Trans fatty acids (TFAs) mainly arise from 2 major sources: natural ruminal hydrogenation and industrial partial catalytic hydrogenation. Increasing evidence suggests that most TFAs and their isomers cause harmful health effects (that is, increased risk of cardiovascular diseases). Nevertheless, in spite of the existence of an international policy consensus regarding the need for public health action, several countries (for example, France) do not adopt sufficient voluntary approaches (for example, governmental regulations and systematic consumer rejections) nor sufficient industrial strategies (for example, development of healthier manufacturing practices and innovative processes such as fat interesterifications) to eliminate deleterious TFAs from processed foods while ensuring the overall quality of the final product (for example, nutritional value and stability). In this manuscript, we first review the physical–chemical properties of TFAs, their occurrence in processed foods, their main effects on health, and the routine analytical methods to characterize TFAs, before emphasizing on the major industrial methods (that is, fat food reformulation, fat interesterification, genetically modified FAs composition) that can be used worldwide to reduce TFAs in foods.
Trans fatty acids (TFAs) can be produced by isomerization of cis unsaturated fatty acids (UFAs) from a natural source (that is, enzymatic hydrogenation or biohydrogenation) and/or industrial source (for example, mainly partial catalytic hydrogenation (PCH)) (Brouwer and others 2010).
Nevertheless, the overconsumption of most TFAs (that is, except some conjugated linoleic acid (CLAs)) could predispose the consumers to a higher risk of cardiovascular diseases (CVDs) as well as to other noncommunicative pathologies (that is, cancers and type 2 diabetes) (Brouwer and others 2010; Menaa 2010; Menaa and others 2012).
The catalytic hydrogenation of fats (for example, vegetable or fish oils) requires both the hydrogen gas and a metal catalyst (for example, nickel) in order to modify the physical–chemical properties of FAs (that is, reduction of unsaturation) and solidify vegetable fat products, decrease their oxidation, and enhance their stability and taste (Brouwer and others 2010).
The quantitative distribution of industrial TFAs may considerably vary between the processed foods (for example, low-quality compared with high-quality margarines), and major differences in TFA levels were noticed between industrial and natural foods. Indeed, considerable TFA amounts (over 50% of total FAs) were found in industrial products (for example, margarines), which represented 6 to 25 folds the quantity observed in natural (that is, nonprocessed) foods (for example, milk, meats) (Sommerfeld 1983).
However, TFAs are qualitatively similar within processed or nonprocessed foods. In general, industrial TFAs are represented by the oleic acid trans-9 isomer (18 : 1 9t or 18 : 1 Δ9 trans aka elaidic acid) (Sommerfeld 1983; Wolff and others 2000), while natural TFAs are predominately represented by the oleic acid trans-11 isomer (18 : 1 11t or 18 : 1 Δ11 trans aka vaccenic acid) (Sommerfeld 1983; Aro and others 1998) (Figure 1).
In spite of international recommendations (Nishida and others 2004; PAHO/WHO Task Force 2007), only few national governments (for example, Denmark and Canada) have implemented TFA policies to reduce industrial TFAs (that is, preferably <2% of total fat in vegetable oils and margarines, <5% in other foods) as well as TFAs consumption (that is, <1% of the total energy intake (TEI)) (Menaa 2010; Menaa and others 2012). Yet, the public health approaches could involve (i) mandatory labeling of TFAs content in foods; (ii) voluntary use of dietary guidelines and health promotion programs; (iii) agreements with the food industry to minimize TFAs content and produce healthier fat sources (Menaa 2010; Menaa and others 2012).
In this review, we first provide a concise update about the physical–chemical and biological aspects of industrial TFAs, before focusing on the main technological strategies (that is, fat food reformulation, fat interesterification, and genetically modified fatty acid composition) that could be used by the global agroindustry to minimize or eliminate TFAs content in processed foods.
Industrial TFAs: An Overview
Definition of fatty acids
FAs are aliphatic monocarboxylic acids that originate from hydrolysis of natural occurring fats and oils (Fahy and others 2009). FAs play various essential biological functions (for example, energy production, membranes structure, cell signaling, immunity, and inflammation) (Woollett and others 1992; Graber and others 1994; Yaqoob 2003; De Caterina and Massaro 2005; Rustan and Drevon 2005).
