Modified bicinchoninic acid assay for accurate determination of variable length reducing sugars in carbohydrates

The accurate determination of reducing ends of malto-oligosaccharides is essential for calculating the enzyme activities of starch debranching enzymes. The suitability of the 3,5-Dinitrosalicylic acid (DNS) method, the Dygert method, and the Bicinchoninic acid (BCA) method for accurate determination of reducing ends from malto-oligosaccharides of different chain lengths is compared. The results showed that BCA assay was much more accurate than the other assays. The results for the BCA assay showed that different malto-oligosaccharides gave observed (measured) values that were significantly similar to the expected (predetermined) values. In contrast, the DNS and Dygert assays underestimated the amount of reducing sugar present for glucose. Furthermore, both DNS and Dygert methods showed increasing degree of overestimation of the amount of reducing sugar present with the increasing length of the malto-oligosaccharide sugar chains. The BCA assay can suitably quantify reducing sugars even in mixtures of oligosaccharides with different chain lengths. Thus, enzyme activities can be measured without bias towards higher values for enzymes that preferentially cleave the longer chain lengths