FOOD CHEMISTRY AND ANALYSIS (CM9101) (Previously known as CBC 961)

Instructor: Li Tianhu

Contact information of Li Tianhu

Office: CBC-04-21

Telephone: 6513-7364

E-mail: thli@ntu.edu.sg

Web page: http://www3.ntu.edu.sg/home/thli/

There are nine food chemistry and analysis experiments

associated with this module which are supervised by Mrs.

Bontawee Bates and assisted by Li Tianhu

1

2. Essentials of Food Science 3rd

Author: Elizabeth W. Christian; PH.D. Vaclavik Vickie A

Year Published: 2007

Publisher: Springer ISBN 978-0-387-69939-4

1. Food Science & Nutrition

Author: Sunetra Roday

Year Published: 2007

Publisher: Oxford Higher Education

ISBN 978-0-19-568911-2

Recommended textbooks:

The questions of our midterm and final exams will be

exclusively from our lecture notes rather than from our

textbooks 2

Part Topics

1 Introduction to Food

Chemistry and Water

Content

2 Fat and Oil Products

3 Proteins in Food

4 Carbohydrates in Food

5 Food Browning

6 Food Colors

7 Special Topics

Topics to be covered this semester:

Our lecture notes will be posted on Edventure 3 days in

advance 3

There will be two midterm exams. The higher mark out of your

two exams will be taken as the final grade of your midterm

exams (CA).

Mid term exams will be held on 27 September 2012 and 1

November 2012 respectively

There is no correlation between the easiness of the questions

in our midterms and those in our final exams

Weighting of CA, Lab and our final exam:

Module CA Lab Final Exam

CM9101 Food Chemistry

and Analysis

20 30 50

About midterm and final exams:

4

About the formats of our midterm and

final exams:

(1) 20 multiple-choice questions in each of our

two midterm exams;

(2) 40 marks of multiple choice questions and

60 marks of short essay questions

I will provide you with the samples of our

midterm and final exam questions in due course

Again, the questions of our midterm and final exams will

be exclusively from our lecture notes rather than from

our textbooks

5

There will be no makeup test for our midterm

exams (CA)

If you miss both mid term exams, calculation of the

marks of your missing mid term exams will be

given by our division based on standard rules

When you submit your MC documents, please

make sure that you submit them to the right

personnel in SPMS who is in charge of the MC

issue

MC issue:

6

(1) Please feel free to knock my office door after each

lecture on Thursdays and any other time

(2) You may send me an email to make an

appointment with me in advance

Consultation hours:

7

Part 1. Introduction to Food Chemistry and

Water Activity

Section 1: Introduction to Food Chemistry

Definition of “Food Chemistry”:

Food Chemistry is the study of chemical

composition and chemical changes of food

components while the focuses of food chemistry are

often on the three major components in food:

(1) Fats (oil)

(2) proteins

(3) carbohydrates

8

Definition of Food

Foods are edible parts of

(1) Plant

(2) Animal

(3) Single-cell organisms (e.g. algae)

(4) Fungi

which can be eaten and digested by human being

Food is the source of nutrients

9

(1) Examples of food from plant sources

(2) Examples of food from animal source

I personally respect people who don’t eat meat 10

Spirulina algae

(3) Single-cell organisms (e.g. algae)

(4) Fungi products

Mushrooms Yeast 11

Nutrients

A nutrient is a substance that an organism relies

on to live and grow, which must be taken from its

environments.

Nutrients are used to

(1) Build and repair tissues

(2) Provide energy

(3) Regulate some metabolic processes

12

Macronutrients and Micronutrients

Macronutrients (consumed greater than one gram/day):

[1] Fats (Oil)

[2] Proteins

[3] Carbohydrates

[4] Water

Micronutrients (consumed less than 100

micrograms/day):

