Ultrasound-assisted encapsulation of Pandan (Pandanus amaryllifolius) extract

Abstract

Pandan (Pandanus amaryllifolius) is commonly used as a food ingredient in Southeast Asia due to its delicious flavor, appetizing aroma and bright green colour. Pandan plant is uniquely found only in certain parts of the world. Despite its increasing popularity worldwide, its export market is limited by practical issues. One of the main problems for exporting Pandan to global market is its stability during transport. Due to the volatility of its active constituent, the functional properties of Pandan are lost during storage and shipment. In this study, we explored the ability of ultrasound processing technology to encapsulate the aromatic Pandan extract using lysozyme or chitosan as a shell material. 20 kHz ultrasonicator was used to encapsulate the pandan extract at 150 W of applied power. Two parameters, the ultrasonic probe tip and the core-to-shell ratio were varied to control the properties of the encapsulates. The diameters of the probe tip used were 0.3 and 1.0 cm. The core-to-shell volume ratios used were 1:160 and 1:40. The size distribution and the stability of the synthesized microspheres were characterized to understand and explore the possible parameters variation impact. Both size and size distribution of the microspheres were found to be influenced by the parameters varied to certain extent. The results showed that the mean size of the microspheres was generally smallest when using 1 cm probe tip with lower core-to-shell volume ratio but largest when using the 3 mm tip with higher core-to-shell volume ratio. This indicates that the sonication parameters could be fine-tuned to achieve the encapsulation of Pandan extract for storage and export. The pandan-encapsulated microspheres were also found to be stable during storage at least for one month.

Keywords: Chitosan microspheres; Encapsulation; Lysozyme microspheres; Pandan; Ultrasound.

Graphical abstract

Fig. 1

Pandan plant commonly found around houses, and some Pandan-based delicacies.

Fig. 2

The image of Pandan leaf under SEM with 1000 times magnification (a) before and (b) after solvent extraction. The oil glands can clearly be seen on both images. The destruction of these oil glands during pretreatment will affect the extraction rate.

Fig. 3

The extraction curve plot for Pandan with washing process dominating at the beginning, and diffusion process dominating after. Inset: The washing process involves the action of solvent washing the compounds around the oil glands, and the diffusion process involves the diffusing action of solvent into the oil glands.

Fig. 4

The HPLC chromatogram of Pandan extract.

Fig. 5

The images of pandan extract in (a) and (b) lysozyme microspheres and (c) and (d) chitosan microspheres taken by optical microscopy with 100 times magnification.

Fig. 6

The size distribution of Pandan:lysozyme microspheres with (a) volume ratio of 1:160 using 0.3 cm tip probe (●,▬) and 1.0 cm tip probe (○, - - -); (b) volume ratio of 1:40 using 0.3 cm tip probe (■, ▬) and 1.0 cm tip probe (□, - - -); and Pandan:chitosan microspheres with (c) volume ratio of 1:160 using 0.3 cm tip probe (●,▬) and 1.0 cm tip probe (○, - - -); and (d) volume ratio of 1:40 using 0.3 cm tip probe (■, ▬) and 1.0 cm tip probe (□, - - -).

Fig. 7

The size distribution of Pandan:lysozyme microspheres using (a) 0.3 cm probe tip with core-to-shell ratio 1:160 (●,▬) and 1:40 (○, - - -); (b) 1.0 cm probe tip with core-to-shell ratio 1:160 (■, ▬) and 1:40 ((□, - - -); and Pandan:chitosan microspheres using (c) 0.3 cm probe tip with core-to-shell ratio 1:160 (●,▬) and 1:40 (○, - - -); and (d) 1.0 cm probe tip with core-to-shell ratio 1:160 (■, ▬) and 1:40 ((□, - - -).

Fig. 8

The images of Pandan in lysozyme encapsulates (a) upon encapsulation, (b) after a month; and Pandan in chitosan (c) upon encapsulation and (d) after a month.

Fig. 9

Pandan-lysozyme microspheres size distribution as a function of storage time. a) volume ratio of 1:160 sonicated with 0.3 cm probe diameter; b) volume ratio of 1:160 sonicated with 1.0 cm probe diameter; c) volume ratio of 1:40 sonicated with 0.3 cm probe diameter; d) volume ratio of 1:40 sonicated with 1.0 cm probe diameter.

Fig. 10

Pandan:chitosan microspheres size distribution as a function of storage time. a) volume ratio of 1:160 sonicated with 0.3 cm probe diameter; b) volume ratio of 1:160 sonicated with 1.0 cm probe diameter; c) volume ratio of 1:40 sonicated with 0.3 cm probe diameter; d) volume ratio of 1:40 sonicated with 1.0 cm probe diameter.