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Stephanie Chen
Principles of Food Science Lab
24 October 2014
Properties of Lipids
Group 5
Lab Date: 16 October 2014
Introduction
Lipids are water-insoluble molecules based on the methylene group (-CH2), which makes
up acyl chains of varying lengths. There are three types of lipids found in foods. Derived lipids
are chemically and metabolically active, consisting of a long chain of 4-26 carbons with a
reactive carboxylic acid head group (-COOH). Compound (complex) lipids are the structural
component of membranes, tissues, and interfaces. Phospholipids form membrane bilayers, are
amphiphilic, and provide interface capability. The physical property of lipids contribute to their
functional role in foods: viscosity and lubricity, consistency, texture, and mouthfeel, shortening
and aeration of baked goods, flavor carrier and component, aromas and odors, “bread spread,”
structure component of membranes, surface protective agent on fruits and vegetables,
emulsification, heat transfer, and oxidative degradation and limitation of shelf life.
The viscosity, melting point, and crystal properties of different fats and oils determine
their functional properties in foods. Fats are solid - they form a film around air bubbles or oil
drops and a layer between proteins, and adsorbs to food surfaces during frying and cooling. Fats
do not adsorb to starches or proteins, and so they interact less and stay in separate regions, giving
flaky doughs. Oils stay liquid under the same conditions, strongly adsorbing to starches proteins,
decreasing gluten formation and tenderizing the dough structure. Lipids are polymorphic and
crystallize into three forms. The beta and beta prime forms are stable. Beta crystals have the
tightest organization, highest melting point, and densest solid form. Beta prime crystals are
loosely organized with lower melting points, and capable of incorporating large amounts of air,
thus used in baked products. Oils do not crystallize.
Shortening value is the ability of fat to disrupt gluten associations that make up dough
networks, resulting in a range of effects from tenderized breads or cakes to conversion from
doughy matrix to flaky pastry. It is affected by acyl chain length (melting point), the degree of
saturation, the amount of water present, and the degree of mixing. In this experiment, cakes and
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pastries were made in order to examine how melting point and crystal structure of various fats
and oils (hydrogenated shortening, liquid soybean oil, lard, butter, and coconut oil), affect
shortening, aeration, and emulsion formation in cakes, flaking characteristics of pastry, and
consistency, mouthfeel, and texture.
Methods
First, pastry doughs were made. Each of the five groups used a different fat or oil. Group
1 used hydrogenated shortening, group 2 used vegetable oil, group 3 lard, group 4 butter, and
group 5 coconut oil. First, dough was mixed, making sure the ingredients were cold. One cup of
all-purpose flour, ¾ teaspoons of salt, and ⅓ cup of fat was mixed two knives until the mixture
was coarse and even, with the fat particles the size of small peas. Then, 3 tablespoons of ice cold
water was sprinkled over the mixture a few drops at a time, and mixed making sure not to knead.
About ⅔ of this mixture was gathered into a ball, wrapped in plastic wrap, and labeled. The rest
was kneaded until the mixture was homogeneous, wrapped, and labeled. Both doughs were
refrigerated 30 minutes. After chilling, the doughs were pressed flat on a floured surface, rolled
out to ⅛ inch thickness, and transferred to an ungreased baking sheeting to be baked at 400
degrees F until crisp and golden brown, about 20-25 minutes in a conventional oven. For group
5, the doughs did not stick together and were very crumbly so more water was added. Then, the
pastries were removed, cooled, and evaluated.
Cakes were then made. In a small container, 2 cups of all-purpose flour, 2 teaspoons of
baking powder, and ½ teaspoons of salt was blended. In a medium container, 1.5 cups of
powdered superfine sugar, 1 cup of fat/oil, and 2 teaspoons of vanilla were creamed until light
and fluffy. Four eggs were added one at a time to the creamed mixture. Five tablespoons of milk
was then added to the batter and beaten in well. Half the flour mixture was mixed in gradually,
followed by another five tablespoons of milk, and finally the remaining flour mixture, making
sure not to over mix. A piece of waxed paper was cut to fit a flat 15 inch aluminum cake pan,
and placed inside. The batter was poured in and the cake was baked at 350 degrees F for 25-30
minutes. Group 5’s coconut oil cake required 50 minutes baking time. The cakes were removed
and cooled for 10-15 minutes before removing them from the pans to be evaluated.
Results
The kneaded pastries were generally tougher, and the unkneaded pastries were much
flakier.
