Effect of carboxymethylation on properties of fucoidan from Laminaria japonica: Antioxidant activity and preservative effect on strawberry during cold storage

Carboxymethylation modification is commonly used for improving physicochemical and biological properties of nature polysaccharides, effect of carboxymethylation on property of fucoidan from Laminaria japonica (FL) is still unknown even though the polysaccharide has been isolated for several decades. To explore the derivatization-related effect, this study prepared carboxymethyl FL (CMFL) using chloroacetic acid. CMFL was characterized by degree of substitution (DS) determination and infrared spectroscopic analysis. Antioxidant activity of CMFL in vitro was assessed by scavenging capacity of DPPH, hydroxyl and superoxide radicals. Strawberry were used to investigate the effects of CMFL on harvested fruit. DS was determined to be 0.6733, and two characteristic absorption peaks of carboxymethylation were detected at 1602 and 1420 cm−1, suggesting that FL was carboxymethylated. IC50 values of hydroxyl, superoxide and DPPH radicals decreased by 17.8%, 17.5% and 15.7%, respectively, indicating higher in vitro antioxidant activity of CMFL than FL. CMFL reduced water loss and decay more effectively than FL. CMFL and to a lesser extent, FL treated fruit had higher ascorbic acid content and stronger scavenging capacities of DPPH, hydroxyl and superoxide radicals than control fruit during storage. Overall, carboxymethylation can enhance the properties of FL, including its effects on antioxidant activity, which suggests that CMFL can be used as a natural preservative for harvested fruit.