to fatty acid radicals to stabilize
- 20. Antioxidants • Natural − Vitamin E (α-tocopherol) − Vitamin C (ascorbic acid) − Citric acid • Synthetic − BHA (butylated hydroxyanisole) − BHT (butylated hydroxytoluene) − EDTA (ethylenediaminetetraacetic acid)
- 21. Antioxidants • Metal chelators − Citric acid − EDTA • Radical scavengers − Vitamin E − BHA, BHT • Store oils tightly closed away from light and heat.
- 22. Degradation - Hydrolysis • Heat + Water + Triglyceride = Release of Free Fatty Acids (FFA) • Lowers smoke-point − Temperature at which contaminants are driven out as smoke but lipid does not ignite − Overheated can produce acrolein • Overheated glycerol • Odorous and irritating fumes
- 23. Degradation - Hydrolysis • Development of off-flavors and off- odors (hydrolytic rancidity) − High lauric acid (coconut, palm kernel oil) → soapy flavors − Can occur more slowly at room temperature (sour butter) − Naturally occurring lipase • 3M Shortening Monitoring strips test for FFA in fryers
- 24. Degradation - Polymerization • Usually results from extreme heat (frying) − Polymers form at smoke point − Pyrolysis leads to development of undesirable properties • Bonding of FAs into long chains or cross- linked/branched structures − Carbon to carbon bonds − Oxygen bridges between molecules • Associated with the late stages of oxidation − FFAs can link to form large molecules
- 25. Degradation - Polymerization • Lipids lose stability resulting in: − Darkening of oil − Strong bitter flavor − Gum formation • Hard, varnish-like deposits on equipment − Increase in viscosity − Lowers heat-transfer efficiency − Adverse effect on food quality
- 26. Processing of Fats and Oils
- 27. Basic processes include: • Extraction • Refining • Bleaching • Hydrogenation • Deodorization • Plasticizing
- 28. Processing - Extraction • Pressing/expelling − Seeds may be slightly cooked and then squeezed to release oil − Oil may be clarified by filtration or centrifugation − Some consumers prefer as a chemical-free alternative • Solvent extraction − Greater yield than pressing − Oil is separated from cracked oil seeds − Nontoxic solvent (hexane) seeps into seed to dissolve oils − Solvent is distilled leaving behind oil • Combination of pressing followed by solvent extraction
- 29. Processing - Refining • Following extraction, impurities are removed from crude fat or oil − Improve color and flavor • Aldehydes • FFAs • Gums • Lecithin • Ketones • Soaps − Improve safety • Aflatoxins in peanut oil • Gossypol in cottonseed oil
- 30. Processing - Refining • Caustic soda (lye or NaOH) added to crude oil to remove FFAs • Alkali is stirred with fat to produce “foots”, solid masses that settles out of solution (precipitate) • Solids are utilized in soapmaking
- 31. Processing - Bleaching • Refined oil is bleached (decolorized) with clay and activated charcoal. − Diatomaceous earth − Acid activated clays • Color compounds adsorb onto clay. − Chlorophylls − Carotenoids • Peroxides, pro-oxidants, gums, and soaps are also removed. • Clay is filtered from oil.
- 32. Processing - Hydrogenation • Hydrogen is added to carbon double bonds of FAs − Unsaturated fat becomes saturated • Process requires hydrogen gas, heat, pressure, catalyst (nickel) and agitation • Converts liquid fats to solid fats − Margarine − Shortening • Increases melting point • Yields trans fat • Lose some nutritional value of essential fatty acids − Linoleic (essential) becomes elaidic (nonessential) acid
- 33. Processing - Deodorization • Steam application under vacuum (sparging) • Fish oils (also safflower, soy, and canola) • Goal is to achieve: − < 0.05% FFAs − < 0.5 peroxide value (zero is desired) − Almost bland flavor and odor − < 0.05% moisture (water) • RBD: refined, bleached, deodorized
- 34. Processing – Plasticizing • Or, votation − Softening of a hard fat − Creates homogeneous crystal structure • Rate of fat crystallization is dictated by agitation, heating, and subsequent cooling − Rapid cooling = small fat crystals • Good for baking − Slow cooling = large fat crystals • Shortenings (all-purpose, cake & icing) are votated, or plasticized.
