1. INTRODUCTION
⌅Vegetable oils, such as soybean oil, sunflower oil, olive oil, or peanut oil, can replace animal fat as a source of energy. Moderate intake of vegetable oils has many beneficial effects on health, including reducing the risk of cardiovascular disease and improving inflammatory diseases and the immune system (Hashempour et al., 2022Hashempour BF, Farshi P, Alizadeh AM, Azadmard DS, Torbati M. 2022. Nutritional Aspects of Vegetable Oils: Refined or Unrefined? Eur. J. Lipid Sci. Technol. 124, 2100149. https://doi.org/10.1002/ejlt.202100149). Vegetable oil mainly comes from all kinds of oil-bearing crops, and the crude oil is obtained by pressing or extracting, and then processed by degumming, alkaline refining, decolorization, deodorization and other refining processes to finally obtain finished, edible oil. Plant phospholipids mainly exist in the seeds of oil-bearing crops, an important class of lipid concomitants. Most of them exist in the colloid phase, binding with proteins, sugars, fatty acids, sterols, vitamins and other substances. In the process of oil production, phospholipids are extracted with the oil, and the effect of phospholipid removal directly determines the quality index of the refined oil.
Phospholipids are an amphiphilic molecule composed of a water-soluble phosphate group and two hydrophobic fatty acid groups. Phosphate groups usually bind to substances such as choline, ethanolamine, or glycerol to form different types of phospholipids, as shown in Figure 1. The phospholipids in vegetable oils can be divided into hydratable and non-hydratable phospholipids. Hydratable phospholipids are hydrophilic and can be removed by hydration, but in general, some phosphorus in oil exists in the form of non-hydratable phospholipids. A hydratable phospholipid has obvious hydrophobicity, which cannot be completely removed even after washing 16 times.
In the refining process of vegetable oils, the content and nature of non-hydratable phospholipids affect the quality and stability of vegetable oils. Since non-hydratable phospholipids are difficult to remove, their presence increases the cost of oil treatment and leads to problems such as deepening the color of the oil and reducing storage stability (Jiang et al., 2015Jiang X, Chang M, Jin Q, Wang X. 2015. Application of phospholipase A1 and phospholipase C in the degumming process of different kinds of crude oils. Process Biochem. 50, 432-437. https://doi.org/10.1016/j.procbio.2014.12.011). Vegetable oils with a high content of non-hydratable phospholipids are often accompanied by more metal ions, which will not only lead to vegetable oil acid and bad flavor, but also affect the post-sequence refining process (Zhao et al., 2020Zhao Q, Li P, Wang M, Zhang W, Zhao W, Yang R. 2020. Fate of phospholipids during aqueous extraction processing of peanut and effect of demulsifification treatments on oil-phosphorus-content. Food Chem. 331, 1-9. https://doi.org/10.1016/j.foodchem.2020.127367). Therefore, the removal of non-hydratable phospholipids is the main research goal of vegetable oil degumming.
Furthermore, owing to the coexistence of hydrophobic and hydrophilic elements within phospholipids, the phosphate groups of phosphatides undergo esterification through the hydroxyl groups of diverse alcohols (e.g., ethanolamine, choline, inositol, and glycerol). Such diversity poses challenges in their isolation and analysis using conventional methodologies. Conventional phospholipid detection relies on chemical analysis techniques like thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and mass spectrometry (MS) (Antonelli et al., 2020Antonelli M, Benedetti B, Cavaliere C, Cerrato A, Montone CM, Piovesana S, Lagana A, Capriotti AL. 2020. Phospholipidome of extra virgin olive oil: Development of a solid phase extraction protocol followed by liquid chromatography-high resolution mass spectrometry for its software-assisted identification. Food Chem. 310, 1-9. https://doi.org/10.1016/j.foodchem.2019.125860). These approaches often entail intricate sample pretreatment and specialized equipment, making them time-consuming and costly. However, recent technological advancements have introduced novel methods for detecting phospholipids in vegetable oils. Spectroscopic techniques, such as near-infrared spectroscopy, offer non-destructive, real-time, and highly efficient means for rapid detection and quantitative analysis (Meng et al., 2014Meng X, Pan Q, Ding Y, Jiang L. 2014. Rapid determination of phospholipid content of vegetable oils by FTIR spectroscopy combined with partial least-square regression. Food Chem. 147, 272-278. https://doi.org/10.1016/j.foodchem.2013.09.143). To delve deeper into understanding and studying non-hydratable phospholipids, the following section systematically elaborates on previous research in this domain.
2. GENESIS, MAIN MORPHOLOGY AND STRUCTURE OF NON-HYDRATABLE PHOSPHOLIPIDS
⌅2.1. Genesis of non-hydratable phospholipids
⌅According to the strength of the hydrophilic character, the phospholipids in plant crude oil are divided into hydratable phospholipids (HP) and non-hydratable phospholipids (NHP). The formation of non-hydratable phospholipids in vegetable oil is related to many factors, such as oil quality, storage, processing and transportation conditions, etc. Long storage time, high water content and excessive phospholipase D activity all contribute to an increase in non-hydratable phospholipids in oil, which often leads to the hydrolysis of hydratable phospholipids into phosphatidic acid (Zhao et al., 2020Zhao Q, Li P, Wang M, Zhang W, Zhao W, Yang R. 2020. Fate of phospholipids during aqueous extraction processing of peanut and effect of demulsifification treatments on oil-phosphorus-content. Food Chem. 331, 1-9. https://doi.org/10.1016/j.foodchem.2020.127367). Non-hydratable phospholipids form when they bind to divalent metal ions such as calcium and magnesium. The main formation process of non-hydratable phospholipids is shown in Figure 2.