Most of the naturally occurring FAs are present in configuration cis (Z), while trans (E) FAs are mainly obtained by industrial hydrogenation of cis-FAs. The isomerization of cis-FAs into trans-FAs can be either geometrical and/or positional (Figure 1). The formation of geometric and positional isomers during hydrogenation was initially proposed by Allen and Kiess (1955) based on the semihydrogenation/dehydrogenation sequence. In the geometrical configuration cis, the 2 atoms of hydrogen from the double bond are spatially on the same side of the carbon chain (Figure 1A), a situation that produces a bend in the FAs, whereas in configuration trans, they are diagonally opposed to each other, straightening the carbon chain (Figure 1B). The positional configuration can be observed if a double bond has been moved to other positions along the carbon chain (Ratnayake and Galli 2009). For instance, the monounsaturated FA (MUFA) oleic acid (omega 9) can be found either as geometric trans-isomer called elaidic acid (18 : 1 9t) or as positional trans-isomer called vaccenic acid (18 : 1 11t) (Figure 1). Besides, polyunsaturated FAs (PUFAs) can be found in configuration cis, trans, or conjugated cis/trans. Thereby, linoleic acid (omega 6) can be found in 3 possible geometric isomers: 18 : 2 9c, 12t; 18 : 2 9t, 12c; and/or 18 : 2 9t, 12t as well as in 2 positional isomers: 18 : 2 9c, 13t and/or 18 : 2 9c, 11t.
The chemistry of hydrogenation was initially developed in the late 19th century by the Nobel aureate Paul Sabatier, using a nickel catalyst and, shortly after, by the German chemist Wilhelm Normann, using the hydrogen gas (Normann 1903; Sabatier 1966).
This industrial food process, which can be partial or total, selective or nonselective (Gray and Russell 1979), aimed to reduce unsaturation of FAs, subsequently allowing vegetable fats to solidify and resist to oxidation (Normann 1903; Sabatier 1966; Brouwer and others 2010). From the 1960s to 1990s of the last century, PCH of fats was a good alternative to move away from deleterious saturated fatty acid (SFAs)-rich oils (that is, animal and tropical fats) (Elson 1992). Moreover, partial hydrogenated fats were interesting because of their overall functionalities (for example, relatively high physical stability, high plasticity (that is, consistency for mixing and processing)), cost-effectiveness, and good availability (Reddy and Jeyarani 2001). For instance, liquid vegetable oils were and are still often processed by PCH, notably to produce anhydrous fat products largely used for the cooking and the confection of hardstocks (for example, chocolates, cakes, and pizzas) (Perkins and Smick 1987; Ratnayake and others 1998; Kok and others 1999; Eckel and others 2007). Also, high selectivity of fat hydrogenation—obtained by low hydrogen pressure, moderate stirring speed, and high temperatures (Table 1)—was commonly used to lower the formation of SFAs (Nawar 1996) while favoring the formation of TFAs (Ackman and Mag 1998).
Table 1. Industrial hydrogenation: major parameters involved in TFAs formation. According to the process conditions, hydrogenation can be partial or total, and selective or nonselective. Selectivity is related to the preferential hydrogenation of more UFAs, which results in the lowest possible formation of SFAs. To obtain high selectivity, it is common to use low hydrogen pressure, moderate stirring speed, and high temperatures. This leads to scarcity of hydrogen on the catalyst surface, which, in turn, favors the formation of TFAs
The nature and amount of TFAs might vary between processed food products.
Qualitatively, TFAs in general processed foods are mainly composed of elaidic acid and 18 : 1 10t, which may represent 85% to 95% of the 18 : 1 (Sommerfeld 1983; Perkins and Smick 1987; Brühl 1995; Fernandez San Juan 1996; Precht and Molkentin 2000a).
