Transfree fat production

Full hydrogenation offers a simple answer to the search for chemically stable fatty materials, as required for example in frying applications. However, replacing a trans-containing viscous liquid with a solid block of fully hydrogenated fat for frying applications might not be agreeable; particularly because fully hydrogenated oils have slip melting points above 65 °C and would quickly generate a solid fat layer around fried goods. In the recent past there has been a lot of activity from oil suppliers associated with the launch of new trans-free oils. In 2004, Dow AgroSciences, Bunge and DuPont all launched their various brands of zero- or low-trans oils, with Cargill and Bayer CropScience joining in 2005. Most of these oils are supposed to be an answer to the limited chemical stability of conventional oils as these new oils are high-oleic (low-linoleic) fatty acid variants of soybean, canola or other seed oils. The new traits have been developed by conventional breeding or by genetic modification techniques. Alternatively, one could attempt the procurement of more stable oils through fractionation of, for example, palm oil. In doing so, however, it has to be noted that even a double-fractionated palm olein is relatively rich in SFA, approximately 30%, as this is just the nature of the TAGs present in palm oil; it contains a large fraction of palmitic-oleic-oleic acid-based TAGs.

For applications that rely on the structuring function of TFA-containing TAGs, the substitution can be much more difficult. While in the applications focusing on chemical stability the absence of PUFA is the key objective, here specific TAGs that truly functionally substitute for the TFA-containing TAGs have to be identified. This means that, depending on the specific application, tailor-made solutions have to be sought. Applications of fats where high temperature stability and manufacturability are key can be served by fat compositions rich in fully saturated TAGs. These are most easily generated by full hydrogenation, producing a fat composition rich in stearic acid. If, for reasons of consumer preference, hydrogenation has to be avoided then stearin fractions of palm oil also offer the starting point for compositions rich in fully saturated TAGs. Either wet (solvent-supported) fractionation or multiple-step dry fractionation deliver palm stearins with levels of SFA of more than 80%. Both routes outlined above create fat compositions rich in only a single TAG, typically tristearin in fully hydrogenated seed oils and tripalmitin in palm stearin. This may not deliver the functionality of mixed crystals, which tend to be small. To this end, one could either just mix these fats or subject them conjointly to an interesteri-fication process. If the melting behavior of a fat composition is important not only for the stability and integrity of a product, but also for the mouth-feel or deposition behavior, then the fat has to satisfy a much narrower specification. Fully saturated TAGs based solely on palmitic or stearic acid have to be used in very limited amounts on such occasions. The steep melting of partially hydrogenated fats and their good mouthfeel are based on the physical properties of TAGs containing both stearic acid and elaidic acid. These yield a range of individual TAG melting points well above body temperature but below 60 °C. Nature delivers TAGs with melting points in this range very sparingly. These glycerol esters are composed of two saturated and one unsaturated fatty acid with the fatty acids typically arranged in a symmetric fashion (SUS: saturated-unsaturated-saturated). They can be found in, for example, cocoa butter, well appreciated for its melting behavior, and a range of other exotic fats, such as sal fat, kokum fat, shea nut oil, mango kernel oil and obviously also palm oil. A significantly increased use of palm oil and palm oil fractions is already anticipated by oil suppliers as they currently enlarge their production capacities. An alternative way to manufacture a fat composition rich in SUS- and SSU-TAGs is currently promoted by ADM and Novozymes. One of their enzymatically interesterified hardstocks is based on fully hydrogenated soybean oil and native soybean oil. This is particularly interesting for the United States because of the relatively low acceptance of palm oil. Besides this approach there have been numerous attempts to develop seed oils with elevated levels of stearic acid, rich in SUS-TAGs, none of which has yet generated a fat that is available on an industrial scale.

The SUS-TAGs unfortunately have a melting point very close to body temperature and typically show a complicated and slow crystallization behavior. The relatively low melting point of SUS-TAGs necessitates that, for elevated temperature structuring, high levels of these TAG are present. The two features mentioned, in combination with their price and limited availability, make these TAG less suited for robust commodity applications.