2.2. Major morphology of non-hydratable phospholipids in vegetable oils
⌅In vegetable oils, most NHP is mainly in the form of calcium-magnesium salts of phosphatidic acid and phosphatidic acid. Non-hydratable phospholipids (NHP) mainly include phosphatidic acid (PA), lysophosphatidic acid (LPA), lysophosphatidyl serine (PS), lysophosphatidyl ethanolamine (LPE) and calcium and magnesium salts of lysophosphatidic acid, etc. It was confirmed that phosphatidic acid is generated by phosphatidylcholine and phospholithyl ethanolamine subjected to phospholipase D, and can react with calcium to form non-hydratable phospholipids. The percentage of its composition obtained after detection and analysis is shown in Table 1 (Dijkstra, 2017Dijkstra AJ. 2017. About water degumming and the hydration of non-hydratable phosphatides. Eur. J. Lipid Sci. Technol. 119, 1600496. https://doi.org/10.1002/ejlt.201600496). The common features are that they contain fewer polar groups, have obvious hydrophobicity, and are more difficult to bind with water in hydration degumming .
| Constituent | America | Northeast China |
|---|---|---|
| Inorganic phosphate | 15.8 | 24.0 |
| Inositol monophosphate | 2.1 | 0.7 |
| Phasphoglyceric acid (PG) | 18.7 | 5.2 |
| Lysophosphatidic acid (LPA) | 17.9 | 18.5 |
| Phosphatidic acid (PA) | 35.2 | 49.6 |
| Phosphatidyl ethanolamine (PE) | 9.3 | 1.8 |
| Phosphatidyl serine (PS) | 1.0 | 0.2 |
Hydratable phospholipids and non-hydratable phospholipids are mainly distinctive in the different functional groups linked to the hydroxyl group of the acid. The former contains more polar groups, such as choline, ethanolamine, serine, and inositol. Hydratable Phospholipids (HP) are mainly Phosphatidyl Choline (PC) and Phosphatidyl Ethanolamine (PE), so they are highly hydrophilic. They can precipitate in contact with water, but their hydration rate differs.
2.3. The structure of non-hydratable phospholipids
⌅NHPs are a class of compounds with a phosphate ester structure in a nonaqueous environment, and their structure consists of three main parts: glycerol backbone, phosphate group and fatty acid chain. The hydroxyl clusters on the second and third carbon atoms of the glycerol backbone are esterified to phosphorylated functional groups, which can further esterify the hydroxyl groups of various alcohol groups including ethanolamine, inositol, choline and serine. The fatty acid tails of phospholipids are nonpolar and are mainly composed of two fatty acid chains linked to the glycerol backbone via ester bonds. The general formula of the non-hydratable phospholipid structure is shown in Figure 3.
3. COMPOSITION OF NHP IN DIFFERENT KINDS OF OILS
⌅All kinds of oil processed as crude oil will contain a certain amount of NHP. This is especially relevant in the case of soybean, rapeseed and other major oils which are processed as crude oil. The composition of phospholipids in different kinds of vegetable oils is shown in Table 2.
As can be seen from Table 2, the proportion of HP and NHP in some vegetable oils is different, and is related to the longer storage time of crude oil and the conversion of some HP. Oil should be refined immediately after pressing, and soaked before steam heating or microwave treatment to inactivate phospholipase, prevent HP conversion, and lessen the burden of refining.
