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Microencapsulation of bioactive leaf extracts of Eucalyptus camaldulensis by freeze drying technology using sodium alginate and sodium carboxymethyl cellulose as coating materials
* 1 , * 2
1  Natural Products Research Center of Excellence, Department of Microbiology, Prince of Songkla University.
2  Natural Products Research Center, and Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla 90112, Thailand.

Published: 30 October 2019 by MDPI in 5th International Electronic Conference on Medicinal Chemistry session ECMC-5

Bioactive crude ethanolic extracts of Eucalyptus camaldulensis was encapsulated with alginate–CMC using freeze drying technique. The microcapsules were characterized for particle size, morphology, physicochemical parameters such as solubility, swelling index, and micromeritics properties. FTIR was used to evaluate the interactions of the polymer and the extract. Antioxidant and antimicrobial activities of the microcapsules were also demonstrated. Results revealed and irregular shaped microparticles with mean diameter ranging from 6.7–26.6 µm. Zeta potential and polydispersity index ranged from -17.01–2.23 mV and 0.344–0.489 respectively. Percentage yield and encapsulation efficiency ranged between 70.4–81.5 % and 74.2±0.011 – 82.43±0.772 %. In addition, the microcapsules exhibited high swelling index with poor solubility. Antioxidant activity of the microcapsules evaluated using DPPH and ABTS assays increased with increase in the concentration of the extract. Minimum inhibitory and minimum bactericidal concentrations of the microcapsules against gram-positive foodborne pathogens ranged from 0.19–3.12 mg/mL and 0.19–12.25 mg/mL respectively. Moreover, the microcapsules at concentration of 1 mg/mL did not show cytotoxic effects on human colon cell CaCo-2. Alginate–CMC showed good encapsulation properties that preserved the bioactivity of the extract, thus might be employed for application of natural products in processing systems.

Keywords: Microencapsulation; Freeze–drying; Eucalyptus camaldulensis; Bioactive; Cytotoxicity
Comments on this paper
Ozioma Nwabor
Objective of the work
Preliminary results showed that extract of E. Camaldulensis exhibited excellent antimicrobial and antioxidant properties. However, the dark green colour of the extract constitutes a problem to addition in food. In addition, the extract when added directly to minced meat, and milk did not reproduce corresponding activities as seen in the initial antimicrobial screening. Hence the work was mean to encapsulate the extract as a way of reducing the effect of its colour on food and in addition preserve the bioactive of the extract.

Unfortunately, although the microcapsules or particles showed antimicrobial and antioxidant properties, encapsulation did not effectively mask the colour.