Non-Targeted Detection and Quantification of Food Adulteration of High-Quality Stingless Bee Honey (SBH) via a Portable LED-Based Fluorescence Spectroscopy

Abstract

Stingless bee honey (SBH) is rich in phenolic compounds and available in limited quantities. Authentication of SBH is important to protect SBH from adulteration and retain the reputation and sustainability of SBH production. In this research, we use portable LED-based fluorescence spectroscopy to generate and measure the fluorescence intensity of pure SBH and adulterated samples. The spectrometer is equipped with four UV-LED lamps (peaking at 365 nm) as an excitation source. Heterotrigona itama, a popular SBH, was used as a sample. 100 samples of pure SBH and 240 samples of adulterated SBH (levels of adulteration ranging from 10 to 60%) were prepared. Fluorescence spectral acquisition was measured for both the pure and adulterated SBH samples. Principal component analysis (PCA) demonstrated that a clear separation between the pure and adulterated SBH samples could be established from the first two principal components (PCs). A supervised classification based on soft independent modeling of class analogy (SIMCA) achieved an excellent classification result with 100% accuracy, sensitivity, specificity, and precision. Principal component regression (PCR) was superior to partial least squares regression (PLSR) and multiple linear regression (MLR) methods, with a coefficient of determination in prediction (R²_p) = 0.9627, root mean squared error of prediction (RMSEP) = 4.1579%, ratio prediction to deviation (RPD) = 5.36, and range error ratio (RER) = 14.81. The LOD and LOQ obtained were higher compared to several previous studies. However, most predicted samples were very close to the regression line, which indicates that the developed PLSR, PCR, and MLR models could be used to detect HFCS adulteration of pure SBH samples. These results showed the proposed portable LED-based fluorescence spectroscopy has a high potential to detect and quantify food adulteration in SBH, with the additional advantages of being an accurate, affordable, and fast measurement with minimum sample preparation.

Keywords: Heterotrigona itama; authentication; food adulteration; multivariate calibration; portable LED-based fluorescence spectroscopy; stingless bee honey (SBH).

Figure 1

Geographical origin of SBH Heterotrigona itama in Bandar Lampung, Sumatra, Indonesia.

Figure 2

The visual appearance of SBH Heterotrigona itama honey and their adulterated samples.

Figure 3

Sample preparation protocol and fluorescence spectral data acquisition of pure and adulterated SBH samples.

Figure 4

Smoothed fluorescence spectral data of pure and adulterated SBH samples in the range of 357–725.5 nm was obtained using 4 LED lamps as excitation sources (λ = 365 nm).

Figure 5

Unsupervised PCA score plots for the smoothed fluorescence spectral data collected for pure and adulterated SBH samples in the range of 357–725.5 nm.

Figure 6

Unsupervised PCA x-loading plots for the smoothed fluorescence spectral data collected for pure and adulterated SBH samples in the range of 357–725.5 nm.

Figure 7

The plot of sample-to-model distance (Si) versus sample leverage (Hi) of pure SBH samples.

Figure 8

Model development for the quantification of the adulteration level using PLSR (a) Calibration; (b) validation.

Figure 9

Model development for the quantification of the adulteration level using PCR (a) Calibration; (b) validation.

Figure 10

Model development for the quantification of the adulteration level using MLR (a) Calibration; (b) validation.

Figure 11

Scatter plot between actual and predicted adulteration levels in the prediction step (a) PLSR, (b) PCR, and (c) MLR.