Resumen de Critical study of a procedure for the assay of starch in ligneous plants
E. Rubio, F. Lescourret, L. Gómez
Ligneous plants offer a wide variety of matrices that interfere with the assay of starch, which is present at low levels which vary considerably depending on the tissues considered and the phenological stage. Because no reference technique is available, a critical study was developed to validate a method for the enzymatic assay of starch. Analyses were performed on 50 mg samples of plant powder obtained from different parts of peach trees. After the total elimination of soluble components (including glucose) in a water/methanol/chloroform mixture, the starch was extracted from the ligneous residue and solubilised either by autoclaving in an aqueous medium or using 4 M potassium hydroxide (KOH) solution (dispersion stage). After hydrolysis with amyloglucosidase, the starch content was determined indirectly by the enzymatic assay of released sugar. The precision (repeatability and reproducibility), linearity (addition of specified amounts of starch) and accuracy (high rate of starch recovery, 95%) of the method were excellent, whichever dispersion method was employed. The highly significant analogy of the results obtained using such diverse dispersion techniques (autoclaving and dissolution in KOH) was indicative of their specificity and efficacy. The reliability of the enzymatic stages was generally excellent. However, some plant matrices may, during dispersion, release soluble compounds which interfere with amyloglucosidase activity, and this may explain the incomplete recovery of starch. This moderate and unpredictable interference was, in principle, the only critical point concerning the method for the enzymatic assay of starch in ligneous plants with very low starch content, the reliability of which was clearly demonstrated.
