Nuclear Science and Technology - Volume 10, Number 1, March 2020

ty 
The results presented in Fig. 3 indicated 
that all chitosan- contaning solutions (CTS and 
CTS-GA solutions) exhibited ATBS
•+
 radical 
scavenging ability while GA solution did not. 
Moreover, the ATBS
•+
 radical scavenging 
ability of chitosan solution was higher than 
CTS-GA solution (A0 sample). This finding 
was suggested to be due to the obstacle of 
glucosamine over chitosan on scavenging 
ATBS
•+
 radical. Furthermore, the irradiated 
CTS-GA solutions manifested high ability on 
scavenging ATBS
•+
 radical in dependence on 
the irradiation dose and reaction time, namely 
the higher irradiation dose and/or reaction time 
the higher ATBS
•+
 radical scavenging capacity.
The formation of antioxidant compound by 
heating sugar-amino solution has been reported 
[23]. This result indicated that MRPs formed 
upon irradiation of chitosan-glucosamine 
solution possessed significant antioxidant 
potential. In addition, the dose-dependent 
antioxidant activity of irradiation treating 
chitosan-glucose solution has also been 
recorded in other study [16]. As the above 
discussion, during irradiation treatment, the 
early MRPs was almost saturated at the dose of 
25 kGy, while the late MRPs were produced 
continuously up to 100 kGy, so this results 
suggested that the formation of antioxidant 
compounds were mainly taken place at the late 
stage of Maillard reaction. 
Fig. 4. The result of agar well diffusion test (GA: glucosamine; A0, A25, A50 and A100 were the A 
solutions irradiated with the dose of 0, 25, 50, 75 and 100 kGy respectively). 
LE ANH QUOC et al. 
53 
Evaluation of antibacterial activity 
In Fig. 4, the A solutions prepared at 
different irradiation doses were able to form 
inhibition zone against E. coli while the GA 
sample was not. This meant that 
glucosamine did not exhibit the antibacterial 
activity in contrast to other A samples. 
Interestingly, around the well of A0 sample 
(a CTA-GA solution without irradiation), 
the presence of inhibition zone indicated that 
the antibacterial activity of this solution was 
due to the role of chitosan. The antibacterial 
ability of samples could be primarily compared 
through the diameters of their inhibition zones 
formed on the plate [21], therefore the result 
indicated that the antibacterial activity 
decreased obviously in A25, A50, A75 and 
A100 sample respectively. 
Fig. 5. Viable bacteria density of the suspension after exposing time (A0, A25, A50 and A100 were the A 
solutions irradiated with the dose of 0, 25, 50, 75 and 100 kGy respectively). 
Modification of chitosan via Maillard 
reaction has been widely studied and it is 
suggested that MRPs produced from chitosan-
sugar model system have been associated with 
the formation of compounds with high 
antibacterial [16, 22, 24]. However, there is no 
information of the influence of irradiation dose 
on the information of these compounds. Thus, 
in this study the antibacterial activities of 
MPRs prepared with different dose were 
examined and further compared with chitosan. 
Namely, after exposing time, the bacterial cell 
density of the suspensions at pH 5 and 7 was 
determined and described in Fig. 5. The result 
revealed that the antibacterial activity of A0 
sample was affected deeply by the pH value, 
namely been high at pH 5 and low at pH 7. As 
above discussion, the antibacterial activity of 
A0 sample was mainly contributed by chitosan, 
which was precipitated and reduced its 
bioactivity at neutral or alkaline solution, 
hence the antibacterial activity of A0 sample at 
pH 5 was greater than at pH 7. This finding is 
totally in concurrence with other studies where 
the pH-dependent antibacterial activity of 
chitosan has been reported [17, 25]. In 
addition, the obtained results also indicated 
that all testing samples had the lower bacterial 
cell density in comparison with the control, this 
meant that these samples exhibited an effective 
antibacterial activity against E. coli at both pH 
5 and 7. The lower viable bacteria density 
represented the stronger antibacterial activity. 
Therefore at pH 5 and 7, the antibacterial 
activity of irradiated samples decreased along 
with the increasing dose and A25 was the most 
antibacterial sample. This record completely 
matched with the results of agar well diffusion 
MAILLARD REACTION PRODUCTS OF CHITOSAN AND GLUCOSAMINE  
54 
test above. Furthermore, the higher 
antibacterial activity of chitosan-glucosamine 
derivatives prepared by heat-induced Maillard 
reaction than acid-soluble chitosan was also 
recorded in the study of Chung et al. (2005). 
In addition, because during irradiation 
treatment, the early MRPs were created prior 
to the formation of late MRPs so the results 
above suggested that the antibacterial 
activities of irradiated solutions were probably 
due to the role of early MRPs. Interestingly, 
the antibacterial activities of MRPs in 
irradiated solutions were maintained at high 
level at both pH 5 and 7. Hence, this result is 
one of the most demonstrations of Maillard 
reaction effectiveness in chitosan 
modification strategies. 
III. CONCLUSIONS 
This study demonstrated that the 
Maillard reaction can be easily occurred in the 
CTS-GA admixture solution by gamma 
irradiation. Moreover, the concentration of 
glucosamine suitable for Maillard reaction is 
much lower than the concentration of chitosan 
in the CTS-GA admixture solution, namely 
about 0.18% GA for 1% CTS (w/w), and as-
prepared CTS-GA MRPs exhibited high 
antioxidant activity and strong antibacterial 
activity at pH 5 and 7. These findings indicated 
that CTS-GA MRPs can be used as potential 
natural products replacing for synthetic 
additives in food or cosmetic. Further studies 
are necessary to elucidate mechanism of 
compounds formed during irradiation treatment 
and their application in practice. 
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