Category: Formulation and Quality
Purpose: Film coatings impart mechanical integrity, gloss, light and moisture protection to tablets. Inclusion of pigments to coatings enhance appearance, brand differentiation and acceptability of coated tablets to consumers. With consumer preferences for clean label ingredients in dietary supplements and nutritional products increasing, this move is driving the need for titanium dioxide (TiO2) free and non-synthetic (natural or naturally derived) pigments. Coating formulations that include naturally derived pigments may create color stability challenges not typically encountered with synthetic pigments. The objective of this study was to evaluate on-tablet stability of 10 naturally derived pigments included in a Nutrafinish®, TiO2 Free Formulated Film Coating.
Methods: An aqueous based Nutrafinish TiO2 free coating containing pigment, polymer (hypromellose), opacifier (calcium carbonate) and plasticizer was used to evaluate the color stability of naturally derived pigments. In this study carmine, caramel, riboflavin, radish, spirulina extract, red beet, copper chlorophyll, safflower, curcumin and vegetable carbon black were included at a typical 5.6% w/w level. The film coating formulations were prepared at 20% w/w solids dispersions and applied onto 1.3 kg of placebo tablets (10 mm, round, biconvex) in a fully perforated 12” side-vented pan (Labcoat II, O’Hara Technologies Inc., Canada). Tablets were packaged in HDPE bottles (100cc without desiccant) for stability testing at 25°C/60% RH and 30°C/65% RH for 12 months. Coated tablets were removed at defined time points and visually assessed for color fading. Samples were also measured using a Datacolor spectrophotometric instrument to determine any change in color. With Datacolor, Delta E was used to assess color change and it is an equally weighted combination of the coordinate (L, a, b) differences between 2 samples in a 3-dimensional plane, ΔL is the lightness difference, Δa is the red/green difference and Δb is the yellow/blue difference.
Results: Figure 1 shows the change in Delta E values for all colorants at 25°C/60% RH and 30°C/ 65% RH conditions. Stable pigments such as copper chlorophyll showed minimal change in DE values for the entire duration of the study whereas radish showed higher DE values after 2 months under storage conditions. Some pigments like safflower and spirulina extract faded more quickly at 30°C/65% RH. However, other piments like riboflavin, carmine, were quite stable for 12 months independent of storage conditions. There was correlation in fading trend between DE values and visual assessment.
Conclusion: While providing clean label pigment options for dietary supplement and nutritional applications, some naturally derived ingredients also tend to be less stable, which can impact the shelf-life of the final film coated products. As the demand for alternative pigments continues, formulators must ensure in-use stability has been evaluated and meets shelf-life expectations.
Tom Mehaffey– Harleysville, Pennsylvania
Charles Cunningham– Sr. Manager- Product Dev., Colorcon, Inc., Harleysville, Pennsylvania
Ali Rajabi-Siahboomi– Vice President and Chief Scientific Officer, Colorcon, Inc., Harleysville, Pennsylvania