Comparison of ergocalciferol nanodispersions prepared using modified lecithin and sodium caseinate: Insights of formulation, stability and bioaccessibility

https://doi.org/10.1016/j.jff.2017.08.047Get rights and content

Highlights

  • Successful formulation of nanodispersions loaded with ergocalciferol.

  • ML formulated smaller particles than SC via solvent displacement method.

  • Nanodispersions have good stability against pH, ionic strength and heating.

  • Both emulsifiers formulated nanodispersions with longer storage stability.

  • Bioaccessibility of nanodispersions increased after addition in milk.

Abstract

In this work, we compared the formulation, stability and bioaccessibility of ergocalciferol nanodispersions using modified lecithin (ML) and sodium caseinate (SC) as natural emulsifiers. The mean particle size of nanodispersions stabilized by ML (56 nm) was much smaller than those stabilized by SC (112 nm). The ML-stabilized nanodispersions were stable over a wide range of pH, NaCl concentrations and heating, but became unstable with slight increase in particle size when exposed to CaCl2 solution. In comparison, SC-stabilized nanodispersions were relatively unstable to particles aggregation at pH 4 and 5, CaCl2 addition and heating. Long-term stability for ergocalciferol were observed in both ML- and SC-stabilized nanodispersions. In the absence of milk, the ergocalciferol bioaccessibility was strongly dependent on the emulsifier type, with ML providing much higher bioaccessibility than SC. During in vitro gastrointestinal digestion, the incorporation of milk into nanodispersions could increase the bioaccessibility and stability for ergocalciferol.

Introduction

Vitamin D is one of the essential bioactive compounds for human being, due to its special health-promoting functionality. Previous studies have demonstrated that this substance contributes to the development of bone, teeth and cartilage (Cranney, Weiler, O'Donnell, & Puil, 2008 and Hark & Deen, 2005). Moreover, it also prevents cancer, and enhances the heart and immune system (Haham et al., 2012 and Holick, 2001). Ergocalciferol is a type of plant-based vitamin D, which is naturally present in a low amount in wild mushrooms, whereas another type called cholecalciferol can be produced in the human skin via the exposure of sunlight (Guttoff, Saberi, & McClements, 2015). However, there is still an estimated one billion people worldwide who either have vitamin D deficiency or insufficiency due to limited sun exposure, extensive UV-protecting sun cream usage, or poor dietary intake (Guttoff et al., 2015 and Khalid et al., 2015). For these above-mentioned reasons, fortified food and beverage products with vitamin D are gaining attention in food industry nowadays. However, vitamin D has poor water-solubility, chemical instability towards environmental stresses and variable oral bioavailability (Haham et al., 2012 and Tsiaras & Weinstock, 2011), which strongly limit the application of this vitamin as a functional ingredient to be incorporated into aqueous-based food products. In order to overcome these drawbacks in commercial usage, numerous efforts have been carried out to improve their water-solubility, stability and bioavailability through entrapment of this nutraceutical component into various types of colloidal delivery systems (Abbasi et al., 2014, Guttoff et al., 2015, Mohammadi et al., 2014, Ozturk et al., 2015a, Patel and San Martin-Gonalez, 2012).

Among these delivery systems, lipid-free nanodispersions consisting of fine nano-sized dispersed particles (20–200 nm) in aqueous phase have received great attention recently in food, cosmetic and pharmaceutical applications, due to their high optical clarity and impressive improvement in solubility, stability and bioavailability (Anarjan et al., 2015 and Acosta, 2009). There are two approaches, namely high-energy or low-energy methods, used to produce fine nanodispersions. In the high-energy approach, e.g. emulsification-evaporation method, certain expensive instrument such as high-pressure homogenizers, microfluidizers or ultrasonic probes are required to generate huge amount of disruptive forces to break large particles into nanoparticles. However, this approach might be undesirable for preparing nanodispersions containing heat-sensitive bioactive components due to the considerable generation of heat during the processing (Tan et al., 2016a). Thus, the low-energy approach, including methods such as solvent displacement, emulsification-diffusion and spontaneous emulsification, is starting to gain popularity currently due to its simplicity and cost-effectiveness (Tan et al., 2016a).

