Xylanase production by Streptomyces xantholiticus K7 using agro-industrial by-products: statistical optimization,...

Streptomyces xantholiticus K7, isolated from an Algerian saline lake, achieved efficient xylanase production exclusively on agro-industrial by-products, without additional nutrient supplementation. Statistical optimization using a Central Composite Design within the Response Surface Methodology framework yielded a maximum xylanase activity of 75.24 ± 1.77 U/mL, in close agreement with the predicted value (72.5 U/mL). Production kinetics indicated that maximum enzyme activity (~ 69 U/mL) was reached on the eighth day of fermentation, representing the optimal harvest time. The enzyme was purified to homogeneity with an approximately 30-fold increase in specific activity and exhibited a molecular weight of 59 kDa. Optimal activity was observed at pH 6.0 and 50 °C, with 40% residual activity after 120 min at this temperature. The xylanase showed maximum activity in the absence of NaCl and retained more than 50% activity at 1.5 M NaCl, demonstrating halotolerance. Kinetic analysis revealed a K _m of 11.81 mg/mL, a V _max of approximately 65 U/mg K _cat of 64 s⁻¹, and K _cat/K _m 5.42 s⁻¹·mg⁻¹·mL for Beechwood xylan. Enzyme activity was strongly enhanced by Ca²⁺ and Mg²⁺, whereas Cu²⁺ and Hg²⁺ were inhibitory. The enzyme retained more than 50% of its activity in the presence of SDS, Tween 20, Tween 80, EDTA, and ethanol. Functional evaluation confirmed effective juice clarification, improving clarity by 26.2% in apple juice and 59.6% in pear juice within 60 min, accompanied by moderate increases in reducing sugars. These results demonstrate the potential of S. xantholiticus K7 xylanase as a robust biocatalyst for sustainable applications in food processing and related biotechnological industries.

The online version contains supplementary material available at 10.1007/s13205-026-04878-w.