Fingerprinting lime juice: When portable spectroscopy meets chemometrics – An innovative technique for fraud identification

Abstract

With industrial lime juice dominating the market, the risk of adulteration has significantly increased. To address this, we investigated the adulteration of industrial lime juices using a two-tiered analytical approach. The first tier consisted of two portable spectrometers: Vis-NIR (sensor 1: 400–1000 nm) and NIR (sensor 2: 900–1700 nm) sensors combined with chemometrics. The second tier utilized a validated LC-MS/MS method for confirmation. Adulterated samples were prepared by adding citric acid-containing water (1–40 %) to authentic lime juice to maintain Brix values within acceptable limits. Samples with a citric to isocitric acid ratio below 300 were classified as authentic. Using a one-class classification approach (SIMCA), sensor 1 achieved 100 % sensitivity, 82 % specificity, and 91 % overall efficiency following smoothing and autoscaling of data. In comparison, sensor 2, after SNV or MSC transformation, yielded improved performance with 100 % sensitivity, 90 % specificity, and 95 % efficiency. Discriminant models (PLS-DA and SVM) did not produce substantial improvements in classification performance. However, regression models such as PLS-R (R²p = 0.95; RMSEP = 1.30 %) and RBF (R²p = 0.94; RMSEP = 1.22 %) demonstrated that sensor 2 (900–1700 nm) could reliably predict the degree of adulteration. In conclusion, a two-tiered strategy is recommended: the first tier involves rapid screening using a portable NIR sensor, followed by confirmatory analysis with LC-MS/MS as the second tier.