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In this study,the effects of different extraction methods on the structure,physicochemical properties,and functional activities of lemon peel pectin were determined.Pectin was extracted from lemon peels using microwave-assisted acid(MA),ultrasonic-assisted acid(UA),ultrasonic-assisted microwave(UM),and ultrasonic microwave-assisted acid(UMA)extraction procedures and the effects of these four extraction methods on the structural characteristics,physicochemical properties,and functional activities of the pectin were compared.The results showed that,pectins extracted using all four methods had a predominantly rhamnogalacturonan I(RG-I)structure,among which the pectin extracted using UMA was found to have the highest yield,whereas that extracted using UM retained alarger proportion of the RG-I structure.The Fourier transform infrared spectroscopy revealed that the pectins obtained using all four procedures were characterized by typical polysaccharide absorption peaks and lacked a triple helix structure,whereas scanning electron microscopy analysis revealed that pectin extracted using the MA method had a looser structure.Furthermore,compared with the pectin obtained using other extraction processes,that extracted using the UA approach was found to have significantly(P＜0.05)higher water retention(22.98±0.24 g/g),oil retention(4.56±0.22 g/g),and emulsifying properties(40.00％±0.10％),whereas the pectin obtained via UM extraction had stronger DPPH·(0.813±0.17 mg/mL),·OH(0.800±0.12 mg/mL),and ABTS+·(0.731±0.02 mg/mL)radical scavenging properties,and showed superior inhibitory activity against α-glucosidase(3.245±0.07 mg/mL)and α-amylase(6.868±0.22 mg/mL),all significantly(P＜0.05)higher than the pectin obtained by enzymatic methods.Collectively,these findings indicates that pectins extracted using the four assessed methods all have hypoglycemic potential,although using different extraction methods can yield pectins with varying functional characteristics(such as water retention,emulsification,antioxidant properties and so on).The findings of this study will provide a valuable reference for the comprehensive utilization of lemon peels.

Objective: This study aimed to optimize the preparation process of polysaccharides from lemon peel and screen out the components with high hypoglycemic activity. Methods: Ultrasonic assisted enzymatic extraction of lemon peel polysaccharide, combined with response surface test to explore the best extraction process, through DEAE-52 anion chromatography and Sephadex G-100 gel column chromatography separation and purification to obtain a homogeneous polysaccharide fraction (named as LPs-1a). The effective hypoglycemic components of lemon peel polysaccharides were screened by α-glucosidase and their relative molecular weight, monosaccharide composition and characteristic groups were analyzed. Results: The optimal extraction process of lemon peel polysaccharide was ultrasonic treatment for at 55 ℃ for 44 min with solid-liquid ratio 1∶20 (g/mL) and cellulase addition rate 1.1%. Under the control of these conditions, the yield of lemon peel polysaccharide was 6.83%, which was close to the predicted value. The LPs-1a fraction significantly inhibited the activity of α-glucosidase with （1.22±0.04） mg/mL of IC50(P＜0.05). The relative molecular weight of this component was 195 260, and it was connected by α-glycosidic bonds and β-glycosidic bonds with a pyranose ring. The morphology of the polysaccharide was fibrous, and it was composed of mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose and arabinose Conclusion: Ultrasound-assisted enzymatic method is helpful in screening the highly hypoglycemic active components of lemon peel polysaccharides.

In order to utilize lemon seed resources effectively , the antioxidant activities of its protein and enzymolysis peptide were studied. Lemon seed protein(LSP) was extracted from lemon seed meal powder with the alkaline extraction and acid precipitation. Response surface methodology was used to optimize the extraction process of LSP and analyze its amino acid composition. Papain, trypsin, compound protease and flavor protease were applied on the enzymatic hydrolysis of LSP. The antioxidant capacity (scavenging capacity of 1,1- diphenyl -2- picrylhydrazyl radical (\begin{document}$\mathrm{D}\mathrm{P}\mathrm{P}\mathrm{H}\cdot$\end{document}), hydroxyl radical(\begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document}) and superoxide anion(\begin{document}${\mathrm{O}}_{2}^{-}\cdot$\end{document})) of the enzymatic hydrolysate was studied, and the infrared spectrum analysis of the above four enzymatic peptides was carried out. The results showed that, the optimum extraction conditions of LSP were as follows: pH was 10.5, extraction time was 60 min, liquid-to-material ratio was 41:1 mL/g, and extraction temperature was 40 ℃. Under these conditions, the actual extraction rate of protein from lemon seed reached 12.25% ± 0.01%. The essential amino acids of LSP were complete in variety, accounting for 31.8% of the total amino acids. The flavor protease-hydrolyzed peptide had strong antioxidant capacity. The IC50 of papain enzymolysis peptide, trypsin-hydrolyzed peptide, peptide of compound protease and peptide of flavourzyme against DPPH free radical scavenging was 3.54, 1.75, 1.52 and 1.02 mg/mL, respectively. The IC50 against \begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document} free radical scavenging was 8.77, 8.92, 8.29 and 5.02 mg/mL, respectively. The IC50 against \begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document} free radical scavenging was 2.70, 0.90, 0.97 and 0.81 mg/mL. Theinfrared reflectance spectroscopy analysis suggested that all four samples had absorption peaks near 3400, 1600, 1300, and 1000 cm-1, and contained functional groups with antioxidant activity. The study considered that LSP had high antioxidant activity and nutritional value, and could be used as a functional component in the development of antioxidant-related functional foods and health care products.