NONENZYMATIC BROWNING

1.0 INTRODUCTION

The term “browning” in relation to food refers to several different processes

which can be divided into enzymatic and non-enzymatic browning reactions1.

The most common type of non-enzymatic browning is the Maillard reaction. It

refers to a series of chemical reactions between sugars and proteins that make foods more

appetizing1. Maillard browning of foods as a result of the Maillard reaction, and the

brown pigments that form are called melanoidins. Unwanted brown colors and off- odors

can develop during extended storage of foods as baked products, dried egg whites, instant

mashed potatoes, and certain food ingredients. However, not everything about the

Maillard reaction is negative. The pleasant aroma and browned surfaces of baked bread

and other baked goods, the development of chocolate flavors in roast beef and other

cooked meats is due to this reaction. The Maillard reaction known as nonenzymatic 1browning because enzymes are not part of the reaction and its can be viewed as a

sequence of three chemical reactions such as condensation, rearrangement and

polymerization2.

The second type of non-enzymatic browning is caramelization, which is occurs when

carbohydrates or sugars in any food are heated. Caramelization results in light to dark

brown and new flavours in the product. Caramelization plays an important role in

roasting of coffee and commercial caramels are added as food colours or flavours1.

2.0 MATERIALS

Sample A (glucose solutions), sample B (glycine solutions), sample C (Whey protein

isolate), sample D (hydrolyzed Whey protein isolate), sample E (cookie dough @ bread)

spectrophotometer and cuvettes, hot plate &boiling water bath, oven set at 200ºC, baking

trays, filter paper, foil, frying pan and oil, small paint brushes.

3.0 PROCEDURE1 http://www.food-info.net/uk/colour/enzymaticbrowning.htm

2 Murano, S. Peter. 2003. Understanding Food Science and Technology. Texas A&M University. Thomson & Wadsworth. (pg 123, 124)

3.1 Liquid Model System Browning.

1. 20 ml of glucose solution (A) is mixed well with 20 ml of glycine (B) in 250 ml

beaker. 4 ml of the mixture is poured into the cuvett, and the absorbance (450 nm)

is measured quickly. This sample is labeled as 0 minute interval. The beaker is

covered with aluminum foil.

2. The beaker is heated in water bath, then at intervals (10, 20, 40, 80, 100 min) and

removed beaker from the water bath, 4ml of mixture is poured into the cuvett and

the absorbance (450 nm) is measured quickly. All used samples are kept for

comparison.

3. At the end of the experiment the cover is removed and the aroma is described.

The smell of the product is compared with the smell of starting compounds.

3.2 Solid Model System Browning

1. Two points are marked on a piece of filter paper about 2 cm apart.

2. One drop of glucose (A) is applied to one point and one drop of amino acid (B) to

the other. The liquid circles should expand and partly overlap. The paper is fried

for a few seconds.

3. The procedure is repeated by applying one drop of glucose to one point and one

drop of each of the protein solutions (C & D) to the other. The liquid circle should

expand and partly overlap. The paper is fried for a few seconds.

4. These papers is photocopied onto a single sheet it is included in the results.

3.3 Browning of Baked Goods

1. The dough is shaped into 25 g cookies as described on the packaging and is

arranged on parchment paper on a cookie sheet.

2. A glass rod is used to press two small lines into the cookie surface to divide it

into quarters.

3. The cookie is painted half with amine solution and half with glucose as shown in

lab manual. The cookie is left 5 min to let the surface dry.

4. The parchment paper is marked under the cookie which one quarter got glucose

and amine solution, one just glucose, one just amine, and one nothing.

5. The cookie is baked for 5 min and the color and aroma of the samples are

described.

3.4 Unknown Sample for Liquid Model System Browning

1. 4 test tubes are taken and placed each of it with ~5 ml of unknown (albumin)

samples.

2. 1 test tube is placed in the water bath at temperature 55ºC and left it for 30 min.

3. The sample is cooled in tap water.

4. The absorbance is taken at 450 nm. The unheated sample is used to zero the

spectrophotometer.

5. The procedures are repeated to the other test tubes at temperature 60 ºC, 63 ºC

and 65 ºC.

4.0 RESULT

4.1 Liquid Model System Browning

From this experiment the result is recorded in data and figure out with graph

which involved absorbance and time for the model systems. The aromas also

recorded for unheated reagents and model systems.

Intervals (min) Absorbance (A)

0 0.02710 0.04820 0.05340 0.05980 0.064100 0.066

Table 4.11

Sample Aromas

Unheated reagents No aroma

Model systems Caramel-like flavor

Table 4.12

Graph 4.11 : Absorbance versus Time

4.2 Solid Model System Browning

Sample Observation

Sample A and sample B are overlap after fry the paper. Sample B is more browning compare with sample A.

Sample A and sample C are not overlap after fry the paper. Sample A is more browning compare with sample C.

Sample A and sample D are not overlap after fry the paper. Sample A is more browning compare with sample D.

Table 4.21

4.3 Browning of Baked Goods

AB

Figure 4.31

The quarter of baked goods is describes as follows:-

Quarter Contents Observation

A Glycine This quarter is less browning compare with quarter C

B None This quarter is the less browning compare with others.

C Glucose This quarter is more browning compare with quarter A

D Glucose + Glycine This quarter is the most browning compare to others.

Table 4.31

4.4 Unknown Sample For Liquid Model System Browning

DC

From this experiment the result is recorded in data and figure out with graph

which involved absorbance and time for the model systems. The appearance of

the solution also recorded for each temperature.

Temperature (°C) Absorbance (A) Appearance 55 0.195 Cloudy 60 0.142 Slightly cloudy63 0.139 Less cloudy65 0.124 Most less cloudy

Table 4.41

Graph 4.41: Absorbance versus Temperature

5.0 DISCUSSION

1. The model system experiment is conducted in pH 8 buffer rather than a

more typical food pH (3-7) because Maillard reaction undergo particularly

in alkaline solution.

2. The structure of the aldehyde formed from Glysine and Lysine via the

Strecker degradation is described below:-

- Aldehyde formed from Glysine

O

CH 3C-H

- Aldehyde formed from Lysine

O

NH2(CH2)4CH 2C-H

3. The Hydrolyzed protein will brown slower than an intact protein because

most of the chain of protein break and the amount of amino acid less than

its origin so that the protein can’t brown faster as intact protein.

4. In the model systems the paper samples browned the fastest due to the

present of water that inhibit browning. The solution samples did not go

brown because it contains high water concentration and take a lot of time

to make it brown. Furthermore, the paper brown so rapidly compared to

the solutions because of the present of high temperature while fry it. The

protein hydrolysis will make the differences because of the lower amount

of amino acids inside it.

5. The other ingredients in the cookie that take part in the reactions and

heating different are like sugars, oil and baking powder.

6. From the graph 4.41, the curve decrease slightly compare to visual

observation due to the molecules of protein become far apart so that the

spectrophotometer will penetrate the medium easily and finally give a

lower reading.

7. The effect of heat on protein will make it structure denatured.

6.0 CONCLUSION

In nonenzymatic browning, the solid model system browning undergoes the reaction

more rapidly compare to the liquid model system browning. The samples will easily

browning due to the concentration of protein and water.

7.0 REFERENCES

1. Murano, S. Peter. 2003. Understanding Food Science and Technology. Texas

A&M University. Thomson & Wadsworth. (pg 123, 124)

2.