Rapid detection of authenticity and adulteration of bear bile powder using infrared spectroscopy combined with chemometrics
Bear bile powder is a dried product obtained from the gallbladder surgery of Selenaretos thibetanus Cuvies, a member of the bear family. It has the effects of clearing heat, calming the liver, and improving vision, and is one of the four precious animal medicinal materials in China. Due to the special source and high price of bear bile powder, there are cases in the market where other animal bile powders are sold as bear bile powder. In addition, our research group found in the early stage of market research that due to the considerable production and low price of pig bile powder and cow bile powder, their appearance and characteristics are similar to bear bile powder. In addition to being counterfeited as bear bile powder, they are often mixed into bear bile powder for sale, and compared with counterfeit products, the detection difficulty of adulterated products is higher. This phenomenon leads to uneven quality of commercially available bear bile powder, seriously affecting clinical efficacy and consumer rights. Therefore, the identification of authenticity and prediction of adulteration ratio of bear bile powder are of great significance for quality control of bear bile powder.
The commonly used identification methods for bear bile powder include thin-layer chromatography, high-performance liquid chromatography, and specific polymerase chain reaction (PCR), but these methods have problems such as long time consumption, complex operation, and destructive effects on the sample. In addition, some methods require a large amount of organic reagents when the sample size is large. Near infrared spectroscopy has the advantages of fast analysis speed, minimal sample destruction, and no need for preprocessing. It has been widely used in the identification of authenticity and adulteration of traditional Chinese medicine. However, due to the strong hygroscopicity of bear bile powder, it is prone to losing some samples when used for near-infrared spectroscopy analysis. Therefore, this method has certain limitations when applied to bile medicinal materials. Compared with near-infrared spectroscopy, infrared spectroscopy also has the characteristics of fast and sensitive analysis, and requires a very small sample size, making it more suitable for quality control of valuable medicinal materials. At present, there are few reports on the use of infrared spectroscopy to identify bear bile powder. Only Yan et al. compared the infrared spectra of bear bile powder with the other three animal bile powders, but their sample size is small, and there is a lack of attention to adulteration behavior and no visualization of results combined with chemometrics. This study prepared adulterated samples with different ratios of bear bile powder, pig bile powder, and cow bile powder. Infrared spectra of genuine products, 7 types of adulterated products, and 2 types of adulterated products were collected. Baseline correction, smoothing, differentiation, and other preprocessing methods were used to optimize the obtained spectra. Combined with orthogonal partial least squares discriminant analysis (OPLS-DA) and partial least squares regression (PLSR) methods, the feasibility of using infrared spectra for the identification of bear bile powder authenticity and prediction of adulteration ratios was explored, providing a reference for the quality control of bear bile powder and other valuable medicinal materials.

This study, for the first time, used infrared spectroscopy combined with chemometrics to establish OPLS-DA qualitative models for genuine bear bile powder, different categories of counterfeit products, and adulterated products, as well as PLSR quantitative models for two types of adulterated bear bile powder adulteration ratios. Through different spectral preprocessing methods, the established identification models for genuine, counterfeit, and adulterated bear bile powder, as well as the identification accuracy of the adulterated product category model and adulterated product category model for the calibration set and validation set, exceeded 95%; In addition, the R2c and R2v of the quantitative model for the proportion of adulterated bear bile powder in two types are both greater than 0.95. The above results indicate that infrared spectroscopy technology can quickly detect the quality of bear bile powder and the results have good accuracy.

Compared with the current conventional analysis methods for animal bile medicinal materials, infrared spectroscopy not only ensures the accuracy of results but also saves time and cost, achieving quality control of valuable medicinal materials in a nearly non-destructive manner. Based on the current sample collection and quantitative model of bear bile powder established by our research group, infrared spectroscopy has shown excellent detection ability. However, the spectral model is based on a large number of samples and requires continuous sample supplementation to improve model accuracy and stability. Therefore, in the future, we will further increase the types and numbers of samples to more accurately evaluate the quality of bear bile powder.

With the development of chemometrics, infrared spectroscopy has broad application prospects in the quality control of medicinal materials. This study provides a simple and fast new method for the quality control of valuable medicinal materials, and also provides a reference for the quality control of bear bile powder.