Chem Presentation Food Chem

8/3/2019 Chem Presentation Food Chem

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Hydrolysis is the splitting of a compound by reactionwith water.

After kept for too long, fat will become rancid/smelly

because of the release of fatty acid by the process ofhydrolysis

Hydrolysis occur rapidly in the presence of lipase(actas enzyme)

Hydrolysis also occurs during deep-fat frying becauseof the large amounts of water introduced from thefood and the relatively high temperature

Hydrolytic rancidity can be reduced by refrigeration


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Alkenes are more reactive than alkanes

because of the C=C bonds

Unsaturated fats are more reactive thansaturated fats


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Occurs in air

Absence of enzyme

Oxidize by oxygen Oxidative rancidity: Fat molecules break

down to form volatile unpleasant aldehydes

and carbox

ylic acids Free radical reaction

Can also be initiated by light(photo-

oxidation), enzymes or metal ions.


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The more unsaturated the oils(more C=C

bonds), the faster the rate of oxidation.

The rate can be reduced by usingantioxidants and by refrigeration.


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Initiation

Propagation

Termination


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Carbon to hydrogen bond R-H bond ofunsaturated fatty acid is broken downBy the action of sunlight orThe presence of metal catalyst


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Radicals react with oxygen to form peroxide radicalsThen it reacts with more unsaturated fatty acid molecules toform hydroperoxides and other alkyl free radicals


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Removal of free radicals from the system.

3 possible combinations.


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O-O bond in ROOH is weak and unstable.


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Fe2+ can catalyse the break-up of the hydroperoxdies by

reducing the free radicals to the more stable hydroxideions.

Fe2+ is regenated as the Fe3+ oxidizes the H atoms tomore stable H+ ion.


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Addition of hydrogen Catalyst = nickel, copper, or zinc Temperature of 140-225 degrees Celcius Increases hardness and melting point Used in manufacturing solid margarine and

spreads Increases chemical stability of fats by making it

less susceptible to oxidation Can be controlled by varying the pressure of

hydrogen and the nature of catalyst


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Advantages Disadvantages

Changes a liquid to semi solid or solid Unsaturated fats are more healthier thansaturated fats

Make the melting point of unsaturatedfats more like a saturated fats

In partial hydrogenation, trans fatty acidscan be form

Decrease the rate of oxidation Trans fatty acids:-are hard to metabolize

-accumulate in fatty tissues-difficult to excrete from body

-increase level of low-density (LDL)cholesterol

-low quality of energy source

Increase hardness

Controls the feel and plasticity(stiffness)

Chem Presentation Food Chem

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Chem Presentation Food Chem