Quantitatively, TFAs in margarines can vary from 1% to 2% (for example, high-quality margarines) to 60% (for example, low-quality margarines) of total FAs (Sommerfeld 1983; Precht and Molkentin 2000a). Tremendous efforts have been made in some countries (for example, Denmark, U.S.A., and Canada) to rapidly decrease the overall TFAs content in foods.
Effects of TFAs on the cardiovascular system
Most retrospective case-control studies and prospective cohorts have reported positive associations between the high consumption of TFAs (>3 g/d) and the risk to develop CVDs, a leading cause of mortality worldwide (Ascherio and others 1994; Aro and others 1995; Kromhout and others 1995; van de Vijver and others 2000; Chardigny and others 2008; Mozaffarian and others 2009). In fact, the consumption of TFAs corresponding to 2% TEI could increase the risk of CVDs to 23% to 25% (Oomen and others 2001; Mozaffarian and others 2006), suggesting that a necessary lower threshold TEI (that is, < 1%) shall be defined by the worldwide competent authorities for consideration by the global agroindustry (Menaa 2010; Menaa and others 2012).
Mechanistically, intake of industrial TFAs could be involved in the endothelial dysfunction and the development of CVDs, through the following molecular alterations: (i) increase of plasmatic cholesteryl ester transfer protein (CETP) activity (Abbey and Nestel 1994; van Tol and others 1995); (ii) increase of low-density lipoprotein (LDL)-cholesterol (LDL-c), increase of triglycerides (TGs), and decrease of high-density lipoprotein (HDL)-cholesterol (HDL-c) levels (Mensink and Katan 1990; Zock and Katan 1992; Judd and others 1994; Katan and others 1995; Lichtenstein and others 1999; Mozaffarian and others 2006; Mozaffarian and Clarke 2009), making them more atherogenic than SFAs, which increase both LDL-c and HDL-c (Zock and Katan 1992); (iii) stimulation of proinflammatory molecules (for example, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), C-reactive protein (C-RP), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), reactive oxygen species (ROS)), as well as reduction of nitric oxide (NO) production/bioavailability importantly involved the vasodilatation (Mozaffarian 2006; Harvey and others 2008; Mozaffarian and Clarke 2009; Iwata and others 2011).
Main Physical–Chemical Properties and Characterization of TFAs
Physical–chemical properties of TFAs
TFAs display particular physical–chemical properties that analytically distinguish them from cis-FAs. Comparatively to cis-FAs, TFAs are characterized by (i) a higher rigid carbon (acyl-) chain; (ii) a different polarity; (iii) a much higher melting point (Valenzuela & Morgado 1999; Wassel and Young 2007). For instance, oleic acid in its configuration cis (18 : 1 9c) melts at 4 to 13 °C, whereas its trans-isomers, the elaidic acid (18 : 1 9t) and vaccenic acid (18 : 1 11t), melt at 42 to 44 °C and 44 to 45 °C, respectively.
Regardless important health concerns, TFAs are more advantageous than cis-FAs for the production of fat foods (Eckel and others 2007; Wassel and Young 2007), because they can (i) enhance their structure, lubrication, and texture (that is, consistency/hardness, springiness, brittleness, and chewiness); (ii) increase their shelf life; (iii) increase their flavor stability; (iv) decrease their food sensitivity to oxidation; (v) increase their stability against liquefaction; (vi) increase their stability during storage at room temperature; (vii) increase their stability during frying; and (viii) enhance their emulsion stability.
Analytical methods for TFAs characterization
Nowadays, gas chromatography (GC) and Fourier transform infrared spectroscopy (FTIR) represent the 2 main routine methods. In opposite to FTIR, GC allows the identification of individual FAs when suitable standards are available (Ackman 2008; Ratnayake and Galli 2009). However, in complex mixtures of isomeric FAs (for example, foods containing partially hydrogenated vegetable or fish oil), all FAs isomers are rarely resolved by GC alone, resulting in an overlap of cis- and trans-isomers and biased data (Ackman 2008; Ratnayake and Galli 2009). In this case, GC coupled to FTIR (GC-FTIR) is recommended (Mossoba and others 2004; Ratnayake and Galli 2009). Eventually, FTIR coupled to attenuated total reflection infrared cell technique (FITR-ATR) can rapidly determine the total content of TFAs in pure fats and oil samples (Mossoba and others 2004; Ratnayake and Galli 2009).
