Development of a non-destructive on-line pungency measurement system for red-pepper powder

Capsaicinoids are the main components of red pepper that determine the spiciness level of red-pepper powders. Current methods for pungency measurement are mostly dependent on HPLC measurement technique, which is a sample-destructive, labor-intensive, time-consuming, and expensive method. In this research, a nondestructive on-line pungency measurement method for red-pepper powder was developed using a Visible/Near-Infrared spectrometer with the wavelength range of 400-1000 nm. The system was constructed with a charge-couple device (CCD) spectrometer, a reference-measuring unit for calibration, and a sample transfer unit, which conveyed the red-pepper powder during measurements. Typically powder samples with eleven different spiciness levels were produced by controlling the mixture of predetermined non-spicy and spicy red-pepper powder. A total of 33 different samples, spanning 11 spiciness levels in three particle sizes (below 0.425 mm, 0.425 to 0.71 mm and 0.71 to 1.4 mm) were prepared for spectral measurements using the developed pungency measuring system. Partial Least Square Regression (PLSR) models were developed to predict the content of capsaicinoids in red-pepper powder from the visible/NIR spectra and reference values measured by HPLC. The Rv² and SEP of the PLSR model for red-pepper powders without regard to particle size were 0.973 and ±6.98mg/100g, respectively. The best result of the PLSR models (R²=0.991, SEP=±4.33mg/100g) was achieved from the raw spectra of red-pepper powders for particle sizes below 0.425 mm. The obtained results demonstrate the potential of NIRS technique for non-destructive and on-line measurement of capsaicinoids content in red-pepper powder.