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• list the role(s) of visible and invisible fat in foods.
• diagram the structure of fatty acids, glycerol and triglycerides.
• explain the relationship of structure to melting point, crystallinity, and plasticity of fat.
• summarize various processes used in producing fats for the consumer.
• list types of rancidity and how it is accelerated and prevented and relates to food quality.
• discuss factors and process of hydrolytic and oxidative rancidity.
• identify food emulsions.
• describe the particle structure of lipid emulsion.
• list factors that affect emulsion formation and stability.
• produce a temporary, semi-permanent, and permanent emulsion.

The major fat structures within the fats and oils, are dominantly triglycerides; however, the other categories of types of lipids are important. Certainly, the monoglycerides and diglycerides are well-established emulsifiers in a variety of food products. Other lipids importance may be more subtle. For example, the lipoprotein complex in gluten has a major role in the elasticity and strength of gluten; however, it is generally not extensively discussed as gliadin and glutenin are so important. The role of the lipid in the plastid of green and yellow vegetables is rarely mentioned; however, it functions to solubilize the pigment. The sterols in the wax of shiny apples is another compound lipids. There are other examples which are mentioned throughout this site and elsewhere.

Much of the fat used in food preparation is hidden. Did you eat any fat or oil today? What fat is represented in each of these images?

The use of fat in foods continues to expand as they become more healthy and as the industry learns to modify the natural product. The role of fat in a food product can be as varied as the product itself. In shortened cake it serves to tenderize, incorporate air, and possibly add flavor. In salad dressing it is part of the structure, the small droplets in a second liquid. These roles and other roles can be listed as:

textural qualities

emulsions

shortening or tenderizers

medium for transferring heat

aeration and leavening

spray oils

These uses are impacted by the functionality of the particular fat or oil. These functionality's or roles are: gives satiety; heat transfer; flavor; texture: body, mouthfeel; tenderizes: gluten, starch; decreases temperature shock in frozen desserts; "solubilizes" flavors and colors; dispersal; foaming; incorporation of air.

The differing roles of fat and oil can be seen in the following recipes:

Recipe	Role or Purpose
Mayonnaise	The oil primarily serves the function of the dispersing phase.
Frosting	The butter fat to allow the creation of a foam.

There are several classes of lipids. In food preparation, we are most concerned with simple lipids. These are the triglyceride lipids, the major component of fat, butter, shortening, oil, etc.

They have a simple formulas composed of glycerol and a variety of fatty acids. Fatty acids have a basic formula consisting of hydrocarbons and carboxyl group. The "R" group refers to the many possibilities.

The composition of the "R" group makes the fatty acid either saturated, stearic fatty acid, or unsaturated, oleic fatty acid. The hydrogen ions around the double bond can be either on opposite sides (trans) or on the same side (cis).

The image below gives an example of glycerol plus one fatty acid to form a monoglyceride. Water is split off from the hydroxyl group of the glycerol molecule and the carboxyl group of the fatty acid.

In order to have crystalline fat, one must have the fat be a solid. For that reason, the following melting points are pertinent. Plasticity occurs due to a mixture of solid fat crystals and liquid oil.

Fatty Acids	# of Carbon Atoms	Formula	Melting Point	Solubility	References
Saturated Fatty Acids
Butyric	4		-7.9C
Caproic	4		-3.9C
Caprylic	8		16.3
Capric	10		31.3
Lauric	12		44.0
Myristic	14		54.4
Palmitic	16		62.8
Stearic	18		69.6
Arachidic	20		75.4
Behenic	22		80.0
Lignoceric	24		84.2
Unsaturated Fatty acids
Palmitoleic	16		-0.5 to 0.5
Oleic	18		13
Linoleic	18		-5 to -12
Linolenic	18		-14.5
Arachidonic	20		-49.5

In review each of the above fatty acids and the melting point, a number of generalizations can be made. It is apparent that the following factors affect the melting point.

longer chain increases melting point

number of double bonds (more double bonds the lower the melting point)

cis conformation (lower melting point than trans)

arrangement on the glycerol molecules affect crystallization

shorter chain or more double bonds more ability to emulsify.

It is not enough to know the characteristics of the fatty acids. Their arrangement of these fatty acids upon the glycerol backbone will make a difference. If one reviews the characteristics of different fats and oils one will note that fats differ in melting point, flash point and smoke point. That is because of the heterogeneity fatty acids and triglycerides.

Smoke, flash, and fire points of oils(C)

OIL/FAT	SMOKE	FLASH	FIRE
	Castor, Refined	200	298	335
	Corn, Crude	178	294	346
	Corn, Refined	227	326	359
	Olive, Virgin	175-199	321	361
	Soybean, Refined	.	.	.

