Development of colorimetric multi-sensor Arrays for rapid determination of Sodium Metabisulfite in dried Longan

Abstract

Longan (Dimocarpus longan Lour.) is a valuable tropical fruit that shortly storage times after harvesting. Therefore, most of the longan fruit should be preserved as dried longan for longer consumption period. Sodium metabisulfite has been commonly used as additive chemical to slow down the spoilage process of the dried longan and to prevent the gradual discoloration. Nevertheless, the excessive use of this sulfiting agent can result in allergic symptoms, especially for sulfite-sensitive people. In this research, a colorimetric multi-sensor array strip was fabricated to determine the concentration of sodium metabisulfite residual in dried longan. The detection was based on reactions of a series of colorimetric reagents including three different Fuchsine compounds and an Ellman’s reagent. The dilution series of each reagent including the mixed reagents, were optimized to expand the calibration range of the developed strip. As a result, the maximum change of the reagent colors was observed within 3 min after the reactions. The content of metabisulfite ion could be approximated by comparing the color of the sensors using naked eye observation. To perform a quantitative analysis, the image of the strip was captured using a commercial scanner, and it was converted into an RGB color mode to be digitally analyzed by chemometrics. Using partial least square (PLS) regression, the most effective calibration range (5.00–250.00 mg/kg) provided R2 and Q2 values of 0.994 and 0.908, respectively. The limits of detection and quantitation were 5.48 and 16.60 mg/kg, which were sensible for the detection of the sulfiting agent in dried longan samples. The developed colorimetric strip was applied to determine the concentration of metabisulfite residual in dried longan fruits purchased from local markets in Chiang Mai, Thailand. The results agreed well with the findings obtained from the reference method. The developed strip could be an alternative solution for rapid, simple, and low-cost detection of the sulfiting agent in dried agricultural products, where test results could be instantly obtained without the requirement of any sophisticated analytical instruments. Moreover, the multi-sensor array based on several chemical reactions of the reagents coupled with chemometrics can improve accuracy, selectivity and expand the calibration range when compared to the conventional single sensor.