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

Abstract

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 m M), 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.