PRACTICAL 1: BIOCHEMISTRY OF FOOD AROMA

ABSTRACT

            Food aroma is the odor arising from the food and especially the good odor. Although the natural flavor and odor from food contains nearly a hundred different compound, single esters approximate the natural odor and are often used in food industry for artificial flavor and fragrance.

In this practical we were investigating the aroma of different food substances but from the synthesized ester compounds. The objective was to understand different scents of food substances we can get from esters. The esters were prepared from the reaction of carboxylic acid with alcohol on the presence of sulfuric acid catalyst. It was found that different esters produced from reactions of different alcohol and carboxylic acid has got different scents.

INTRODUCTION

            Anything that we smell has to contain some sort of volatile chemical, a chemical that evaporates and enters a person’ nose. Any natural flavor is normally quite complex, with dozens or hundreds of chemicals interacting to create the taste/smell. But it turns out that many flavor especially fruity flavors have just one or few dominant chemical components that carry bulk of the smell signal. Although there chemical are other chemicals with pleasant smell but many of these are called Esters. For example the ester isomy acetate synthesized in this practical has a fundamental component of banana flavor. If you add this ester to the product the product will taste to some degree as banana. Food and beverage manufacturers they exploit this property of esters and to make more realistic flavors they add other chemical in correct proportions to get closer and close to the real thing. This is done through chemical analysis of the real thing. In this practical we investigated different odors of ester. The esters compounds were synthesized from alcohols and carboxylic acids on the presence of sulfuric acid as a catalyst. Strangely the odor of esters was found to be quite different from its constituent’s alcohol and carboxylic acids.

The ester group is an important functional group in organic compound which can be synthesized in a number of different ways. The low-molecular-weight esters have very pleasant odors and indeed are the major components of the flavor and odor aspects of a number of fruits. Esters are used in the food industry for artificial flavors and fragrances. This is because a single ester contains approximate the natural odor. Esters can be prepared by the reaction of carboxylic acid with alcohol on the presence of sulfuric acid. Sulfuric acid acts as a catalyst and a dehydration agent which forces the condensation of reaction between the alcohols and the carboxylic acid. This reaction is called Fischer esterification reaction. This is the esterification of carboxylic acid by heating it with alcohol on the presence of strong acid. Its general formula can be written as follows:

R₁COOH + R₂OH         ^H+          R₁COOR₂ + H₂O

MATERIALS AND METHODS

 Apparatus

Test tubes

Water bath

Conical Flask

Droppers

Alcohols which are

·         Amyl alcohol

·         Methyl alcohol

·         Ethanol

·         N-butyl alcohol

Carboxylic acids which includes

·         Acetic Acids

·         Butyric acids

·         Salicylic acid

As catalyst

Sulfuric acid

EXPERIMENTAL PROCEDURES

1.      45 drops of amyl alcohol were added to a clean, dried test tube labeled no 1

2.      30 drops of methyl alcohol were added to a clean, dried test tube labeled no 2

3.      40 drops of methyl alcohol were added to a clean , dried test tube labeled no 3

4.      30 drops of ethanol were added to a clean , dried test tube labeled no 4

5.      42 drops of n-butyl were added to a clean dried test tube labeled no 5

6.      To a test tube 1, 30 drops of acetic acid were added

7.      To a test tube 2, 20 drops of butyric acid (butanoic acid) were added

8.      To a test tube 3, 0.5g of salicylic acid was added. The test tube was gently swirled to ensure salicylic acid goes into the solution.

9.      To a test tube 4, 30 drops of butyric acid were added

10.  To a test tube 5, 40 drops of acetic acid were added

11.  To each of the fives test tubes, 10 drops of concentrated sulfuric acid were added carefully followed by shaking the test tubes to mix the reactants.

12.  The five test tubes were then placed in a water bath of near-boiling water and left to be heated for about 10-15 minutes.

13.  After 15 minutes the test tubes were removed from the water bath and the mixture poured into a conical flask followed by diluting it in half in a conical flask and smelled the newly synthesized ester.

