Valorization of protein-rich waste for industrial enzyme production: Purification and cheese making performance of a novel milk clotting protease from Streptomyces thermolineatus GZ1B10.

Proteases from the genus Streptomyces exhibit diverse biochemical properties with significant industrial potential. This study explores the valorization of protein rich waste as a substrate for the production, purification, and characterization of a novel milk clotting protease from the endophytic isolate GZ1B10, recovered from wild Beta vulgaris tubers. Molecular identification based on 16 S rDNA sequencing revealed 99.75% similarity to Streptomyces thermolineatus. The extracellular protease was purified by size exclusion chromatography followed by desalting, yielding 10.51 ± 0.8 mg of homogeneous enzyme. SDS-PAGE analysis revealed a single protein band with an estimated molecular weight of 21.8 kDa. Purification enhanced milk clotting activity (14.55 to 85.12 RU) and specific activity (0.21 to 8.09 RU/mg), approaching the activity profile of commercial rennet. Casein hydrolysis assays indicated selective κ-casein degradation (72%) supporting a rennet-like mode of action. Both crude and purified proteases exhibited optimal coagulation at pH 5.5, 60 °C, and 0.03 M CaCl₂, indicating high thermostability compared with rennet. Cheese yield measurements showed comparable results (16.25 g/100 mL) with similar syneresis (34.25%) and slightly improved moisture retention. This study reports S. thermolineatus as an endophyte of wild B. vulgaris for the first time and presents, to our knowledge, the first evidence of milk clotting protease production by this species, highlighting its potential as an alternative coagulant for industrial cheese production.