Comprehensive Guide to Edible Oil Refining Process

Vegetable oils and fats are essential constituents of food and an integral part of our daily diet. Extracted through mechanical expelling or solvent extraction from oleaginous seeds and fruits like soybeans, rapeseed, sunflower, palm, and olive, vegetable oils are primarily composed of triglycerides along with a minority of other substances. While certain compounds in vegetable oils, such as diglycerides, vitamins, phytosterols, tocopherols, and polyphenols, offer significant health benefits, others, including free fatty acids, waxes, pigments, and contaminants, can negatively impact the oil’s quality and stability. Thus, the edible oil refining process is crucial to eliminate these undesirable components and ensure the oils meet safety and quality standards.

This article delves into the comprehensive “Edible Oil Refining Process“, comparing chemical and physical refining methods, and highlighting their effects on oil quality and composition. Additionally, we will discuss how INVEXOIL’s “Engine Oil Refinery Services” and “Used Oil Re-refining Plants” incorporate similar principles and technologies to deliver high-quality outputs.

Table: Undesirable Constituents in Edible Oil Removed During Refining

Component	Origin	Effect
Free fatty acids	Hydrolysis of triglycerides	(i) Taste, smoke if heating (ii) Hydrolysis
Phosphatides (phospholipids)	Natural compounds	(i) Cloudy aspect (ii) Deposit a residue in the oil flavors (iii) Dark color if heating
Oxidation products	Oxidation of unsaturated fatty acids	(i) Undesirable flavors (ii) Stability (iii) Color—nutrition
Flavors	Natural compounds of seeds, autooxidation	(i) Odorous components (ii) Flavors
Waxes and pigments	Natural components of seeds	(i) Odorous components (ii) Flavors
Metals (iron and copper)	Technological pollution	(i) Oxidation catalysts (ii) Stability
Chemical pollutants Heavy metals Pesticides PAHs (B[a]P) Mycotoxins Dioxins	Pollution during storage transport and processing	(i) Safety toxicity

 

Types of Edible Oil Refining Process

Edible oil refining happens in two main ways: Chemical and Physical Refining.

This is an overview (summary) of both types; next, we expand each one by providing details and properties:

1. Chemical Edible Oil Refining Steps

• Degumming
• Neutralization
• Washing and Drying
• Bleaching
• Dewaxing
• Deodorizing

Chemical Edible Oil Refining Overview

• Best suited for low-acidity oils.
• Produces soapstock at rates up to 5% of crude oil volume.
• High effluent treatment costs.

2. Physical Edible Oil Refining Steps

• Degumming
• Bleaching and Filtration
• Deodorization
• Dewaxing

Physical Edible Oil Refining Overview

• Utilizes steam distillation to remove FFAs.
• High yield efficiency (up to 98%).
• Optimal for high-acidity oils; sensitive to phospholipid content.

 

Chemical Edible Oil Refining

Chemical edible oil refining is the traditional method used since ancient times for all fats and oils, including those slightly degraded.

The Chemical Edible Oil Refining involves six main steps:

1. Degumming

Degumming eliminates “gums” or mucilage from crude oil, primarily composed of phospholipids, carbohydrates, proteins, and trace metals. Phospholipids, vital for plant cell function, can trap metallic ions and act as antioxidants. However, their presence complicates storage and processing, necessitating their removal.

• Objective: Eliminates phospholipids, enhancing oil stability and refining readiness.
• Process Insights:
  • Phospholipid levels decrease by 85–90% post-treatment.
  • Acid degumming applies phosphoric acid at concentrations of 0.05–0.1%.
  • Centrifugation ensures up to 95% removal efficiency.

Different Types of Degumming:

Degumming in edible oil refining consists of 4 types: Water Degumming, Acid Degumming, Dry Degumming, Enzymatic Degumming.

Water Degumming: Removes hydratable phospholipids.

Acid Degumming: Uses acid to dissociate nonhydratable phospholipids.

Dry Degumming: Utilizes concentrated acid and bleaching earth for oils with low phospholipid content.

Enzymatic Degumming: Converts nonhydratable phospholipids into lysophospholipids using enzymes.

Table: Degumming (in Edible Oil Refining) Types, Description, and Application

Type of Degumming	Description	Application
Water Degumming	Uses water to remove hydratable phospholipids.	Suitable for oils with high hydratable phospholipids.
Acid Degumming	Uses acid to dissociate nonhydratable phospholipids.	Effective for oils with nonhydratable phospholipids.
Dry Degumming	Combines acid degumming with bleaching earth	Suitable for oils with low phospholipid content.
Enzymatic Degumming	Converts nonhydratable phospholipids into lysophospholipids using phospholipase C.	Efficient and environmentally friendly.