| References | Plant oil species | Total phospholipids | HP | NHP | ||||
|---|---|---|---|---|---|---|---|---|
| PC | PE | PA | LPA | PI | PG | |||
| Nash et al., 1984Nash AM, Frankel EN, Kwolek WF. 1984. Degumming soybean oil from fresh and damaged beans with surface-active compounds. J. Am. Oil Chem. Soc. 61, 921-923. https://doi.org/10.1007/BF02542167 | Soybean oil | 1-3 | - | - | 55 | 28 | - | 15.0 |
| Hu et al., 2011Hu J, Zhang B. 2011. Resarch on the refining process of green soybean oil in northeast China. J. Wuhan Instit. Technol. 30, 1-3. | Green bean crude oil | 2-6 | 4 | 15 | 80 | - | 1 | - |
| Diosady et al., 1982Diosady LL, Sleggs P, Kaji T. 1982. Chemical degumming of canola oils. Am. Oil Chem. Soc. 59, 313-316. https://doi.org/10.1007/BF02662234 | Rapeseed oil | 1-1.5 | 40.2 | 23.0 | 7.0 | - | 11.6 | 18.0 |
| Pérez et al., 2019Pérez EE, Baümler ER, Crapiste GH, Carelli AA. 2019. Effect of Sunflower Collets Moisture on Extraction Yield and Oil Quality. Eur. J. Lipid Sci. Technol. 121, 1-7. https://doi.org/10.1002/ejlt.201800234 | Sunflower seed oil | 0.5-1 | 31.6 | 5.67 | 31.75 | - | 31 | - |
| Liu et al., 2018Liu H, Liu T, Fan H, Gou M, Li G, Ren H, Wang D, Cheng Z. 2018. Corn Lecithin for Injection from Deoiled Corn Germ: Extraction, Composition, and Emulsifying Properties. Eur. J. Lipid Sci. Technol. 120, 1-11. https://doi.org/10.1002/ejlt.201700288 | Maize germ oil | 2.37 | 57.5-68.1 | 10.3-13.9 | - | - | 14.5-19.8 | - |
| Ji et al., 2012Ji H, Liu Y, Wang X, Peng M. 2012. Analysis of phospholipid components and fatty acid composition in sesame oil. Agric. Machin. 15, 34-37. | Sesame oil | 0.8-1.2 | 34.22 | 31.23 | 15.54 | - | 14.68 | - |
| Zhao et al., 2020Zhao Q, Li P, Wang M, Zhang W, Zhao W, Yang R. 2020. Fate of phospholipids during aqueous extraction processing of peanut and effect of demulsifification treatments on oil-phosphorus-content. Food Chem. 331, 1-9. https://doi.org/10.1016/j.foodchem.2020.127367 | Peanut oil | 0.3-0.7 | 59.3 | 11.0 | 2.0 | - | 27.7 | - |
| Boukhchina et al., 2004Boukhchina S, Sebai K, Cherif A, Kallel H, Mayer PM. 2004. Identification of glycerophospholipids in rapeseed, olive, almond, and sunflower oils by LC-MS and LC-MS-MS. Canadian J. Chem. 82, 1210-1215. https://doi.org/10.1139/v04-094 | Olive oil | 2.3 | 5 | 9 | 12 | - | 11 | 63 |
| Sengar et al., 2013Sengar G, Kaushal P, Sharma H, Kaur M. 2013. Degumming of rice bran oil. Rev. Chem. Eng. 30, 183-198. https://doi.org/10.1515/revce-2013-0030 | Rice bran oil | 1-4 | 20.4 | 17.8 | - | - | 5.8 | - |
| Uitterhaegen et al., 2016Uitterhaegen E, Sampaio KA, Delbeke EIP, De Greyt W, Cerny M, Evon P, Merah O, Talou T, Stevens CV. 2016. Characterization of French Coriander Oil as Source of Petroselinic Acid. Molecules. 21, 1-13. https://doi.org/10.3390/molecules21091202 | French cilantro oil | 0.3 | 25 | 17 | 33 | - | 17 | - |
| Rao et al., 2009Rao, K.S., Chakrabarti, P.P., Rao, B.V.S.K., Prasad, R.B.N. 2009. Phospholipid Composition of Jatropha curcus Seed Lipids. J. Am. Oil. Chem. Soc. 86, 197-200. https://doi.org/10.1007/s11746-008-1325-8 | Curcas oil | 1.45 | 60.5 | 15.5 | - | - | 24 | - |
| Supansa et al., 2017Supansa P, Pakamas C, Sininart C. 2017. Assessment of water degumming and acid degumming of mixed algal oil. J. Envir. Chem. Eng. 5, 5115-5123. https://doi.org/10.1016/j.jece.2017.09.045 | Alga oil | 5.1 | - | - | - | - | - | - |
HP: hydratable phospholipids, NHP: non-hydratable phospholipids, PC: Phosphatidyl Choline, PE: Phosphatidyl Ethanolamine, PA: phosphatidic acid, LPA: lysophosphatidic acid, PI: Phosphatidyl inositols, PG: Phasphoglyceric acid
4. DETECTION OF NON-HYDRATABLE PHOSPHOLIPIDS
⌅Stable and accurate PL quantification methods are needed to detect and analyze the process of oil degumming. Currently, techniques such as liquid chromatography, mass spectrometry, and spectrophotometry have been applied to the quantitative analysis of PL in edible oils. The Table 3 shows the detection limit for these methods, along with their advantages and disadvantages.
