Stability of bioactive solid lipid nanoparticles loaded with herbal extracts when exposed to simulated gastrointestinal tract conditions

Highlights

• Phenolic compounds from sage and savoury extracts are entrapped in SLN.

• SLN loaded with savoury extracts showed higher antioxidant activity.

• The digestion of SLN is affected by the type of wax used at production.

• At the small intestine all SLNs showed ca. 100% release of rosmarinic acid.

• Witepsol SLNs showed to be the most stable vehicles for sage and savoury extracts.

ABSTRACT

Solid lipid nanoparticles (SLN) can be used as vehicles for phenolic compounds rich extracts. In the present work two types of waxes — witepsol and carnauba were tested for the first time in the production of solid lipid nanoparticles (WSLN and CSLN, respectively) loaded with sage and savoury extracts. Physical characterization and association efficiencies calculation were performed. Discrimination of loaded phenolic compounds from each extract was made using HPLC assays. Antioxidant activities of SLN were characterized using two different methods — ABTS and ORAC. Finally, the phenolic compound release profile from SLN and stability when exposed to simulated gastrointestinal tract (GIT) conditions were also evaluated. Different phenolic compounds from sage and savoury extracts were entrapped in SLN. The highest antioxidant activity was obtained for the SLN loaded with savoury extract. Stomach simulated condition provokes a partial release of rosmarinic acid from SLN, whereas at small intestine simulation step, all SLN showed a release of ca. 100%. Witepsol SLN were the ones that best maintained their physical integrity during digestion, showing to be the most stable vehicles for sage and savoury extracts. These SLN show to be suitable for the production of food functional ingredients bearing antioxidant activity.

Introduction

Sage and savoury (common English names for Salvia sp. and Satureja montana, respectively) are herbs often used in Mediterranean traditional medicines. These herbs are widely applied as seasoning, but also have been used as anti-diarrheic, digestive aid, wound-healing, anti-inflammatory, anti-insomnia and anti-hypertensive vectors; some of these biological activities have been accounted for the presence of rosmarinic acid (RA) (Gião et al., 2009, Giao et al., 2010). Extraction of antioxidants (mainly phenolic compounds) from these herbs can be easily achieved using boiling water and powdered plant material. The majority of the phenolic compounds in Salvia species are derivatives of caffeic acid, which is the building block of a variety of plant metabolites. Caffeic acid plays a central role in the biochemistry of the Lamiaceae plants, and occurs mainly in a dimer form as RA (Kamatou, Viljoen, & Steenkamp, 2010). Savoury on the other hand, contains rutin and RA (ca. 10 and 4%, respectively) (Gião et al., 2009). The use of herbal extracts can reduce the production costs of antioxidant nano/microparticles and also the toxicological risk associated with the use of pure or synthetic compounds.

These extracts have a variety of compound types and with different stability behaviours when incorporated in a food compound or when at gastrointestinal tract (GIT) conditions. The loss of part of the extract constituents can result on bioactivity decreases. Some of these compounds also have low bioavailability, and are poorly absorbed either due to their large molecular size and poor lipid solubility and cannot be absorb by passive diffusion (Manach, Williamson, Morand, Scalbert, & Rémésy, 2005). In phyto-formulation research, it is believe that the development of nanodosage forms of phyto-compounds could overpass these disadvantages (Nunes et al., 2015).

Hence, the development of a system that can protect these compounds and maintain them stable or even that improve their bioavailability was sought. The systems proposed here are at nanoscale and have lipidic nature. For their formulation and for oral administration destination, lipid, emulsifier and water are required as essential components and all need to hold a generally recognized as safe (GRAS) status (Olbrich et al., 2002, Severino et al., 2011). Encapsulation of pure RA using witepsol and carnauba waxes was already performed elsewhere. These systems had mean diameters between 270 and 1000 nm, with ca. 99% of association efficiencies, and demonstrated to be highly stable (Madureira et al., 2015). At the time, the best formulations were selected as the ones having 1.0% (w/v) lipid, 2.0% (v/v) polysorbate 80 and 0.15 mg/mL RA.

Thus, this research describes the production of SLN loaded with extracts from sage and savoury herbs using these two lipid matrices. These SLN were characterized in terms of their physical and morphological characterization and association efficiencies. The antioxidant activities were determined using two different methods based on single electron transfer (SET) – 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), and hydrogen atom transfer reaction (HAT) – ORAC assays. Stability of SLN and phenolic compound release at a dialysis bag and when exposed to a simulated gastrointestinal tract (GIT) were also evaluated, in what concerns the release of phenolic compounds and physical properties of SLN stabilities. These nanoparticles could be further used as functional ingredients bearing antioxidant activity, for incorporation in several food matrices.