Potential quality evaluation method for Radix Astragali based on sweetness indicators

Abstract

Sweetness is a traditional sensory indicator used to evaluate the quality of the popular Chinese herb Radix Astragali (RA). RA roots with strong sweetness are considered to be of good quality. However, neither a thorough analysis of the component(s) contributing to RA sweetness, nor a scientific investigation of the reliability of this indicator has been conducted to date. In this study, seven kinds of sweetness components were identified in RA and a quality evaluation method based on these components was established and used to characterize the quality of 48 RA samples. The sweetness evaluation method of RA was first built based on the sweetness components, and a comprehensive evaluation index commonly used in quality control of RA was also derived, which was based on the contents of four indicators (astragaloside IV, calycosin glucoside, polysaccharides and extracts). After evaluating the correlation of these indexes the results showed that the level of sweetness exhibited a strong positive correlation with the proposed comprehensive index. Our results indicate that sweetness is one of the most important quality attributes of RA and thus provide a scientific basis for the utility of the sweetness indicator in quality assessment of this Chinese herb.

Figure 1

Chromatograms of the total ion current of the acetylated monosaccharide, disaccharide standards and determination of RA samples. Saccharide mappings of the perennial membranaceus var. Mongholicus (Bge.) (A); fast-growing membranaceus var. Mongholicus (Bge.) (B); perennial membranaceus (Fisch.) Bge. (C); fast-growing membranaceus (Fisch.) Bge. (D); and chromatogram of the total ion current of the acetylated monosaccharide and disaccharide standards (E). Peak identities: (1) meso-erythritol (RT: 12.43 min, m/z: 145, 115, 103); (2) 2-deoxy-d-ribose (RT: 12.76 min, m/z: 81, 98, 141); (3) 2-deoxy-d-ribitol (RT: 16.20 min, m/z: 159, 103, 117); (4) d-xylopyranose (RT: 18.64 min, m/z: 128, 170, 157); (5) L-rhamnopyranose (RT: 19.32 min, m/z: 115, 157, 142); (6) L-fucopyranose (RT: 19.60 min, m/z: 115, 157, 142); (7) L-arabinopyranose (RT: 20.02 min, m/z: 128, 170, 115); (8) l-rhamnitol (RT: 20.25 min, m/z: 128, 170, 115); (9) d-ribitol (internal standard, RT: 22.35 min, m/z: 115, 145, 103); (10) l-fucitol (RT: 22.81 min, m/z: 128, 170, 115); (11) l-arabinitol (RT: 23.02 min, m/z: 115, 145, 103); (12) d-xylitol (RT: 23.48 min, m/z: 115, 145, 103); (13) d-galactopyranose (RT: 24.32 min, m/z: 115, 157, 98); (14) d-glucopyranose (RT: 25.04 min, m/z: 115, 157, 98); (15) d-fructopyranose (RT: 25.95 min, m/z: 187, 128, 101); (16) d-mannopyranose (RT: 26.17 min, m/z: 115, 101, 98); (17) myo-inositol (RT: 26.35 min, m/z: 168, 115, 126); (18) d-mannitol (RT: 26.58 min, m/z: 115, 145, 139); (19) d-sorbitol (RT: 26.91 min, m/z: 115, 145, 128); (20) d-dulcitol (RT: 27.09 min, m/z: 115, 187, 127); (21) N-acetyl-d-glucosamine (RT: 27.26 min, m/z: 114, 156, 241) and (22) sucrose (RT: 42.54 min, m/z: 169, 109, 211); The IS peak indicates the internal standard.

Figure 2

Contents of calycosin-glucoside, astragaloside IV, total polysaccharides and extracts in RA samples and RA sweetness levels across different species, regions, and growth years. Sweetness indicates relative sweetness of RA with the sweetness of 10% sucrose solution considered to be 1.0; The contents of calycosin-glucoside (mg/g), astragaloside IV (mg/g), total polysaccharides (g/g) and extracts (g/g) of RA are shown in Figure A1, A2, B1, B2, C1, C2, and D1, D2, respectively; MG (A. membranaceus var. Mongholicus (Bge.)) and MJ (A. membranaceus (Fisch.) Bge.) represent the two species of RA; FA (fast-growing RA (1–2 years samples)) and PA (perennial RA (5–7 years samples)) represent the two different growth years of RA; Sx (Shanxi province), Ssx (Shaanxi province), Gs (Gansu province), Nm (Inner Mongolia), and Hlj (Heilongjiang province) represent the five regions of RA.

Figure 3

Correlation between sweetness and the contents of total polysaccharides, astragaloside IV, calycosin-glucoside, and extracts of RA. Plot showing the correlation between sweetness of RA and the contents of total polysaccharides, astragaloside IV, calycosin-glucoside, and extracts of RA; Results of correlation analysis between every pair of elements in RA are expressed in the form of bands with ranges between −1 and +1; band colors from blue (−1) to reddish brown (+1) represent correlation ranging from negative to positive. Deeper color indicates stronger correlation.

Figure 4

Scatter plots of sweetness (A) and F-value (B) of comprehensive evaluation of RA. Scatter plot showing the averages and degrees of dispersion of sweetness and comprehensive evaluation of RA; Sweetness indicates relative sweetness of RA with the sweetness of 10% sucrose solution considered to be 1.0; F value indicates the quality of RA with higher F value corresponding to higher integrated quality of RA; MG (A. membranaceus var. Mongholicus (Bge.)) and MJ (A. membranaceus (Fisch.) Bge.) represent the two species of RA; FA (fast-growing RA (1–2 years samples)) and PA (perennial RA (5–7 years samples)) represent the two different growth years of RA; Sx (Shanxi province), Ssx (Shaanxi province), Gs (Gansu province), Nm (Inner Mongolia), and Hlj (Heilongjiang province) represent the five regions of RA.