Physiochemical properties of leather manufacture from yellowfin tuna (Thunnus albacares) fish skin

Abstract

Yellowfin tuna (Thunnus albacares) skin is a primary by-product of the tuna filleting industry in Sri Lanka. It holds the potential for valorization due to its distinct scale patterns. Traditional chromium-based tanning used in the leather industry may pose significant environmental problems. The present study was conducted to evaluate the physicochemical properties of yellowfin tuna skin leather with two vegetable tannins: tea leaves (Camellia sinensis) and kumbuk bark (Terminalia arjuna). Fish skins were cleaned and proceed with chemical pre-treatments including soaking, liming, degreasing and pickling. Pre-tanned skins were tanned separately with solutions prepared from tea leaves and kumbuk bark over two weeks. After tanning, the skins were dyed, fat liquored and dried. Physical characteristics (tensile strength, elongation, strain), color values (L*, a*, b*) and microbial resistance were tested. Kumbuk-tanned leather had greater tensile strength (269.20 ± 3.19 N force-break; 19.83 ± 0.34 N/mm² stress-break) and elongation (48.34 ± 2.6 mm at break) compared to tea-tanned leather (159.80 ± 1.31 N; 11.04 ± 0.12 N/mm²; 22.94 ± 0.66 mm). Strain-break values also revealed the superior strength of kumbuk tanned leather (201.41 ± 10.94%). Sensory evaluation with 30 untrained panelists rated kumbuk-tanned leather as superior in color, texture and acceptability (4.00 ± 0.79 to 3.97 ± 0.77) compared to tea-tanned leather (3.33 ± 0.76 to 3.27 ± 0.64). Microbial evaluation showed less bacterial colonizing on kumbuk-tanned leather (7.17 × 10⁶ ± 0.11 CFU/g vs 8.6 × 10⁶ ± 0.57 CFU/g). According to the findings, kumbuk bark, enhances leather strength, elasticity and microbial resistance, making it a suitable agent for transforming yellowfin tuna fish skins into quality leather. The study paves the way to convert fish skins into value-added products, addressing ecological and economic gaps in the leather industry.