Lactose plays a significant role in daily lives as a constituent of various food and pharmaceutical products. Yet, lactose intolerance conditions demand low-lactose and lactose-free products in the market. These increasing nutritional claims and labels on food products entail simple and reliable methods of analysis that can be used for meeting quality standards, nutritional claims and legal requirements. In this study, terahertz time–domain spectroscopy (THz-TDS) was employed to analyse α-lactose monohydrate qualitatively and quantitatively in food products. Both absorption spectra and absorption coefficient spectra were investigated for their prediction performance. Regression models for lactose quantification using peak area and height of the absorption peaks 0.53 and 1.37 THz were developed and assessed in infant formula samples. Satisfactory prediction results were achieved in ideal conditions with pure standards, but not in all predictions of infant formula samples. Reasons and further implications are discussed.
An alternative technique to verify terahertz (THz) Smith-Purcell radiation (SPR) was proposed by using different grating periods. A compact DC electron gun, serving as a THz source, was modified to generate continuous 35 keV electron beam that passes by a metal-coated silicon grating in order to induce SPR. A design on beam optics to generate high-brightness beam was carried out by using Computer Simulation Technology (CST) Studio Suite ® software package. The optimization of beam parameters was obtained and experimentally performed. Results show that the root-mean-square (rms) beam size (diameter) is about 1 mm when supplying beam current of 200 µA, and rms beam emittance is about 3π mm mrad. The CST simulation software was, furthermore, employed to observe radiation spectra when using different grating structures. A liquid-helium cooled silicon bolometer together with a low-pass filter was used to detect radiation power. The results reveal that incoherent THz signal with power of 1.5 µW cm −2 is observed when the continuous-beam current is about 200 µA. The dependence of THz frequency and power on the grating period, that is associated to the SPR, was also investigated in this work.
Caffeine, quinic acid, and nicotinic acid are among the
significant
chemical determinants of coffee quality. This study develops a chemometric
model to quantify these compounds in ternary mixtures analyzed by
terahertz time-domain spectroscopy (THz-TDS). A data set of 480 THz
spectra was obtained from 80 samples. Combinations of data preprocessing
methods, including normalization (Z-score, min-max
scaling, Mie baseline removal) and dimensionality reduction (principal
component analysis (PCA), factor analysis (FA), independent component
analysis (ICA), locally linear embedding (LLE), non-negative matrix
factorization (NMF), isomap), and prediction models (partial least-squares
regression (PLSR), support vector regression (SVR), multilayer perceptron
(MLP), convolutional neural network (CNN), gradient boosting) were
analyzed for their prediction performance (totaling to 4,711,685 combinations).
Results show that the highest quantification performance was achieved
at a root-mean-square error of prediction (RMSEP) of 0.0254 (dimensionless
mass ratio), using min-max scaling and factor analysis for data preprocessing
and multilayer perceptron for prediction. Effects of preprocessing,
comparison of prediction models, and linearity of data are discussed.
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