RESULTS

TEST TUBES	ALCOHOL	QUATITY	ACID	QUANTITY	ESTER	ODOR
1	Amyl alcohol	45 Drops	Acetic acid	30 Drops	Isoamyl acetate	Ripe Banana
2	Methyl alcohol	30 Drops	Butyric acid	20 Drops	Methyl  butanoate	Fruity apple smell
3	Methyl alcohol	40 Drops	Salicylic acid	0.5g	Methyl salicylate	Rubbing ointment
4	Ethanol	30 Drops	Butyric acid	30 Drops	Ethyl butyrate	Pineapple smell
5	N-butly	42 Drops	Acetic acid	40 Drops	n-butyl acetate	Pea fruity smell

DISCUSSION

            The experimental data from this practical was useful in studying the relationship which can be found on the smell food substances that occurs naturally from plant materials and that of synthetic esters. Synthetic esters have odors which resemble that of natural fruits. Esters have fruity smell due to their chemical composition and conformation.

The Fischer esterification reaction is a reversible reaction that’s why we employ the use of concentrated sulfuric acid which acts as a catalyst and speed up the reaction process. Sulfuric acid acts as dehydrating agent which remove the water produced favoring the forward reaction producing enough ester.  

The result tends to vary in other groups and this is due to different reasons happening during the practical which have to be corrected in order to get data which resemble for all participants. Care should be taken during measuring chemical reagents so as to measure right proportions as instructed in the protocol to get right results.

CONLUSION

            Food and beverage manufactures have used this chemical property of esters into manufacturing different food products ranging from juices, chewing gums, biscuits and many others which have artificial flavor of different natural occurring fruits. Although this is a good step towards improving food quality but care should be taken towards using this chemicals since they may be associated with different healthy problems depending on the users. Manufacturers should be able to label the constituents chemicals used in developing their food products so that the consumers may know exactly what type of chemicals they are taking in their body and the risk they have towards their health. 

QUESTIONS AND ANSWERS

1.      Describe the odor of carboxylic acid before the reaction

The odors of carboxylic acid before the reaction are as follows

Carboxylic acid	Odor
Acetic acid	Smells like vinegar
Butyric acid	Strong irritating smell
Salicylic acid	Strong irritating odor

2.      Describe the odor of alcohol before the reaction.

The odors of alcohol before the reaction were as follows:

Alcohols	odor
Amyl alcohol	Strong irritating alcoholic odor
Methyl alcohol	Weak alcoholic odor
Ethanol alcohol	Strong alcoholic odor
N-butyl alcohol	Sweet alcoholic odor

3.      What do your final product, the esters smells like:

            The smell of the final product esters were as follows:

ESTERS	ODOR
Isoamyl acetate	Fruity banana smell
Methyl butyrate	Fruity apple smell
Methyl salicylate	Rubbing ointment
Ethyl butyrate	Fruity pineapple smell
Butyl acetate	Fruity pea smell

    

4.      Write the balanced the balanced chemical equation for the synthesis of each ester

     The following are the balanced equation for the synthesis of esters

i)         CH3-CH(CH3)-CH2CH2-OH + CH3-COOH           H+         CH3-COO-CH2CH2-CH(CH3)-CH3 + H2O

ii)      CH₃-OH + CH₃CH₂CH₂COOH             ^H+                 CH₃CH₂CH₂COOCH₃ + H₂O

iii)    CH₃-OH + C₆H₄ (OH)COOH                 ^H+         C₆H₄ (OH) COOH-CH₃  + H₂O

iv)    CH₃CH₂OH + CH₃CH₂CH₂COOH            ^H+        CH₃CH₂CH₂-COO-CH₂CH₃   +  H₂O

v)      CH₃CH₂CH₂CH₂OH  + CH₃COOH               ^H+          CH₃COO-CH₂CH₂CH₂CH₃   + H₂O

5. Was the concentrated sulfuric acid a reactant? Describe the role of concentrated sulfuric acid. Where does it go after the reaction

Concentrated sulfuric acid is was not one of the reactant. Its role is to act as the catalyst and a dehydrating agent which forces the condensation reaction between alcohol and the carboxylic acid. Like most catalysts sulfuric acid speed up the rate of reaction and it is regenerated at the end of chemical reaction.

REFERENCE & LITERATURE CITED

http://science.howstuffworks.com/question391.htm

http://science.uvu.edu/ochem/index.php/alphabetical/e-f/fischer-esterification/