Revolutionizing White Coatings: A Titanium-Free Approach

Reimagining the future of coatings without TiO₂.

Titanium dioxide (TiO₂) has long been the go-to for perfectly white tablet coatings. But with growing regulatory scrutiny and consumer demand for cleaner labels, drug manufacturers could use a reliable alternative. Scientists at Roquette set out to investigate whether a combination of xylitol and magnesium stearate could offer a viable solution.

The good news? It delivered equivalent, if not better, performance, and even shortened the coating process, while also unlocking more eco-conscious manufacturing practices.​

Discover more about this breakthrough coating method in our new case study:

Introduction

Titanium dioxide (TiO₂) has long been regarded as the most effective whitening agent for achieving a perfectly white tablet coating. However, concerns about its potential toxicity have sparked debate. Despite testing numerous alternatives, an efficient substitute remains elusive, even with increased coating weight and extended processing times.

The traditional sugar-coating process, which dates back to the mid-18th century, is labor-intensive and requires specialized equipment and skilled personnel. Leveraging insights into the optimal conditions for polyol crystallization, a novel coating process has been developed. Using xylitol as a base, this innovative approach simplifies and accelerates the hard-coating process, transforming it into a near-continuous crystallization cycle. Remarkably, this new process is compatible with existing equipment and operates at the same speed as film coating techniques.
Unlike film coating, hard coating is thicker and features a crystalline structure, offering a different pathway to achieving whiteness. This opens the door to exploring new substitutes for TiO₂, such as magnesium stearate, which shows promise as an alternative whitening agent.

Objectives

The aim of this study was to compare the whiteness of xylitol coatings containing varying ratios of magnesium stearate with a standard coating formulated using titanium dioxide, a well-established whitening agent. Additionally, the study sought to determine the magnesium stearate concentration required to achieve a comparable level of whiteness.

Materials and Methods

Materials

XYLISORB® 300 xylitol, Roquette Magnesium Stearate (MgSt), LYCOAT® RS 720 modified pea starch from Roquette Frères (Lestrem, France).
Titanium dioxide from Kronos.

Methods

Mannitol tablets (400 mg, 130 N hardness) were coated with a red-colored, ready-to-use blend, ReadiLYCOAT® hydroxypropyl pea starch-based film coating system.

A mixture of xylitol, modified pea starch, and either magnesium stearate or titanium dioxide powders was prepared by blending in a DIOSNA high-shear granulator for 5 minutes (impeller speed: 250 rpm; chopper speed: 1800 rpm). The coating suspension was then formulated in water at room temperature with a dry substance concentration of 60%.

Due to xylitol’s high cooling effect, the suspension temperature initially dropped to 2°C. It was subsequently mixed for 1 hour to allow the temperature to rise naturally to ambient conditions. Tablets were coated up to 30% weight gain using standard film coating equipment with samples collected at regular intervals.

The whiteness index (WI) was measured using a Konica Minolta CM-5 spectrocolorimeter under the following conditions: Reflectance mode; Standard illuminant: D65; Viewing angle:10°; Disc aperture:8mm; UV:100%.

Results

Initially, a red film coating was applied to the tablets to achieve a deep color, allowing for an effective evaluation and quantification of the coverage provided by the second white coating.

One titanium dioxide (TiO₂) ratio and three magnesium stearate (MgSt) ratios were tested (Table 1).

Read more here

Source: Roquette, website XYLISORB® 300 xylitol as sugar free sugar coating

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