Non Enzymatic Browning

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

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browning 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 PROCEDURE 1

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

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 10 20 40 80 100

0.027 0.048 0.053 0.059 0.064 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

B

C

A

D

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

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) 55 60 63 65

Absorbance (A) 0.195 0.142 0.139 0.124

Appearance Cloudy Slightly cloudy Less cloudy 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

C-H

3

- Aldehyde formed from Lysine

O NH2(CH2)4CH

2

C-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.