[4] Minerals

[5] Vitamins

Note: Definition of macronutrients and micronutrients varies depending

on textbooks

13

Components of food

Components of food generally include

1. Proteins

2. Saccharides

3. Lipids

4. Water

5. Minerals

6. Vitamins

7. Nonprotein

nitrogenous compounds

8. Colorants

9. Flavour and aroma compounds

10. Others

Nutrients

Little is known

about their

nutritional roles

14

Example of sources of nutrients

15

Part 1. Introduction to Food Chemistry and

Water Activity

Section 2: Water Content

1. “Water content” or “Moisture Content” is the quantity of

water contained in a food:

w (water content) = mw / mb

where mw is the mass of water and mb is the bulk mass

2. “Water Content” is a useful concept for us to

understand the chemical composition and nutritional

value of food

16

Examples of food that contain high percentage of water

Besides “Water Content”, there is a useful concept called “Water

Activity”, which will be discussed in CBC 963 (Food Processing and

Preservation)”

17

CM9101 Food Chemistry and Analysis

Experiment 1: Determination of Moisture

Content in Food

Food: Sesame seeds

Method to remove water: keep your sesame

seeds at 130°C for specified time periods

(following Mrs. Bates’ instruction)

18

Components of food

Components of food generally include

1. Proteins

2. Saccharides

3. Lipids

4. Water

5. Minerals

6. Vitamins

7. Nonprotein

nitrogenous compounds,

8. Colorants,

9. Flavour and aroma compounds,

10. Others

Nutrients

Little is known

about their

nutritional

value

19

Section 1: Fatty acids

Section 2: Triglycerides

Section 3: Modification of fats

Part 2. Fat and Oil Products

20

Section 1: Fatty acids

A fatty acid is a carboxylic acid with a long and un-

branched aliphatic chain (usually with carbon number

>8). The smallest fatty acid found in triglycerides is

butyric acid (C4)

Fatty acids can be divided into:

1. Saturated fatty acids

2. Monounsaturated fatty acids

3. Polyunsaturated fatty acids

3. Triglycerides are the main components of food oil

while fatty acids, if they exist in food oil, are

considered as decomposition products. That is, fatty

acids exist in their triester forms in food oil rather than

in the forms of free fatty acids

21

Long-chain fatty acid: hydrocarbon chain contains 12

to 26 carbons

Medium-chain fatty acids: C8 to C10

Short-chain fatty acids: C4 to C6

Natural fatty acids nearly always contain an even

number of carbon atoms

22

Saturated fatty acid is fatty acid that contains only carbon-

carbon single bonds in its aliphatic chain

An example of saturated fatty acids is lauric acid that

contains 12 carbons in its hydrocarbon chain:

Lauric acid

Saturated fatty acids

The values “Hydrophilic-Lipophilic Balance” of a molecule is

a measure of the degree to which it is hydrophilic

or lipophilic

hydrophilic lipophilic

23

Fatty acid No. of carbon atoms

Food Source

Butyric acid 4 Butter

Caproic acid 6 Butter

Caprylic acid 8 Coconut, palm kernel

Lauric acid 12 Palm kernel, coconut

Mysteric acid 14 Coconut, butter

Palmitic acid 16 Palm, soya, sesame, butter, lard, cotton seed

Stearic acid 18 Beef tallow, cocoa butter, lard

Examples of saturated fatty acids (in the form of

triglycerides) and their food source

Butyric acid is the smallest fatty acid found in triglycerides

24

Monounsaturated fatty acid is fatty acid that contains

one carbon-carbon double bond in its hydrocarbon

chain

The configuration of biochemically important

monounsaturated fatty acids is nearly always “cis”

Oleic acid is an example of monounsaturated fatty acid.

It is a type of ω-9 fatty acids

An ω-9 fatty acid is a fatty acid that contains a double

bond (C=C) starting after the ninth carbon atom from

the end of the carbon chain

Oleic acid One cis double bond

Monounsaturated fatty acids

ω

10 9 7 5 3 1

11 8 6 4 2

25

Polyunsaturared fatty acid is fatty acid that contains

two or more (up to six) carbon-carbon double bonds

in its hydrocarbon chain

Linolenic acid is an example of polyunsaturated fatty

acids. It is also a type of w-3 fatty acids

An ω-3 fatty acid is a fatty acid that contains a double

bond (C=C) starting after the third carbon atom from

the end of the carbon chain

Linolenic acid 3 cis double bonds

Polyunsaturated fatty acids

ω

10 9 7 6 4 3 1

11 8 5 2

26

1) “Essential fatty acids (EFAs)” are polyunsaturated fatty acids

that cannot be synthesized by human body. There are

basically two types of essential fatty acids known for

humans:

a) α-Linolenic acid (an omega-3 fatty acid), which contains

an 18-carbon chain and three cis double bonds.

i. Flax seed oil contains 55% of α-linolenic acid.

ii. "The weight of the evidence favors

recommendations for modest dietary

consumption of α-linolenic acid (2 to 3 g per day)

for the primary and secondary prevention of

coronary heart disease1.