Industrial Strategies to Reduce TFAs in Processed Foods
The public health concerns associated with the presence of TFAs in processed foods are prompting the global agroindustry to change their manufacturing practices and develop alternative processes to hydrogenation in order to minimize or eliminate TFAs and produce healthier fat foods (L'Abbé and others 2009; Menaa 2010; Mozaffarian and Stampfer 2010; Mozaffarian and others 2010).
Three relevant technical approaches could be used by the food manufacturers to accomplish this task (Hayes and Pronczuk 2010; Menaa 2010) (Table 2): (i) food reformulation (that is, TFAs replacement/reversion by an edible base stock of FAs; (ii) modification of FAs composition by fat interesterification (that is, chemical or enzymatic); and (iii) genetic modification of FAs composition (for example, customization of transgenic crops through biotechnological/genetic systems enabling the incorporation of a range of selected FAs into oilseed species of interest).
Table 2. Industrial hydrogenation: main biomedical aspects and alternative strategies. While industrial hydrogenation generates high levels of deleterious TFAs for health, food reformulation and interesterifications represent 2 most valuable alternative strategies for the industry to reduce the TFAs content in foods without possibly altering the human health status. Although genetic modification of oils can be of great industrial interest, the health effects remain unknown, and longitudinal studies are still definitively required
Food reformulation represents a valuable alternative strategy to PCH if both TFA and SFA levels are minimized. Indeed, a recent analysis showed that selected TFAs-free products contained substantial amounts of SFAs, mitigating health benefits (that is, enhanced risk of CVDs) (Stender and others 2009), in spite of their functionality and stability requirements in solid fats (Nestel and others 1994; Aro and others 1997; Eckel and others 2007). Insipidity, relatively high oxidation and low melting point can be noted in food products exempt of SFAs and rich in PUFAs (Parthasarathy and others 1990; Wang and others 2006). In this context, a recent report suggesting the reformulation of fat foods by increasing cis-UFAs over SFAs and TFAs content, in order to maximize health benefits (Mozaffarian and others 2010), might be debated if the oil stability is not also considered. Nevertheless, oleic acid, a model molecule routinely included in food processing (for example, blending foods), could be a great alternative to SFAs and PUFAs as this MUFA displays both interesting physical–chemical features and health benefits such: (i) relatively high stability during storage and frying (that is, stability against thermal deterioration processes of oxidation, hydrolysis, and polymerization) (Eckel and others 2007); (ii) contribution in slowing down atherosclerosis, notably by its capacity to lower LDL-c (Parthasarathy and others 1990; Warner and others 2001).
Eventually, stable frying oils shall be characterized by increased amounts of oleic acid (preferably 50% to 65%) and decreased amounts of PUFAs (preferably 20% to 30% linoleic acid and ≤3% linolenic acid) (Eckel and others 2007). In addition to oils modified with rational amounts of certain UFAs (for example, mid-oleic corn, high-oleic/low-linolenic canola, mid-oleic/low-linolenic soybean oils), naturally stable oils (for example, corn, palm, peanut, and cottonseed oils) can be used for commercial frying (van Duijn and others 2006; Eckel and others 2007). Many of those quality edible oils and TFAs-reduced products, developed by few food companies (for example, Cargill, Dow Agrosciences LLC), are already available in U.S.A. (Eckel and others 2007).
Fat interesterification is an innovative technological process, during which TFAs are not formed and SFA levels minimized, representing a valuable alternative to PCH (Bell and others 2007). This process first documented in 1969 (Fondu and Willems 1969) consists to treat a fat at low temperatures in the presence of glycerol added in excess and a catalyst (that is, chemical or enzymatic). This causes a rearrangement of FAs on the glycerol portion of the TG molecule that can be controlled without altering the FAs composition (Figure 2).
