Bromothymol-blue paper strip indicator sensor for real-time monitoring of buffalo meat spoilage in modified-atmosphere refrigerated storage

This study developed and validated a low-cost, on-pack freshness tag for buffalo meat (carabeef) stored under commercial modified-atmosphere refrigeration (30 CO2 : 20 O2 : 50 N2, 4 1 C). Bromothymol blue (BTB, 1 wv) was immobilised on Whatman No. 1 paper strips, affixed to high-barrier pouches, and evaluated both in an ammoniachallenge model and alongside 500 g muscle cuts over nine days. Indicator hue shifted reproducibly from yellow very pale green greenish yellow light bluish green as spoilage progressed. The first discernible change coincided with pH 5.9, TVBN 10 mg 100 g¹ and total viable counts 3 log CFU g¹ (day 3); the final bluish-green stage appeared when TVBN reached 18 mg100g, ammonia 5 mg100g, and microbial loads exceeded 6 log CFUg (day 9), matching sensory rejection (overall acceptability 2.0). Parallel physicochemical trends, declining water-holding capacity (86.6 to 77.8 ), rising TBARS (0.09 to 0.71 mg MDAkg), tyrosine (0.19 to 20.1 mg100g) and free amino acids (5.1 to 31.7 mg100g), confirmed progressive spoilage and underpinned the colour transitions. The strip remained stable during handling, showed no dye bleed and responded within minutes to 25 mg gaseous ammonia in the model system, demonstrating sensitivity to volatile bases typical of carabeef decomposition. These findings establish the BTB paper sensor as an effective, non-invasive tool for real-time monitoring of buffalo-meat freshness in MAP supply chains, offering processors and retailers a practical means to enhance safety, minimise waste and bolster consumer confidence.