Valorization of corn cobs for xylanase production by Aspergillus flavus AW1 and its application in the production of antioxidant oligosaccharides and removal of food stain

Xylanases are hemicellulolytic enzymes specifically catalyze xylan hydrolysis that constitutes the most abundant polysaccharide in the hemicellulose fraction of the lignocellulosic biomasses. The effective conversion of these biomasses to valuable commodities required the use of economic effective biocatalysts. In this study, xylanase production was performed by corn cobs fermentation using Aspergillus flavus AW1 in which the highest productivity was 356.36 U/g dry substrate. The partially purified enzyme was aflatoxin-free as estimated by high performed liquid chromatography. The enzyme was optimally active over a wide pH range from 5.5 to 7.5. Additionally, it was optimally active at temperature of 55 °C and at 60 °C it possessed 95% of its maximum activity. The enzyme half-lives were estimated as 83.81 and 44.69 min at 55 and 60 °C, respectively. The Vmax and Km for the purified enzyme fraction were 250 U/mg protein/min and 5.55 mg/mL, respectively. Moreover, beech wood xylan hydrolysis as well as the hydrolysis of the hemicellulosic fraction of corn cobs was examined by applying the produced enzyme. The obtained results indicated hydrolysis percentage values of 39 and 19% for beech wood xylan and the hemicellulosic fraction of corn cobs, respectively with the release of a mixture of xylooligosaccharides confirmed by thin layer and high performed liquid chromatography analysis. The antioxidant activities for the dried oligosaccharide mixtures were estimated by scavenging activity of 1,1-diphenyl-2-picrylhydrazyl free radical. Finally, the efficiency of the purified enzyme fraction in the removal of mango stain was investigated in comparison to the commercial detergent.