Basics of Alkali Refining
Basics of Alkali Refining of Vegetable oils.
Unlock the secrets of refining vegetable oils! 🧪
This guide delves into the fundamental principles of alkali refining, a crucial step in transforming raw vegetable oils into high-quality products. Explore the process, understand the chemistry behind it, and discover how it removes impurities for a refined, stable, and delicious result.
The objective of refining:
1.
Removal of undesired products from crude oils
· Free fatty acids (FFA)
· Phospholipids (gums)
· Oxidized products
· Metal ions
· Color pigments
· Others
2.
Preservation of valuable vitamins
3.
Minimize oil losses.
4. Protection of the oil against degradation.
Steps of the chemical refining process:
1. Degumming: Reduction of
phospholipid (gum) content
2.
Neutralization: Removal of free fatty acids and residual gums
3. Bleaching:
Removal of colour pigments and metal ions
4. Deodorization: Removal of odors
Degumming.
Degumming may be considered the first step in the refining process. This process is designed to remove the phosphatides that interfere with subsequent processing, especially for processors with an integral disposal option of gums. Crude soybean oil has high levels of phosphorus, which can be removed in the degumming step. The oil has two kinds of gums, hydratable (phospholipids) and non-hydratable (partially hydrolyzed phospholipids, which form salts of calcium, magnesium, and iron). The hydra tables are easily separated by treating crude oil with hot water (deionized water at 75°C, at a rate of 1-3%, of oil weight), followed by centrifugation. Contrarily, nonhydratable gums are more soluble in oil than the first and require additional treatment with phosphoric acid (0.1-0.3% of 85% solution) during this operation, phosphorus levels are reduced from 800-1200 to 100 ppm when hydratable gums have been removed and they can be reduced to 30 ppm if non-hydra tables are efficiently removed. It is important to know the amount of tocopherols that are lost with gums in order to maintain the nutritional quality of oil in this operation.
Neutralization:
1.
neutralizes the free fatty acids by saponification them into sodium salts.
2.
Saponification and hydrates phospholipids
3.
Removes colour pigments
4. Concentration: 12 – 24 °Bé
Addition: stoichiometric amount to neutralize the phosphoric acid and the free fatty acids plus an excess of 0 – 40 %
Calculation: 0,142 kg NaOH (100%) per kg FFA + 0,816 kg NaOH (100%) per kg H3PO4 (100%)
The
addition of an alkali solution to crude or crude degummed soybean oil results
in chemical reactions and physical changes. The alkali combines with the free
fatty acids present to form soaps; the phosphatides and gums absorb alkali and
are coagulated through hydration or degradation; much of the coloring matter is
degraded, absorbed by the gums, or made water-soluble by the alkali; and the
insoluble matter is entrained with the other coagulable material. If excess
caustic is used, prolonged exposure to heat will result in saponification of
the oil, with resultant oil losses.
Bleaching:
Bleaching is the most delicate stage.In this step, unwanted substances are removed, such as pigments, trace metals, phospholipids and some degradation products. However, some valuable compounds such as tocopherols and sterols can be removed, resulting in significant loss of oxidative stability and increased fatty acid content. To avoid this negative oil change, bleaching parameters such as bleaching clay concentration, temperature and duration should be optimized. Since the bleaching conditions depend on the properties of the bleaching clay as well as the type of crude oil, the bleaching parameters should be optimized with different types of clay for each vegetable oil. Since such optimization has not yet been reported for soybean oil treated with Tonsil Supreme Bleaching Absorbent, this study investigated the effect of bleaching parameters (tocopherols and sterols) on bleaching efficiency, oxidative stability, and composition of constituents and bioactive compounds. By doing this type of oil uses the soil mentioned above. The results showed that clay content had the greatest effect on bleaching efficiency, especially on clarity and phosphorus content, according to the Lovibond scale. Temperature and clay content significantly affect oxidative stability, particularly the formation of secondary oxidation products. Increasing the clay content decreases the tocopherol content of the bleached oil. Neutralized soybean oil at 105 °C for 20 min at 1% Tonsil supreme activated bleaching clay showed the highest oxidative stability, the best bleaching performance and the most favorable sterol content, although the tocopherol content was reduced.Deodorization:
Deodorization is a very important consideration in soybean oil processing. With currently known deodorization equipment the temperature should not exceed 255oC with an optimum range of 245oC ~ 250oC. Often questions are asked about the correct temperature, time. Pressure to deodorize etc. Most importantly, the type of oil is aromatically or physically refined as well as its local acceptability. Deodorization efficiency is a function of the following parameters: Absolute pressure. Maximum temperature time or throughput rate, and stripping stream rate. However these parameters are adjusted, the objective is to produce the best quality soybean oil. Such oils shall exhibit a maximum of 0.03% FFA and a Lovibond color value of a maximum of 10.0 yellow and less than 1 red. Of course. Must be basically tasteless. For best quality soybean oil. Deodorization equipment in contact with oil must be stainless steel. The use of mild steel will not produce good quality soybean oil although it is still used in some parts of the world. A final critical consideration in deodorization is the addition of at least 50 ppm citric acid to the cooling section of the deodorizer. Although some manufacturers recommend adding citric acid before and after deodorization, this is of questionable value. Citric acid added prior to deodorization is thermally destroyed in the process and thus may have no obvious benefit. Refine soybean oil must be stored below 40oC.
RSO |
Before bottling filling 15 to 30 ppm Vitamin add into the oil.
Post a Comment