Semirational Engineering of a Novel GH107 Fucoidanase Enables Efficient Production of Fucoidan Oligosaccharides for Postharvest Preservation of Winter Jujube Fruit.

Fucoidan oligosaccharides (FOS) have attracted attention due to improved solubility and bioactivity, but efficient preparation remains challenging. Herein, a GH107 fucoidanase FcnC from Polaribacter sp. was identified, characterized, and improved by semirational engineering. FcnC hydrolyzed fucoidans from Fucus vesiculosus and Kjellmaniella crassifolia Miyabe, with higher activity toward F. vesiculosus-derived fucoidan (432.46 U/mg) than K. crassifolia-derived fucoidan (110.32 U/mg). The mutants A285P, S329A, and H448P exhibited enhanced activity, with A285P and H448P reaching 859.34 and 685.20 U/mg, respectively. FOS prepared using FcnC-A285P consisted of oligosaccharides with degrees of polymerization of 2-6. Postharvest treatment of winter jujube fruit (Ziziphus jujuba Mill. cv. Dongzao, a cultivated fruit crop) showed that FOS reduced decay incidence; delayed weight loss and firmness decline; maintained reducing sugar, organic acid, and vitamin C contents; and slowed antioxidant capacity loss. These findings demonstrate that engineered FcnC enables efficient FOS production and that FOS has potential applications in postharvest preservation.