Comparison of Flaxseed Oil Production Processes

1) Cold Pressing Method for Flaxseed Oil

Flaxseed Cold Pressing Process:

Harvesting and sorting flaxseeds → Flaxseeds → Cleaning impurities → Dehulling → Crushing → Cold pressing at low temperature → Crude flaxseed oil → Rough filtration → Fine filtration → Low-temperature crystallization → Low-temperature filtration → Cold-pressed flaxseed oil

Features of the Cold Pressing Process:

1. Avoids the degradation of fats and sugars, as well as the denaturation of proteins that occur in high-temperature pressing, which can create harmful substances.
2. Prevents the darkening of flaxseed oil and the development of a burnt taste caused by high temperatures.
3. Multiple filtration steps eliminate the need for chemical degumming, alkali refining, and bleaching (common in hot pressing), thus avoiding direct contact with chemicals and preventing secondary contamination.
4. Avoids high-temperature deodorization, effectively preserving the polyunsaturated fatty acids, especially α-linolenic acid, and maintaining the natural, complete nutrients that are more easily absorbed by the body.

Advantages: Retains almost all of the nutritional components of flaxseeds. The taste is light and non-greasy, with a high content of polyunsaturated fatty acids.

Disadvantages: Lower oil yield, higher production costs.

2) Hot Pressing Method for Flaxseed Oil

Flaxseed Hot Pressing Process:

Harvesting and sorting flaxseeds → Flaxseeds → Cleaning impurities → Dehulling → Crushing → Roasting → Pressing crude flaxseed oil → Rough filtration → Fine filtration → Degumming → Water washing → Dehydration → Bleaching → Deodorization → Hot-pressed flaxseed oil

Features of the Hot Pressing Process:

1. Increases oil yield and enhances flavor, producing a more aromatic oil.
2. High temperatures can lead to oxidation and polymerization, producing peroxides and harmful substances, which can destroy nutritional components.
3. High heat causes protein denaturation, significantly reducing the polyunsaturated fatty acid content and even leading to the formation of trans fats.
4. More impurities, such as flaxseed hull particles, phospholipids, and free fatty acids, can affect the oil’s color and overall quality.

Advantages: Rich, aromatic flavor and higher oil yield.

Disadvantages: Roasting seeds at high temperatures reduces the effective nutrient content in the oil and causes protein denaturation.

3) Solvent Extraction Method for Flaxseed Oil

Advantages: Extremely high oil yield, low production cost, and higher economic efficiency. This is the most common processing method in the modern oil industry.

Disadvantages: Destroys nearly all of the nutritional content, and may leave traces of organic solvents.

4) Temperature Analysis

The key influence of temperature on cooking oils: In the past, flavor was the main focus, but today, the emphasis is on nutritional value.

When cooking oil is heated above 80°C, its nutrients begin to break down. The pleasant aroma that arises when oil is added to a hot pan signals the start of nutrient loss. Ideally, the temperature for stir-frying should be around 70-80°C, while frying food can reach up to 150°C. Any higher, and harmful byproducts may form as the oil continues to break down.

At temperatures above 250°C, oils undergo oxidation, hydrolysis, polymerization, and cracking, and these compounds evaporate along with the boiling oil.

Flaxseed oil has a boiling point of 287°C. If it is heated beyond this for prolonged periods, it will turn black, oxidize, and decompose, potentially becoming carcinogenic. Additionally, cooking oils often contain mutagenic substances. Oils rich in unsaturated fatty acids, like vegetable oil and soybean oil, are particularly prone to this risk.

Recommendation 1: When stir-frying with flaxseed oil, keep the temperature below 80°C.
Recommendation 2: Keep cooking oil temperatures below 180°C to minimize pollutants. Be cautious when considering using oil for deep frying.