Detection of pig bristles in brushes: A halal verification approach using microscopy and chemical methods

Abstract

The reliable identification of animal-derived bristles, specifically pig hair, in industrial and consumer brushes poses a persistent challenge for halal compliance, as conventional DNA-based methods are often limited by severe genetic material degradation in processed hair samples. This study proposes and validates a dual-platform, non-DNA approach that exploits the intrinsic biochemical and morphological stability of keratin to verify fibre origin. Using a composite brush sample, fibres were sub-categorised by colour (dark brown and white) to account for potential material heterogeneity. The dark brown fibres were identified as animal-derived based on their solubility in NaOH and characteristic sulphurous odour upon combustion. Both are hallmark indicators of the cystine-rich keratinous matrix. High-resolution microscopic analysis (Stereomicroscopy and SEM) further confirmed this origin by the presence of a distinct, broad medulla and imbricate cuticle scales, structural features unique to keratinised mammalian hair. Conversely, the white fibres exhibited chemical insolubility and a lack of organised surface morphology, confirming their synthetic nature. By focusing on the robust, degradation-resistant properties of the keratin protein rather than labile DNA, this integrated methodology offers a rapid, cost-effective, and unambiguous standard for halal verification in the food and cosmetic supply chains.