The albedo, the white, spongy inner layer of the grapefruit peel, contains the
highest concentration of pectin. Situated between the outer colored rind (flavedo) and
the juicy segments, the albedo is rich in pectin because it serves as a structural
component, providing rigidity and integrity to the cell walls. This makes it the primary
source of pectin in grapefruits, far surpassing the pulp or juice, which are composed
mainly of sugars and acids. As a result, the albedo is the preferred part of the
grapefruit for pectin extraction, ensuring higher yield and quality.
Application of pectin extraction from pomelo
Pectin extracted from pomelo peels plays a significant role in sauce processing,
enhancing texture, stability, and overall quality. As a natural thickening agent, pectin
improves the viscosity of sauces such as ketchup, barbecue sauce, and fruit-based
condiments, providing a smooth and uniform texture. It acts as a stabilizer in
emulsified sauces like salad dressings and mayonnaise, preventing oil and water
separation to maintain consistency. In low-fat or reduced-fat sauces, pectin serves as a
fat replacer, delivering a creamy texture without adding extra calories, making it ideal
for health-conscious products. Additionally, it prevents syneresis (water separation)
during storage, ensuring the sauces remain stable and visually appealing. Pectin also
enhances the mouthfeel of sauces, giving them a rich and cohesive texture. As a
natural, plant-based ingredient, pectin meets the growing demand for clean-label and
sustainable food products, making it a valuable addition to modern sauce
formulations.
1. Acid extraction method
1.1. Preparation of Grapefruit Peels
- Peel Collection: Start by collecting the peels, focusing on the white inner layer
(albedo), which is richer in pectin.
- Cleaning: Rinse the peels thoroughly with water to remove dirt or other
contaminants.
- Size Reduction: Chop or grind the peels into smaller pieces (approximately 5 -
10 mm). This increases the surface area, facilitating the extraction process.
1.2. Hydrolysis and Extraction
Preparation of Acid Solution:
- Prepare an acidic solution using food-grade acids like citric acid,
hydrochloric acid (HCl), or nitric acid. Citric acid is preferred for food-grade
applications as it is generally recognized as safe (GRAS).
- Adjust the pH of the solution to around 1.5–3.0. A lower pH enhances
pectin solubility, aiding in extraction.
Peel and Acid Mixture:
- Add the prepared peels to the acidic solution. A common ratio is 1 part
peel to 10–20 parts acid solution.
Heating:
- Heat the mixture at a temperature between 60°C and 90°C for about 30
minutes to 2 hours, depending on the desired yield and pectin quality.
- Stir occasionally to ensure even heating and extraction.
1.3. Precipitation of Pectin
Alcohol Addition:
- To precipitate the pectin, add an equal volume or more of ethanol or
isopropanol (usually at 70–95% concentration) to the filtered liquid. Alcohol causes
the pectin to precipitate out of the solution.
1.4. Centrifugation
- Let the solution sit for 1–2 hours, allowing the pectin to form as a gel-
like precipitate.
- Collect the precipitated pectin by centrifugation.
2. Ultrasound-Assisted Extraction Method
2.1. Pretreatment
- Peel Collection: Start by collecting the peels, focusing on the white inner layer
(albedo), which is richer in pectin.
- Cleaning: Rinse the peels thoroughly with water to remove dirt or other
contaminants.
- Air-dry or oven-dry the peels at a low temperature (40–50°C) until moisture
content is reduced.
- Alternatively, use fresh peels directly if processing immediately.
2.2. Ultrasound-Assisted Extraction
Preparation of Solvent:
- Prepare an acidic solvent, typically a dilute solution of citric acid, hydrochloric
acid, or acetic acid.
- Adjust the solvent pH to 1.5–3.0 for optimal pectin extraction.
Mixing Peels and Solvent:
- Place the pomelo peels in the ultrasonic bath or extraction vessel.
- Add the prepared acidic solvent, maintaining the peel-to-solvent ratio.
Ultrasound Treatment:
- Apply ultrasound waves at a controlled temperature (50–70°C) for a short
duration (15–45 minutes).
- Stir the mixture continuously to ensure even ultrasonic treatment and prevent
localized heating.
- Monitor the extraction time carefully, as prolonged exposure may degrade
pectin.
2.3. Filtration
Separate Solids and Liquids:
- Filter the mixture using a fine mesh or filter cloth to remove solid peel
residues.
- Collect the liquid extract, which contains the dissolved pectin.
2.4. Pectin Precipitation
Alcohol Addition: To precipitate pectin, add ethanol or isopropanol (70–95%)
to the liquid extract in a 1:1 or 2:1 ratio (alcohol).
Settling: Allow the solution to sit for 1–2 hours, during which the pectin will
form a gel-like precipitate.
Collection: Use filtration or centrifugation to separate the precipitated pectin
from the liquid.
3. Microwave-Assisted Extraction Method
3.1. Preparation of Pomelo Peels
- Peel Collection: Collect pomelo peels, focusing on the albedo (the white
spongy layer), which is rich in pectin.
- Cleaning: Rinse the peels thoroughly with water to remove any dirt or surface
contaminants.
- Size Reduction: Chop or grind the peels into smaller pieces (5–10 mm) to
increase surface area and improve extraction efficiency.
3.2. Microwave-Assisted Extraction (MAE)
Preparation of Solvent:
- Prepare an acidic solvent, such as citric acid, hydrochloric acid, or acetic acid
solution.
- Adjust the pH of the solution to 1.5–3.0 for optimal pectin extraction.
Mixing Peels and Solvent:
Combine the pomelo peels and solvent in a microwave-safe container. Maintain the
peel-to-solvent ratio.
Microwave Treatment:
- Place the container in the microwave reactor or oven.
- Set the microwave power (typically 300–800 W) and extraction temperature
(50–90°C).
- Heat the mixture for a short duration, typically 3–15 minutes.
- Ensure intermittent stirring for uniform heating and to avoid localized
overheating.
Cooling: Allow the mixture to cool to room temperature after microwave
treatment.
3.3. Filtration
Separate Solids and Liquids:
- Filter the mixture using cheesecloth, a fine mesh, or filter paper to remove solid
peel residues.
- Collect the clear liquid extract containing dissolved pectin.
3.4. Pectin Precipitation
- Alcohol Addition: Precipitate pectin by adding ethanol or isopropanol (70–
95%) to the liquid extract in a 1:1 or 2:1 ratio (alcohol).
- Settling: Let the mixture sit undisturbed for 1–2 hours to allow the pectin to
form a gel-like precipitate.
- Collection: Separate the precipitated pectin using filtration or centrifugation.
3.5. Purification
- Wash the precipitated pectin with ethanol several times to remove impurities,
including residual acids, pigments, and sugars.
