Pea Starch, a Versatile Soft Capsule Shell Material – Study of Marketing Differentiation Options with Color Agents
INTRODUCTION
Soft capsules are a dosage form that encapsulates a predetermined volume of liquid, suspension, or semi-solid material in a film shell.1 The filling of the inner material and the sealing of the outer shell are achieved in a single step, typically using the rotary die process invented by R.P. Scherer in 1933.² Such dosage forms offer many advantages: not only do they provide a faster onset of action as the active ingredient is readily available as a solution, suspension, or emulsion in oil vehicles, but also, they are easy to swallow3 and mask unpleasant taste or odor of fill ingredients. These attributes are expected to result in an improved patient compliance. In addition, brand owners can develop marketing differentiation with various existing shape, size, or color options. Even though today about 90% of softgels are manufactured with gelatin, consumers demand more and more plant-based alternatives, which is reflected in the growth of the vegetarian softgel market at 8% CAGR4. This work aims at studying the versatility of a pea starch shell material to produce vegetarian soft capsules with different colors.
MATERIALS AND METHODS
Colored soft capsules and upstream corresponding ribbons and gel masses were produced using a rotary die soft capsule equipment (Changsung OLUS® SRD, Korea). The vegetal shell formulation consisted in LYCAGEL® VS 720 Premix (Roquette Frères, France), a pea starch-based shell system. Various coloring agents (synthetic or natural pigments) from many suppliers were added to study the influence of different color options.
Regarding the colorant addition step, the process and quantities were adjusted depending on the colorant water solubility. Soluble colorants (dyes) were poured directly into the melting tank with the rest of shell components, including LYCAGEL® VS 720 Premix, vegetal glycerin 99.5% (Arcane Industries) and demineralized water. Considering that lakes, or iron oxides are water insoluble, they were first dispersed in 1 liter of water taken from the general formulation using a high shear mixer (POLYTRON® PT 2500 E, Kinematica AG, Switzerland) and further filtered on a 100 µm sieve, before being added to the melting tank.
After gel mass preparation, ribbons were casted at about 700 µm thickness, then used to encapsulate around 500 mg of medium chain triglycerides (IOI Oleo GmbH) in oval #10 capsule. The behavior of all the formulations was evaluated in terms of processability and resulting capsule appearance and color homogeneity.
RESULTS
A total of 19 colored shell combinations, were produced using either synthetic (Red Lake 40, Blue dye E133, black iron oxide, red iron oxide, Candurin® Gold Lustre, Candurin® Silver Lustre) or natural (Exberry® Brilliant Orange – paprika/carrot, Exberry® Vivid Red – carrot carrot/blackcurrant, Exberry® Purple Plum – carrot/blueberry, Exberry® Blue Lagoon – spirulina) color agents. The combinations used total concentrations of pigments from 0.02 to 0.94% w/w, in comparison with the initial gel mass formulation.
Table 1 summarizes the quantity of coloring agent in gram added to each batch of gel mass (25,210 g).
Table 1. Quantities in g of coloring agents added per formulation.
Figure 1. LYCAGEL® based capsules colored with Blue Lake n°2, formulation 1 of table 1 (left) and not colored (right)
It was possible to successfully produce capsules with no visual defect, capsule color homogeneity and acceptable seam thickness when using every colorant combination tested. From a processability standpoint, it was easier to use water-soluble colorants than water-insoluble ones, as the number of process steps were reduced.
Figure 2. LYCAGEL® based capsules colored with Red iron oxide at 0.20% concentration (formulation 17 of table 1)
Moreover, it was observed that the addition of water-insoluble pigments was impacting the texture of the gel ribbon as well as the quality of capsule seam. Indeed, two trials were done by increasing the quantity of either Red iron oxide from 0.20 to 0.94 % (formula 13 to 17 of table 1) or a combination of Candurin® Silver Lustre and Red Lake 40 from 0.30 to 0.49% (formula 8 to 12 of table 1). It resulted in capsules with no change in color even though colorant concentration was increased. However, the ribbon texture appeared less smooth, and the seam thickness was lower with increased colorant concentration. In that specific case, it is recommended to adapt the pigment concentration to achieve the desired opacity while limiting the impact on gel ribbon and capsule properties.
Figure 3. LYCAGEL® based capsules colored with Exberry® Purple Plum at 0.21% (formulation 4 of table 1).
In the case of natural colors, the example of Exberry® Purple Plum giving capsules with a dark translucent color instead of purple as expected indicated that heat sensitive colors are modified by the process conditions. The same observation was made with other natural colors except with the Exberry® Brilliant Orange that gave the expected color.
CONCLUSION
Soft capsules can be used as products to support companies' branding and marketing strategies, as they feature many shape, size and color options. With the growing trend of vegetal origin materials in pharmaceutical and nutraceutical products, LYCAGEL® VS 720 Premix offers a starch-based alternative to gelatin as shell material for soft capsules. This study demonstrates that this plant-based system can be selected to formulate colored soft capsules, using either natural or synthetic coloring agents.
REFERENCES
1. Merriam-Webster.com Medical Dictionary, s.v. “softgel,” accessed July 26, 2023
https://www.merriam-webster.com/medical/softgel.
2. Apparatus for Forming and Filling Capsules, U.S. Patent 2,288,327 (June 30, 1942)
3. Lisa Schofield, Softgels’ clear advantages. Natural products Insider® deep dive report 2019.
https://www.naturalproductsinsider.com/supplements/softgels-clear-advantages-deep-dive
4. Global Vegetarian Softgel Capsules Market 2020-25, LP Information
CANDURIN® is a trademark of Merck KGaA. EXBERRY® is a trademark of GNT GROUP BV.
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