Abstract
In this study, jujube polysaccharides (JP) were extracted from Jinsixiaozao, and carboxymethylated jujube polysaccharides (CMJP) were prepared. The optimum carboxymethylation conditions optimized by Response Surface Methodology (RSM) were as follows: the reaction temperature was 60°C, the concentration of sodium hydroxide (NaOH) solution was 2.8 mol/L, and the content of chloroacetic acid was 2.12% with a degree of substitution (DS) of 0.2275 ± 0.0108. Physicochemical characterizations and in vitro antioxidant and prebiotic activities of JP and CMJP were evaluated. Compared with unmodified JP, water solubility and viscosity were improved in CMJP. Chemical analysis revealed that CMJP was composed of Rha: Ara: Xyl: Glc: Gal = 0.18 : 9.09 : 0.45 : 0.36 : 0.98 with a molecular weight of 3.04 × 105 Da. The signals of carboxymethyl were observed at 1600, 1420, and 1328 cm−1 in FT-IR. In addition, CMJP showed obviously strong hydroxyl radical scavenging ability compared with JP and also exhibited stronger abilities than JP on the proliferation growth of Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus rhamnosus strains. These results indicated that CMJP could be explored as a promising resource for the development of functional foods.
Highlights
Polysaccharides are complex biopolymers comprised of monosaccharides chains and widely distributed in plants, animals, and microorganisms
E Degree of substitution (DS) of carboxymethylated jujube polysaccharides (CMJP) had been increasing when chloroacetic acid content increased from 1% to 2% as shown in Figure 1(b). e maximum DS (0.2133) of CMJP was observed when chloroacetic acid content was 2%
At chloroacetic acid concentration greater than 2%, NaOH was neutralized and further increasing the concentration of chloroacetic acid has no advantages on the modification of carboxymethylation. erefore, 2% was used as the optimal condition for the chloroacetic acid content
Summary
Polysaccharides are complex biopolymers comprised of monosaccharides chains and widely distributed in plants, animals, and microorganisms. Natural polysaccharides have been proved to possess antitumor, antioxidant, antimicrobial, antiviral, immunomodulatory, hypoglycemic, gastrointestinal-protective, and gut microbiota-modulating properties for health promotion [1, 2]. E biological activities of natural polysaccharide could be strongly affected by molecular modifications, such as sulfation [3], phosphorylation, carboxymethylation [4], and acetylation [5] due to the changing of their structural and conformational properties. E application of natural polysaccharides as bioactive ingredients and food additives was limited by their complex structure and various bioactivities mechanism. Carboxymethylation, as a versatile modification method, has been found to have great influence on the physicochemical properties and biological activities of various polysaccharides. Xu et al [8] found that the addition of carboxymethyl groups improved the relatively poor water solubility and in vitro antioxidant activities of Ganoderma lucidum polysaccharide. Carboxymethylated polysaccharides from Sargassum fusiforme had a much higher antioxidant and antimicrobial activities in vitro than the native ones [4]
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