Use of pea starch maltodextrins in nutraceutical formulations
Use of pea starch maltodextrins in nutraceutical formulations
The market for nutraceutical food ingredients is continuously growing – 383bn in 2017 and estimated with 560bn in 2023 – although technological and biological issues remain unsolved.1 Common formulation difficulties such as an insufficient resorption of nutraceutical ingredients under the conditions in the human corps (pH, electrolytes, food matrix in digestion) as well as their instability due to environmental factors (temperature, humidity, light, oxygen) persist. A different challenge is its poor water solubility. All these biological and physical parameters are of major relevance for enhancing their initially poor bioavailability from the gastrointestinal (GI) tract. To overcome some of these issues, solubility improvement has been investigated. Particularly using the potential of starch-derived products, such as amylose or cyclodextrins, to form inclusion complexes. As a matter of fact, pea-starch is naturally rich in amylose and has the capability to complex hydrophobic molecules such as ibuprofen or lipids by forming single-helix2 inclusion compounds. A specific maltodextrin obtained from pea starch (with about 35% amylose) is commercially available. It has been developed to overcome practical formulation issues when using pure amylose, such as a rapid retrogradation in aqueous solution. It has a perfect cold water solubility, solutions are physically stable. We investigated its use to enhance the solubility of target molecules.
Figure 1: 1-naphthol, carvacrol and thymol structures.
A short proof-of-concept with 1-naphthol as model substance was used to define the methodologies and the proper analytical tools. In a second phase, we extended the study on real nutraceutical food active ingredients (AI) such as thymol and carvacrol. The studies validated the established model and explored a possible solubility enhancement.
Produced from thyme essential oil, both molecules thymol and carvacrol are known for their antifungal and antimicrobial activities and could be of real interest as antibiotic alternatives in pig farming.3
Materials and method
1-naphthol (99% purity), thymol (99.8% purity), carvacrol (99% purity) and n-Hexane were acquired from Sigma-Aldrich. The pea maltodextrin, KLEPTOSE® Linecaps (Dextrose Equivalent “DE” 17), was provided by Roquette.
The maltodextrin (MD) solutions with the two active ingredients (AI) were prepared under stirring at room temperature by simple addition of the AI – initially dissolved at 10 mol.l-1 in ethanol – into the solution. Several concentrations of KLEPTOSE® Linecaps solutions in distilled water were tested (from 10 to 30% m/v). After mixing, the preparations were stirred for two hours in an ice bath at 4°C to limit the evaporation of the AIs. All samples are stored at -18°C for one night and then lyophilized at -40°C under 1Pa (Labcongo Corp., USA).
The possible solubilization enhancement of thymol and carvacrol was investigated with phase-solubility diagrams. We adapted the methodologies already published4 using an UV-spectrometer (Shimadzu UV 2600-2700). Structural measurements were done by NMR and vibrational spectroscopy. 1H-NMR and 2D-ROESY experiments were performed at 298K in a Bruker Advance III 400MHz equipped with a prodigy cryoprobe. FTIR (iS50, Thermofisher) and Raman (XploRa Plus, Horiba Ltd.) were performed on pelleted samples. The microstructure of the powders were also studied by SEM (Thermofisher ESEM Quanta 200F); Cryo-TEM experiments were carried out on a FEI-TITAN equipped with a VITROBOT sample-freezing system.
The model study using 1-Naphthol as guest molecule showed significant solubility enhancement using KLEPTOSE® Linecaps. In addition, structural observation by NMR and vibrational spectroscopy confirmed specific interactions between the MD and the 1-Naphthol. Moreover, microstructural investigations by SEM and cryo-TEM exhibited a coil-like structure, induced by the 1-naphthol (figure 2), already described in the literature for the encapsulation of Ag nanoparticles by MD.5
Figure 2: Cryo-TEM picture of freezed MD-1-Naphthol solution. Ordered and unordered structure respectively in yellow and pink.
Titration of both AI, monitored by UV photometric dosage, resulted in a solubility enhancement up to 170% for carvacrol and up to 300% for thymol. The thymol solubility reaches a plateau, when increasing MD concentration, indicating a solubilization threshold.
The specific AI-MD interactions were confirmed by 1H-NMR: we clearly observe a shifting of the AI-characteristic peaks in presence of MD (figure 3), indicating hydrogen bonding between the molecules. However, in opposition to the cyclodextrins, no evidence of encapsulation were highlighted from the 2D-ROESY-NMR experiments.
Figure 3:1H-NMR of the thymol (red) and thymol-MD (blue) solutions. The chemical shifts of thymol signals are zoomed.
The two-dimensional layer-like microstructure of the KLEPTOSE® Linecaps evolves to a tri-dimensional network in presence of carvacrol or thymol.
Structural studies – including 2D-ROESY NMR and vibrational spectroscopy – indicated that the hydroxylated benzene structure of the 1-Naphthol is interacting with the MD. These interactions are mostly believed to be hydrogen bonding. By the TEM observation of nano-region of coil-like structures, we concluded to have a supramolecular planar organization of 1-naphthol layers between KLEPTOSE® Linecaps layers.
According to these interesting preliminary results, the choice of the carvacrol and thymol was mainly based on their planar morphology, close to that of 1-naphthol. The large difference in the solubility enhancement between carvacrol and thymol confirm the 1-naphthol results: the hydroxyl groups play a key-role for the hydrogen bonding. Moreover, the 1H-NMR shifts corroborate structurally these observations: the interaction strength of [KLEPTOSE® Linecaps – AI] is higher when using the thymol. In opposition to cyclodextrins,3 the solubilization with the KLEPTOSE® Linecaps is driven by hydrogen bonding without forming inclusion complexes and involves mainly the hydrophilic part of the AI. However, we have highlighted clear evidence of a microstructural network closely related to the AI structure.
We succeeded to enhance the solubility of carvacrol and thymol by the use of commercially available pea-maltodextrin KLEPTOSE® Linecaps. Structural and microstructural observation concluded on a tri-dimensional network based on hydrogen bonding, without any evidence of inclusion complexes. This study will be followed by in vitro testing to assess the bioavailability enhancement.
2. Perez, S.; Bertoft, E. The molecular structures of starch components and their contribution to the architecture of starch granules. Starch/Stärke 62, 389-420 (2010). https://doi.org/10.1002/star.201000013
3. Kfoury, M.; Fourmentin, S. Determination of formation constants and structural characterization of cyclodextrin inclusion complexes with two phenolic isomers: carvacrol and thymol. Beilstein Journal of Organic Chemistry 12, 29-42 (2016). https://doi.org/10.3762/bjoc.12.5
5. Bell, N. S.; Boyle T. J. In situ characterization of silver nanoparticle synthesis in maltodextrin supramolecular structures. Colloids and Surfaces B: Biointerfaces 134, 98-104 (2015). https://doi.org/10.1016/j.colsurfb.2015.06.030
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