Reducing value methods for maltodextrins. I. Chain-length dependence of alkaline 3,5-dinitrosalicylate and chain-length independence of alkaline copper

Molar reducing values for maltodextrins (maltose-maltoheptaose) were obtained using alkaline 3,5-dinitrosalicylate and alkaline copper reagents. It was found that equimolar quantities of the maltodextrins gave absorbance values with alkaline 3,5-dintrosalicylate that increased with the number of glucose units in the dextrin. Calcium ion (40 mM), however, repressed the increase in the absorbance values but did not completely eliminate overoxidation. The alkaline copper reagent gave a constant absorbance value for equimolar quantities of the maltodextrins. Thus, alkaline copper reagent gives a stoichiometric relationship with the number of hemiacetal, reducing groups, and alkaline 3,5-dinitrosalicylate gives a nonstoichiometric relationship. These results have an important consequence on the measurement of carbohydrase activity. The assay of α-amylase by alkaline 3,5-dinitrosalicylate gives a curvilinear relationship with enzyme concentration, whereas the assay by alkaline copper gives a linear relationship. The use of dinitrosalicylate will give erroneously high estimates of α-amylase activity, and it is clear that the effect of calcium on dinitrosalicylate reducing values has misled some workers into concluding that this ion affects α-amylase action patterns.