Effects of Different Extraction Processes on the Structure and Antioxidant Properties of Soluble Dietary Fiber from Celery
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Abstract:
Three types of soluble dietary fibers (SDF) were prepared from celery residue by water extraction (W-SDF), alkali extraction (A-SDF), and ultrasound-assisted alkali extraction (UA-SDF), and the differences in their structure and antioxidant properties were compared. The structures of the SDF samples were characterized by Fourier-transform infrared spectroscopy (FT-IR), thermal analysis techniques and scanning electron microscopy. The results showed that alkali treatment could cause ester bond cleavage, while ultrasound-assisted alkali treatment could increase the content of SDF through breaking the ether bonds. The endothermic peak temperatures of W-SDF, A-SDF, and UA-SDF were 146.99, 150.09, and 153.44 ℃, respectively, and the thermal stability followed the order of UA-SDF>A-SDF>W-SDF. The W-SDF had a smooth and compact surface with the largest average particle size (1 481 nm), whilst the A-SDF and UA-SDF showed porous and loose structures with average particle sizes being 841 nm and 588.34 nm, respectively, indicating that the alkali treatment and ultrasound treatment resulted in the cleavage of ester and ether bonds thereby causing the conversion of insoluble fiber to soluble fibers. The in vitro antioxidant activity results showed significant differences (P<0.05) among the three kinds of fibers. Among them, the UA-SDF exhibited the strongest abilities to scavenge •OH and DPPH• with IC50 values being 0.67 and 0.31 mg/mL, respectively, followed by A-SDF (which had IC50 values of 1.25 and 0.58 mg/mL, respectively), and W-SDF (which had IC50 values of 1.72 and 0.86 mg/mL, respectively). Comprehensive analysis suggests that the differences in the antioxidant properties of the soluble dietary fibers from celery residue were caused by the differences in their chemical compositions and surface structures.
