Quality assessment of processed Eucommiae Cortex based on the color and tensile force

Eucommiae Cortex (EC), the dried stem bark of Eucommia ulmoides Oliv, has been traditionally used to strengthen the muscle and bone tissues and improve liver and kidney functions in East Asian countries, including China, Japan, and Korea. Salty-fried EC (SFEC) is made by using mixing EC and saline together based on the protocol of Chinese Materia Medica Processing (CMMP) for clinical use. However, the clinical effectiveness of SFEC is directly impacted by the frying temperature and time. But precise techniques for evaluating the caliber of SFEC have yet to be developed. Thus, this study aimed to establish a fast and accurate quality-check method for SFEC decoction pieces. According to the frying temperature and time, four different categories of SFEC had been got according to the Chinese Pharmacopoeia method as Raw (R), Under (U), Moderately (M), and Overly (O). The red (R), green (G), blue (B), and light (L) color values of the decoction pieces were quantitated using the Photoshop software to determine the standard value range of the L color (raw [104.44 ​± ​15.06], under [67.28 ​± ​8.20], moderately [39.94 ​± ​6.40], and over [15.02 ​± ​5.03]). Additionally, the tensile strengths and pinoresinol diglucoside (PDG) levels of EC gum-silks were measured using the mechanical tensile test and HPLC, respectively. We also conducted Pearson correlation analysis on the L color value, EC gum-silk tension (FbcN), and PDG level, and established the following multiple-linear regression equation: the decline in PDG level (w) ​= ​0.829–0.001 ​× ​FbcN – 0.009 ​× ​L. In conclusion, the L color value and FbcN could be used for cluster analysis of four categories of SFEC. Additionally, based on the correlation among the L color value, gum-silk tensile test, and PDG level, a rapid and accurate quality-control method for SFEC decoction pieces with different frying temperatures and durations was established. This method facilitates the manufacturing of efficacious SFEC.