Introduction

Honey is a widely consumed product globally, so it is interesting to develop rapid and inexpensive methods for its authentication and quality control. On this line, two of the most studied parameters are total phenolic content (TPC) and antioxidant activity (AOX) [1].

The most common methods to analyze both parameters are spectroscopic assays using the Folin-Ciocalteu reagent (TPC) and 2,2′-azino-bis(3-ethylbenzothiazoline-6 sulfonic acid) diammonium salt (ABTS) as a radical source (TEAC) [2]. These methods require a large expenditure of money and time and specialized personnel.

This study's main objective is to develop a suitable method that allows us to quantify the total phenolic content and determine the antioxidant activity in a faster and cheaper way than the conventional methods. To achieve this objective, a chromogenic sensor has been developed for the rapid and low-cost determination of the both parameters mentioned above in a single measurement. In addition to being a faster and cheaper method, as it is a polymeric sensor, it has advantages of lack of migration of the sensor subunits, manageability, and possibility of working in solid-state.

Experimental

This method is based on hydrophilic colorimetric films with pendant benzenediazonium salt motifs, which react with phenols rendering highly colored diazo groups. The preparation of the starting material is based on vinylpyrrolidone (VP), methyl methacrylate (MMA) and 4-amino styrene (SH₂). The benzenediazonium salt was formed from aniline pendant groups by immersion in an aqueous acid solution of sodium nitrite [3]. The intensity of the color allows us to determine both TPC and TEAC of the sample by analyzing a picture taken with a smartphone analyzed using the color-definition-parameters (RGB).

For the analysis with the honey samples, our film's 8 mm diameter discs were dipped in 10 ml of each honey sample for 2 h. After that time, the discs were removed from the sample and washed 3 times with NaOH 0.1M. Finally, photographs of the discs were taken, RGB parameters were analysed, and were compared with the antioxidant activity results and total polyphenol content obtained by conventional methods mentioned above.

Conclusions

We have developed a new method to quantify the total polyphenol content and determine the antioxidant activity with a single analysis in all honey samples studied. This method reduces the time and the cost of the analysis and does not require trained personnel, so it has great potential in the quality control of honey samples.

Acknowledgment

We gratefully acknowledge the financial support provided by FEDER (Fondo Europeo de Desarrollo Regional), and both the Spanish Ministerio de Economía, Industria y Competitividad (MAT2017-84501-R) and the Consejería de Educación—Junta de Castilla y León (BU061U16 and BU041G18) are gratefully acknowledged.

References

1. Thrasyvoulou, A., Tananaki, C., Goras, G., Karazafiris, E., Dimou, M., Liolios, V., Gounari, S. (2018). Span. J. Agric. Res, 57(1), 88-96.
2. Re, R., Pellegrini, N., Proteggente, A., Pannala, A., Yang, M., Rice-Evans, C. (1999). Free Biol. Med. 26(9-10), 1231-1237
3. Vallejos, S., Moreno, D., Ibeas, S., Muñoz, A., García, F. C., García, J. M. (2019). Food Control. 106, 106684.