Pectin Extraction from Grapefruit Peel using a Sonicator

Pectins from fruit by-products such as peels or pulp are highly efficiently extracted using ultrasonic extractors. As a reliable simple and safe to operate pectin extraction method, sonication increases the pectin yield and pectin quality at accelerated production speed. Below, we demonstrate the efficacious technique of ultrasonic pectin extraction from grapefruit peel.

Ultrasonic Pectin Extraction Step-by-Step

Ultrasonic pectin extraction describes the application of power ultrasound in order to promote the release of pectins from a raw material (e.g. fruit peels, citrus fruit by-products). Sonication is a well-established technique to disrupt cell walls and release pectin from plant material.
The following protocol for ultrasonic pectin extraction from grapefruit peels using a probe-type sonicator and subsequent ethanol precipitation:


Materials Used:

• 50gr grapefruit peel
• 200mL purified water
• 400mL ethanol
• Sonicator UP200St + sonotrode S26d14
• Glass beakers

Preparation of Raw Material:

• Obtain citrus peel as the raw material. In this protocol we use grapefruit peels.
• Wash the citrus peel thoroughly to remove any dirt or debris.
• Cut the citrus peel into small pieces to increase the surface area for extraction.

Solvent Selection:
Water is the preferred solvent for extraction, which is inexpensive and non-toxic. Water is commonly used for pectin extraction due to its ability to solubilize pectin without causing degradation. Adding a small amount of acids (e.g. citric acid, acetic acid, nitric or hydrochloric acid) to water as a solvent aids in solubilizing pectin from plant materials and enhances the extraction process. Adjusting the solvent to a pH value of approx. 2-3 pH is a good guiding value.
 
Ultrasonic Extraction Procedure:

• Place approx. 50 gr finely chopped citrus peel pieces in a beaker or flask.
• Add approximately 200 ml of the selected solvent to the citrus peel.
• Use a probe-type sonicator to treat the mixture with ultrasonic waves. We use the UP200Ht, 200 watts powerful ultrasonic extractor equipped with the sonotrode S26d14. Set the amplitude to 100%.
• Sonicate the mixture for approximately 10 min until optimal extraction is achieved.

Filtration:
After sonication, filter the mixture using a pre-wetted fine mesh or filter cloth to separate the extracted pectin solution from the solid residue, the grapefruit peel particles. Repeating this filtration steps several times makes sure that all solid remains are removed.
 

Ethanol Precipitation:

• To precipitate pectin from the extracted solution, ethanol is commonly used as a precipitating or quenching agent.
• Transfer the filtered pectin solution to a clean container.
• Gradually add ethanol to the pectin solution while stirring continuously. The ratio of ethanol to pectin solution varies but is typically around 2:1 (ethanol: solution) by volume.
• Continue adding ethanol until a final concentration of approximately 70-80% ethanol in the solution is reached. This concentration promotes the precipitation of pectin.
• Allow the mixture to stand for a sufficient period, usually several hours or overnight, to facilitate precipitation.
• After precipitation, collect the precipitated pectin by centrifugation or filtration.
• Wash the precipitated pectin with ethanol to remove impurities and residual solvent.
• Finally, dry the purified pectin under vacuum or at low temperature to remove any remaining moisture.

As the pectin content and the fruit-based raw material are subject to natural variations, the extraction procedure might require to be adapted accordingly. This means that the specific extraction and precipitation conditions may need to be optimized depending on the type of citrus peel, ripeness, pectin yield, and desired pectin properties. Analytical techniques such as gravimetric analysis or spectrophotometric methods can be employed to quantify pectin content and assess extraction efficiency.

SEM of residual sugar beet pulp at 1000x magnification: (a) before extraction, and after extraction of pectin using (b) Xylanasae (250 U/g), (c) Cellulase (300 U/g), (d) Xylanasae+Cellulase (1:1), and (e) Xylanasae+Cellulase (1:1.5), and (f) Xylanasae+Cellulase (1:2).
(study and images: Abou-Elseoud et al., 2021)

Industrial Pectin Extraction with Hielscher Sonicators

The same procedure of ultrasonic pectin extraction demonstrated above can be linearly scaled to industrial inline production. The use of an ultrasonic flow cell reactor allows to process large volumes of fruit by-products in a continuous inline treatment.
Hielscher Ultrasonics offers a sophisticated line of industrial sonicators for the processing of fruit and vegetable material for pectin production.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.