Changes In Fats During Processing

Food Chemistry Library

PaperPresented By: Archita Thakur Ashish Sahoo Ashish Mishra Ashwin Menon

What processes FATS has to undergo?• Fats and oils are heated during frying for commercial purposes. Heating during processing

mainly involves hydrogenation, physical refining and deodorization. • Temperature in these processes may range from 12O0C to 27O0C, oxygen exposure us limited.• At these elevated temperatures, several chemical changes may take place particularly in

unsaturated fatty acids: randomization of the glyceride structure/interesterification dimer formation, cis-trans isomerisation formation of conjugated fatty acids (positional isomerization)

Processing Of FATS• Rendering or Extraction• Degumming• Refining• Bleaching• Deodorization• Fractionation• Hydrogenation• Interesterification• Esterification

Rendering or Extraction• Rendering and Extraction, terms used separately depending upon the

source of fats i.e. Rendering of animal fats and Extraction from oilseeds.

Bacon renders -- or gives up -- its fat when cooked over low to medium heat. Cooking the bacon melts the fat, which separates from the connective tissue and meat, and becomes what is otherwise known as bacon fat.

Degumming• For the removal of excess of Phosphatides from the crude oil (e.g.,

soybean oil).• Treating crude oil with water to hydrate phosphatides and make them

separable by centrifugation.

Refining• Performed on vegetable oils to reduce the free fatty acid content and to

remove other impurities such as phosphatides, proteinaceous and mucilaginous substances.

• Most common method is the treatment of fat or oil with alkali solution. • Reduction of free fatty acids to high specific gravity soaps. • After alkali refining, the fat or oil is water washed to remove residual

soap.

Bleaching• Bleaching, the process for removing color producing substances and

further purification of oil or fat. • Adsorption of color producing material on an adsorbent surface. • Bentonite, acid–activated bleaching earth or clay has been used

extensively. Consists of hydrated aluminium silicate.• Other adsorbents used are- Anhydrous silica gel and activated carbon.

Deodorization• Vacuum steam distillation process for the removal of undesired odours, flavours and

colours. • Removal of volatile compounds of fats or oils using steam. Feasible because of the

difference between volatility of substances that give undesired flavours, colours and odours to fats and oils and the triglycerides.

• Carried in vacuum to avoid undue hydrolysis of fat and to make most use of the steam. • Doesn’t effect the composition of most fats or oils. • Depending upon the degree of unsaturation of oil being deodorized, small amounts of

trans fatty acids may be formed.

Fractionation & Winterization • Fractionation- Removal of solids by controlled crystallisation and

separation techniques involving the use of solvent or dry processing. • Relies upon the differences in melting points to separate the oil

fractions.• Winterization- Crystallization process of material for removal by

filtration to avoid clouding of liquid fraction at cooler temperatures

Hydrogenation• Addition of hydrogen to the points of unsaturation in the fatty acids.• Hydrogenation was developed as a result of the need to-

convert liquid oils to semi-solid form for greater utility in certain food uses.

increase the oxidative and thermal stability of the fat or oil. • Important process to food supply, provides desired stability and

functionality to many edible oil products.

What is Hydrogenation?• Hydrogen gas reacts with oil at elevated temperature and pressure in

the presence of a catalyst. Most widely used catalyst is Nickel.

• Hydrogenation is easily controlled and can be stopped at any desired point.

Change:- Gradual increase in the melting point of the fat or oil.

Interesterification• Redistribution of fatty acids on the glycerol fragment of the molecule.

This doesn’t change the composition of fatty acid from the starting materials.

• May be accomplished by :- Chemical Interesterification Enzymatic Interesterification

Types of Interesterification • Chemical Interesterification: process by which fatty acids are randomly distributed

across the glycerol backbone of triglyceride. Carried out by blending the desired oils, drying them and adding a catalyst such as Sodium methoxide. When the reaction is complete, the catalyst is neutralized and rearranged product is washed, bleached and deodorized to give a final oil product with different characteristics than original oil blends.

• Enzymatic Interesterification: process rearranges the fatty acids on the glycerol backbone of triglyceride through the use of an enzyme. Higher temperatures will result in inactivation of the enzyme. After interesterification, the oil is deodorised for the final product.

Esterification• Fatty acids are present in the form of esters and are consumed as such.

Triglycerides the predominant constituents of fats and oils are examples of esters.

• When consumed and digested, fats are hydrolysed initially to diglycerides and then gradually to monoglycerides, which are also esters. Hydrolysed to glycerol and fatty acids.

Others• Additives and Processing Aids• Emulsifiers

List Of Additives & Processing Aids Used

List Of Emulsifiers And Their Functional Characteristics

Changes caused due to heating• The oil is not in with direct contact with air, which eliminates the

possibility for oxidation. • At high temperatures used in physical refining and deodorization,

several chemical changes may take place, like:Randomization of glyceride structureDimer formationcis-trans isomerizationFormation of conjugated fatty acids of polyunsaturated fatty acids

Dimer Formation• High temperature and the presence of air

(say in frying process), favour the development of polymerization reactions accounting for the most complex group of new compounds formed in used frying fats and oils.