In natural fats and vegetable oils, the taxonomic standard for TGs obeys the 1,3-random-2-random distribution (that is, SFAs located almost exclusively at the stereopositions sn-1 and sn-3 and UFAs preferentially located at the position sn-2), whereas the interesterification results increase the participation of SFAs at the central stereoposition (Marangoni and Rousseau 2002).
Interestingly, the physical properties of the fat (for example, melting profiles) (Yusoff and Dian 1995) are determined by the stereopositions of FAs that, in turn, can affect its absorption, metabolism, and distribution into tissues, subsequently modulating the risk of CVDs (Berry 2009).
Importantly, the fat interesterification does not alter the quality of FAs, favorably modifies their melting point, and slows their rancidification/chemical decomposition, thereby creating more suitable oils for deep frying or spreadable products, especially when a suitable crystallization behavior is reached (Özay and others 1998; Sato 2001; Eckel and others 2007; Soares and others 2012).
The crystallization (that is, TGs fractionation or chromatographic separation of solid/liquid lipid phases) can be controlled, and the ratio between the 2 phases as well as the crystalline character of the solid phase can determine the sample consistency and firmness of the fat food product (van Duijn and others 2006; Wassel and Young 2007; Zhang and others 2011). The crystallization is divided into 2 subsequent steps: (i) the nucleation (that is, formation of stable molecular aggregates) (Herrera and others 1998) and (ii) the crystal growth (that is, incorporation of additional molecules) (Foubert and others 2006). The factors influencing the process are: (i) the fat composition that influences the functional properties of the edible oils (for example, oxidative stability, solid fat content (SFC) aka solid/liquid ratio of a fat at various temperatures) (Marangoni and Rousseau 1995); (ii) the crystallization conditions (Foubert and others 2006) such as the temperature. Thereby, if the fat is melted and cooled slowly, the TGs with highest melting point will eventually form a crystalline material, which can be simply filtered off from the lipid parent (Wassel and Young 2007).
Nowadays, it is possible to fractionate individual oil fractions into precise subfractions, which depending on the predominant presence of 1 of the 3 basic polymorphic crystals known as α, β´, and β allow to achieve specific solid fat curves, melting points, and possibly textural qualities (Wassel and Young 2007). These polymorphs display a specific melting temperature that increases with their stability (α→β′→β) and their molecular packing density (that is, hexagonal chain packing, orthorhombic perpendicular packing, and triclinic parallel packing, respectively) (Rousseau and others 1996; O'Brien 2004; Martini and others 2006).
In general, interesterified TG groups lead to changes in the speed/kinetics of growth and dimensions (that is, size and form) of the crystals (Narine and others 2006), which subsequently cause important alterations in the properties of fats and oils (for example, rheological such as the density and plastic such as the texture) (Lida and others 2002; Shi and others 2005; Piska and others 2006). Nevertheless, the control and improvement of the fat crystallization rate can be gained by: (i) varying the concentration and the nature of the crystallizer (for example, addition of 1% to 2% of highly saturated TG; addition of selected emulsifiers such polyglycerol behenic esters) (Sakamoto and others 2004; Cerdeira and others 2006; Wassel and Young, 2007) and (ii) accounting for the diglycerides (DGs) content (Siew and NG 1990; Wassel and Young 2007).
Overall, it is recommended to rely both on SFC and crystalline elements (for example, crystallization kinetics and polymorphism) to decrease TFAs content in commercial fat blends without affecting too much their properties (for example, stability and plasticity) and functionality (Mayamol and others 2004; Wassel and Young 2007). For that purpose, the experimental methodology associated with the study of interesterified fats shall routinely include the use of: (i) low-resolution pulsed NMR and XRD, to determine their crystallization kinetics; (ii) differential scanning calorimetry (DSC), to assess their thermal behavior; (iii) polarized light microscopy (PLM), to visualize their microstructural network and explain textural differences between fat blends; (iv) cone penetrometry, to assess their consistency/hardness; and (v) chromatographic techniques (for example, GC, HPLC, and gas liquid chromatography (GLC)), to fractionate TGs (Marangoni and Rousseau 2002; Martini and others 2005; Szydlouska-Czerniak and others 2005; Cerdeira and others 2006; Ribeiro and others 2009).
