Chemical reactions involved autoxidation of milk fat are grouped in to three categories. viz. intiation, propogation and termination. The initial step in the autoxidation of unsaturated fatt acid and their ester is the formation of free radical. In the case of monounsaturated and non conjugated polyene fatty acids the reaction is initiated by the removal of hydrogen atom from the methylene group of adjacent to the double bond. The resulting free radical stabilized by resonance adds oxygen to form peroxide containing free radicals these in turn react with another mole of unsaturated compound to produce two isomerichydroperoxides

1. Assignment on
Chemical reaction of milk lipid:
Overview
Submitted By
Jadhav Shanthilal Nayak
22-P-DT-02
Ph.D. (Dairy Technology)
Submitted to
Dr. Laxman Nayak
NDRI SRS Banglore

2. Introduction
Definition : Lipids are organic compounds formed mainly from alcohol and fatty
acids combined together by ester linkage
Milk fat glycerides are subject to all the general chemical reaction of glyceride, but
only a few have been studied.
Lipid molecules of all classes (i.e., fatty acids, acylglycerols, sterols) undergo
some degree of chemical reaction, especially in the presence of heat.
1 Hydrolysis,
2 Hydrogenation, and
3 Oxidation

3. Conti…
It is represented the major types of chemical re actions occurring to food lipids.
Fatty acids liberated by hydrolysis reactions contribute substantially to the
flavors typical of meat and dairy products.
Hydrogenation is a chemical process used to change carbon-carbon double bonds
to single bonds.
The reaction is used on an industrial scale to convert oils into fats with desirable
end use properties and greater stability. However,
Hydrogenation is also responsible for trans-fat, a form of fatty acid in which
some carbon-carbon double bonds are isomerized from cis to trans.

4. Hydrolysis involves breaking the ester bond between fatty acids and glycerol,
releasing them into the matrix . The rate of ester bond hydrolysis is faster at the
extremes of pH and at high temperature.
Chemically, hydrolysis is a reversible reaction in which fatty acids are removed from
(hydrolyzed) or linked to (esterified) glycerol’s hydroxyl (OH) groups.
Hydrolysis reactions have many practical applications.
Hydrolysis chemistry is the basis of making soap from fats in a process called
saponification

5. Analytical reactions
Such as with alkali in determining saponification values and with halogens in
determining the degree of unsaturation.
It is standardized and need not be discussed here.
Two reaction that result in deterioration of milk fat in commercial usages
1.Hydrolysis
2.Oxidation
3.Hydrogenation
4.Saponification

6. Hydrolysis
• Hydrolysis of milk fat involves a reaction between the glycerides and
water.
• Enzymatic and acid hydrolysis glycerol and free fatty acid are produced.
• It may stop at partial hydrolysis, with the formation of mono and
diglyceride or process to a complete splitting of the component fatty acids
and glycerol.
• When reaction is obtained than in the enzymatic hydrolysis of fat
occurring in biological system.
• Lipolysis in milk has been described as being of two different type,
Spontaneous and induced

7. Conti..
• Kelley and Dunkley(2002) believed that the specific differences are
related to changes in the nature of the surfaces of the fat globules.
• Lipases as a class have a low degree of specificity, being able to bydrolyze
not only fats but also simple esters.

8. Cont..
• It is indicate that the ease with which glycerides are split increases with
the chain length-- perhaps contrary to enzyme systems generally, where
activity may decrease with increasing molecular weight and with
imsaturation of fatty acids.
• Johnson and Gould determined the chemical characteristics-including acid
degree, Reiehert-Meissl, Polenske, saponification and iodine values--of
fractions obtained from fresh and rancid milk fats, but the data gave no
definite indication of selective fat hydrolysis by the lipase system.

9. Conti…

10. Oxidation
• Oxidation of fats by molecular oxygen is generally caused by an initial reaction
between oxygen and the component fatty acids.
• Both saturated and unsaturated fatty acids are susceptible to oxidation, but the
rate of uptake of oxygen increases with the degree of unsaturation of the fat and
tile postulated mechanisms of oxidation for the various types of fatty acids are
different.
• It is generally aecepted that in the autoxidation of noneonjugated fatty acids a
free radical first forms on the methylene group, adjacent to a double bond.
• The free radical absorbs an oxygen molecule, which then accepts hydrogen to
form a hydroperoxide.

11. Cont..
• The hydrogen usually comes from another fatty acid or ester, to form
another free radical, and thus the ehain reaction continues.
• In the oxidation of monoethenoid acids, which have less active methylene
groups.
• The addition of oxygen occurs initially at the double bond instead of at the
a-methylene group, providing the free radicals necessary for the
usual,methylenic free radical chain reaction to proceed.

12. Reaction

13. Hydrogenation
• Hydrogenation is a chemical reaction that modifies carbon-carbon double bonds
in lipids through addition of hydrogen atoms and an inert meat catalyst.
• The predominant use of this chemistry is to change oils to solid fats by reducing
double bonds in polyunsaturated fatty acids.

14. Other reactions
• Patton et al. (2018) reported in dry whole milk and butter oil a lipid-phase
deteriorative flavor that they believed to be nonoxidative in nature but to invoh'e
laetone formation in glycerides containing 9-deeenoic and 9-dodenoic acids.
• Baur and Feuge (2003) studied inter-esterifieation of glycerides with triacetin and
with acetic anhydride.
• Formo (1997) reviewed ester reactions of fatty materials. Interesting compounds
can be produced that have a wide range of properties, including melting point

15. Reaction

16. Thank you