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Pastry Evaluation
Group
Kneaded
Unkneaded
1: Hydrogenated Shortening
Flakiness: Flaky
Air spaces: Small
Puff: Slightly puffy
Flakiness: Flaky
Air spaces: small
Puff: Slightly puffy
2: Vegetable Oil
Flakiness: Slightly flaky
Air spaces: Small
Puff: Slightly puffy
Crispness: Tougher than unkneaded
Mouthfeel: Tough
Flakiness: Very flaky
Air spaces: Medium
Puff: Not puffy
Crispness: Soft
Mouthfeel: Soft, tender
3: Lard
Flakiness: Flaky
Air spaces: Small
Puff: Not puffy
Crispness: Slightly
Mouthfeel: Savory, dry
Flakiness: Very flaky
Air spaces: Medium
Puff: Not puffy
Crispness: Crispy
Mouthfeel: Savory and crispy
4: Butter
Flakiness: Flaky
Air spaces: Small
Puff: Slightly puffy
Crispness: Slightly crispy
Mouthfeel: Chewy
Flakiness: Very flaky
Air spaces: Small
Puff: Slightly puffy
Crispness: Tougher
Mouthfeel: Brittle
5: Coconut Oil
Flakiness: Minimal
Air spaces: Small
Puff: Very puffy
Crispness: Tough
Mouthfeel: Dry, burnt:
Flakiness: Some layers
Air spaces: Medium
Puff: Slightly puffy
Crispness: Very brittle
Mouthfeel: Dry, burnt
The cakes varied in tenderness and height, as well as appearance and mouthfeel. Before baking,
group 5’s batter was flowy, viscous, cream colored, and smooth.
Evaluation of Cakes
Group
Mouthfeel
Crumb/Air
1: Hydrogenated Shortening
Tender, fluffy
Big air cells, thick cell walls
2: Vegetable Oil
Very soft, smooth. Dried as the
cake cooled.
Tender, small even air cells, thick
cell walls
3: Lard
Crisp crust, soft interior. Slightly
savory, very moist.
Tender, big air cells of mixed size,
thick cell walls
4: Butter
Very moist, soft.
Tender, medium air cells, thick cell
walls
5: Coconut Oil
Soft, oily, smooth. Not too light or
dense.
Tender, small to medium uneven air
cells, thick cell walls.
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Vegetable oil and lard yielded the most tender cakes.
The tallest cakes was the one made with vegetable oil.
Discussion
The pie doughs made from the fats and oils had different properties. All the doughs were
chilled before rolling and baking in order to solidify the fat particles and allow the gluten matrix
to relax. The pie dough would not be as flaky if this step were omitted. All the ingredients,
especially fats and water were cold in order to cut into the flour better: warm ingredients stick to
the dough, does not hold its shape, and leaks liquid oil/fat (McGee, 2004). The fat was cut in the
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flour into pea size - this bigger size allows more separation of the fats, yielding bigger flakes.
Smaller particles of fat would not yield such a flaky pastry. The vegetable oil gave the toughest
pastry, and lard yielded the most tender, flaky pastry. This is because the oil, liquid at room
temperature, was not separated enough and stuck too much to the dough. The lard, which was
very solid at room temperature, stayed separate enough to produce flakes in the dough. Kneading
the dough developed gluten excessively, leading to a tough pastry. The unkneaded pastries were
therefore more tender. The solid fats, hydrogenated oil, lard, butter, and coconut oil, generally
yielded flaky pastries while the vegetable oil yielded a tougher product, because the solid
properties allowed for separation. When they were kneaded, the fats melted slightly and
contributed to tougher pastries. If a food manufacturer were making a frozen pie dough, he or she
would most likely use hydrogenated vegetable oil because it is cheap, stable, and stays solid at
room temperature. He or she would take caution not to over mix or knead in order to prevent
excess gluten development and maintain flakiness.
For cakes, the ingredients should be a room temperature in order to ensure better
emulsification. The most tender cakes was made with vegetable oil, and the densest and solid
cake was made with the solid fats. This is due to the degree of interaction with the flour. The oil
interacted with proteins, decreasing gluten formation and tenderizing the dough structure. The
fats interacted less with the starch and proteins, giving a tender and delicate product, but since
they were solid at room temperature, they also contributed to a denser product. The lard
produced a cake with a slightly savory taste due to the nature of the fat. The butter and coconut
oil produced cakes that were very moist and slightly greasy due to the higher melting point. The
vegetable oil yielded a very soft product because of the low melting point of the oil. The fat was
mixed with sugar and egg first and then flour and milk was added afterwards in order to ensure
smooth mixing. The liquid and semi-liquid ingredients intermixed better with sugar as an
abrasive. Flour molecules are larger so it was added last. If everything were mixed at the same
time, the mixture would likely explode and create a mess. Various cakes call for different fats. A
light wedding cake would be best made using a solid fat - the high melting point would lead to a
very tender product. A strawberry shortcake is more versatile, and any type of fat could be used.
A fruit or vegetable cake or bread is denser, and therefore oil should be used. A gateau, with
many layers, would be made well with butter. Butter is a solid fat at room temperature, but it has
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a slightly lower melting point than lard or coconut oil suiting a gateau well since it is not too
light or dense.
Conclusion
Through the various formulations used to make pastry and cake, the properties of fats and
oils could be observed. In general, the solid fats (hydrogenated vegetable oil, lard, butter, and
coconut oil) yielded flaky pastries and moist, but denser cakes. The vegetable oil did not create
as many flakes in the pastry, with its low melting point preventing fat separation, but it did result
in a very soft cake due to its interaction to dough proteins.
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References
McGee, H. (2004). On food and cooking: The science and lore of the kitchen. New York:
Scribner.