Effects of Modification Methods on the Structural and Functional Properties of Lemon Peel Residue Powders

In this study, lemon peel residue powders were modified by microwave, high-speed shear and ultra-fine grinding, respectively, to improve its quality and the comprehensive utilization rate of lemon processing by-products. The morphological structure and thermal stability before and after modification were characterized by scanning electron microscopy, Fourier infrared spectroscopy and thermogravimetric analysis. The physicochemical and functional properties were measured to evaluate the overall quality of the lemon peel residue powders after different modifications. The results showed that the structure of lemon peel residue powders was loosened after these three modifications and the main functional groups were not significantly changed after the modification. The thermal stability of lemon peel residue powders was significantly improved after microwave and high-speed shear modification (P<0.05). Overall, the physicochemical and functional properties of the lemon peel residue powders modified by high-speed shearing were the best. Its total dietary fiber (TDF), soluble dietary fiber (SDF), water holding capacity, oil holding capacity and swelling capacity were 81.88%, 33.07%, 20.05 g/g, 2.00 g/g and 34.99 mL/g, respectively, as well as had the best cation exchange capacity, ability to delay glucose dialysis, glucose adsorption capacity, and cholesterol adsorption capacity, and therefore had similar physicochemical and functional properties to dietary fiber (DF). Correlation analysis suggested a highly significant positive correlation between the SDF content in lemon peel residue powders and each physicochemical and functional index (P<0.01). In conclusion, increasing the SDF content could be used as a reference indicator to improve the quality of lemon peel residue powders, and the lemon peel residue powders modified by high-speed shear had the potential to be a high quality source of DF, which could provide some theoretical reference to improve the quality of lemon peel residue powder and its potential as functional food ingredient.