Effects of ultrasonic and ozone pretreatment on the structural and functional properties of soluble dietary fiber from lemon peel

In this study, the effects of ultrasonic (US), ozone (O-3), or ozone-ultrasonic (O-3-US) pretreatments on the structural and functional properties of soluble dietary fibers (SDFs) obtained from lemon peel were investigated. Scanning electron microscopy observation showed that, US-SDF, O-3-SDF, and O-3-US-SDF showed more looser surface and porous characterization, compared to the lemon peel SDF without treatment (untreated-SDF). Pretreatment led to a significant increases of SDFs yield, which increased by 16.70%, 85.44%, and 92.36% for US-SDF, O-3-SDF, and O-3-US-SDF, compared to untreated group, respectively. X-ray diffraction results showed that the crystal structure of the pretreated-SDFs was disrupted and possessed lower crystallinity. TGA analysis showed that pretreated-SDFs exhibited lower thermal stability. All three pretreatments led to a redistribution of monosaccharides in SDFs. In addition, functional properties, including water swelling capacity (WSC), water-holding capacity (WHC), oil holding capacity (OHC), and binding capacity of SDF for heavy metals ions (Pb, Cd, and Cu), were enhanced by the three different pretreatment methods. Especially, O-3-SDF showed the highest hydration ability. Principal component analysis (PCA) showed that untreated-SDF and pretreated-SDFs were effectively distinguished. In summary, our study suggested that the O-3 pretreatment could be used as the ideal pretreatment method for lemon peel SDF, and O-3-SDF has the greatest potential to be applied as functional ingredients in food products. Practical Applications Ultrasonic (US) treatment is one of the green nonthermal technologies, it has been widely used to assist in the extraction of dietary fiber. Ozone (O-3) is commonly used in agricultural waste disposal, while O-3 treatment is still in the blank stage in the field of assisting the extraction of dietary fiber, and has great potential for development. In this experiment, the effects of US and O-3 pretreatment on the structural and functional properties of SDFs from lemon peel were studied. The results showed that pretreated-SDFs existed different structural and functional properties compare with the untreated-SDF. And O-3 pretreatment could be used as the ideal pretreatment method for lemon peel SDF.