• This complexity results with a high proportion of triacylglycerols containing more than one unsaturated acyl group per molecule.

• Significant information on mechanisms of polymerization reactions has been limited

trans-cis Comparison• A conversion into the trans configuration

can be stimulated only by thermal or catalytic influences. Such an isomerisation is proceeding from a stable cis configuration via an unstable radical structure with free rotatability around the C-C-bond into the trans configuration which is stable again.

• For acyclic systems trans isomers are more stable than cis isomers. This is typically due to the increased unfavourable steric interaction of the substituents in the cis isomer.

Formation of conjugated fatty acids (positional isomerization)

• Conjugated linoleic acid (CLA) is a collective term to describe one or more positional and geometric isomers of linoleic acid

(cis-9, cis-12 octadecadienoic acid). • Conjugated double bonds are usually at

positions 9 and 11 or 10 and 12; each double bond can be in either the cis or trans configuration.

CH3(CH2)5CH=CH-CH=CH(CH2)7COOH9,11-Conjugated Linoleic Acid

• CLA, also known as rumenic acid and is found naturally in meats, eggs, milk and milk products.

Reactions Occurring During Deep Frying

Thermal Properties Of Fats

• Smoke Point- In cooking, the smoke point of an oil or fat is the

temperature at which it begins to break down to glycerol and free fatty acids, and produce bluish smoke.

The glycerol is then further broken down to acrolein which is a component of the smoke.

It is the presence of the acrolein that causes the smoke to be extremely irritating to the eyes and throat.

The smoke point also marks the beginning of both flavour and nutritional degradation.

Therefore, when selecting a fat for frying, with the smoke point of the specific oil dictates maximum usable temperature of oil

Deep frying is a very high temperature process, it requires a fat with a high smoke point.

Refining affects smoke point for an oil. The smoke point of an oil tends to increase with degree of refinement

• Flash/Fire point: The flash point is the temperature

at which the volatile products are evolved at such a rate that they are capable of being ignited but not capable of supporting combustion.

The fire point is the temperature at which the volatile products will support continued combustion.

For typical fats with FFA content of below 0.05%, the smoke, flash, and fire points are around 200 to 215º, 325º, and 355º F, respectively.

What Is Rancidity And Why Is It A Problem?• Rancidity is the condition reached in certain foods as the lipid material (fat) undergoes

oxidation reactions producing compounds which are responsible for the odour and off-flavor producing stale foods– aldehydes, – hydroxyl acids,– keta acids, and other compounds. An oxygen ion is replaced with a hydrogen ion in the fatty acid.

• Foods that are high in lipids and might become rancid include potato chips, peanut butter, crackers and others.

• Light, oxygen, trace elements such as iron and zinc, salt, water, bacteria, and molds are factors that speed up the oxidation process.

Types Of Rancidity• There are two types of Rancidity

Hydrolytic Rancidity Oxidative Rancidity

Hydrolytic Rancidity Oxidative Rancidity

Rancidity

Hydrolytic Rancidity

• caused by a breakdown of the fat into glycerol and fatty acid. (in general known as lipolysis and also lipolytic rancidity)

• Important in milk and milk product - undesirable flavour mainly due to low fatty acids

• In most of the product other type of rancidity is observed.

Oxidative Rancidity

• results from oxidation of unsaturated and polyunsaturated fatty acids producing undesirable flavors and odors.

• by reacting with oxygen in the air.• Air, Heat/Sun Exposure, moisture further supports

OR Unsaturated fats are more susceptible to oxidative rancidity than saturated fatty acids.

• The reaction occur due to free radical formation at the site of double bonds

• Antioxidants added to foods prevent rancidity/autooxidation

• As antioxidants have lower energy for making free radicals so enter in to reaction preventing attack on unsaturated fat

Examples• Masters and Smith have investigated the character

of the changes in fat during cooking. They state that the changes occurring in the fat in cooked pastry are slight, unless the pastry is very thin or over-cooked.

• Woodruff and Blunt have reported the changes in fats absorbed by-potato chips and a dough mixture. They state that the iodine number is lowered, and the percentage of free fatty acids increased. These changes are not great, but the fat absorbed by the food undergoes greater changes than the fat in which the food is cooked. Long cooking or use of the fat increases the amount of decomposition of the fat. The higher the temperature to which the fat is heated, the greater the decomposition products formed. Thus during cooking the fat should NOT be heated higher than the temperature needed for cooking the food.

Examples

• Morgan and Cozens found that fats used for frying a standard dough showed consistent decreases in iodine number, lowering of the melting point and increases in acidity and refractive index. They state that in general the increase in acidity is greater in those fats showing the larger amounts of absorption.

References• Journal Foods Fats And Oils by Institute of Shortenings and Oils, New

York.• Principles of Food Chemistry by John M. Deman• Food Lipids by Casimir C. Akoh and David B. Min