From Flower to Anthocyanin-Powered Optical Tooth Whitening: A Peroxide-Free Optical Tooth-Whitening Approach Using Butterfly Pea Flower (Clitoria ternatea) Extract

Figure 1. Principle of optical colour correction using complementary colour theory

Table 1. Comparative overview of marketed purple whitening formulation types

1.4 Tooth-whitening strips and the role of anthocyanin

Dissolving/oral whitening strips are thin polymeric films designed for direct, sustained contact with the tooth surface.⁶˒¹² Anthocyanins are water-soluble flavonoid pigments responsible for red, purple and blue colouration in numerous fruits, flowers and vegetables (e.g., blueberry, purple cabbage, blackberry, grape, black rice, hibiscus, jamun and butterfly pea) and possess antioxidant, anti-inflammatory and antimicrobial activity in addition to their colouring function.⁷˒⁹˒²⁰ Among natural anthocyanin sources, butterfly pea flower (Clitoria ternatea) yields a comparatively true blue-violet pigment (through its principal ternatin anthocyanins) rather than the red-leaning shades typical of berry-derived anthocyanins, which makes it more suited to neutralising yellow tones, produces a lower staining tendency on surrounding tissue, and is compatible with common film-forming and toothpaste excipients (HPMC, CMC, glycerine).⁷˒¹¹˒¹³˒²⁰

1.5 Need for the study and research gap

• Conventional whitening products remain reliant on peroxide-based agents with well-documented sensitivity and enamel-safety concerns.
• Butterfly pea flower is a well-characterised Ayurvedic plant with documented antioxidant activity and pH-dependent colour behaviour, yet it remains largely unexplored as the pigment source in oral film and toothpaste formulations for cosmetic whitening since most marketed purple whitening products instead use synthetic colourants such as blue covarine or PAP dyes, which are not edible-grade.
• There is a clear need for an affordable, natural, edible-grade, peroxide-free purple whitening system suited to the Indian consumer base and regulatory context.

This represents a research gap that the present study addresses by using a fully edible, GRAS-recognised, Ayurvedic-origin anthocyanin source, rather than a synthetic dye as the active optical colour-correcting agent in both a toothpaste and a dissolving strip format.

1.6 Aim and objectives

Aim: To formulate and evaluate herbal purple toothpaste and dissolving whitening strips using butterfly pea flower (Clitoria ternatea) anthocyanin extract as a natural optical colour-correcting agent for cosmetic teeth whitening a safe, peroxide-free, enamel-friendly alternative to conventional chemical whitening products.

Objectives:

• To prepare a herbal purple whitening formulation using anthocyanin as the active natural pigment.
• To apply colour-theory principles for reducing the visual yellow appearance of teeth.
• To assess whitening effectiveness on stained tooth models or enamel surfaces.
• To evaluate physicochemical parameters such as pH, appearance, colour, thickness, and stability.
• To develop a safer, herbal, and cost-effective whitening product for cosmetic oral care.

2. LITERATURE REVIEW

Table 2. Literature Review

3. MATERIALS AND METHODS

3.1 Materials and their Functions

Table 3. Function of key excipients used in the two formulations

3.2 Preparation of butterfly pea flower anthocyanin extract

• Harvested flowers were sun-dried for 48 hours.
• Dried flowers were ground into a coarse powder.
• The powder was extracted with water at 80 °C for 1 hour.
• The extract was filtered to obtain a clear filtrate.
• The filtrate was concentrated by solvent evaporation at 60 °C
• The concentrated extract was stored in an amber (light-protected) container.

3.3 Pre-formulation studies

Organoleptic evaluation of the raw extract indicated a deep blue/purple colour (pH-dependent), a mild characteristic herbal odour, and a slightly bitter/astringent taste. Solubility of the anthocyanin extract was assessed in distilled water, ethanol, and buffer solutions across pH 3–8, with maximum colour stability observed under acidic conditions (pH 3–5); the extract appeared red/pink at acidic pH, purple/blue at neutral pH, and faded greenish under alkaline conditions, consistent with the known pH-dependent chromic behaviour of anthocyanins.

3.4 Formulation of the dissolving whitening strips

Table 4. Composition of the dissolving whitening strip formulation

Preparation proceeded in five stages: (1) preparation of the polymer solution — HPMC dispersed with continuous stirring in purified water at 40–50 °C, followed by gradual addition of CMC-Na and hydration for 30 minutes; (2) addition of plasticisers/humectants (glycerine, sorbitol, PEG 400) with continuous stirring; (3) separate dissolution of the butterfly pea extract in a small volume of purified water, protected from light, and its incorporation into the polymer mixture with gentle stirring to obtain a uniform purple solution; (4) addition of mint oil, followed by a 10–15 minute deaeration period to remove entrapped air, casting onto a clean glass plate/Petri dish, and drying at room temperature or in a hot-air oven at 40–45 °C until a flexible, non-sticky film formed; and (5) peeling and cutting of the dried film into strips of 6 × 1.5 cm (female-sized) or 7 × 1.5 cm (male-sized).

Figure 2. Stepwise preparation of anthocyanin-based dissolving whitening strips

3.5 Formulation of the herbal purple toothpaste

Table 5. Composition of the herbal purple toothpaste formulation

The gel base was prepared by hydrating CMC-Na into a sorbitol–glycerine mixture with continuous stirring for approximately 30 minutes until smooth. Purified water was then added gradually under stirring, followed by gradual incorporation of calcium carbonate and tamarind seed powder to ensure uniform dispersion. SLS was added slowly to minimise excessive foam generation during mixing, followed by the butterfly pea extract with continuous stirring until a uniform purple colour developed. Sweetening and flavouring agents were then incorporated, the pH was adjusted with citric acid solution and the final homogeneous paste was packaged into tubes and stored at room temperature.

