Development and evaluation of PANI-PecPaper strip sensor for detection of total plate count in milk and milk products

Traditional total plate count (TPC) methods are time-consuming and labor-intensive. To address this, a Polyaniline-Pectin (PANI-Pec) paper strip sensor was developed for rapid TPC detection in milk and milk products. The sensor detects bacterial growth by measuring pH and conductivity changes, triggering a color shift from blue to green as PANI-Pec transitions from emeraldine base to emeraldine salt form. A glucose-activated PANI-Pec solution was synthesized and characterized for particle size, zeta potential, and electrical conductivity. The optimized solution was immobilized onto Whatman filter paper No. 4 using a printing device. The growth medium composition was optimized to enhance microbial load detection based on conductivity and pH variations. To further reduce detection time, the sample volume was increased to 500 μL.The developed paper strip sensor was capable of detecting 4.0 ± 0.15 log CFU/mL of microorganisms in milk within 4 ½ ± ¼ hours at 30 ± 2 °C. The presence of preservatives such as formalin and hydrogen peroxide completely inhibited sensor performance, preventing the color change due to microbial growth suppression. However, detergents like NaOH and urea had no effect. The sensor maintained consistent performance across various bacterial groups, except for endospore formers and antibiotics. The PANI-Pec paper strip sensor was validated in raw and pasteurized milk, butter, ice cream, and milk powder, demonstrating high accuracy, precision, bias, linearity, and repeatability compared to IS 5402:2012, AOAC-approved methods, and MBRT.This rapid, cost-effective, and reliable sensor enhances milk safety and quality and can be applied at RMRD centers for assessing raw milk and dairy products.