Characteristics & Reaction

Fat versus Oil

A fat is a lipid that is solid at room temperature, while an oil is liquid. What determines if a lipid is fat or oil is:

• the length of the fatty acid chain. The longer the chains, the more solid the fat is at room temperature.
• the degree of saturation. The more saturated the chains, the more solid at room temperature.

Melting Point

The more saturated the higher the melting point. As would follow, the more unsaturated the fatty acids, the lower the melting point.

Crystallization

The solid property of fat is influenced by the presence of crystallized fat. Crystal sizes range from

0 - 5 µ

50 - 100 µ

Larger crystals result in grainy mouth-feel and sometimes even in grainy appearance.

Fat crystals are held together by Van der Waals forces and thus are not terribly strong. They can be rearranged, broken, and reformed.

Polymorphism is the existence of more than one crystal form in fat. The forms are alpha, beta-prime, and beta, and range from least stable to the most stable, respectively.

Crystallization can be modified through the process of interesterification. Interesterification is the process of changing the position of naturally occuring fatty acid radicals on the glyceride backbone to effect different properties. Interesterification is used to:

FLAVOR

While fats & oils are not generally thought of for their flavor, they do contribute to a product's flavor in significant ways. Some of the more bland tasting lipids are selected for use in a product for just that reason; they are bland. Deterioration of the flavor components in lipids often leads to disaster in food and beverage products because of the noticeable off tastes. Care must be given to build the correct system such that the selected fat or oil remains stable for the maximum length of time.

AUTOXIDATION

This is the process whereby some or all of the unsaturated bonds react with oxygen, leading to deterioration in flavor.

Rate of Autoxidation can be effected by:

amount of oxygen present

degree of unsaturation of lipids

presence of catalysts ("prooxidants like copper & other metals

light exposure

temperature

Autoxidation can be reduced by:

• antioxidants present (BHT, citric acid, etc)
• packaging material

What's the Autoxidation Story?

The initial stage of the autoxidation reaction yields "free radicals", due to the removal of hydrogen. A significant note here is that this reaction feeds on and perpetuates itself.

Antioxidants work by reacting with the free radical & thereby stopping the cycle of destruction. Note: If too high in concentration, the antioxidant can actually accelerate the rancidity. This is a common mistake amongst developers who are new to their use.

Combining different antioxidants can have a synergistic effect on preventing/slowing rancidity.

The more unsaturated, the more likely the rancidity is to occur.

Some of the compounds that results from rancidity, for example aldehydes, are strong flavor compounds with extremely low thresholds of detection (can be less than 1 part per billion).

Hydrolysis

Digestion of Triacylglycerols

We digest triacylglycerols by hydrolysis (using water). For example:

triacylglycerol + 3 water ==> glycerol + 3 fatty acids

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