Elsevier

Colloids and Surfaces B: Biointerfaces

Volume 148, 1 December 2016, Pages 333-342
Colloids and Surfaces B: Biointerfaces

Formulation and characterization of esterified xylo-oligosaccharides-stabilized oil-in-water emulsions using microchannel emulsification

https://doi.org/10.1016/j.colsurfb.2016.09.003Get rights and content

Highlights

  • Successful xylo esters-stabilized droplets were generated from MCE.

  • Mixture of xylo esters and Tween series were optimized emulsifiers in MCE.

  • Xylo esters have limitation to produce monodisperse emulsions droplets.

  • Xylo esters have stabilizing effect on O/W emulsion droplets in MCE.

  • Mixture of xylo ester and Tween enhanced the storage stability of emulsion.

Abstract

A series of amphiphilically esterified xylo-oligosaccharides (xylo esters) with different fatty acids residues – decanoic acid (C-10), lauric acid (C-12) and palmitic acid (C-16) – were enzymatically modified at 60 °C for 4 h. These xylo esters were used as emulsifiers to formulate oil-in-water (O/W) emulsions by microchannel emulsification (MCE). Grooved and straight-through MCE was used to investigate the droplet generation and/or emulsion stability. Xylo ester-stabilized oil droplets were generated smoothly from microchannels arranged linearly or two dimensionally, while xylo ester-stabilized emulsions were less monodispersed owing to low surface activity of the xylo esters. The combined use of xylo esters (2.5% (w/w)) and Tween series (0.1% (w/w)) in the continuous phase can improve the monodispersity of the resultant oil. Successful droplet generation was achieved with the straight-through MCE using 2.5% (w/w) xylo laurate and 0.1% (w/w) Tween 20. The optimized combination of xylo laurate and Tween 20 inhibited coalescence and oiling off more efficiently than the droplets solely stabilized by Tween 20 during 30 days of storage.

Introduction

Amphiphilically esterified xylo-oligosaccharides (xylo esters) have both hydrophilic and hydrophobic sub-regions. Their functional properties can be fine-tuned by adjusting the ratio between the hydrophilic part (xylo-oligosaccharide) and the hydrophobic part (fatty acid), as well as the amount and chain length of the alkyl residue. Therefore, xylo esters have the ability to act as low-molecular-weight surfactants and may exhibit good stabilizing ability, probably owing to steric stabilization based on their macromolecular structure [1]. The emulsion stabilization effect of xylo esters may be attributed to the fatty acid tails combined with the xylo-oligosaccharide backbone. This newly established interaction with the oil surface and hydrophilic parts protects the emulsions against flocculation [2], [3]. Enzymatic processes offer an attractive alternative route for the synthesis of xylo esters, as they are environmentally and health-friendly processes [4]. Udomrati and Gohtani [5] used xylo esters as stabilizers to improve the stability of Tween 80-stabilized Oil-in-Water (O/W) emulsions, which were produced by a high-pressure homogenizer. Their results showed that xylo esters extended the critical flocculation concentration and delayed creaming rate. Xylo esters were used as sole emulsifiers in n-hexadecane O/W emulsion at a concentration range of 5–35% (w/w) [6] and in soybean O/W emulsion with concentrations of 10–50% (w/w) [7]. These emulsions were also prepared by a high-speed homogenizer. These papers reported that xylo esters exhibit both emulsifying and stabilizing activities. For xylo ester (10–20% (w/w))-stabilized soybean O/W emulsion, oiling off was observed during 7 days of the storage period because of insufficient emulsion stabilization in terms of coalescence. However, there was no oiling off at concentrations of 30–50% (w/w) and no creaming at a concentration of 50% (w/w), suggesting that the stability of the emulsion was remarkably improved by increasing the xylo ester concentration as a result of the increasing viscosity of the continuous phase and/or the sufficient emulsion stabilization. The emulsion systems described above were polydisperse emulsions with the coefficient of variation (CV) ranging from 28 to 50%.

Microchannel emulsification (MCE) is an advanced technique for producing monodisperse emulsions with the CV values lower than 5%. MCE involves a very mild droplet generation process that is further driven owing to interfacial tension difference at the micrometer scale [8], [9]. Monodisperse emulsions have the advantage of controllable properties such as texture and stability of food and cosmetic products, and bioavailability, dispersibility, and permeability for pharmaceutical products. Several researchers have encapsulated hydrophilic/lipophilic bioactive molecules using MCE, such as β-carotene [10] and L-ascorbic acid [11], [12], [13]. The emulsion stabilization mechanism for xylo esters in O/W emulsions is assumed to be the adsorption of their hydrophobic part on the oil droplet surface, and they later act as a stabilizing agent [7]. MCE may be a suitable method to produce polysaccharide-stabilized emulsions, since MCE enables formulation of oil droplets under a very mild process, thereby avoiding emulsifier particle degradation. Udomrati and Gohtani [5], [6], [7] have reported that the surface activities of xylo esters are rather low, and hence, the combination of xylo esters and Tween-series may increase the stabilization effect. The main aim of this research is to reduce the amount of Tween-series when formulating monodisperse emulsions by MCE. The preparation and stability of monodisperse O/W emulsions stabilized by xylo esters are of particular interest, since there are no reports on this in the literature. The purpose of the present study was to investigate the effect of the concentration and type of xylo esters and Tween-series on the emulsion droplet generation by MCE, to study the effect of the combination of xylo esters and Tween-series on the emulsion droplet generation by MCE, and to evaluate the stability during the storage period.

Section snippets

Materials

Xylo-oligosaccharide extracted from corn was supplied by San-Ei Gen F.F.I. (Osaka, Japan). The range of degree polymerization of the xylo-oligosaccharide was 2–7. Lipase from Thermomyces lanuginosus solution, containing 2% (w/v) lipase, was purchased from Sigma-Aldrich (Buchs, Switzerland). Thermomyces lanuginosus lipase was used, because the present work set out to complement the results of our previously published research [14] that investigated optimum reaction condition for esterified

Effect of concentration of xylo laurate on emulsion formulation

Udomrati and Gohtani [6] reported that xylo laurate has more efficient emulsifying properties and a greater potential for the stabilization of emulsion in a centrifugal field, as compared to xylo decanoate and xylo palmitate, because xylo laurate may cover more of the emulsion droplet surface and/or cover the oil surface with more a stable film. Hence, we focused on xylo laurate for producing and stabilizing monodisperse emulsions using MCE. For the droplet generation by grooved MCE, the

Conclusion

According to our findings, xylo esters have a limitation to formulate monodisperse O/W emulsions by MCE because of their low surface activity. Adding an appropriate concentration of xylo ester in the continuous phase reduced the amount of a Tween emulsifier to formulate monodisperse emulsion with CV less than 5%, because of the synergetic activities of xylo ester and Tween to make droplet generation smooth for both grooved and straight-through MCE. Storage stability of the resultant O/W

Acknowledgment

This research was supported by the UNU-Kirin Fellowship Program at the National Food Research Institute (NFRI), Tsukuba, Japan, in 2015-2016.

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