FACULTY OF APPLIED SCIENCES
LABORATORY REPORT
CHEMISTRY OF FOOD COMMODITIES
(FST 663)
TITLE OF EXPERIMENT NON-ENZYMATIC BROWNING: MAILLARD REACTION
NO. OF EXPERIMENT 5
NAME OF STUDENT NUR SYAFIQAH BINTI SUHAIMI (2018287486)
DATE OF EXPERIMENT 6/5/2020
LECTURER’S NAME DR. MOHAMAD ZAREI
INTRODUCTION
Non-enzymatic browning are the chemical reaction which does not involve the enzyme. The
reaction occurs in many foodstuffs at high temperatures and low moisture. It is also responsible
for the desirable aroma and flavours in food.
Non-enzymatic browning are classified into caramelization and Maillard reaction.
Caramelization is the complex series of reaction that occur when a sugar heated to a
temperature greater than its melting point which include dehydration, decomposition and
polymerization of sucrose molecule which results in the formation of caramel colour and
flavoured compound.
Meanwhile, Maillard reaction is the reaction between one carbonyl group from reducing
sugar and free amino group from amino acids or proteins to produce N-glycosylamines.
Reducing sugar contain aldehyde or ketone group in its chemical structure. Glucose, fructose
and lactose are the examples of reducing sugar. Sucrose are categorized as non-reducing sugar
but when applying high temperature and lower the pH, it will hydrolysed. Once hydrolysed,
sucrose will break down into glucose and fructose. Then, the available glucose will be able to
participate in the reaction and then cascade into melanoidin.
There are some factors that affect Maillard reaction which are temperature and pH.
Higher temperature results in a rapid increase of rate of browning for 2-3 times for each 10 o C
rise in temperature. Yet, at a lower temperature, Maillard reaction still be occur but at a slower
rate of reaction. Rate of the reaction increases with increase pH, though pH 6-8 is the optimum
condition where more hexoses in open chain.
OBJECTIVES
1. To observe the colour and flavour changes when glycine is mixed and heated with
glucose
2. To monitor the progress of browning by measuring the increase in absorbance at 490 nm
over time using spectrophotometry
MATERIALS /APPARATUS
Cuvettes 0.1 M HCl
Spectrophotometer 0.1 M NaOH
Vortex Mixer Sodium metabisulphite
pH meter Analytical balance
Distilled water Spatula
3 g glucose (0.1M, 0.2M, 0.3M ,0.4M and 0.5M)
0.5 g glycine
METHODS
1. Blank reagent was prepared by adding 3 g solid glucose and 0.5 g solid glycine into 5 ml
distilled water in a test tube. The test tube then was warmed slightly before using the
vortex mixer to dissolve the mixture.
2. The pH of the prepared solution was then measured. The test tube was placed in the
boiling water bath. The exact time for the appearance of a brown colouration were noted
together with the smell of the contents. The pH of the solution was measured again.
3. Step 1 and 2 were repeated using 5 ml of 0.1 M HCl in place of distilled water. The
solution was heated for the same length of time as in step 2.
4. Step 1 and 2 were repeated using 5 ml of 0.1 M NaOH in place of distilled water. The
solution was heated for the same length of time as in step 2.
5. Step 1 and 2 were repeated using 5 ml of 0.1 M , 0.2 M, 0.3 M, 0.4 M and 0.5 M sodium
metabisulphite in place of distilled water. The solution was heated for the same length of
time as in step 2.
6. The absorbance of all tubes were measured at490 nm, and reagent blank was used to set
as zero to the spectrophotometer.
7. A graph of absorbance vs concentration of sodium metabisulphite was plotted.
RESULTS AND DISCUSSION
Table 1: pH reading (before and after) and smell of the samples
Time pH
Samples Smell
(min) Before After
Blank 5.26 5.00 Sweet
0.1 M HCl 3.46 3.49 Sweet
0.1 M NaOH 7.13 6.97 Sweet
0.1 M 5.32 5.14 Sour
6
0.2 M 5.21 5.11 Sour
Sodium
0.3 M 5.15 5.09 Sour
metabisulphite
0.4 M 4.99 4.91 Sweet
0.5 M 4.81 4.83 Sweet
Based on Table 1, it shows the pH reading of the samples solution before and after being
heated in boiling water bath for 6 minutes. All of the samples records a decrease in pH reading
except for the samples in 0.1 M HCl and 0.5 M sodium metabisulphite.
For the samples in 0.1 M HCl, 0.1 M NaOH, 0.4 M sodium metabisulphite and 0.5 M sodium
metabisulphite, all of them give out sweet smell similar to the blank. Meanwhile, the samples in
0.1 M, 0.2 M and 0.3 M gives out sour smell due to reduction of pH reading.
Table 2: Absorbance of different concentration of sodium metabisulphite
Samples Absorbance at 490 nm
Blank 0.000
0.1 M 0.000
0.2 M 0.002
Sodium metabisulphite 0.3 M 0.007
0.4 M 0.010
0.5 M 0.014
Based on the Table 2, it shows the increase in absorbance in the series of concentration of sodium
metabisulphite at 490 nm.
CONCLUSION
In conclusion, enzymatic browning will still occur after the tissue as the entrapped enzyme in
the fruits has contact with the oxygen. However, there are both physical and chemical method
can be applied in order to prevent or slow down the enzymatic browning to make the fruits more
palatable and desirable. Therefore, the objectives of the experiment were successfully achieved.
QUESTIONS
1. Describe changes in physical appearance and chemical structure as dry glucose is heated
to 160 o C and above.
2. Why is Maillard reaction important in food processing?
It is important in food processing such that its result in desirable effect in food products.
For instance, formation of brown crust on bread.
3. Explain the steps involved in Maillard reaction.
Maillard reaction involves a number of steps such as the following:
i. Condensation reaction between the free amino group of amino acids or proteins
and carbonyl groups of reducing sugar. The condensation compound will lose
water to form Schiff’s base and undergoes cyclization to produce N-substituted
glycosylamine.
ii. The unstable N-substituted glycosylamine undergo transition and rearrange from
aldose to ketose sugar derivative (1-amino-1-deoxy-2-ketose).
iii. After the formation of ketose derivatives, it undergoes degradation of two
different pathways which are methyl dicarbonyl intermediates and 3-
deoxyhexosones intermediates.
iv. In the final stages of Maillard reaction, a caramel like aroma is evident and
colloidal with the presence of insoluble melanoidin as a result of complex aldol
condensation and polymerisation.
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https://www.ifst.org/lovefoodlovescience/resources/fruit-and-vegetables-enzymic-
browning
Irina, I., & Mohammed , G. (2013). Preventionof Enzymatic Browning in Fruit and Vegetables.
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Noriham, A., Halimahton Zahrah, M., & Hariyah , H. (2007). Food Chemistry : A Laboratory
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