| References | Test method | Detection limit | Advantages | Disadvantages |
|---|---|---|---|---|
| Yang et al., 2008Yang M, Zhou X, Jin Y. 2008. Non-hydratable phospholipids and their quantitative detection. Chinese J. Health Inspect. 1, 71-72. | Molybdenum blue colorimetry | 0.42 mg/kg | RSD < 6%. Suitable for the accurate analysis of factory refined oil products. | There are more processes, more than 7 reagents required for detection, and need for high temperature carbonization, time-consuming. |
| Kou et al., 2018Kou W, Zhang H, Lu H, Zhu L, Liu A, Huang K, Chen H. 2018. Determination of Phospholipids in Soybean by Titanium Dioxide Nanowires Array Enrichment Combined with Internal Extractive Electrospray Ionization Mass Spectrometry. Chinese J. Anal. Chem. 46, 1913-1922. | Fe3O4/TiO2 composites Electrospray ionization mass spectrometry | 0.01 μg/L | RSD=1.6-6.5%. Less sample consumption, fast analysis speed and simple operation. It can be used for direct and rapid detection of phospholipids in soybean oil. | Various parameters in the process, such as the elution ratio, are needed to be optimized. |
| van Rijn et al., 2020van Rijn JHJ, Lankhorst PP, Groen PBM, Muntendam R, de Souza AC. 2020. Robust and Reliable Quantification of Phospholipids in Edible Oils Using 31P NMR Spectroscopy. J. Am. Oil Chem. Soc. 97, 253-262. https://doi.org/10.1002/aocs.12296 | 31P nuclear magnetic resonance spectrometry | 5 μmol/100g | Less interference factors, simple pretreatment, fast, high accuracy. | A large sample size is required, and the composition and proportion of the extraction agent are relatively strict. |
| Antonelli et al., 2020Antonelli M, Benedetti B, Cavaliere C, Cerrato A, Montone CM, Piovesana S, Lagana A, Capriotti AL. 2020. Phospholipidome of extra virgin olive oil: Development of a solid phase extraction protocol followed by liquid chromatography-high resolution mass spectrometry for its software-assisted identification. Food Chem. 310, 1-9. https://doi.org/10.1016/j.foodchem.2019.125860 | Liquid chromatography-High-resolution mass spectrometry | 9-36 ng/g | The sensitivity is high and applied to oil detection with low phospholipid content. | The pretreatment process is complex, large sample consumption, but also requires a large number of chemical solvents, resulting in resource waste and environmental pollution. |
| Beneito-Cambra et al., 2020Beneito-Cambra M, Moreno-González D, García-Reyes JF, Bouza M, Gilbert-López B, Molina-Díaz A. 2020. Direct analysis of olive oil and other vegetable oils by mass spectrometry: A review. Trends Anal. Chem. 132, 1-18. https://doi.org/10.1016/j.trac.2020.116046 | Environmental mass spectrometry analysis | 0.53-1.14 μg/mL | With a small amount or even no sample manipulation, the analysis was rapid and accurate. | Incomplete or inadequate sample status may cause instrument problems with a residual effect. |
| Meng et al., 2014Meng X, Pan Q, Ding Y, Jiang L. 2014. Rapid determination of phospholipid content of vegetable oils by FTIR spectroscopy combined with partial least-square regression. Food Chem. 147, 272-278. https://doi.org/10.1016/j.foodchem.2013.09.143 | FTIR spectroscopy combined with partial least-square regression | 0.0001 mg/kg | Simplified calibration, sample preparation and analysis, and facilitated automation. | The oil type has a significant influence and produces a significant deviation. |
| Aleksandra et al., 2003Aleksandra SC, Edward S. 2003. Spectrophotometric determination of total phosphorus in rape seeds and oils at various stages of technological process: calculation of phospholipids and non-hydratable phospholipids contents in rapeseed oil. Food Chem. 81, 613-619. https://doi.org/10.1016/S0308-8146(02)00562-9 | MG spectrophotography | 5.00×10-7 -8.00×10-6 mol/L | RSD < 1%. With a high sensitivity and recovery rate. | Not suitable for the determination of oils with low phospholipids. |
Due to the high sensitivity and selectivity of detecting phospholipids, more and more researchers have established qualitative and relative quantitative methods of non-hydratable phospholipids in vegetable oils, which are applied to vegetable oil categories of different characterizations. These methods to reveal the changes in composition can lead to the removal of non-hydratable phospholipids and the quality improvement of refined oil products.
5. REMOVAL TECHNIQUES FOR NON-HYDRATABLE PHOSPHOLIPIDS
⌅Degumming is an important step in refining, where PLs are removed from crude vegetable oils. NHP is a world-class problem in the oil industry. Water, acid, enzyme and membrane degumming methods have been used in vegetable oil degumming in recent years.
5.1. Traditional degumming method
⌅The traditional methods are mainly hydration and the simple acid method.
5.1.1. Hydration degumming
⌅In the industry, the method of removing PL is mainly hydration. That is, a certain amount of hot water is added to crude oil so that the phospholipids in crude oil expand and are then separated after condensation to be removed, The process is generally carried out at 40-45 ºC, which is relatively energy-efficient, has a short production cycle, and reduces the acid value. The crude oil phospholipid content and temperature determine the amount of water added during degumming. For example, at high temperatures, the amount of water added is about 3-5 times that of the crude oil PL content (Dijkstra, 2017Dijkstra AJ. 2017. About water degumming and the hydration of non-hydratable phosphatides. Eur. J. Lipid Sci. Technol. 119, 1600496. https://doi.org/10.1002/ejlt.201600496). In addition, metal ions in tap water may combine with HP in oils to form NHP, which affects the degumming effect.
