European Journal of Lipid Science and Technology | Year: 2012
It is just over a century ago that the first industrial hydrogenation plant for edible oils was commissioned. Although at that time several fatty acids had been identified, the analytical characterization of these oils was mainly by physical properties like melting point, density and refractive index and chemical properties like saponification value and iodine value. Some of these properties were used to follow a hydrogenation reaction. Early kinetic studies of the hydrogenation reaction focused on triglycerides but with the advent of GC, fatty acid compositions became so readily available, that kinetic studies switched to the 'common fatty acid pool' concept. According to this concept, the rate of reaction of an unsaturated fatty acid in a triglyceride molecule does not depend on the chemical nature of the other fatty acid moieties in this molecule. The concept greatly simplified the understanding of what happens during a hydrogenation reaction and thereby stimulated research. It took more than 50 years before this concept was shown to be an incorrect assumption. Kinetic studies of the hydrogenation process have also been hampered by the lack of an instrument that can measure the hydrogen concentration in oil. That may well be the reason why this concentration has received rather little attention and that its effect on the relative rates of the various, simultaneously proceeding reactions has only fairly recently become clear. Accordingly, the present review will describe the mechanism of the various reactions that occur during the hydrogenation process and highlight the effect of the hydrogen concentration and the triglyceride composition rather than that of the fatty acid composition. It will discuss industrial process conditions rather than laboratory conditions and therefore limit itself to nickel catalysts. It will also paint the most simple picture that is consistent with generally accepted observations. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
OCL - Oleagineux Corps Gras Lipides | Year: 2010
Formal training has the disadvantage that trainees may simply accept what they are taught without questioning it, unlike the autodidact who can only learn by asking questions all the time. Sometimes, he will not get an answer and that need not be because the question is stupid, but may be because his peers are used to there being no satisfactory answer and have simply accepted the conventional mythology without further question. So it is about time to ask some assorted questions and where possible, suggest how to find an answer: 1) Why does the composition of the solvent used to extract oil from oilseeds affect the amount of oil being extracted and its phosphatide content? 2) Why does a heat treatment (Alcon, Exergy, expander) increase the phosphatide content of the crude oil and decrease its non-hydratable phosphatide (NHP) content? 3) Why does water degumming of crude oil remove relatively more magnesium than calcium? 4) What is the mechanism of phosphatide removal by silica hydrogel and why is it enhanced by simultaneous soap removal? 5) What is the mechanism of NHP-removal during alkali neutralisation? 6) Could it be that the Long Mix neutralisation process as used in the US leads to insufficient removal of the pro-oxidants copper and iron and that this explains why oil tends to less stable in the US than in Europe, especially when it contains linolenic acid? 7) Could different deodorisation conditions explain this geographically determined anomaly? 8) What happens during flavour reversion? 9) Why is walnut oil more stable in the nut than in the bottle? 10) How much oil is lost by saponification or hydrolysis during refining? 11) What is the mechanism of colour fixation? 12) Does the activity of interesterification catalysts depend on their counter cation? 13) What is the chemical nature of the colour formed on interesterification catalyst activation? 14) What is crystal memory? Does it exist? However, we should not forget the Dutch proverb that: "One fool can ask more questions than ten wise men can answer." On the other hand, exposing myths is half the fun and asking the right question often provides half the answer.
Lipid Technology | Year: 2011
The oldest enzymatic degumming process (the Lurgi EnzyMax® process) was launched in 1992. It used porcine phospholipase A2, which has the disadvantages of limited availability and not being kosher/halal. To overcome these disadvantages, various microbial enzymes have been developed; they have different specificities and therefore offer different advantages. Phospholipase C for instance has the advantage that it leads to the formation of diacylglycerols that remain in the oil being degummed. This constitutes a significant yield improvement which also results from the formation of lysophospholipids that retain less oil than their precursors. In the laboratory, a fine dispersion of the aqueous enzyme solution in the oil can be maintained so that the phospholipase enzymes can be made to interact with non-hydratable phosphatides (NHP) in the oil phase and catalyse their hydrolysis. On an industrial scale, dispersions coalesce before the enzymatic NHP hydrolysis is complete. Accordingly, enzymatic degumming processes that claim NHP-removal and a low residual phosphorus content in the enzymatically degummed oil are invariably preceded by an acid treatment in which a degumming acid (citric acid) is finely dispersed into the oil to be degummed and made to react with the NHP present in the oil before the enzyme is added. This enzyme then only interacts with the phospholipids present in the water phase. This raises the question whether the yield increase resulting from the use of enzymes should be realised by treating the oil to be degummed or the gums that have already been isolated from the oil during a degumming treatment. Lack of experimental evidence prevents a firm answer to this question but the arguments in favour of treating the gums look more impressive than what can be said in favour of treating the oil. In short: Enzymes do not degum the oil but can be used to de-oil the gums. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Lipid Technology | Year: 2013
Originally, oils were not refined but with the introduction of solvent extraction, refining became necessary. Crude cottonseed oil was refined by treating the oil with caustic soda and the same process was used for all other oils that needed refining. The subsequent introduction of centrifugal separators converted the original batch process into a continuous process. Degumming was introduced to obtain lecithin but limited to soya bean oil. Physical refining was introduced for high acidity oils like palm oil after the oil had been degummed to low residual phosphorus levels in the dry degumming process, in which the oil is first of all treated with an acid and then with bleaching earth. In Europe, further degumming processes were developed that allowed seed oil to be physically refined and later phospholipase enzymes were introduced to reduce oil retention by the gums and improve oil yield. Given these various oil purification processes, the refiner must decide which process to use for which oil in which circumstances. The paper provides a survey of what to do and when. It also discusses several topics that require further investigation and development. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Lipid Technology | Year: 2012
With the increase in palm oil production, the dry fractionation process has also gained in importance, both in comparison with other fractionation processes and in terms of the number of tonnes per annum. This has been assisted by the development of far less labour-intensive processes and improved understanding of the physical chemistry involved. This new insight indicates that temperature uniformity in a crystalliser is not necessary, which opens the door to continuous crystallisation. Combining this continuous crystallisation with a proven continuous separation system such as the conical sieve centrifuge could well lead to a fully continuous dry fractionation process. It is not there yet but likely to arrive. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Lipid Technology | Year: 2015
The interesterification process is one of the oil modification processes the refiner can use to alter the physical properties of oils and fats, The reaction requires a catalyst to proceed. This can be a base or a lipase enzyme. In the currently accepted mechanism of the base-catalysed interesterification reaction, two anionic intermediates are involved: the enolate anion and the glycerolate anion. The presence of the enolate anion explains why an equivalent amount of FAMEs are formed when sodium methanolate is added to oil and why FFAs are formed when the catalysts is inactivated with water. Based on this insight, process development can aim at avoiding these by-products and thereby increase the cost advantage of the chemical process over the enzymatic process even further. The chemical process is also more flexible than the solely continuous enzymatic process, which latter requires extensive purification of the oil to be interesterified. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.