Alternatively, TAGs composed of saturated medium-chain and long-chain fatty acids also melt in the desired intermediate temperature range (see also Garti and Sato, 1988). Unfortunately these do not exist naturally. They can be fabricated by esterification of a mixture of fats containing adequate amounts of long-chain SFA, derived from palm oil from full hydrogenation, and medium-chain fatty acids present in palm kernel or coconut fat. Since interesterification always delivers a statistical mix of triglycerides in accordance with the starting fatty acid mixture, the concentration of the targeted, high-melting (HM) TAGs, of di-long-chain, mono-medium-chain fatty acids is always limited.

Alternatively, similar high melting fats with good crystallization properties can be fabricated by full hydrogenation of palm kernel fat. To further optimize the characteristics of this fat, highly suitable for coating and other cocoa-butter-like applications, it is often subsequently interesterified to randomize the distribution of its fatty acids. In spite of the suggestion that interesterified fully hydrogenated palm kernel fat is a good alternative for partially hydrogenated fats, its application in other products remains limited due its price and its interaction with enzymes.

For the replacement of partially hydrogenated fats in spreads and similar applications other constraints apply. In the first place, modern spreads, soft tub products, are typically designed to deliver high amounts of healthy liquid oils. This implies that the structuring fat, in general referred to as hardstock, is used in limited quantities. Similar fats as discussed above qualify for use in spreads. As already outlined, for manufacturing processes under high supersaturation, the kinetics of the polymorphic transition is of prime importance. It turns out that fat rich in TAGs composed of medium-and long-chain SFA (HM-TAG) actually have short transition times. Furthermore, this type of TAG, possibly driven by the fairly complex packing at the molecular level into the crystal lattice, produce smaller crystals than for example fully saturated long-chain fatty acid-based TAGs. This makes the mixed saturated TAGs particularly suitable candidates for the substitution of partially hydrogenated fats. It has to be noted here that, in this substitution, the melting profile of the products will also change according to the illustration in Fig. 15.1. Interesterified fats yield relatively straight SFC versus temperature lines that can be manipulated by the composition of the interesterification mixture. With straightforward application of inter-esterified fats, the limits of a high SFC at 20 °C in combination with very low SFC levels at 35 °C are quickly reached. In order to create significantly steeper SFC lines, either TAGs of the SUS type or HM-TAG levels have to be optimized in the formulation. This can be achieved by combination of different hardstocks. However, in mixing, for example, an HM-TAG hard-stock with cocoa butter fat, economically not very attractive for spreads, one can find that instead of a synergistic benefit quite the opposite occurs. At certain mixing ratios, immiscibility of the TAG in the solid phase occurs and both SFC and structuring potential actually drop. This illustrates that the mixing behavior of the TAGs, which can be influenced by the processing conditions, is a key element in the design of functional fat compositions. In the attempt to fabricate highly functional hardstocks, fractionation plays an important role. There are two possible applications of fractionation: it can be applied either pre- or post-interesterification. The economics of the application of fractionation depend heavily on the value and usage of the secondary fraction evolving from the separation process. For example, to increase the concentration of HM-TAG in a fat, one could improve the yield of the interesterification with respect to the HM-TAG concentration by optimizing the fatty acid composition of the starting materials towards two-thirds of stearic plus palmitic acid mixed with one-third of lauric acid. The elimination of unsaturated fatty acids from the interesterification mixture can be achieved by utilization of fully hydrogenated starting materials. However, for non-hydrogenated fat compositions, fractionation of the starting materials is the only tool available to move in this direction. The abundant use of palm stearin in interesterifications, which due to the good market value of palm olein is economically attractive, is the most prominent example of this process. Again this supports the installation of increased palm oil manufacturing capacities as mentioned before. Higher yields of functional TAGs in the hardstock fats can be achieved by fractionation applied after interesterification. However, there are two downsides to this manufacturing approach. First, the TAGs one wants to concentrate are characterized by mixed crystal formation with relatively small crystal sizes. This feature obviously has adverse effects on the smooth execution of the fractionation process, as the separation of the stearin and the olein fractions will be negatively affected. Remedies to this drawback can either be the use of solvent fractionation, with significant cost implications, or redesign of the process. Secondly, the by-product from post-fractionation processes is less likely to be of high value, hence possibly creating prohibitive cost for the overall application. In general it is fair to conclude that post-fraction-ation of hardstock fats is considered a last resort in the substitution of partially hydrogenated fats as it will add substantial cost. However, for other high-value applications, the process discussed might very well be suitable.

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