During the production of nanodispersions via either high-energy or low-energy methods, an emulsifier/surfactant is crucial for the formation of nanodispersed particles and to prevent them from aggregation against the destabilization process. In addition, it has been reported that this emulsifier layer could act as a barrier to protect the coated bioactive compounds from degradation by limiting the attack of oxidation inducers like free radicals and metal ions (Coupland & McClements, 1996 and Tan et al., 2016b). Many previous studies used synthetic surfactants (such as polysorbates, polyglycerol ester of fatty acids, sodium dodecyl sulfate and so on) to produce nanodispersion-based delivery system for nutraceuticals with poor water-solubility (Tan and Nakajima, 2005, Tan, Tang, et al., 2016, Tan et al., 2016b). However, consumers nowadays are demanding commercial food or beverage products containing ‘label-friendly’ ingredients in consideration of their health. Therefore, there is considerable interest in utilizing the more label-friendly emulsifiers (such as natural emulsifiers) to produce nanodispersion- or nanoemulsion-based delivery systems. Sodium caseinate (SC), is a natural protein emulsifier, widely used as an effective emulsifying agent in the food industry. SC is a good alternative to synthetic surfactants, since it can facilitate the formulation of colloidal delivery systems and stabilize the emulsified droplets/particles against aggregation owing to a combination of electrostatic and steric repulsion (Liu, McClements, Cao, & Xiao, 2016). In comparison to other protein emulsifiers (such as whey protein isolate and whey protein concentrate), SC has better thermal stability due to its relatively disordered structure (Chu, Ichikawa, Kanafusa, & Nakajima, 2008). Natural lecithin derived from soybean, egg or milk, should be modified via chemical or enzymatic techniques before it is effective at stabilizing emulsion/dispersion (Weete, Betageri, & Griffith, 1994). Modified lecithin (ML) is a zwitterionic emulsifier with effective emulsifying property, and provides high electrostatic repulsion to prevent the coated droplets/particles from growth. The ML emulsifier used in our work is an enzymatically modified phospholipid derived from the hydrolysis of soy lecithin. This kind of modified phospholipid could also be considered as a natural emulsifier, because both the materials and the enzymatic process used to produce the phospholipids is natural (Van Hoogevest & Wendel, 2014).

To the best of our knowledge, information related to the formulation of ergocalciferol nanodispersions using SC or ML via low-energy methods is still limited. In the current work, we aimed to produce ergocalciferol nanodispersions using the natural emulsifiers (SC or ML) via solvent displacement method, and then compare the stabilizing properties of the two emulsifiers against different environmental conditions (such as pH, ionic strength and thermal treatment) and during long-term storage at 4 °C. In addition, the bioaccessibility of ergocalciferol nanodispersions in commercial lemon juice and milk as model system was also investigated using an in vitro gastrointestinal digestion model. The study provides important information for utilizing natural emulsifiers in the development of label-friendly nanodispersion-based delivery system for water-insoluble vitamins or other hydrophobic functional compounds.

Section snippets

Materials

Ergocalciferol, sodium caseinate, HPLC grade methanol, acetonitrile and ethanol were purchased from Wako Pure Chemical Industries (Osaka, Japan). Pepsin (from porcine gastric mucosa, P7000), pancreatin (from porcine pancreas, P7545) and bile extract (porcine, B8631) were purchased from Sigma Aldrich (St. Louis, MO, USA). Modified lecithin (SLP WhiteLyso) was kindly provided by Tsuji Oil Mills Co. Ltd. (Tokyo, Japan). The modified lecithin (ML) used in our study consists of a mixture of

Formulation of ergocalciferol nanodispersions

Fig. 1 shows the dav, PDI and size distribution of ergocalciferol nanodispersions stabilized by ML and SC. The results indicated that both ML- and SC-stabilized nanodispersions have monomodal size distribution. The nanodispersions produced using ML had smaller dav of 56 nm with a PDI of 0.213 in comparison to the SC-stabilized nanodispersions which showed a dav of 112 nm and PDI of 0.137. During solvent displacement process, ML and SC molecules in the aqueous phase adsorbed onto the surface of

Conclusion

In the current study, nanodispersion-based delivery systems for ergocalciferol were successfully fabricated via solvent displacement method using ML and SC as emulsifiers. In comparison with SC, ML was a more effective emulsifier at forming nanodispersions containing smaller particles. SC-stabilized nanodispersions were unstable to particle growth when near the isoelectric point (pH 4 and 5) of protein, heating and in the presence of CaCl2 addition. However, instability with slight increase in

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