Anthocyanin from the flower Ruelila tuberosa L was successfully extracted by maceration using methanol. The total extract obtained was 19.22% with a concentration of 1.503 mg/L correspondingly. Retention time was analyzed using Thin Layer Chromatography and an Rf value of 0.43 was achieved. The analytical determination of functional groups was conducted using FTIR. The sensitivity of anthocyanin towards phosphate buffer pH is 0.222 at the range of pH 6 - 8 with R2 = 0.996 at maximum wavelength of 635 nm. On the other hand, its sensitivity towards citrate buffer is 0.022 at pH range 6 - 8 with a linearity of R2 = 0.999 at 625 nm maximum wavelength. The anthocyanin showed good in sensitivity and dynamic range in 0.1 M Phosphate buffer solution.

A simple optical pH sensor using the active compound anthocyanin (ACN), derived Ruellia tuberosa L. flower immobilized in a pectin membrane matrix, was been fabricated and employed to monitor the freshness of tilapia fish at room temperature and 4oC storage. The quantitative pH values were measured based on the UV-Vis spectroscopy absorbance. The optimum pectin weight and ACN concentrations were 0.1% and 0.025 mg/L. The sensor showed good sensitivity at 0.03 M phosphate buffer solution. The sensor’s reproducibility was evaluated using 10 replicate sensors where a standard deviation of 0.045 or relative standard deviation of 9.15 was achieved. The sensor displayed an excellent response after 10 minutes of exposure, possessing a response stability for 10 consecutive days. The decrease in pH value of the Tilapia fish from 7.3 to 5 was observed in a 48 hour test, which can be used as the parameter when monitoring fish freshness. Overall, this reported optical pH sensor has a novelty as it could be used to monitor the rigor mortis phase of fish meat, which is useful in food industry.

A simple optical pH sensor using the active compound anthocyanin (ACN), derived Ruellia tuberosa L. flower immobilized in a pectin membrane matrix, was been fabricated and employed to monitor the freshness of tilapia fish at room temperature and 4oC storage. The optimum pectin weight and ACN concentrations were 0.1% and 0.025 mg/L. The sensor showed good sensitivity at 0.03 M phosphate buffer solution. The sensor’s reproducibility was evaluated using 10 replicate sensors where a standard deviation of 0.045 or relative standard deviation of 9.15 was achieved. The sensor displayed an excellent response after 10 minutes of exposure, possessing a response stability for 10 consecutive days. The decrease in pH value of the Tilapia fish from 7.3 to 5 was observed in a 48 hour test, which can be used as the parameter when monitoring fish freshness.