Glucomannan-based biodegradable film modified with turmeric and selenium powder for ammonia sensing and smart shrimp packaging

This study reports the development of glucomannan-based biodegradable films (from salep) incorporating bioactive compounds of turmeric powder (TP) and selenium powder (SP) to improve physicochemical properties and enable ammonia sensing. Films were fabricated by the solvent-casting method and evaluated for thickness, mechanical properties, moisture content, solubility, water vapor permeability (WVP), chemical structure, crystallinity, surface morphology, and thermal stability. Results showed that SP, with its mineral nature, increases crystallinity and enhances thermal stability. TP and SP significantly affected film thickness; the TP effect was stronger and more linear, with thickness increasing as its amount rose. Mechanical properties were notably influenced by the type and distribution of the additive in the polymer matrix. Turmeric addition reduced moisture content, while TP increased solubility. SP markedly increased WVP, and TP also raised WVP, though to a lesser extent. SEM images indicated that TP and SP caused substantial changes in surface morphology; SP directed crystallinity while TP promoted amorphousness. The combination yielded a stable semi-amorphous/crystalline structure. Turmeric accelerated degradation of the composite, whereas SP enhanced ultimate thermal stability. The salep-based composite film containing 0.4 g TP and 0.05 g SP (K0.4-0.05) was used as a colorimetric ammonia sensor kit. The optimized formulation (K0.4-0.05) exhibited a linear response to ammonia, high sensitivity, good repeatability (RSD = 1.19%), and a short response time (2 minutes). It showed clear color change and high selectivity toward ammonia under gaseous conditions and in real shrimp spoilage tests. This system indicates potential for smart packaging and visual spoilage indicators in the food industry.