Antioxidant Activity of biodegradable PLA film Reinforced with Chitin Nanocrystals

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Wageningen Universiteit, VLAG Graduate School, Food Process Engineering, Hollanda

Tezin Onay Tarihi: 2020

Tezin Dili: İngilizce

Öğrenci: Pien van Streun

Danışman: Murat Yanat

Özet:

For the development of a bio-based and biodegradable food packaging with antioxidative functionality, the

antioxidant activity of PLA reinforced with chitin or chitosan nanoparticles (NPs) is investigated. Literature

indicates that chitin can reinforce PLA film at 5% w/w filler content. As there are indications that chitin and

chitosan portray antioxidant activity, this could add relevant functionality to this biodegradable film. Although

the mechanism is not completely clear, the hydroxyl and acetylamino/amino groups of chitin and chitosan are

expected to play a role in the antioxidant effect.

For the nanocomposites, particles with a reproducible size and a small variation within the batches are needed.

Therefore the size and the reproducibility of the chitosan NPs is determined. The reproducibility of the particle

size needs to be improved. After 4 or more minutes of Ultra-Turrax agitation, the standard deviation of the

particle size decreases, so this can be a helpful tool for reducing the polydispersity of the chitosan NPs. The size

of the chitosan NPs decreased upon sonication The average particle size of the chitosan NPs is 6095 ± 1721 nm

before, and 332 ± 37 nm after sonication treatment.

The antioxidant activity of the chitin and chitosan NPs is evaluated with the DPPH radical scavenging assay, and

compared to their respective powders. The maximum radical scavenging inhibition capacities are 2.82, 1.49,

0.48, and 0.00 %/(g/L) for respectively chitin NPs, chitosan NPs, chitin powder, and chitosan powder. The fact

that chitin has higher antioxidant activity than chitosan is contradicting literature. One option is that this can be

attributed to the difference in zeta potential. The chitin NPs have a higher average zeta potential (+60 ± 6.6 mV)

than the chitosan NPs (+39 ± 7.7 mV), indicating a higher amount of protonated amino groups for chitin. This is

remarkable, as chitosan contains more free amino groups due to its higher degree of deacetylation. Another

option is that there are other mechanisms involved than the proposed primary antioxidant action involving the

hydroxyl and amino groups. The DPPH inhibition of the chitin and chitosan nanocomposites is <1% after 12

hours, at 15% filler content. The acquired nanocomposites are not homogeneous and fragile. In this report, there

is a relation observed between antioxidant activity and total surface area for the chitin and chitosan particles.

Although more research has to be done to substantiate this relation, it can be used to make estimations on the

potential maximum antioxidant activity of chitin NPs. Therefore, to improve the antioxidant activity of the chitin

NPs in nanocomposites, it is suggested to increase the total surface area of the NPs. In the current paper, the

maximum surface area of chitin NPs is ~65 m2

, whereas a total surface area of ~ 350 m2

is reported for

individually dispersed chitin NPs. It can be concluded that the development of an antioxidative PLA – chitin

nanocomposite would be promising, under the condition that the antioxidant within the matrix is improved.

This could be achieved by surface modification with fatty acids to increase the hydrophobicity of chitin, or

strategies to make the NPs smaller could be implemented (acidic environment, sonication, and Ultra-Turrax

agitation, low molecular weight chitin or chitosan). Further research into the effect of degree of deacetylation

on antioxidant activity, and on the antioxidative mechanisms of chitin and chitosan is required.