Solvents in olive oil

This is how we begin our discussion on the secret behind the varying quality of oils in the market. It's not just about the type of olive or the pressing method, but also how the oil was extracted, and whether it's truly pure or mixed with other oils that are invisible to the naked eye.

In the world of oil production, it's not enough for oil to look clear or have an attractive color; behind this appearance, complex industrial processes may be hidden, and sometimes—unfortunately—adulteration methods that rely on mixing virgin olive oil with refined or solvent-extracted oils. This is where the importance of science emerges, providing us with precise tools that reveal what our senses cannot perceive.

Solvent extraction is one of the most widespread methods in vegetable oil production, due to its ability to extract the highest possible percentage of oil. However, it simultaneously poses a significant challenge: How do we ensure the final oil is free from solvent residues? And how do we detect if olive oil has been adulterated with refined oils?

We will embark on an interesting scientific journey, starting from the heart of factories where extraction processes take place, then moving to laboratories where oils are examined with the most precise equipment, to reveal how science ensures the quality of what reaches our tables.

First: Solvent Extraction in Oil Production

1. Concept of Solvent Extraction

Solvent extraction is a process that relies on using an organic solvent (often hexane) to dissolve oil and separate it from the raw material. Hexane possesses characteristics that make it ideal for this process, such as:

• High efficiency in dissolving fats.
• Low boiling point (63-69°C).
• Easy recovery and recycling with a rate exceeding 95%.

So, what is Hexane?

It is a liquid, transparent, colorless, and highly volatile organic solvent belonging to the alkane hydrocarbon family. It is widely used in industries as a non-polar solvent, especially for extracting vegetable oils, and in the manufacture of glues, paints, and coatings, due to its high ability to dissolve fats and greases.

This technique is widely used for extracting oils from soybeans, canola, cottonseed, sunflower, in addition to olive pomace.

Second: Solvent Extraction of Olive Pomace Oil

1. Purpose of the Process

After mechanical pressing of olives, a percentage of oil, ranging from 5-10%, remains within the pomace. To utilize this, solvent extraction is employed to produce olive pomace oil.

2. Industrial Process Steps

• a. Raw Material Preparation: Cleaning and crushing the olive pomace, and drying it when necessary to facilitate solvent penetration.
• b. Extraction Process: Adding hexane into a special extraction apparatus to dissolve the oil and form a 'miscella' mixture (oil + solvent).
• c. Solvent separation (distillation): Heating the miscella to evaporate the hexane, then condensing and recovering it for reuse.
• d. Solvent removal from the pomace: Heating the de-oiled pomace in a special desolventizer to ensure complete evaporation of any residual solvent.

3. Characteristics of the resulting oil

The resulting oil is Olive Pomace Oil, and is characterized by:

• Lower nutritional quality than virgin olive oil.
• Less distinctive flavor.
• Its need for refining before use.
• Its use in cooking and in food and non-food industries.

III: Detection of solvent residues and adulteration in olive oil

1. Gas Chromatography (GC):

It is the most accurate method for measuring hexane residues and volatile organic compounds, relying on separating compounds according to their volatility and determining their concentration with high precision.

2. Ultraviolet (UV) Spectrophotometry:

Used to measure the photometric absorption indices:

• K232: An indicator of primary oxidation.
• K270: An indicator of secondary oxidation or the presence of refined oils.
• Elevated levels of these values often indicate adulteration or deterioration in oil quality.

3. ΔK (Delta K) Analysis:

It is used to detect the blending of virgin olive oil with lower quality oils.

4. Analysis of Waxes and Alcohols (Waxes & Erythrodiol /Uvaol):

This test serves as the oil's "chemical fingerprint." The mechanical extraction process (for virgin oil) cannot dissolve the strong wax layer present on the olive's skin and pit, whereas hexane solvent successfully dissolves and extracts it. Therefore, elevated levels of waxes and the compounds erythrodiol and uvaol definitively confirm that the oil has been chemically extracted (pomace oil) or blended with it, and is not pure virgin oil.

5. Detection of other contaminants:

such as polycyclic aromatic hydrocarbons (PAHs) and benzopyrene, which are compounds that may be present in olive pomace oil due to drying or refining processes.

Fourth: Importance of Conducting Analyses

1. Detecting Adulteration: To determine if extra virgin olive oil is blended with refined oils.
2. Ensuring Food Safety: To ensure the oil is free from toxic solvent residues.
3. Quality Control: To ensure the oil complies with international standards (IOC, Codex).

Fifth: Effect of Temperature on Extraction Efficiency

• Increased temperature reduces the viscosity of the oil and solvent, thereby increasing extraction speed.
• Optimal range for hexane: 61 –62 °C.
• Very high temperatures may cause:
  • Excessive solvent evaporation.
  • Deterioration of oil quality.
  • Loss of sensitive compounds such as antioxidants.

6. Removal of Free Fatty Acids (FFA)

1. Chemical Refining:

• Adding sodium hydroxide to form soap, which is then separated by centrifugation.
• Advantages: Effective in reducing FFA.
• Disadvantages: Loss of some oil due to saponification.

2. Physical Refining:

• Removal of FFA by vacuum distillation.
• Advantages: Leaves no chemical residues.
• Disadvantages: Less effective with oils high in FFA.

Conclusion

Solvent extraction is a pivotal technique in the edible oil industry, owing to its high efficiency and ability to yield a significant amount of oil. Conversely, tests for detecting solvent residues and adulteration in olive oil are essential to ensure quality and protect consumers.

Therefore, understanding extraction methods, refining techniques, operational factors, and chemical analysis methods enables professionals in this sector to improve their processes, achieve the highest levels of quality and safety, and ensure consumers receive a high-quality, contaminant-free product, with Food Safety standards applied at all production stages.

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