 

2. Neutralization

Neutralization involves treating oil with an alkali solution (caustic soda) to neutralize free fatty acids and convert them into soap stock. This process also removes impurities such as residual proteins, gums, carbohydrates, and oxidation products. Proper execution minimizes oil loss and enhances oil quality.

• Objective: Eliminates phospholipids, enhancing oil stability and refining readiness.
• Process Insights:
  • Caustic soda treatment lowers FFAs from 3.5% to under 0.05%.
  • Soapstock generation amounts to 2–4% of crude oil weight.
  • Effluent treatment requirements range from 200–300 liters per ton of oil processed.

Table: Neutralization (in Edible Oil Refining) Properties and Values

Property	Value
Chemical Formula	R-COOH + NaOH ⟶ R-COONa + H2O
Free Fatty Acid Removal	High
Soap Separation	Mechanical (centrifugation)
Residue Elimination	Proteins, gums, carbohydrates, oxidation products, pigments
Bioactive Molecule Loss	Tocopherols, polyphenols

 

3. Washing and Drying

This step eliminates alkaline substances, soaps, metallic traces, and impurities from neutralized oil. The washing water is heated, and the oil is dried under a vacuum to reduce moisture content.

Table: Washing and Drying (in Edible Oil Refining) Properties and Results

Process	Description
Washing	Removes soap and impurities
Drying	Reduces moisture content
Temperature	358-363°K (85-90°C)
Moisture Level Target	<0.1%

 

4. Bleaching

Bleaching reduces colored pigments, phosphatide residues, and impurities through adsorption using bleaching earth, activated carbon, or silica. It improves oil color and stability.

• Objective: Enhances visual clarity and removes unwanted compounds.
• Process Insights: 
  • Adsorbent dosage varies between 0.5% and 2% of oil weight.
  • Optimal processing conditions: 100°C–120°C, vacuum applied for 20–40 minutes.
  • Achieves a 90% reduction in carotenoids and residual soap below 50 ppm.

Adsorbent Efficiency in Bleaching

• Activated Bleaching Earth: Achieves a 95% reduction in polycyclic aromatic hydrocarbons (PAHs).
• Activated Carbon: Improves clarity and reduces organic contaminants to trace levels (<2 ppm).
• Efficiency Factors: Dependent on contact time (20–40 minutes) and temperature (80–120°C).

 

Table: Bleaching (in Edible Oil Refining) Adsorbent and Description

Adsorbent	Description
Bleaching Earth	Removes colored pigments
Activated Carbon	Adsorbs organic contaminants
Silica	Adsorbs impurities
Temperature	353-393°K (80-120°C)
Contact Time	20-40 min

 

5. Dewaxing (Winterization)

Dewaxing removes waxes that cause oil cloudiness, especially in cold conditions. The process involves controlled cooling and filtration.

• Objective: Prevent cloudiness by removing waxes.
• Proecess Insights:
  • Cooling rate: 1–2°C per hour to achieve 10°C–15°C crystallization temperature.
  • Reduces wax content from 0.3% to below 0.05%.

Table: Dewaxing (in Edible Oil Refining) Process and Description

Process	Description
Heating	Ensures oil is fully liquid
Cooling	Slowly reduces temperature
Filtration	Separates wax from oil
Temperature	283-288°K (10-15°C)

 

6. Deodorization

Deodorization uses steam distillation under a high vacuum to remove volatile compounds, odors, and contaminants. It improves oil stability and flavor but may also remove bioactive molecules.

• Objective: Removes volatile compounds and unwanted odors.
• Metrics:
  • Operates at temperatures between 180°C–240°C under vacuum (2–4 mmHg).
  • Reduces FFAs to below 0.01%.
  • Tocopherol retention ranges from 70% to 90%, dependent on parameters.

Table: Deodorization (in Edible Oil Refining) Process Parameter and Values

Process Parameter	Value
Temperature	453-513°K (180-240°C)
Vacuum Pressure	2-8 mmHg
Stripping Steam	High
Bioactive Molecule Loss	Tocopherols, sterols, polyphenols

 

Physical Edible Oil Refining

The process consists of the same steps described in chemical refining, except for the alkali neutralizationprocess. The difference between chemical and physical refining is that the chemical refining consists of removing free fatty acids by adding caustic soda and separating the soap by centrifugation (mechanical separation), while physical refining, in the last step, removes free fatty acids and other compounds by steam distillation. ,is process is also known as steam refining.

