[Establishment of near-infrared on-line monitoring model and determination of endpoint in frying process of Hordei Fructus Germinatus]

Abstract

Hordei Fructus Germinatus has been always used by "stir-frying" as a traditional medicine and the endpoint judgment of "fragrant" and "yellow" has been the focus and difficulty in frying process research. In this study, a quantitative calibration model between index components and NIRS was established in order to rapidly detect the contents of reducing sugar, total amino acids, total flavonoids, A420 and moisture; besides, an endpoint judgment method of frying process was put forward based on the "component change rate". Near-infrared spectra of samples with different frying time were collected, and a quantitative analysis model based on near-infrared spectroscopy was established to optimize the parameters such as spectral pretreatment and modeling band. HCA and PLS-DA were used to study the relationship between component and "stir-frying", and the endpoint of frying process was determined. The established calibration model had a good performance that the correlation coefficients between the predicted results and the actual measured values were both more than 0.9, with predicted relative deviations less than 10%. Hordei Fructus Germinatus with different frying time was divided into 4 categories by HCA analysis. PLS-DA analysis showed that total reducing sugar had a significant contribution to distinguishing the Hordei Fructus Germinatus of different frying time. When the change rate of total reducing sugar was 80%, it could judge that the endpoint of frying had been obtained. Results showed that NIRS could not only quickly and accurately determine the contents of reducing sugar, total amino acid, total flavonoid, A420 and moisture in Hordei Fructus Germinatus samples of different frying time, but also judge the endpoint of frying in the process. This study provided a new method for the evaluation and endpoint judgment of "stir-frying" process in research of traditional Chinese medicine.

Keywords: Hordei Fructus Germinatus; endpoint judgment; near-infrared spectroscopy; on-line monitoring; stir-frying process.