1Mozaffarian D (2005). "Does α-linolenic acid intake reduce the risk of coronary heart disease? A

review of the evidence". Alternative therapies in health and medicine 11 (3): 24–30;

Essential fatty acids

27

i. A lack of linoleum acid and other n-6 fatty acids in

the diet causes dry hair, hair loss, and poor wound

healing.

ii. Safflower, sunflower, and corn oils contain over half

(by weight) of linoleic acid . Achieving a deficiency

in linoleic acid is nearly impossible when a person

consumes any normal diet. Thus deficiency in

linoleic acid is not considered to be of clinical

concern.

iii. This is the reason why we don’t often see that

“linoleum acid” or essential fatty acids are sold in

nutrition store

b) Linoleic acid (an omega-6 fatty acid), which contains a

18-carbon chain and two cis double bonds

2. It should be emphasized again here that essential fatty acids in

all food sources do not exist in their free fatty acid forms.

Instead, they occur in the forms of triglycerides (triester forms) 28

Section 2: Triglycerides

Glycerol:

Secondary carbon

Secondary carbon

Tertiary carbon

sn1

sn2

sn3

CH2

CH2

CH

OH

OH

OH

“sn” is stereospecific numbering of triglycerides

Glycerol is polyol (triol), which can also be considered

as a sugar alcohol

29

Triglyceride is a triester formed between glycerol and

three fatty acids:

30

Triglyceride can be divided into simple and mixed triglycerides

Triglycerides:

30

A fat is a triglyceride mixture that is solid or semi-solid

at room temperature (25 oC).

An oil is a triglyceride mixture that is a liquid at room

temperature (25 oC).

Fat and oil

However, the terms “fat” and “oil” are used sometimes

interchangeably. For example, when we say “artificial

fat substitute”, we are in fact talking about “artificially

synthesized cooking oil”

31

Visible fat is the type of fat

that can be seen through our

naked eyes. e.g. salad oil

and vegetable oil for cooking

Invisible fat the fat present

in food, which we cannot

easily seen through our

naked eyes. e.g. the fat in a

whole milk

Visible fat and Invisible fat

32

Section 3: Modification of fats

1. Hydrogenation

2. Interesterifcation

3. Acetylation

4. Winterization

33

Hydrogenation (of fat)

O

O

O

C

C

C

O

O

O

O

O

O

C

C

C

O

O

O

O

O

O

C

C

C

O

O

O

m

n

o

Ni catalyst

partially hydrogenated

trans fat

+

H2

Hydrogenation is a

process of adding

hydrogen to

unsaturated fatty acid

residue of a

triglyceride to reduce

the number of double

bonds (food

processing)

Many food products

are produced via

partial hydrogenation

rather than complete

hydrogenation

34

The purposes of hydrogenation in general are twofold:

i. To convert liquid oils to semisolid or plastic fats.

For examples:

a) some peanut butter is produced from

vegetable oil through partial hydrogenation

b) Solid cooking shortening and stick

margarine are produced from liquid plant oil

through partial hydrogenation

ii. To increase the thermal and oxidative stability of

the fat, and thus the shelf life. That is,

polyunsaturated fats are subject to oxidative

rancidity. Thus, reducing the number of double

bonds by hydrogenation increases their stability

35

The process of hydrogenation causes conversion of

some cis double bounds to the trans configuration

Tub margarines usually contain trans fatty acid at least 13-

20%

Trans fatty acid is undesirable. Preliminary studies indicate

that trans fat raises ‘low-density lipoproteins (LDL)”, which

consequently increases the risk of coronary heart disease

36

37

Question 1.

Please describe correlation between food and

nutrients

Question 2.

Please tell why food manufacturers often

carry out hydrogenation on food oil