Fats and Oils Flashcards
- Loosely defined term for substances of biological origin that are soluble in nonpolar solvents
- Consist of saponifiable lipids (such as glycerides), phospholipids, and nonsaponifiable lipids (steroids)
Lipid IUPAC Definition
- A statement of the number of grams of total fat in a serving defined as total lipid fatty acids and expressed as triglycerides
- If serving contains less than 0.5 g, the content shall be expressed as 0
Total Fat FDA Definition
Function of lipids in diet
- Energy
- Flavor and texture
- Flakiness and tenderness
- Emulsifier
- Transfer heat during cooking
- Satiety
State of matter of fats at room temperature
solid
State of matter of oils at room temperature
liquid
Three types of glycerides
mono, di, and tri-glycerides
Function of monoglycerides
emulsifier
Function of Diglycerides
emulsifier
Characteristic of Triglyceride
most abundant in foods
The acid-catalyzed reaction of a carboxylic acid with an alcohol to form an ester
Esterification
A triglyceride that contains three identical fatty acids
Simple triglyceride
- A triglyceride that contains two or three different fatty acids
- Exist in a stair-step (chair) or tuning-fork conformation to overcome space limitations
Mixed triglyceride
Contains
1. two hydrophobic fatty acids esterified to glycerol
2. hydrophilic polar group with phosphoric acid/group and glycerol
3. nitrogen containing group in the position of third fatty acid position
Phospholipid
- Most common phosphate lipid
- Found in nearly every living cell
- Promotes stable formation of oil-in-water and water-in-oil emulsions
- Can be found in egg yolk and soybean
- both liquid and powder form
Lecithin
The percentage of acetone-insoluble material
AI
The relative composition of the water-loving (polar) and fat-loving (non-polar) elements
HLB (Hydrophilic/lipophilic balance)
AI of lecithin
62-64%
HLB of lecithin
2-4
- Contain a steroid nucleus = 8-carbon side chain and an alcohol group
- nonpolar lipids all have three 6-C rings and a 5C ring
- Round in shape
Sterols
Animal Sterols
cholesterol
Plant Sterols
Sitosterol and stigmasterol
- important minor components of most vegetable oils
- animal fat contains little/none of this component
- antioxidant, help prevent oxidative rancidity
- sources of vitamin E
- partially removed by heat of processing and may be added after processing to improve oxidative stability of oils
Tocopherols
- ADEK are soluble in fat
- added to foods to increase nutritive value
Vitamins
- Carotenoids and chlorophylls
- May be removed by bleaching during processing
Pigments
Long hydrocarbon chains with a methyl group at one end and a carboxylic group at the other
Fatty Acids
- The smallest fatty acid, with four carbon atoms
- found in butter (NOT lard or tallow)
butyric acid (butyrate)
- Fatty acids that contain single carbon-to-carbon bonds and have the general formula CH3(CH2)nCOOH
- Linear shape
- Appear solid at room temperature
- high melting point
- strong interactions between chains
- ex. butter, milk, animal products
Saturated Fatty Acids
- Fatty acids that contain one or more double bonds
- liquid at room temperature
- have low melting points
- Monounsaturated and polysaturated
- few interactions between chains
- non-linear shape
- ex. vegetable oils
Unsaturated fatty acids
- Hydrogen atoms attached to carbon atoms of the double bond are located on the same side of the double bond
- Causes a kink in the chain (42 degree)
- Almost all naturally occurring fats and oils that are used in food exist in cis configuration
Cis configuration
- The hydrogen atoms are located on opposite sides of the double bond, across from one another
- higher melting points
Trans configuration
- Naturally occurring trans-Fatty acid found in small amounts in the fat of ruminants and dairy products (milk, butter, yogurt)
Vaccenic acid [11-octadecenoic acid]
Effect of trans fats on the body
Increase LDL cholesterol
Decrease HDL cholesterol
Formation of Trans fatty acid
During hydrogenation of oils, a conversion of some double bonds to trans configuration
Trans fat labeling rules
food manufacturers may only be required to list trans fats if they total more than 0.5 g/serving
- Fats that have the same number of carbons, hydrogens, and oxygens
