Discrimination of aflatoxin B1 contaminated pistachio kernels using laser induced fluorescence spectroscopy

Aflatoxin contamination of pistachio is one of the most significant issues related to its quality. The conventional ultraviolet (UV) induced fluorescence spectroscopy method of assessment is difficult to use for the screening of samples contaminated with low levels of aflatoxin due to its weak signal intensity and the interference of background constituents. Laser induced fluorescence spectroscopy (LIFS) technique is a highly sensitive and specific approach which has been successfully used to determine of the trace compounds in agricultural products. In this study, the feasibility of classifying aflatoxin B 1 (AFB 1 ) contamination in 250 kernels of two pistachio varieties (“Wanlong”, WL and “Hengkang”, HK) using LIFS was investigated. Four low concentration AFB 1 solutions (5, 10, 20, and 50 ppb) were artificially applied on the surface of the kernels. The contaminated pistachios presented lower fluorescence intensity in the range 400 nm–610 nm when compared to uncontaminated control kernels. Principal component analysis (PCA) showed a pattern of separation between uncontaminated and contaminated kernels. Similar accuracy (92.3%–100%) was found in both varieties using a support vector machine (SVM) technique, indicating that changes in variety or kernel type are unlikely to have an influence on classification accuracy. Good discriminant ability (accuracy ≥ 98.4%) was achieved for AFB 1 contamination of the pooled samples based on a combination of the standard normal variate (SNV) and the second derivative. Although these preliminarily results demonstrated that it is feasible to screen pistachios artificially contaminated with low concentration of AFB 1 by LIFS, further work is necessary to test the performance of the LIFS method for detecting naturally contaminated samples.