- 35. Processing – Plasticizing • Shortenings for baking − 10 to 12% nitrogen gas is injected − Soft texture with low density − Improves whiteness • Margarines and fluid shortenings (frying or pan & grill) votated without N2 Fat crystals in margarine
- 36. Other processes: • Dewaxing − Removal of natural waxes • Tempering − Determine crystalline state • Fractionation − Splits oil into components based on melting point − Same raw material can yield frying oil and shortening • Winterization − Oil is chilled and then filtered to remove crystalline solids − Salad oil • Interesterification − Rearrangement of fatty acid configuration to achieve desired properties − Conversion of lard to various types of shortenings
- 37. Methods for Analysis of Fats and Oils
- 38. Common tests for quality • Lovibond color • Oxidative stability index (OSI) • Free fatty acids (FFA) • Peroxide value (PV) • Flavor • Filterable impurities • Acid value • Moisture Karl Fischer
- 39. Quality indicators – Lovibond color • Method developed in 1860s by Joseph Lovibond • Tintometer measures visual color of oil in units of red and yellow − Red range 0-20 − Yellow range 0-70
- 40. Quality indicators – Oxidative stability index (OSI) • Automated, accelerated test − Relative stability of oils − Antioxidant effectiveness • Air bubbled through oil, captured in water, conductivity measured • Presence of oxidation/rancidity compounds
- 41. Quality indicators – Peroxide value • Measures degree of lipid oxidation • Low PV indicates little to no oxidation Quality indicators – Acid value • Quantifies hydrolytic rancidity, due to lipase activity (not due to oxidation) • Measures FFAs present in fat or oil
- 42. Common tests of physical properties • Smoke, flash, fire point − Oil smokes but does not ignite − Fitness of oil for frying • Solid fat index (SFI) − Solid to liquid ratio based on density • Solid fat content (SFC) • Cold test − Held at cool temp until cloudiness occurs − Selection of oils for mayonnaise emulsion • Capillary melting point (CMP) • Specific gravity
- 43. Common tests of physical properties • Viscosity − Resistance of liquid to flow (thinness or thickness) − Depends on molecule size and saturation − Longer chain FAs increase viscosity − Saturated fat more viscous than unsaturated fat
- 44. Common tests for chemical composition • Iodine value (IV) • Fatty acid composition (FAC) • Saponification value (SV) • Trans fatty acid (TFA) • Trace metals • Alpha monoglycerides • Chlorophyll • Phosphorous • Tocopherol
- 45. Chemical composition – Iodine value • Measures degree of saturation • High IV indicates more carbon double bonds Chemical composition – Fatty acid composition • Assesses fatty acids on percentage basis • Fatty acid “fingerprint” − FAs separated from TG − Identified by gas chromatography
- 46. Chemical composition – Trans fatty acid • Spectroscopy or chromatography • Need reliable and sensitive method to back up claims (trans fat free) Chemical composition – Saponification value • Average molecular weight of FAs • Indicator of: − Suitability of oil for food preparation vs. candle and soap making − Flavor and odor properties
- 47. Analytical specifications for RBD soybean oil Quality test Max/min AOCS method Lovibond color Max. 10Y/1.0R Cc 13b-45 Free fatty acids Max 0.05% Ca 5a-40 Peroxide value Max 1.0 Cd 8b-90 Oxidative stability index Min. 8 h Cd 12b-92 Flavor 9 min. Cg 2-83 AOCS: American Oil Chemists’ Society
- 48. Trans Fat
- 49. Trans fat • Once a scientific oddity, trans fat is now mainstream. “A hidden health hazard flushed out of hiding…” USA Today “The stealth fat…it’s not labeled…and it’s bad for your heart.” Consumer Reports “Food labels must soon reveal the worst kind of fat…” USA Today “Trans fats found even in diet foods” Star Tribune
- 50. Trans fat - History • Since 1900, hydrogenated oil has been part of the human diet. • Usage levels have steadily increased since then. • Hydrogenated oils replace animal fat − No cholesterol − Reduce saturated fat intake
- 51. Trans fat - Background • Oils seeds naturally contain: − Saturated fat − Monounsaturated fat − Polyunsaturated fat − Trans fat • Hydrogenation stabilizes the oil. • Oil has improved shelf life, flavor and performance. • BUT, level of trans fat is elevated.