- Form different arrangements that create different chemical and physical properties
Isomer fatty acids
Example of Geometric > Cis/Trans Isomerism
Oleic Acid (cis) vs Elaidic Acid (trans)
** produced during hydrogenation
Example of Positional Isomerism
C9,12,15 in alpha linolenic acid vs C6,9,12 in gamma linolenic acid
** produced during interesterification/rearrangement
Nomenclature of Fatty Acids
- Common/Trivial Name
- Systemic/Geneva Name
- Omega System
- Two numbers
- Name describes the structure of the fatty acid to which it belongs
-Ex: octadecanoic acid
18 carbon = “octadec”
no double bonds = “anoic”
acid group = “acid”
-Ex: cis, 9-octadecenoic acid
18 carbon = “octadec”
1 double bond @ C9 = “9-“ and + “enoic”
cis double bond = “cis”
acid group = “acid”
Systematic/Geneva Naming System
- Classifies fatty acid according to the position of the first double bond, counting from methyl end of the molecule
- used for unsaturated fatty acids
- body lengthens fatty acid chains by adding carbons at the acid chain of the chain
Omega Naming system
Naming system in which:
- first number signifies the number of carbon atoms in the chain
- second number indicates the number of double bonds present
2 Number naming system
Omega-6 Fatty acid
Linoleic Acid
linoleic acid with 2 added carbon atoms
arachidonic acid
Omega-3 Fatty acid
linolenic acid
linolenic acid with 2 added carbon atoms
eicosapentaenoic acid (EPA)
EPA with 2 added carbon atoms
docosahexaenoic acid (DHA)
Omega Naming System
Ex. Linolenic Acid (18:2w6) - what do the numbers mean?
18 carbon fatty acid
2 double bonds
Double bond closest to the acid end of the methyl end
- when a liquid fat is cooled, molecular movement slows down as energy is removed, and molecules are attracted to each other by van der waals forces
- forces are weak and of minor significance in small molecules
- their effect is cumulative, and in large/long-chain molecules, total attractive force is appreciable
- Fat molecules can align and bond
Crystal formation of fats and oils
Crystal formation properties of symmetrical molecules
- easily form crystals
- less energy needs to be removed before crystallization
- high melting point
- large crystal size
Crystal formation properties of asymmetrical/kinked molecules
- less easily form crystals
- more energy needs to removed before crystallization
- low melting point
- small crystal size
Process of Polymorphism
- Fats can exist in different
- smallest and least stable crystals = alpha crystals, formed if fats are chilled rapidly
- alpha crystals of most fats are unstable —> readily change to beta prime crystals (1 micrometer long)
- Beta prime —-> intermediate crystal form (3-5 micrometers)
- intermediate crystal —> coarse beta crystals (25-100 micrometers) (highest melting point)
Properties of Alpha Triacylglycerol Polymorphs
- obtained after rapid cooling of liquid fat
- Thermodynamically most unstable
- Lowest melting point
- Most loosely packed
Properties of Beta Prime Triacylglycerol Polymorphs
-Obtained after slow cooling of liquid fat
- Polymorphic transformation of the alpha form
- Thermodynamically unstable
- intermediate melting point
- more closely packed
Properties of Beta Triacylglycerol Polymorph
- Obtained after very slow cooling of liquid fat
- Polymorphic transformation of the beta- prime form
- most stable form
- most closely packed
Fats with smaller crystals
- have more crystals
- have much greater total crystal surface area
- harder fats
- smoother and finer texture
- appear less oily because oil is present as a fine film surrounding the crystals
Fats with larger crystals
- have few crystals
- less total crystal surface area than a fat with smaller crystals
- softer fats
- rougher, coarser texture
- more oily appearance
Techniques to form small crystals
- rapid cooling
-agitation - heterogeneous fat
An index of the force of attraction between molecules
melting point
Fats with lower melting points and broader melting range
mixture of several triglycerides
melting range is dependent on the fatty acid content
Effect of chain length on melting point
- Long-chain fatty acids have a higher melting point than short-chain fatty acids
—-> because there is more potential for attraction between long
Effect of double bonds on melting point