The degumming process parameters and the final degumming results differ for different oil samples. The results show that the phospholipid removal rates for soybean oil, rapeseed oil, rice bran oil, sunflower oil and olive oil are 98.3, 67.1, 89.8, 80.6 and 48% respectively. The phospholipid removal rate of mixed algal oil was only 19.4% (Supansa et al., 2017Supansa P, Pakamas C, Sininart C. 2017. Assessment of water degumming and acid degumming of mixed algal oil. J. Envir. Chem. Eng. 5, 5115-5123. https://doi.org/10.1016/j.jece.2017.09.045). Hydration degumming can only remove hydratable phospholipids with strong hydrophilic properties, while NHP with weak polarity and hydrophobicity is difficult to remove. After degumming, the phospholipid content is still 80-200 mg/kg, which cannot guarantee low phosphorus content (Aleksandra et al., 2003Aleksandra SC, Edward S. 2003. Spectrophotometric determination of total phosphorus in rape seeds and oils at various stages of technological process: calculation of phospholipids and non-hydratable phospholipids contents in rapeseed oil. Food Chem. 81, 613-619. https://doi.org/10.1016/S0308-8146(02)00562-9). Moreover, due to the high content of NHP, it is not always the best for all kinds of oil.
5.1.2. Acid degumming
⌅The acid degumming method entails adding a certain amount of phosphoric acid or citric acid in order to dissociate NHP by adjusting the pH, and then cool the phospholipids to form crystals. The phosphorus content can be reduced to less than 30 mg/kg.
Phosphoric acid was used to refine palm oil to remove phospholipids, and the optimal dose of phosphoric acid was determined to be 0.05 wt% by adopting the wet degumming process (Harrison et al., 2022Harrison LNL, Yi ST, Mieow KC, Soek ST. 2022. Phosphorus Removal and Phytonutrients Retention in the Refining of Solvent Extracted Palm-Pressed Mesocarp Fiber Oil. J. Oleo Sci. 71, 177-185. https://doi.org/10.5650/jos.ess21256). The researchers used a 1:1 mixture of citric acid and phosphoric acid to degum sunflower oil, and the degumming effect was better and the amount of phospholipid remaining was 0.05 mg/kg (Pan et al., 2000Pan LG, Campana A, Toms MC, n MCA. 2000. A kinetic study of phospholipid extraction by degumming process in sunflower seed oil. J. Am. Oil Chem. Soc. 77, 1273-1277. https://doi.org/10.1007/s11746-000-0200-8).
Some studies have shown that phosphoric acid is used for degumming vegetable oils with high phospholipid contents, such as soybean and algal oil. As a result, the phosphorus content of crude algal oil was reduced from 530 ppm to 93 ppm in the optimal acid degumming process, with a phospholipid removal rate of 82.5%, which is much higher than that of 19.4% for water degumming (Supansa et al., 2017Supansa P, Pakamas C, Sininart C. 2017. Assessment of water degumming and acid degumming of mixed algal oil. J. Envir. Chem. Eng. 5, 5115-5123. https://doi.org/10.1016/j.jece.2017.09.045).
At present, acid degumming has been widely used in oil processing. The technology is simple, but closely correlated with the crude oil quality, and is suitable for low phosphorus oil such as palm oil. Some vegetable oils with high non-hydratable phosphorus contents are still not up to the requirements.
5.2. New degumming method
⌅The main disadvantages of the above conventional degumming processes are considerable oil loss, significant wastewater, and high energy consumption, which cannot guarantee the low phosphorus levels required for physical refining. These techniques are not suitable for oils containing high levels of non-hydratable phospholipids.
5.2.1. Enzymatic degumming
⌅In recent years, research on the application of phospholipase in vegetable oil degumming has become more and more in-depth. Enzymatic degumming uses the biological enzymatic method to convert NHP into HP, and then the hydration method to maximize the phospholipids’ removal and recovery. There are four types of phospholipases used for vegetable oil degumming. Phospholipase A1 (PLA1) and phospholipase A2 (PLA2) remove fatty acids from positions 1 and 2, respectively, and phospholipids are hydrolyzed to free fatty acids and soluble phospholipids. Phospholipase B (PLB) eliminates fatty acids from glyceryl. Phospholipase C (PLC) hydrolyzes the bond between acylglycerol and the phosphate group to release Diacylglycerol (DAG) (Jiang et al., 2015Jiang X, Chang M, Jin Q, Wang X. 2015. Application of phospholipase A1 and phospholipase C in the degumming process of different kinds of crude oils. Process Biochem. 50, 432-437. https://doi.org/10.1016/j.procbio.2014.12.011). The site of action of phospholipase D is after the phosphate group. The action sites of four different phospholipases are shown in Figure 4.