The degree of crystallization of a triglyceride determines whether it is a solid or a liquid. The more crystalline the fat the more likely it will be a solid. There are a number of factors which will effect the crystal type and characteristics. The most important is fatty acid composition. Generally, the more saturated and/or the longer the chain length the more likely it will be a solid. The arrangement of fatty acids on the glycerol backbone will also make a difference. In addition to the solidity or melting point of each individual triglyceride, we are also concerned with the combination of triglycerides throughout the fat mixture. This impacts the plasticity and the melting point range. There are four main types of lipid crystals. Types of Lipid Crystals alpha crystals: small beta prime crystals: stable and fine intermediate crystals beta crystals: course In crystals that are polymorphic, the chemical formula is the same. They form different crystals depending upon the temperatures and rate of cooling.

Fats and oils are extracted from either plants or animals. Extraction methods vary. For example, the adipose tissue of the pig is heated, melts the fat and it is further processed. Butter is made by reversing the oil in water emulsion of cream into a water in oil emulsion. Plant extraction procedures involve a variety of different extraction methods.

Following are Processed Fats butter margarine lard hydrogenated shortening

refined oils -soybean oil -cottonseed oil -sunflower oil -peanut oil -olive oil -corn oil -canola oil -safflower oils -coconut oils -palm oil -palm-kernel oils

After removal of the plant fat from the seed, pod or grain, it is further refined as follows.

	Degumming The first step in the refining process of many oils is degumming. Oils are mixed with water to hydrate phosphatides, which are removed by centrifuging. Phosphoric or citric acid or silica gel are added to enhance the process. Degumming removes valuable emulsifiers such as lecithin. Cottonseed oils are not degummed, but degumming is necessary for such oils as soybean and canola.
	Alkali Refining The degummed oil is then treated with an alkali to remove free fatty acids, glycerol, carbohydrates, resins, metals, phosphatides and protein meal. The oil and alkali are mixed allowing free fatty acids and alkali to form a soap. The resulting soapstock is removed through centrifuging. Any residual soap is removed with hot water washings. Cottonseed oil is also refined using a process call miscella though this process oil is refined in the miscella stage prior to removal of the solvent. The oil produced using this method has higher yields and has what some consider a lighter, more desirable color.
	Bleaching Trace metals, color bodies such as chlorophyll, soaps and oxidation products are removed using bleaching clays which adsorb the impurities. Bleached oils are nearly colorless and have a peroxide value of near zero. Depending on the desired finished product, oils are then subjected to one or more processes of the following processes..
	Winterization (Fractionation) Oils such as as salad oils, or oils that are to be stored in cool places undergo a process called winterization so that they will not become coudy when chilled. The refined, deodorized oils are chilled with gentle agitation, which causes higher melting fractions to precipitate. The fraction which settles out is called stearin. Soybean oil does not require winterization, but canola, corn, cottonseed, sunflower, safflower and peanut oils do.
	Hydrogenization Treatement of fats and oils with hydrogen gas in the presence of a catalyst results in the addition of hydrogen to carbon-carbon double bond. Hydrogenation produces oil with mouth feel, stability, melting point and lubricating qualities necessary to meet the needs of many manufacturers. It is important to note that hydrogenation is a selective process that can be controlled to produce various levels of hardening.
	Deordorization Deordization is a steam distillation process carried out in a vacuum, removing volatile compounds from the oil. This may be a batch or continuous process. The end product is a bland oil with a low level of free fatty acids and a zero peroxide value. This step also removes any residual pesticides or metabolites that might be present. Some manufacturers favor the use of cottonseed oil because it can be deodorized at lower temperatures, which results in more tocopherols (natural antioxidants) being retained. Deordization produces some of the purest food products available to consumers. Few products are as thoroughly clean as refined, bleached, and deodorized oil.
	This process allows fatty acids to be rearranged or redistributed on the glycerol backbone. This is most often accomplished by catalytic methods at low temperatures. The oil is heated, agitated and mixed with the catalyst at 90C. There are enzymatic systems which may be used for interesterification. It does not change the degree of saturation or isomeric state of the fatty acids, but improves the functional properties of the oil.

Excerpted with permission from The National Cottonseed Products Association Guide to Edible Oils.

When discussing the stability of a fat or oil, generally, the emphasis is on oxidation or hydrolysis of the triglyceride molecule. However, if one uses the definition that rancidity is the development of any disagreeable flavor or odor, one might list the following forms of rancidity.

absorption of odors

action of microorganisms

action of enzymes (hydrolytic rancidity)

atmospheric oxidation

-common oxidative rancidity

-flavor reversion

-enzymatic oxidations

-oxidized flavors in milk and milk products

An understanding of the two major forms of rancidity, hydrolytic and oxidative, is critical. Of the two, oxidative rancidity is considerably more complex. There are a number of additives which not only impact rancidity but also the flavor and color of the fat or oil. Some of these are listed:

Deterioration of fat due to hydrolysis occurs primarily in dairy products. Hydrolytic rancidity is hydrolysis of triglyceride into its component fatty acids and glycerol. The reason it causes an odor and flavor deterioration is because we taste individual fatty acids more than the total triglyeride. Since lipase naturally occurs in dairy products, it happens that short chain fatty acids are a major component. These short chain fatty acids like butyric acid are particularly able to be perceived by the tongue sensory buds.

