Ultrasound and pressure assisted method for extracting pectin rich in RG-I

An ultrasound and pressure assisted method for extracting a pectin rich in rhamnogalacturonan I, comprising:

• (1) drying and crushing citrus peel to acquire citrus peel powders, sieving the citrus peel powders with a 50 mesh sieve, then dispersing the citrus peel powders in an alkaline solution containing sodium borohydride to obtain a mixed solution;
• transferring the mixed solution into a closed container, keeping a reaction temperature at 25 to 40° C., and introducing an inert gas into the closed container to control an internal static pressure at 0.2 to 0.4 mpa;
• carrying out an ultrasonic treatment on the mixed solution simultaneously, wherein an ultrasonic intensity is controlled at 0.5 to 3.5 W/ml, an ultrasound and pressure treatment time is controlled within 20 to 40 min;
• (2) centrifuging a solution subjected to step (1) at a speed of 6000 to 8000 rpm to remove residues, retaining a supernatant, adding absolute ethanol to the supernatant to precipitate pectic polysaccharide and isolating a pectic polysaccharide precipitant;
• and
• (3) adding water to the pectic polysaccharide precipitant subjected to step (2) to obtain a redissolved solution, transferring the solution to a dialysis bag with a molecular weight cut-off of 3000 to 3500 Da, dialyzing with running water for 48 hours, and drying in a vacuum freezer to obtain the pectin rich in rhamnogalacturonan I.