Applying PLA1 and PLC to eight crude oils, the researchers found that the PLA1 degumming process significantly reduced residual phosphorus to less than 10 mg/kg and that PLC degumming improved the oil yield of most oil samples (Jiang et al., 2015Jiang X, Chang M, Jin Q, Wang X. 2015. Application of phospholipase A1 and phospholipase C in the degumming process of different kinds of crude oils. Process Biochem. 50, 432-437. https://doi.org/10.1016/j.procbio.2014.12.011). The enzyme mixture Purifine® 3G was applied to crude soybean oil to reduce the residual phosphorus content to 8.9 mg/kg (dos Passos et al., 2022dos Passos RM, da Silva RM, de Almeida Pontes PV, Morgano MA, Meirelles AJA, Stevens CV, Ferreira MC, Sampaio KA. 2022. Phospholipase cocktail: A new degumming technique for crude soybean oil. Food Sci. Technol. 159, 1-9. https://doi.org/10.1016/j.lwt.2022.113197). To improve the stability and reusability of phospholipase, magnetic immobilized PLA was used for degumming soybean oil. The results showed that even after 5 cycles of degumming, magnetic immobilized PLA2 retained more than 80% of its initial activity (Qu et al., 2016Qu Y, Sun L, Li X, Zhou S, Zhang Q, Sun L, Yu D, Jiang L, Tian B. 2016. Enzymatic degumming of soybean oil with magnetic immobilized phospholipase A2. Food Sci. Technol. 73, 290-295. https://doi.org/10.1016/j.lwt.2016.06.026). Immobilized phospholipases show excellent potential for enzymatic degumming.
Enzymatic degumming has many advantages over traditional methods, including higher degumming efficiency, lower chemical requirements, higher product yield, and less environmental pollution. Despite the obvious advantages of this approach, it has drawbacks, particularly the cost of the enzyme. Moreover, the quality of different crude oils is different, so a specific enzymatic degumming process should be selected (Jiang et al., 2015Jiang X, Chang M, Jin Q, Wang X. 2015. Application of phospholipase A1 and phospholipase C in the degumming process of different kinds of crude oils. Process Biochem. 50, 432-437. https://doi.org/10.1016/j.procbio.2014.12.011). For example, for oil samples with low NHP content and high initial phosphorus content, PLC degumming with acid pretreatment can meet the requirements of physical refining and improve the yield simultaneously. For oil samples with high NHP content and low initial phosphorus content, acid-pretreated PLA1 degumming is the best choice.
5.2.2. Membrane filtration degumming process
⌅Membrane degumming is a non-thermal process that selectively separates phospholipids based on the size or properties of the membrane and is an emerging method for efficient degumming at low energy costs. Different types of membranes are applied to the crude vegetable oil membrane degumming process, such as polyethersulfone (PES) membranes, polysulfone (PSf) membranes, polyvinylidene fluoride (PVDF) membranes and ceramic membranes have shown good permeation flow with good degumming effect.
The PVDF membrane is more stable to hexane reagent than PES and PSf membranes (de Souza Araki et al., 2010de Souza Araki M, de Morais Coutinho C, Gonçalves LAG, Viotto LA. 2010. Solvent permeability in commercial ultrafiltration polymeric membranes and evaluation of the structural and chemical stability towards hexane. Sep. Purif. Technol. 71, 13-21. https://doi.org/10.1016/j.seppur.2009.10.005). The filtration of rice bran gross oil (CRBO) using 50 kDa PVDF membranes mixed with hexane solvent achieved 95.5% phospholipid removal (Sehn et al., 2016Sehn, G.A.R., Gonçalves, L.A.G., Ming, C.C. 2016. Ultrafiltration-based degumming of crude rice bran oil using a polymer membrane. Grasas Aceites. 67, 1-8. http://dx.doi.org/10.3989/gya.0498151). It was shown that membrane degumming combined with hydration degumming and acid degumming could improve the phospholipid removal rate of crude oil. By combining conventional acid degumming with PES membrane separation, the phospholipid content of jatropha oil can be reduced to less than 20 ppm (Liu et al., 2012Liu KT, Gao S, Chung TW, Huang C, Lin YS. 2012. Effect of process conditions on the removal of phospholipids from Jatropha curcas oil during the degumming process. Chem. Engin. Res. Design 90, 1381-1386. https://doi.org/10.1016/j.cherd.2012.01.002).
In addition to the above polymeric membranes, ceramic membranes have a highly repulsive reaction to phosphorus. In a recent study using ceramic membranes to degum CRBO, phosphorus was reduced by 95%, along with a 42-62% reduction in color. The average phospholipid retention was 95±2% using 5 kDa ceramic membranes (Abdellah et al., 2020Abdellah MH, Scholes CA, Liu L, Kentish SE. 2020. Efficient degumming of crude canola oil using ultrafiltration membranes and bio-derived solvents. Innovative Food Sci. Emer. Technol. 59, 1-9. https://doi.org/10.1016/j.ifset.2019.102274). It has been shown that a three-stage hybrid membrane process of ultrafiltration, nanofiltration and permeation vaporization treats crude canola oil with almost complete rejection of phospholipids (> 99.9%) (Abdorrezaee et al., 2021Abdorrezaee Z, Raisi A. 2021. A hybrid ultrafiltration/nanofiltration/pervaporation membrane process for intensifying the refining of crude canola oil and solvent recovery. Chem. Engineer. Processing-Process Intensificat. 169, 1-15. https://doi.org/10.1016/j.cep.2021.108598).
The membrane filtration de-adhesive process replaces the traditional energy-intensive process. It has the advantages of low energy consumption, safety, no chemicals, good retention of nutrients, reduced wastewater production, simple operation and so on. Despite these advantages, the poor stability and low osmotic flux of some organic membranes during membrane filtration and degumming lead to problems such as scaling and clogging, requiring high operation and maintenance costs, making the process economically unfeasible and unlikely to be applied on a large scale.
