Evaluating the applicability of several colorimetric methods for analyzing sugar plant immunity inducer formulations

Given the limited research on current methods for detecting the product quality of sugar-based plant immunity inducers, this study systematically evaluated the applicability and influencing factors of the sulfuric acid-phenol method, sulfuric acid-anthracenone method, and Elson-Morgan method for detecting various sugar active ingredients in sugar plant immunity inducer formulations, and effective colorimetric methods were established. Results showed that the three colorimetric methods presented different responsiveness to glucose, galacturonic acid and glucosamine, and the composition of monosaccharides was particularly important for the selection of colorimetric methods. Dextran, polygalacturonic acid and oligosaccharins, which composed of the corresponding monosaccharides, were used as representative glycan compounds, and suitable methods for these polysaccharide compounds were established by optimizing the colorimetric conditions. Method validation results showed excellent linear correlation (R² > 0.998), good reproducibility (relative standard deviation range of 0.4%-0.9%) and high recoveries (100%-101%). Combined with ion chromatography, this study revealed that the active ingredients of current oligosaccharin formulations are oligo-glucosamine, and pointed out that the active ingredients of the sugar plant immunity inducers were not clearly defined in the current registration data. Furthermore, the present study established and validated the colorimetric methods for analyzing the fungous proteoglycan, oligosaccharins and chitosan formulations, and the methods presented good linearity, excellent reproducibility and high accuracy, which met the requirements for the product quality analysis methods of formulations. This study provides strategies and method support for the quality analysis of sugar plant immunity inducers and helps to promote the healthy development of related industries.