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Quinoa is a naturally gluten-free pseudocereal receiving growing attentions worldwide. Herein, front-face synchronous fluorescence spectroscopy (FFSFS) was applied for the fast and non-invasive authentication of quinoa flour adulteration with maize and soybean flours. The cases of both single and dual adulterants (6–50 wt%) were investigated. For single adulteration with either maize or soybean flour, principal component analysis coupled with linear discriminant analysis (PCA–LDA) was used for preliminary qualitative discrimination. Then first-order prediction models were constructed based on the combination of unfolded total synchronous fluorescence spectra and partial least square (PLS) regression, and were validated by five-fold cross-validation and external validation. For dual adulterants, a general PLS2 model for the simultaneous determination of maize and soybean flours was developed, which produced suitable results, with the determination coefficient of prediction (R p 2) > 0.9, root mean square error of prediction (RMSEP) < 5% and residual predictive deviation (RPD) > 3. The limits of detection (LODs) are 9.0% and 6.9% for maize flour and soybean flour, respectively. Furthermore, most spike recoveries are in the range of 80–120%. This study not only has important applications in the authentication of quinoa flour adulteration but may also shed light on the quantitative component analysis of other cereal flour mixtures from different botanical origins. • Front-face synchronous fluorescence of quinoa flour is presented. • Its emission is distinct from those of maize and soybean flours. • Quinoa flavonoids contribute most to the distinction, followed by tryptophan. • Front-face fluorescence affords non-destructive detection of its adulteration. • Simultaneous determination of maize and soybean flours can be rapidly achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Front-face fluorescence of ground black and white pepper is observed. • Their emissions are distinct from those of several possible adulterants. • Piperine in pepper and tryptophan in adulterants yield the distinction. • Simultaneous detection of multiple adulterants in ground pepper is feasible. • Rapid and non-destructive analysis of piperine is achieved as well. Based on the distinct fluorescence of piperine and tryptophan, and their different profiles in pepper and several possible adulterants, front-face synchronous fluorescence spectroscopy (FFSFS) was applied for the fast and non-invasive authentication of ground black pepper adulterated with papaya seed powder and buckwheat flour, and ground white pepper adulterated with whole wheat and maize flours. For either single adulterant or dual adulterants in the range of 10–40% w/w, prediction models were constructed based on the combination of unfolded total synchronous fluorescence spectra and partial least square (PLS) regression, and were validated by both five-fold cross-validation and external validation. The built PLS2 models produced suitable results, with most of the determination coefficients of prediction (R p 2) greater than 0.8, the root mean square error of prediction (RMSEP) < 5% and residual predictive deviation (RPD) greater than 2. The limits of detection (LODs) were 11.1, 5.5, 10.6 and 12.0% for papaya seed powder, buckwheat, whole wheat and maize flours, respectively. Most relative prediction errors for simulated blind samples were within ± 30%. Besides, piperine in ground black and white pepper was also determined with acceptable PLS results. [ABSTRACT FROM AUTHOR]

The authentication of traditional herbal medicines in powder form is of great significance, as they are always of high values but vulnerable to adulteration. Based on the distinct fluorescence of protein tryptophan, phenolic acids and flavonoids, front-face synchronous fluorescence spectroscopy (FFSFS) was applied for the fast and non-invasive authentication of Panax notoginseng powder (PP) adulterated with the powder of rhizoma curcumae (CP), maize flour (MF) and whole wheat flour (WF). For either single or multiple adulterants in the range of 5–40% w /w, prediction models were built based on the combination of unfolded total synchronous fluorescence spectra and partial least square (PLS) regression, and were validated by both five-fold cross-validation and external validation. The constructed PLS2 models simultaneously predicted the contents of multiple adulterants in PP and gave suitable results, with most of the determination coefficients of prediction (R p 2) >0.9, the root mean square error of prediction (RMSEP) no >4% and residual predictive deviation (RPD) >2. The limits of detections (LODs) were 12.0, 9.1 and 7.6% for CP, MF and WF, respectively. All the relative prediction errors for simulated blind samples were between −22% and + 23%. FFSFS offers a novel alternative to the authentication of powdered herbal plants. [Display omitted] • Front-face fluorescence of Panax notoginseng powder is observed and utilized. • Simultaneous detection of multiple adulterants in Panax notoginseng powder by PLS2. • Protein tryptophan, phenolic acids and flavonoids contribute to the detection. • Front-face fluorescence affords rapid and non-destruction drug authentication. [ABSTRACT FROM AUTHOR]