5.2.3. Other degumming processes
⌅In addition to the above degumming processes, some novel degumming technologies are less widely used, such as Ultrasonic Assisted Enzymatic Degumming (UAED), saturated steam degumming, cavitation reactor-assisted ethanolamine degumming and electrolyte degumming. The comparison of new degumming processes for different kinds of vegetable oils is shown in Table 4 below.
| Oil | Degumming method | Reference | Degumming condition | Phosphorus content (ppm) | Removal (%) | |
|---|---|---|---|---|---|---|
| Crude | Degummed | |||||
| Soybean oil | Degumming with saturated water vapor | Sun et al., 2011Sun B, Guan Y, Li H, Jiang L, Yu D. 2011. Nonhydratable phospholipids in soybean oil were removed by water vapor method. Food Sci. 32, 49-52. | T=110 ºC, t=50 min, speed agitation=90r/min, 2% saturated water vapor | 1148 | 17.9 | 98.4 |
| Ultrasonic assisted enzymatic degumming | More et al., 2018aMore NS, Gogate PR. 2018a. Ultrasound assisted enzymatic degumming of crude soybean oil. Ultrason. Sonochem. 42, 805-813. https://doi.org/10.1016/j.ultsonch.2017.12.031 | Working volume=100 ml, Enzyme load=2.0 ml/L, pH=5, 5% water, Ultrasonic power=100 W | 73.13 | 93.63 | ||
| Cavitation reactor-assisted degumming | More et al., 2018bMore NS, Gogate PR. 2018b. Intensified degumming of crude soybean oil using cavitational reactors. J. Food Eng. 218, 33-43. https://doi.org/10.1016/j.jfoodeng.2017.08.029 | Volume=250 ml, T= 60 ºC, t=100 min, P=4 bar | 72.90 | 93.65 | ||
| Electrolyte degumming | Nasirullah, 2005Nasirullah. 2005. Physical refining: Electrolytic degumming of nonhydratable gums from selected vegetable oils. J. Food Lipids. 12, 103-111. https://doi.org/10.1111/j.1745-4522.2005.00009.x | 1.5% Potassium chloride: 0.5% SCS=95:5 | 0.574 | 99.95 | ||
| Rapeseed oil | MEA degumming | Zufarov et al., 2009Zufarov O, Schmidt Š, Sekretár S, Cvengroš J. 2009. Ethanolamines used for degumming of rapeseed and sunflower oils as diesel fuels. Eur. J. Lipid Sci. Technol. 111, 985-992. https://doi.org/10.1002/ejlt.200900025 | 0.5 wt% MEA, T=20-30 ºC | 445 | 3.5 | 99.2 |
| Acid+ultrasonic degumming | Gaber et al., 2020Gaber MAFM, Juliano P, Mansour MP, Shrestha P, Taylor C, Smith R, Trujillo FJ. 2020. Improvement of the Canola Oil Degumming Process by Applying a Megasonic Treatment. Indus. Crops Prod. 158, 1-10. https://doi.org/10.1016/j.indcrop.2020.112992 | T=40 ºC, 2 MHz, t=30 min | 11 | 97.53 | ||
| Coriander oil | Electrolyte degumming | Zhang et al., 2022Zhang L, Akhymetkan S, Chen J, Dong Y, Gao Y, Yu X. 2022. Convenient method for the simultaneous production of high-quality fragrant rapeseed oil and recovery of phospholipids via electrolyte degumming. Food Sci. Technol. 155, 1-8. https://doi.org/10.1016/j.lwt.2021.112947 | 3% SCS | 508 | 47.2 | 90.7 |
| Curcas oil | Acid+ultrasonic degumming | Liu et al., 2012Liu KT, Gao S, Chung TW, Huang C, Lin YS. 2012. Effect of process conditions on the removal of phospholipids from Jatropha curcas oil during the degumming process. Chem. Engin. Res. Design 90, 1381-1386. https://doi.org/10.1016/j.cherd.2012.01.002 | 65 ºC, 4% phosphoric acid, speed agitation =1600 rpm | 1200 | 20 | 98.3 |
| Rice Bran oil | Membrane filtration degumming | Sehn et al., 2016Sehn, G.A.R., Gonçalves, L.A.G., Ming, C.C. 2016. Ultrafiltration-based degumming of crude rice bran oil using a polymer membrane. Grasas Aceites. 67, 1-8. http://dx.doi.org/10.3989/gya.0498151 | 50kDa PVDF membrane | 640.5 | 29 | 95.5 |
| Electrolyte degumming | Nasirullah, 2005Nasirullah. 2005. Physical refining: Electrolytic degumming of nonhydratable gums from selected vegetable oils. J. Food Lipids. 12, 103-111. https://doi.org/10.1111/j.1745-4522.2005.00009.x | 1.5% Potassium chloride:0.5% SCS= 95:5 | 0.38 | 99.94 | ||
| Sunflower oil | MEA degumming | Zufarov et al., 2009Zufarov O, Schmidt Š, Sekretár S, Cvengroš J. 2009. Ethanolamines used for degumming of rapeseed and sunflower oils as diesel fuels. Eur. J. Lipid Sci. Technol. 111, 985-992. https://doi.org/10.1002/ejlt.200900025 | 0.5 wt% MEA, T=20-30 ºC | 163 | 2.2 | 98.6 |
SCS: sodium chloride solution, MEA: monoethanolamine.
