Nondestructive determination of ash content in wheat flour via terahertz time-domain spectroscopy

As a global dietary staple, wheat flour is a primary commodity in the milling industry, where ash content serves as a critical indicator of flour purity, grade, and milling efficiency. Traditional incineration methods are time-consuming and labor-intensive. This study explores the potential of employing Terahertz time-domain spectroscopy (THz-TDS) coupled with chemometric algorithms for the rapid, nondestructive quantification of ash content in wheat flour. Based on three distinct wheat cultivars (Nongmai 126, Zhongyou 206, and Changhan 58), a total of 183 samples were analyzed using a fiber-optic coupled THz-TDS system. The raw time-domain signals were transformed into frequency-domain signals, absorption coefficients, transmittance, and refractive index for comparative evaluation. Among these optical parameters, the absorption coefficient exhibited the most robust correlation with ash content, attributed to the distinct spectral fingerprints of inorganic mineral constituents. Savitzky-Golay (SG) smoothing was identified as the optimal preprocessing technique to attenuate stochastic noise. Competitive adaptive reweighted sampling (CARS) was subsequently implemented to screen 31 characteristic wavelengths closely associated with ash components. To optimize predictive performance, four regression frameworks-Partial Least Squares Regression (PLSR), Multiple Linear Regression (MLR), Principal Component Regression (PCR), and Support Vector Regression (SVR)-were constructed and rigorously compared. The optimized SG-CARS-PLSR model achieved superior predictive accuracy, yielding a correlation coefficient of prediction (Rp) of 0.976, a root mean square error of prediction (RMSEP) of 0.011%, the Ratio of Performance to Deviation (RPD) of 4.804, and the Bias of 0.004%. These findings suggest that THz-TDS, integrated with CARS feature selection and PLSR modeling, provides a rapid, reliable, and nondestructive methodology for the quantitative analysis of ash content in wheat flour.