- as the number of double bonds increases, the melting point decreases
- because of kinks make molecules hard to attract to each other
Effect of isomeric configuration on melting points
- cis isomer has a lower melting point
- because of the kink it forms
Typical DSC Curve of an Edible Fat
- Initial deflection proportional to the heat capacity of the sample
- part of the DSC curve with no thermic effects/baseline
- Melting peak
- Onset of oxidation in air
Polyunsaturated Fats
Source: Plants
State at room temperature: liquid
Monounsaturated Fats
Source: Plants
State at room temp: liquid
- Associated with a decrease in serum cholesterol + decreased risk of coronary heart disease
Saturated Fats
Source: Animals
State at room temp: solid
- implicated in greater rise in serum cholesterol than that produced by intake of dietary cholesterol
Composition of Animal Fat
- typically have 18 carbons in fatty acid chain
- majority is saturated
- may decline in flavor of vegetable oil
- rendered from hogs
- 43% saturated fatty acids
Lard
- rendered from cattle
- 48% saturated fatty acids
Tallow
- Oils derived from plants grown in tropical areas of the world are referred to as tropical oil
- high in saturated fat content and contain a significant amount of short-chain fatty acids
- ex. Cocoa butter, coconut oil, palm oil, palm kernel oil
Tropical Oils
Conventional Production and processing methods
cross-breeding and selection
- developed low-linolenic soybean oil with 2.5-3% linolenic content
—–> increased stability and protects against rancidity
Unconventional Production and processing methods
gene modification
- produces a more stable oil that does not require hydrogenation
- Oils that have undergone the process of removing odors by heat and vacuum or by adsorption onto charcoal
Deodorized oils
- solid, usable fat derived from animal fat after it is heated, freed from connective tissue, and then cooled
rendered fat
- moldable because it contains both liquid oil and solid crystals of triglycerides
- two-phase system containing solid fat crystals, surrounded by liquid oil: liquid phase acts as a lubricant, enabling the solid crystals to slide past one another —> conferring moldability to the fat
- consistency depends on the ratio of solid to liquid triglycerides
Plastic Fats
If plastic fats have more liquid triglycerides:
the softer the fat will be
If plastic fats have more solid triglycerides
the harder the fat will be
Plastic fat should be plastic over _____ temperature range
wide
- so that creaming can be carried out at different (high/low) temperatures
- obtained by commercial modification, including processes of hydrogenation and interesterification
Polymorphism preferred by creamed fats
Beta prime form
ex. shortened and rearranged lard
Plasticity of butter
- narrow plastic range
- not a good choice for fat that needs to be creamed
- the process of adding hydrogen to unsaturated fatty acids to reduce the number of double bonds
- occurs when hydrogen gas is reacted with oil under controlled conditions of temperature and pressure and in the presence of a catalyst
- as reaction progresses, there is a gradual production of trans-fatty acids, which increases the melting point of the fat/oil
- oil becomes more solid and more stable in storage
- to convert liquid oils to semisolid/plastic fats
- to increase the thermal and oxidative stability of the fat, and thus the shelf life
- if the reaction is taken to completion, saturated fat is obtained
Hydrogenation
- provides an intermediate degree of solidification, reducing the number of double bonds, but not eliminating all double bonds
Partial Hydrogenation
FDA Decision on Hydrogenation
- Partially hydrogenated oils are NOT GRAS (not allowed after June 18, 2018)
- 2020: fully hydrogenated rapeseed oil is safe for sparing use in food products
- aka rearrangement
- causes the fatty acids to migrate and recombine with glycerol in a more random manner
- forms new glycerides
- increases the heterogeneity of the fat
- doesn’t change the degree of unsaturation
- doesn’t change the isomeric state of the fatty acids
- the exchanging reaction of two acyl groups between two esters
- reversible reaction
- requires a catalyst to speed up reaction to equilibration