Physical refining of crude oils, therefore, overcomes the disadvantages of neutralization by sodium hydroxide. Indeed, this process, which is deemed to be eco-friendly, minimizes liquid effluents generation. Another advantage of this process over chemical refining is that it is more economical (e.g., fewer chemicals used, lower investment cost, lesser energy input, and improved yield). However, this process is not suitable for all types of oils since it is hypersensitive to the crude oil quality. (Hindawi Scientific World Journal. Volume 2022, Article ID 6627013)

Indeed, physical refining is used for oils with high acidity. Considering the phospholipids content, Dumont and Narine proposed two physical refining processes depending on the phospholipid content in the crude oil. This method includes:

1. Degumming

Similar to chemical refining, degumming in physical refining removes phospholipids, ensuring the stability and readiness of the oil for further processing.

• Water Degumming: Uses water to remove hydratable phospholipids.
• Acid Degumming: Uses acid to dissociate nonhydratable phospholipids.
• Dry Degumming: Combines acid degumming with bleaching earth.
• Enzymatic Degumming: Uses phospholipase C to convert nonhydratable phospholipids into lysophospholipids.

2. Bleaching and Filtration

Bleaching in physical refining involves using adsorbents to remove colored pigments and impurities. The process ensures that the oil meets visual and quality standards.

3. Deodorization

Deodorization in physical refining is similar to chemical refining, using steam distillation to remove volatile compounds and improve the oil’s stability and flavor.

4. Dewaxing (if required)

Dewaxing removes waxes that cause cloudiness, ensuring the oil remains clear and visually appealing.

 

 

Comparison of Chemical and Physical Edible Oil Refining

Chemical edible oil refining uses alkali neutralization to remove free fatty acids, while physical refining uses steam distillation, making it more eco-friendly and economical. However, physical refining is sensitive to crude oil quality and not suitable for all oil types. Below, you find a table comparing these two processes:

Table: Comparison of Chemical and Physical Edible Oil Refining Process in Different Aspects

Aspect	Chemical Refining	Physical Refining
Free Fatty Acid Removal	Alkali neutralization	Steam distillation
Effluent Generation	High	Low
Chemical Usage	High	Low
Economic Efficiency	Moderate	High
Sensitivity to Oil Quality	Moderate	High
Application	Suitable for all oil types	Suitable for oils with high acidity

 

Challenges and Innovations in Edible Oil Refining Process

The edible oil refining process faces several challenges, including the loss of nutrients at high temperatures, 3-MCPD ester formation, and effluent disposal. Innovations in the field aim to address these challenges through various emerging solutions:

– Enzyme-assisted Degumming: Achieves up to 98% efficiency in removing phospholipids.

– Eco-friendly Adsorbents: Reduce environmental waste by 30% while maintaining high efficiency.

– Advanced Deodorization Techniques: Preserve up to 90% of bioactive compounds,

– Improved Process Control: Advanced monitoring and control systems enhance the efficiency and safety of the refining process.

– Reduced Effluent Disposal: Implementation of more efficient effluent treatment systems minimizes environmental impact.

 

Conclusion

Generally speaking, high-quality, safe, and stable oils for the achievement of consumer expectations regarding high quality and meeting the recent challenges of food safety depend directly on refining processes; both chemical and physical processes of refining have some potential advantages and drawbacks. That is to say, with broader applicability on wider areas, chemical refining bears potential for higher consumption of more chemicals and increased generation of effluents. Conversely, physical refining has eco-friendliness and economi¬c feasibility, though highly demanding of proper care while dealing with crude oil quality.

From the beginning of this long process of refining by degumming and neutralization, to bleaching, dewaxing, and deodorization, all contribute to the intricacy with which crude oils are made into refined edible oils. This holistic approach has implications for the final product in ensuring safety, stability, and maximum retention of bioactive compounds.

Companies like INVEXOIL, which provides services in the area of “Engine Oil Refinery Services” and “Used Oil Re-refining Plants“, apply principles and technologies that can be relevant to edible oil refining in their respective areas for quality outputs in different fields. The goal of keeping to a minimum the level of harmful compounds and maintaining desirable properties is essentially in agreement with the main objective of producing high-quality oil products.