Since hydrolytic rancidity occurs naturally, the best defense is to keep butter in the refrigerator.

Oxidative Rancidity

If one has an oil or fat with some degree of unsaturation, it is unavoidable that oxidation will take place. It must be minimized through care taken in processing and care taken after purchase. During processing, one may refine, bleach, hydrogenate, deodorize, and give additives [antioxidants] to minimize oxidation. There are mechanisms for inhibiting lipid oxidation. After processing, the consumer wants to minimize the availability of oxygen and decrease the speed of the reaction. This may be done easily by keeping covered and refrigerating.

Before processing even begins the selection of the fat is a critial factor. As noted in table of the relative reactivity of common fats and oils, the greater the number of double bonds. If one selects safflower versus olive oil, the safflower oil, higher in unsaturation, is less stable. Of course, other factors enter into the selection of a particular oil.

Erickson, M.D. and N. Frey. 1994. Property-enhanced oils in food applications. Food Technology 48:63

FOUR PROCESSING MECHANISMS FOR INHIBITING LIPID OXIDATION Hydrogen donation by the antioxidant Electron donation by the antioxidant Addition of lipid to aromatic ring of the antioxidant Formation of a complex between the lipid and the aromatic ring of the antioxidant

Just what is the oxidation reaction. It has been generally shown as follows: Erickson diagramed the many factors influencing lipid oxidation as well. The general formula may be indicated as shown on the left.

Both these figures gives some idea of the reaction and factors influencing.

Antioxidants Used To Decrease Oxidative Rancidity of Fat or Oil

butylated hydroxyanisole (BHA)	improves oxidative stability, antioxidants
butylated hydroxytoluene (BHT)	improves oxidative stability, antioxidants
carotene (Pro-Vitamin A)	enhances color of finished foods; color additive
citric acid	inhibit metal-catalized oxidation and production of dark colors; metal chelating agents.
diacetyl	provides buttery odor and flavor
lecithin	water scavenger to prevent lipolytic rancidity; emulsifier
methyl silicone	inhibits oxidation; antifoam agent
phosphoric acid	inhibit metal-catalyzed oxidation and production of dark colors; metal chelating agent
tertiary butylhydroquinone (TBHQ)	improves oxidative stability, antioxidants
tocopherols	natural antioxidant, improves oxidative stability

antioxidant
butyric acid
cis configuration
diglyceride
fatty acid
glycerol
humectant
hydrolysis
hydrogenation
hydrolytic rancidity
lipids
melting point
mixed triglyceride
monoglyceride
organic acid
oxidative rancidity
phospholipid
plasticity
polymers
polymorphism
polyunsaturated fatty acid
rancidity
saturated fatty acid
simple triglyceride
smoke point
sorbitol
trans configuration
triglycerides
unsaturated fatty acid
visible fat
winterization

What contributions do fats make in foods? Where do we use fat in foods?

Which do you think is the major role of the fat or oil: a tenderizer, flavor contributor, leavener, structure - in the following products?

Mastery of the following reaction is not in itself of critical importance; however, an understanding of it does serve to explain certain phenomena which affect food quality.

Show the synthesis and hydrolysis of a triglyceride relates related to hydrolytic rancidity.

Why would it make a difference in the following fat if they are polymorphic?

Crystal Types

_____________Palmitic
|
|_____________Oleic
|
|_____________Palmitic

_____________Palmitic
|
|_____________Palmitic
|
|_____________Oleic

_____________oleic
|
|_____________Palmitic
|
|_____________Palmitic

In reviewing the three possible arrangements of the fatty acids on the glycerol backbone, it becomes apparent that conformational and structural stress will impact the ability to crystallize. Remember, crystallization is the alignment of like molecules.

What determines the melting point of a fat? Of what importance is the melting point of a fat in food preparation?

Indicate the relationship of polymorphism to crystallization and possible influences on functional properties related to foods.

Discuss how the structure of triglycerides influence the crystallization of a fat.

Which of the above hypothetical fatty acids would be most susceptible to oxidation rancidity?

Which of the above unsaturated fatty acids if on a triglyceride which have the lowest melting point?

Which of the above saturated fatty acids if on a triglyceride which have the lowest melting point?

What determines the melting point of a fat? Of what importance is the melting point of a fat in food preparation?

If there were two isomers of triglycerides B, one having "hydrogen" in CIS form and the other in the TRANS form, which would likely have the higher melting point? Why?

Which of the following triglycerides (fats) would be most firm at room temperature 27C, 70F)?

tristearin (contains 18 carbon saturated fatty acids)

triolein (contains 16 carbon saturated fatty acids)

triliolein (contains 18 carbons and 2 double bonds in fatty acids)

tributyrin (contains 4 carbon saturated fatty acids)

One day some butter melted and Hillary decided to cool it slowly. What would describe this product? (Note: think of the results in comparison of contrast of the melted butter rapidly cooled).

a. CH3-CH2-CH2-COOH b. CH3-(CH2)7CH=CH(CH2)7COOH c. CH3-(CH2)16-COOH

Choose the appropriate fatty acid for the following questions.