- generally used to alter the melting profile of fats, crystalline characteristics, solid fat content, and plasticity
Interesterification
Natural lard before interesterification
- relatively homogeneous fat
- narrow plastic range: too firm to be used straight from fridge vs too soft at near room temp
- contains coarse beta-crystals (large crystals)
- One or two fatty acids in a triglyceride are replaced by acetic acid (CH3COOH)
- Lowers the melting point of the fat because the molecules do not pack together as readily
- enables the fat to form stable alpha crystals
- used as edible lubricants and coating agents/films
Acetylation
Lard after interesterification
- increases heterogeneity
- enables lard to form stable beta prime crystals (more stable, smaller)
- increases the temperature range over which lard is plastic and workable
- may be applied as a shortening product
- oil that has been pretreated
- large, high melting-point triglyceride crystals in oil are subject to crystallization at refrigeration temperatures
- oil is refrigerated and subsequently filtered to remove large undesirable crystals
- used in salad dressing
winterization
- ex. when chocolate fat absorbs the odor of smoke in a candy store environment
- ex. when soap is packaged in the same grocery bag at the supermarket
- ex. butter readily absorbs fridge odors
deterioration of fats a la absorbing odors
- produces a disagreeable odor and flavor in fatty substances
- 2 types: hydrolytic and oxidative
Rancidity
- when triglycerides react with water and free all three of their fatty acids from glycerol
- reaction catalyzed by heat/enzymes (lipases)
Hydrolytic Rancidity
How to prevent hydrolytic rancidity
- Store fat in cold place
- Inactivate the lipase
- Predominant type of rancidity
- more double bonds in the unsaturated FA, the more subject to this type of rancidity
- promoted by heat, light, certain metals, and enzymes (lipoxygenases)
Oxidative Rancidity/Autoxidation
Initiation Stage of Oxidative Rancidity
- Formation of a free radical
- hydrogen on a carbon atom adjacent to one carrying a double bond is displaced to give a free radical
- free radicals that form are unstable and very reactive
Propagation Stage of Oxidative Rancidity
- oxidation of free radical to yield activated peroxide
- displaces hydrogen from another unsat FA –> forms another free radical
- liberated Hydrogen unites with peroxide —> hydroperoxide
- propogation of reaction
- hydroperoxides are very unstable and decompose into compounds with shorter carbon chains (ex volatile FA, aldehydes, ketones) = characteristic odor/flavor of rancid fats/oils
Termination Stage of Oxidative Rancidity
- Involves reaction of free radicals to form nonradical products
- elimination of all free radicals is the only way to halt the oxidation reaction
How to prevent autoxidation/Oxidative rancidity
- fats and oils must be stored in a cool dark environment and in a closed container (to minimize oxygen availability)
- vacuum packaging of fat-containing products controls oxygen exposure
- colored glass/wraps to control fluctuations in light intensity
- fats must be stored away from metals that could catalyze the reaction —> cooking utensils must be free of copper/iron
- lipoxygenases should be inactivated
- sequestering agents
- antioxidants
- BHA
- BHT
- TBHQ
- Tocopherols
- bind metals, preventing them from catalyzing auto-oxidation
- aka chelator
- ex. EDTA, citric acid
sequestering agents
- prevent auto-oxidation with the formation of FA free radicals
- function by donating a hydrogen atom to the double bond in a FA and preventing the oxidation of any unsaturated bond
- halt the reaction along the FA, which would leas to rancidity
- many are phenolic compounds
Antioxidants
- Waxy white solid
- effective in preventing the oxidation of animal fats, not vegetable oils
- Synthetic
BHA
- white crystalline solid
- effective in preventing the oxidation of animal fats
- synthetic
BHT
- white-to-tan colored powder that functions best in frying processes rather than baking applications
- synthetic
TBHQ
- can be added to both animal and vegetable oils
- sources of vitamin E
- naturally found in vegetable oils
Tocopherols
- include both pourable liquids and stiff solids
- hydrogenated oil
- plant, animal, or plant-animal blends of fats may be used