- 52. Trans fat - Background • Most trans fat derived from hydrogenation of edible oils. − 80% of trans fat intake is from hydrogenated oil • 20% of dietary trans fat (naturally occurring) − Meat products (animal fat) • 3-7% of beef fat • 5-8% of mutton fat − Milk products • 6-8% of milk fat 80%
- 53. Trans fat - Background • Minor sources of trans fat − Heat during processing produces some trans fat. − Cooking (especially, frying) forms small amounts of trans fat. − Account for up to 2% of trans fat in foods
- 54. Trans fat - Effect on health • May raise LDL (bad cholesterol) • Increase risk of coronary heart disease − 12.5 million Americans − Leading cause of death (500,000 annually) in U. S. • Saturated fat is major culprit − Americans consumer 4 to 5 times more saturated than trans fat − Trans fat (hydrogenated oils) and dietary cholesterol also contribute to heart disease • Encouraged to eat monounsaturated (olive, canola) and polyunsaturated (soybean, corn, sunflower) fat instead
- 55. Trans fat – Food labeling • Since Jan. 2006 − Trans fat added to Nutrition Facts labels − Sum of all unsaturated FAs with at least one carbon double bond in trans configuration − For retail commerce
- 56. Trans fat - Labeling • Claims − FDA: daily value not established − Reduced/low trans fat • Not allowed − Trans free • Not allowed • If claim is 0 g/serving, must be <0.5 g/serving − Saturated fat free • <0.5 g saturated fat/serving AND <0.5 g trans fat/serving
- 57. Trans fat and food service • Restaurants: disclose as much nutritional information as possible • Labeling is optional UNLESS making a nutritional or health claim. • If claim is made: − Only required for nutrient that is basis of claim − Establishment must comply with claim • Reference amount (free, reduced) • Serve portion size as stated − Disclosure via pamphlets, menu, banners, tray lining, table tent cards, etc.
- 58. Rules of thumb for food service • Restaurant food is exempt from nutritional labeling. − Restaurant definition: • Food is served for immediate on-site consumption • Extended to walk-away and home delivery where food is consumed immediately • In-store bakeries and delis − Food prepared primarily on premises is exempt from nutritional labeling. • Primarily processed/prepared on-site: − Food augmented in a way that alters nutritional profile − Filling, frosting, enrobing, combining/assembling − Custom prepared foods also exempt • Self serve salad bar, sliced deli meats, birthday cake Unless a claim regarding health or nutrient content is made
- 59. Trans fat ban in NYC restaurants • Dept. of Health began auditing July 2007: − Ingredient labels of fats, oils, spreads, margarines − Presence of partially hydrogenated oils − Letter of guarantee from manufacturer that trans fat content <0.5 g/serving • Violations punishable after grace period (July 1-Oct. 1, 2007) − Posted on Dept. of Health website − Fines of $200-$2,000 • Standard menu items must be clearly labeled with caloric content (chains and fast-food)
- 60. Trans fat regulations or proposals by state www.fitfrying.com
- 61. Trans fat - Zero trans alternatives • Tropical fats Food industry − Palm, plam kernel, coconut oil − Stable, readily available route − High saturated faty (55-95%) − Poor public perception • Animal fat (lard) − Low cost, stable, flavor, available − 40-55% saturated fat, cholesterol, solid − public perception, Halal and Kosher? • Non-hydrogenated vegetable oils • Selectively bred oilseed • Genetically modified oilseed
- 62. Zero trans fats – Alternative oils • High oleic sunflower oil (HOSO) − High stability during frying − Non GMO, traditionally cross-bred − High in monounsaturated fat − Clean, light flavor
- 63. Zero trans fats – Alternative oils • Palm − Versatile, inexpensive, and functional − Oil palms: Malaysia and Indonesia − Semi-solid at room temp. − High saturated fat • Palm oil − From fruit, red color • Palm kernel oil − From palm fruit seed
- 64. Additional topics Salmon with white chocolate sauce
- 65. Fat bloom in chocolate • Looks like mold spoilage − Fat crystals • Fat molecules migrate to surface − Storage temperature too high − Temperature change too rapid • How to prevent − Tempering allows seed crystals to dictate overall fat crystal structure − Store properly − Antibloom treatment • TGs with oleic and behenic acids • Mineral supplement • Specialty milk products
- 66. Omega-3 fatty acids • Location of first carbon double bond − Essential (necessary and must be eaten) • Health benefits − Reduce risk of cardiovascular disease • Lowers LDL, blood triglycerides • Increases HDL • Omega-3 − Coldwater fish (salmon, tuna, halibut) − Nut oils − Soybean oil
- 67. Emulsions • Colloidal dispersion of non-miscible liquids (oil and water) − Opaque: dispersed particles scatter light − Unstable food systems − Flocculation desired over coalescence • Oil in water emulsion − Homogenized milk, cream, mayonnaise, hot dogs, gravy • Water in oil emulsion − Butter (two liquid phases form a solid) • Emulsion stabilizers (ampiphilic molecules) • Gums, starches • Egg yolk (lecithin), whey proteins
- 68. Fat substitutes • General properties − Low caloric value (non-digestible, on-absorbable) − Acceptable to excellent sensory properties • Olestra (Olean, 0 kcal/g) − FAs attached to sucrose backbone − Savory snacks − Absorbs vitamins A, D, E, and K • Esterified propoxylated glycerols (EPGs) − Derived from fat (propylene oxide) − Icings and salad dressings, frying oil • Not derived from fat − Oatrim® (oat bran/flour, 1 kcal/g) − Simplesse® (microparticulated egg white and whey protein; 1.2 kcal/g)