Evaluation of milk deterioration using simple biosensor

In this study, a simple pH-colorimetric film was developed to detect the spoilage of pasteurized milk. The biosensor was fabricated by incorporating the pH-sensitive anthocyanins (AC) extracted from blue pea ( Clitoria ternatea L.) flower into a starch-based edible film. The color responses of both AC aqueous extracts and edible films incorporated with different AC concentrations towards different pH buffers (pH 2–11) were measured using Ultraviolet–visible (UV–Vis) spectrophotometer and colorimeter, respectively. Based on the results, there were significant differences (p < 0.05) for both total color changes (∆E) and L*a*b color system of the pH-sensitive edible film in different pH buffers. It indicated that the AC incorporated edible films were able to exhibit color changes over a wide range of pH. The potential application of the pH-sensitive film in spoilage detection was then carried out. Color changes of the film in commercial pasteurized milk were measured at predetermined intervals (24, 48, and 72 h) under storage conditions of 25 °C. Meanwhile, milk samples were collected for the microbiological test [total plate count (TPC)]. Results showed that the pH-sensitive films were able to detect pH changes of pasteurized milk which was associated with milk spoilage with visually observable color changes from deep blue to a light blue and showed a significant ∆E (p < 0.05) of 19.95 ± 0.009. The ∆E of the films in spoilage detection has a significant correlation with the pH changes of milk (R = − 0.9932) and TPC with a desirable coefficient (R = 0.9918). Therefore, the pH-sensitive edible film can provide a highly sensitive and non-destructive way of monitoring the food quality or spoilage without creating safety issues in the food industry.