The ultrasonic treatment of crude vegetable oil can separate the phospholipids completely, which has the enhanced benefit of reducing the reaction time and processing cost. When water, acid and enzyme degumming are combined with ultrasonic degumming, phosphorus content significantly reduces, which can eliminate alkali refining neutralization, improve degumming efficiency, and reduce the use of chemical degumming reagents, temperature and processing time. Cavitation reactor-assisted degumming is used to purify crude soybean oil. The degumming treatment based on cavitation can produce high-quality oil, and reduce reaction time and energy consumption, but this process has high requirements for equipment. Compared to other methods, saturated steam degumming does not add any chemical reagent and has no residual problem, which can provide a theoretical basis for industrial production. The ethanolamine degumming can be carried out at an ambient temperature, and does not need additional energy, uses simple technology, has low production cost, and avoids energy and equipment-intensive problems. The degumming agent is cheap, highly efficient and easy to obtain. By contrast, the electrolyte degumming uses potassium chloride and sodium chloride aqueous solution to improve the degumming performance, with water, total phenol, phytosterol content and taste well retained. The recycled gelatin can be used in commercial applications, which has good potential.
5.3. Model of dynamics
⌅To meet the phosphorus content specifications of the vegetable oil refining process and better optimize the process parameters, many researchers have proposed kinetic models. These models enable the estimation of crucial parameters, such as time, temperature, and acid concentration, based on the initial phospholipid content, thereby optimizing the efficiency of the degumming process. For the refining process already in operation, the data on the degumming process can be dynamically monitored by using the kinetic model to optimize the parameters in real time, so as to improve the effect of the degumming and reduce the production cost. Hydrodynamic models, especially computational fluid dynamic (CFD) models, play an important role in predicting the concentration and polarization thickness of corn oil in the drying process using tubular ceramic films (Wibisono et al., 2015Wibisono Y, Widodo S. 2015. Concentration boundary layer in membrane degumming: A CFD model and neural network approach. Procedia Envir. Sci. 28, 224-233. https://doi.org/10.1016/j.proenv.2015.07.029). By simulating the flow of fluid in the tubular ceramic film, this model can accurately calculate the concentration distribution of corn oil in the pipeline, thus predicting the concentration polarization thickness of corn oil throughout the treatment. To solve the problem of longer computation time, a method combined with an artificial neural network is proposed to enable the model to predict the corn oil concentration polarization thickness more quickly and optimize the production process. The study showed that the kinetic models developed for the degumming and bleaching stages determined the doses of 0.015 wt% and 0.047 wt% for citric acid and bleaching clay, respectively. The phosphorus content in degummed palm oil was reduced from 35 ppm to product specifications and the reversible first order kinetic model was optimal (Serrano-Bermúdez et al., 2021Serrano-Bermúdez LM, Monroy-Pena CA, Moreno D, Abril A, Niño ADI, Riascos CAM, Buitrago Hurtado G, Narváez Rincón PC. 2021. Kinetic models for degumming and bleaching of phospholipids from crude palm oil using citric acid and Super Flo B80® and Tonsil®. Food Bioprod. Proc. 129, 75-83. https://doi.org/10.1016/j.fbp.2021.07.005). Furtherdelving into kinetic studies concerning the refining stages, notably degumming and bleaching in vegetable oil, facilitates a comprehensive grasp of the reaction mechanisms. These studies not only enhance our predictive capabilities regarding these processes but also enable a profound comprehension of the underlying principles governing non-hydratable phospholipid (NHP) removal from vegetable oil. Moreover, they furnish a robust theoretical framework, pivotal in augmenting the efficacy of dephosphorylation techniques.
6. CONCLUSIONS
⌅Non-hydratable phospholipids (NHP) play a crucial role in both the taste and revitalization of oils, making their elimination a primary focus in the realm of vegetable oil refinement. Comprised of a mixture of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), and other components, NHP remain a crucial target for purification. In the quest for purifying these non-hydratable phospholipids, delving into the specific impact of distinct phospholipid components on oil quality warrants further investigation. Attention to the variations in species, origin, and processing techniques of plant oil, coupled with a meticulous exploration of pertinent factors, serves as the bedrock for understanding the nuances within this domain.
By scrutinizing the origins, physical attributes, and chemical properties of non-hydratable phospholipids, a more precise segregation of these compounds from other impurities becomes achievable. This in-depth comprehension paves the way for designing the NHP removal process in vegetable oil more effectively. In summary, the systematic investigation and isolation of non-hydratable phospholipids in vegetable oils hold promise for significant advancements in the oil industry. Through a comprehensive understanding of NHP components and their effects on oil quality, the refinement process can be optimized, producing oils that meet the rigorous benchmarks of safety and health, thereby fortifying their integration into industrial production.