Figure 3. Stepwise preparation of herbal purple toothpaste

4. EVALUATION PARAMETERS AND TESTS

Dissolving whitening strips: physical appearance (colour, transparency, surface texture, dimensions, weight uniformity, edge integrity); thickness (Vernier calliper, multiple measurement points); folding endurance (repeated folding at a single point until fracture); disintegration time (in artificial saliva, simulating oral conditions); tensile strength (maximum stress before breaking); and surface pH (moistened strip surface tested with pH paper/electrode).⁶˒¹²˒¹³

Herbal purple toothpaste: organoleptic properties (colour, odour, taste, texture, consistency, phase separation) by sensory/visual assessment; foaming ability (foam volume generated on shaking a fixed toothpaste quantity in water, recorded initially and after 1 minute); spreadability (area of spread of a fixed quantity of toothpaste under increasing applied load, using an ointment/spreadability test apparatus); pH (of an aqueous dispersion of the toothpaste); and short-term stability (colour, odour, texture, pH, spreadability, foaming, phase separation and microbial growth monitored at Day 0, 7, 15 and 30 under room-temperature storage).¹⁴˒¹⁵˒¹⁶˒¹⁷

4.1 Part A — Dissolving whitening strips

Table 6. Physical appearance of the dissolving whitening strips

The strips displayed a uniform, characteristic violet-blue colour attributable to the anthocyanin content of the butterfly pea extract, with a smooth, defect-free surface and acceptable weight uniformity (CV < 10%), indicating a consistent casting process.

Table 7. Thickness measurement of the whitening strips (Vernier calliper)

Table 8. Folding endurance of individual whitening strips

A mean folding endurance of 289.8 folds indicates good mechanical flexibility, consistent with the plasticising combination of glycerine and PEG 400 alongside the HPMC/CMC film-forming matrix.

Artificial saliva (disintegration-testing medium)

Table 9. Composition of artificial saliva used for strip disintegration testing (per 1000 mL)

Table 10. Disintegration time of the whitening strips in artificial saliva

A mean disintegration time of 11 minutes (range 10–12 minutes) is considered satisfactory for a dissolving whitening strip, providing sufficient tooth-surface contact time to allow optical colour correction before the film fully dissolves.

Surface pH: A surface pH of 6.3 (acceptable range of 6.0–6.5), obtained by wetting the strip with 0.5 mL of purified water and applying pH paper after 1 minute.

4.2 Part B — Herbal purple toothpaste

Table 11. Organoleptic properties of the herbal purple toothpaste

All organoleptic parameters were satisfactory. The violet-purple colour was visually appealing and the peppermint flavour masked the characteristic herbal taste of the extract, which is expected to support patient acceptability and compliance.

Table 12. Foaming ability of the toothpaste

Table 13. Spreadability of the toothpaste under increasing applied load.

Toothpaste pH: A pH of 6.2 (acceptable range 6.0–6.5), each obtained on an aqueous dispersion of the toothpaste. The spreadability data show a progressive increase in spread area with applied load in both sources, consistent with pseudoplastic (shear-thinning) rheological behaviour appropriate for a toothpaste.

Table 14. Short-term stability of the herbal purple toothpaste (room temperature).

The toothpaste remained physically stable over the 30-day observation period, with a slight colour fade and a modest downward drift in pH from Day 15 onward, consistent with the known pH- and light-sensitivity of anthocyanin pigments. No phase separation or microbial growth was observed across the study period.

5. DISCUSSION

The present study successfully formulated and evaluated a herbal purple toothpaste and a dissolving whitening strip containing butterfly pea flower (Clitoria ternatea) anthocyanin as a natural optical colour-correcting agent. Both formulations exhibited satisfactory physicochemical properties and short-term stability, indicating the suitability of anthocyanin for peroxide-free whitening formulations.¹˒²˒²⁰

The dissolving whitening strips showed acceptable thickness, folding endurance, disintegration time, and surface pH, demonstrating that the HPMC–CMC polymer system produced flexible and stable oral films. These findings are consistent with previous reports on HPMC/CMC-based oral dissolving films.⁶˒¹²˒¹³

The herbal toothpaste demonstrated acceptable organoleptic properties, pH, foaming ability, spreadability, and remained physically stable throughout the 30-day study. The slight colour fading observed during storage is consistent with the known pH- and light-sensitivity of anthocyanins.⁹˒¹⁵˒¹⁶˒²⁰

Overall, the findings suggest that butterfly pea flower anthocyanin is a promising natural alternative to synthetic colourants for temporary optical tooth whitening. However, further studies involving objective colour analysis, long-term stability, and clinical evaluation are required to establish its whitening efficacy and commercial applicability.

6. NOVELTY OF THE STUDY

The principal novelty of this work lies in the substitution of the synthetic colourants used in many marketed purple whitening products (e.g., blue covarine, PAP dyes) with a fully edible, GRAS-recognised, Ayurvedic-origin anthocyanin source, butterfly pea flower (Clitoria ternatea) as the active optical colour-correcting pigment, in two complementary formats (a dissolving strip for sustained contact and a toothpaste for routine daily use). ²˒⁷˒¹⁸˒²⁰

Table 15. FLORAWHITE positioning relative to marketed synthetic purple whitening products.