Quantification of Reducing Sugars

The reducing sugar content was determined using the 3,5-dinitrosalicylic acid (DNS) method.⁵² The supernatant (1 mL) of culture, collected during fermentation, was mixed with 1 mL of DNS reagent and then heated at 100 °C for 15 min. The absorbance was monitored at 540 nm by an ultraviolet–visible (UV–vis) spectrometer. The content of reducing sugars was determined by comparing it to a standard curve created by glucose at different concentrations.