Refining edible lipids is a critical stage in the processing of fats and oils, aimed at improving their quality, stability, and safety for human consumption. In Kenya's food industry, refined oils are essential for producing high-quality cooking fats, margarine, and other lipid-based products that meet both local and international standards. This chapter focuses on degumming, the first step in refining edible lipids, which removes impurities such as phospholipids and gums that affect oil stability and clarity. Understanding the different degumming methods is vital for food technologists engaged in edible oil processing within Kenyan agro-industries and manufacturing plants.

2.1 Degumming

Degumming is the process of removing phospholipids and other impurities from crude vegetable oils to enhance their quality and prepare them for further refining steps. In Kenya, where oils such as sunflower, cottonseed, and palm oil are widely processed, effective degumming ensures the oils meet food safety and quality regulations set by bodies like KEBS. The choice of degumming method influences oil yield, purity, and downstream processing efficiency, making it a crucial skill for food technology professionals.

2.1.1 Acid Degumming

Acid degumming is a chemical process that uses acids to convert non-hydratable phospholipids into hydratable forms, allowing their removal by water washing. This method is widely applied in Kenya’s edible oil refineries processing oils with high levels of non-hydratable gums.

Principle of Acid Degumming

Acid degumming involves treating crude oil with a small amount of acid, commonly phosphoric acid or citric acid, which reacts with non-hydratable phospholipids to convert them into hydratable phospholipids. This conversion enables their separation by subsequent water washing. The acid also helps reduce metal ions and other impurities that catalyze oil deterioration.

Process Parameters

Efficient acid degumming depends on controlling several parameters:

• Acid concentration: Typically between 0.05% and 0.3% by weight, sufficient to convert non-hydratable phospholipids without excess acid that could cause oil degradation.
• Temperature: Maintained between 60°C and 80°C to optimize reaction kinetics and viscosity for effective mixing.
• Mixing time: Usually 15 to 30 minutes to ensure complete reaction between acid and gums.
• Water addition: After acid treatment, water is added to hydrate phospholipids, facilitating their separation by centrifugation.

Equipment Used

Advantages and Limitations

Acid degumming offers several advantages including:

• Effective removal of non-hydratable phospholipids, improving oil clarity.
• Reduction of metal ions that catalyze oxidation.
• Compatibility with various crude oils with high gum content.

However, limitations include:

• Use of acids requires careful handling and disposal to prevent environmental harm.
• Excessive acid can cause oil hydrolysis, reducing oil quality.
• Additional water washing steps increase processing time and water consumption.

2.1.2 Hydro Degumming

Hydro degumming is a water-based process that removes hydratable phospholipids by hydration and centrifugation without chemical modification. It is commonly used for oils with low non-hydratable gum content, such as refined sunflower oil processed in Kenyan small-scale plants.

Principle of Hydro Degumming

In hydro degumming, water is added to crude oil to hydrate phospholipids, causing them to swell and separate from the oil phase. The hydrated gums form a separate layer or sludge that can be removed by centrifugation. This method does not chemically alter the phospholipids, preserving oil integrity.

Process Conditions

Key factors influencing hydro degumming efficacy include:

• Water dosage: Typically 2% to 4% by weight of oil, sufficient to hydrate phospholipids fully.
• Temperature: Maintained between 60°C and 70°C to reduce oil viscosity and improve hydration.
• Mixing intensity and duration: Adequate agitation for 15 to 30 minutes ensures uniform hydration.
• Centrifugation speed and time: Optimized to efficiently separate hydrated gums from oil.

Equipment and Operation

Benefits and Challenges

Hydro degumming offers benefits such as:

• Simplicity and low chemical usage, reducing environmental impact.
• Preservation of oil quality due to absence of acid or enzymes.
• Lower processing costs, suitable for medium and small-scale plants.

Challenges include:

• Ineffectiveness for oils with high non-hydratable phospholipids.
• Higher water usage leading to increased effluent treatment requirements.
• Potential losses of oil with gum fractions if centrifugation is not optimized.

2.1.3 Enzyme Degumming

Enzyme degumming uses phospholipase enzymes to hydrolyze phospholipids, converting them into hydratable forms or removing them as water-soluble products. This advanced method is gaining interest in Kenya’s edible oil processing industry for its efficiency and environmental benefits.

Mechanism of Enzyme Degumming

Phospholipase enzymes specifically target phospholipids in crude oil, catalyzing their hydrolysis into lysophospholipids and free fatty acids that are more easily removed by hydration and centrifugation. Enzymatic treatment reduces the need for harsh acids and lowers oil losses compared to conventional methods.

Process Requirements

Optimal enzymatic degumming requires:

• Enzyme type and dosage: Phospholipase A1, A2, or C are commonly used; dosage depends on oil type and phospholipid content.
• Temperature: Maintained between 50°C and 60°C to preserve enzyme activity.
• pH control: Enzymes require a specific pH range, often adjusted with mild buffers.
• Reaction time: Typically 1 to 3 hours to achieve complete hydrolysis.
• Water addition: After enzyme action, water is added to hydrate hydrolyzed phospholipids for removal.

Equipment and Handling

Proper enzyme storage at low temperatures and handling to avoid denaturation are essential for consistent performance.

Advantages and Limitations

Advantages of enzyme degumming include:

• High selectivity and efficiency in phospholipid removal.
• Reduced chemical usage and lower environmental impact.
• Improved oil yield due to minimal oil loss with gums.

Limitations involve:

• Higher initial cost for enzymes and specialized equipment.
• Longer processing times compared to acid or hydro degumming.
• Sensitivity of enzymes to temperature and pH fluctuations requiring careful process control.

Chapter Summary

This chapter examined the critical stages involved in refining edible lipids to improve their quality and safety for consumption. It began with degumming, a process that removes phospholipids and other impurities, detailing acid, hydro, and enzyme degumming methods, each tailored to specific lipid types and impurity profiles. The discussion then moved to alkaline refining, which neutralizes free fatty acids to enhance the oil’s stability and taste. Bleaching was explored in two forms: chemical bleaching, which uses adsorbents to remove pigments and contaminants, and physical bleaching that relies on heat and vacuum conditions. Finally, deodorisation was described as the process that eliminates volatile compounds responsible for undesirable odors and flavors, ensuring the final edible oil possesses a neutral aroma and taste suitable for consumer use. Together, these refining steps are essential for producing high-quality edible fats and oils that meet industry standards and consumer expectations.