- function: to physically shorten platelets of protein-starch structure developed in manipulated wheat flour mixture
Shortening
- obtained by partial hydrogenation of refined oils
- pale yellow color
Margarine
Ranking of flakiness in shortening
- Lard
- Butter and margarine
- Hydrogenated fats
- Oils
Tenderness vs Flakiness
- tender: easily crushed/chewed, soft and fragile
- flakiness: contain many thin pieces/layers of cooked dough (ex. puff pastry, lard piecrusts)
Effect of solid fat on texture
Creates layers or flakes in the mixture = flakiness
Effect of liquid oil on texture
Coats flour particles more thoroughly, creating less layers = tenderness
Result of insufficient manipulation on food mixture
Poor distribution of fat throughout the food mixture
Result of excess manipulation on food mixture
Causes the fat to spread/be softened, minimizing the possibility of flakes
Effect of temperature on texture on food product
Cold shortening (solid or liquid) produce more flaky products
Room temperature shortening is less flaky
- rapid heat transfer method that achieves a higher temperature than boiling or dry heat temperature
Frying
- the temperature at which fat may be heated before continuous puffs of blue smoke coming from the surface of the fat under controlled conditions
- presence of smoke indicates that free glycerol has been further hydrolyzed to yield acrolein
smoke point
a mucous membrane irritant produced from free glycerol by heating oil to its smoke point
acrolein
Smoke point of monoglycerides and diglycerides
- hydrolyzed more easily than triglycerides
- lower smoke point
- not recommended as frying oils
- When fat exceeds the smoke point
- point at which small flames of fire begin in the oil
- lowest temperature at which a substance will give off a vapor that will flash/burn for a moment when ignited
Flash point
- the temperature at which a fire is sustained in the oil
Fire point
Changes to food during frying
- removes internal water
- allows a level of oil absorption
- thermal decomposition of oil
- unwanted orange/brown color
- more viscous/foamier
- smoke point decreases as oil is used repeatedly
- reduced quality
Examples of Carbohydrate fat replacements
- starch
- cellulose
- gums
- fiber
- dextrins
- maltodextrins
- polydextrose
- inulin
Examples of Protein fat replacements
- gelatin
- microparticulated protein
- modified whey protein concentrate
Examples of Fat fat replacements
- emulsifiers
- lipid analogs
- olestra
- sorbestrin
- salatrim
- replace 9 kcal/g with 0-4 kcal/g
- hydrocolloid materials
CHO-derived fat replacement
- long-chain polymers
- principally carbohydrates
- thicken/gel in aqueous systems
- create a creamy viscosity that mimics fat
Hydrocolloids
Examples of hydrocolloids
- hemicellulose
- Beta-glucans
- gums
- offer less than 9 kcal/g
- ex. Olestra
Fat-Derived Fat Replacements
- sucrose polyester (mostly octaester)
- synthesized by reacting six to eight fatty acids with the eight free hydroxyl groups of sucrose
- not digestible
- not absorbed
- provides no calories
- distinctive label statement is required
Olestra (Olean)
- replaces 9 kcal/g with 1-4 kcal/g
- heats and intensely blends naturally occurring food proteins (egg white and milk proteins) with water pectin, and citric acid
- remains chemically unchanged, but aggregates under controlled conditions that allow the formation of small aggregates/microparticles
Protein-derived fat replacements
kcal/g of fats
9 kcal/g
Essential PUFAs, required for human growth
linoleic and linolenic acids
Metabolic fate of essential fatty acids
- dietary triglycerides
- Digestion
- EFA
- Fatty Acyl Coa
a) energy
b) desaturation/elongation
c) esterification —-> synthesis of triacylglycerols, cholesterol esters, phospholipids
- hydrogenated form of plant sterols
- saturated 5-6 bond
- have either methyl or ehtyl group attached to the molecule
- known to reduce level of low-density lipoprotein cholesterol in the blood
stanols
Phytosterol and phytostanol role in plants
help maintain fluidity/rigidity of plant cell membranes/walls
- steroids with similar structure to cholesterol
- 5-6 bond is unsaturated
- alcohol group attached to molecule
- cholesterol-like substance that occur naturally at low levels in fruits, vegetables, nuts
Sterols
