Abstract
Developing effective ways for controlling the quality of natural products that are sold in high volume worldwide is currently one of the most urgent goals of analytical chemistry. Black pepper (Piper nigrum) is a major spice that constitutes 34% of the global spice market. Black pepper is highly prone to quality variations, arising from alteration of the piperine content. Miniaturized NIR spectroscopy offers a high-throughput, cost-effective and laboratory independent technique for quality control of black pepper. Handheld NIR spectrometers differ in the implemented technology, with impact on their analytical performance and unit cost. In this work, the performance of three miniaturized NIR instruments in quantification of piperine in whole and milled seeds of black pepper was investigated. With HPLC method used as the reference analysis, partial least squares regression (PLSR) models were constructed for NIR spectra while the prediction accuracy with respect to the spectrometer used was monitored through root mean square error of prediction (RMSEP) determined for an independent test set validation. Prediction of piperine content in milled seeds was achieved with a RMSEP of 0.18% using the benchtop spectrometer Büchi NIRFlex N-500; while handheld instruments offered, respectively, 0.22% (microPHAZIR), 0.26% (MicroNIR 2200) and 0.42% (SCiO). In contrast, for the analysis of the whole pepper seeds, only the Büchi NIRFlex N-500 (RMSEP: 0.30%) and the Viavi MicroNIR 2200 (RMSEP: 0.37%) gained reliable results. The performance of Thermo Scientific microPHAZIR was satisfactory (RMSEP: 0.75%). The consumer-aimed spectrometer SCiO (Consumer Physics) was found adequate for milled samples, while the analysis of the whole seeds was unsuccessful. To gain better understanding of the features of PLSR models of piperine content in black pepper, quantum mechanical simulation of NIR absorption bands of piperine was performed. This step enabled elucidating the chemical information relevant to the calibration model, and interpreting the difference in the analytical performance of the compared spectrometers with statistical parameters of the calibration models below acceptable levels.
Highlights
In recent years a dynamic development of miniaturized, handheld NIR spectrometers enabled the prospect of rapid on-site analysis and marked a significant improvement in practical applications for food and natural product analysis [1]
This study demonstrated the feasibility of quantitative determination of piperine content in either whole or milled black pepper seeds with the use of handheld NIR spectrometers
While the SCiO spectrometer is advertised as a spectrometer suited for examination of food quality, with its use piperine could not be detected in whole black pepper seeds
Summary
In recent years a dynamic development of miniaturized, handheld NIR spectrometers enabled the prospect of rapid on-site analysis and marked a significant improvement in practical applications for food and natural product analysis [1]. While benchtop devices have the capacity to fit larger interferometers or dispersive el ements, a handheld spectrometer is limited in size and available power while facing elevated requirements for mechanical ruggedness. This often comes at the expense of the performance. For MEMS, semiconductor manufacturing enables in-silicon integration of movable parts and al lows for precise movement in micro-scale This reproducible motion offers rotation of miniature gratings using a comb drive and thereby forming the scanning element for the microPHAZIR. This approach of fers unique stability, e.g. in robustness, resistance against mechanical shock and durability and is interesting for a miniaturized near-infrared spectrometer [10]
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