A simple optical pH sensor based on pectin and Ruellia tuberosa L-derived anthocyanin for fish freshness monitoring

Abstract

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.

Fabrication of an Immobilized Polyelectrolite Complex (PEC) Membrane from Pectin-Chitosan and Chromoionophore ETH 5294 for pH-Based Fish Freshness Monitoring

“…At 610 nm, the sensor's response seemed to form a linear correlation with the pH changes (pH 5-9) at a PBS concentration of 0.05 M. Thus, the wavelength was taken for the construction of the calibration curve. This finding is similar to our previous report employing anthocyanin derived from Ruellia tuberosa L. (λ optimum = 635 nm) [14]. The foregoing system yielded a sensitivity value of 0.0306/pH unit.…”

“…analyte [21,35]. Similar occurrences on membrane surfaces resulting from polymer complex formation have been reported previously [13,14].…”

“…Although the hydrophilic property results in the rough surface of the membrane, it could also allow better diffusion of the analyte [21,35]. Similar occurrences on membrane surfaces resulting from polymer complex formation have been reported previously [13,14].…”

“…In addition, biopolymers are closely associated with the green properties of a material, which is important in attenuating the carbon footprint of the fishing industry [13]. Pectin, one of the well-known biopolymers used in foods, has been reported for its ability to immobilize active agents, resulting in optical pH sensors with sensitivity (mean ± standard deviation (SD)) reaching 0.14 ± 0.03 [14]. Furthermore, a pectin-based optical pH sensor only required less than 5 min to detect an optimum response due to its hydrogel properties allowing higher analyte diffusion [14].…”

“…Pectin, one of the well-known biopolymers used in foods, has been reported for its ability to immobilize active agents, resulting in optical pH sensors with sensitivity (mean ± standard deviation (SD)) reaching 0.14 ± 0.03 [14]. Furthermore, a pectin-based optical pH sensor only required less than 5 min to detect an optimum response due to its hydrogel properties allowing higher analyte diffusion [14]. However, for practical applications, its weak mechanical strength must be resolved [15].…”