Up-to-date, 2 major types of fat interesterifications are considered (i) the chemical interesterification and (ii) the enzyme-assisted interesterification.
The chemical interesterification causes a rearrangement in the TG composition of a fat or a blend of fats, often favoring its physical–chemical properties (for example, melting point, thermal behavior, crystallization, and microstructure/crystalline network) and its functional characteristics such as: (i) stability during and after fat processing; (ii) compatibility of the fat base with the product for which it is destined; (iii) plasticity; (iv) spreadability; (v) cream formation; and (vi) aeration properties (Marangoni and Rousseau 2002; O'Brien 2004; Dian and others 2007). A very recent study showed that this process using sodium methoxide as a catalyst is able to confer desirable physical–chemical properties (for example, reduced softening and melting points, reduced SFC and consistency) to certain tested blends of oils (for example, palm stearin (PS), coconut oil, and canola oil), allowing the production of TFAs-free liquid margarines (Soares and others 2012). Alternatively, high-melting fat prepared through interesterification of fully hydrogenated soybean oil and regular soybean before blending it with salad oil represented a model of fat blending for trans-free margarine preparation (Zhang and others 2011). Interestingly, most studies addressing the health effects of a diet rich in chemically interesterified fat—usually compared with a diet high in a noninteresterified fat with the same FA composition—showed no relevant effects on human blood molecular profiles (for example, lipid, glucose, and insulin) (Nestel and others 1995; Meijer and Weststrate 1997; Berry and others 2007a). For instance, a study examining the effects of an interesterified fat blend with 24.7% palmitic acid (16 : 0) on the position sn-2 with a native fat blend containing only 8.7% 16 : 0 on the position sn-2 showed no differences on fasting blood lipids (for example, HDL-c and LDL-c) (Nestel and others 1995). Concordantly, interesterified fat blend predominately containing 16 : 0 on the position sn-2 (18%) did not affect fasting levels of glucose, blood lipids, and blood enzymes measured after 3 wk, when compared to the control blend (7.1%) (Meijer and Weststrate 1997). Recently, another study also found no effects of interesterification on fasting levels of blood lipids, glucose, and insulin when interesterified Shea butter (23% 18 : 0 on the position sn-2) was compared with noninteresterified Shea butter (3% 18 : 0 on the position sn-2) (Berry and others 2007a). This study is in agreement with a number of other human intervention studies (Zampelas and others 1994; Yli-Jokipii and others 2001; Berry and others 2007b). However, in another recent study (Sundram and others 2007) assessing the effects of 3 types of fat (that is, native palm olein, a blend with partially hydrogenated soybean oil, and an interesterified mixture of oils), the authors concluded that (i) both the interesterified blend and the partially hydrogenated fat blend increased the fasting LDL-c/HDL-c ratio; and (ii) the fasting plasma glucose levels were higher after 4 wk on the interesterified fat than after the other diets. Nevertheless, as pointed out in a letter to the editor (Destaillats and others 2007), this study was limited by the differences of overall FAs composition in the diets (that is, interesterified fat had 30% more SFAs and 57% less MUFAs than the untreated palm olein used as control.)
The enzyme-assisted interesterification represents another major type of fat interesterification and involves highly specific enzymes (for example, novozymes such LipolaseTM) that can be selected to cleave specific ester bonds. Comparatively to chemical interesterification, enzymatic interesterification presents these following main features: (i) enhanced control of the reaction; (ii) possibility to carry out the reaction at low temperatures, reducing the molecular thermal degradation; and (iii) no requirement of washing and bleaching; (iv) high cost of the lipase, representing the most relevant barrier to its widespread adoption. Interestingly, the use of rice bran oil, PS, and coconut oil, as substrates for lipase-catalyzed interesterification, was suitable for producing spreadable margarine stocks (Adhikari and others 2010). In another recent study, enzymatic interesterification of PS with Cinnamomum camphora seed oil was a good strategy to produce TFAs-free medium-chain FAs-enriched plastic fat such as shortenings and margarines (Tang and others 2012). Interestingly and similarly to the chemical interesterification, the enzymatic interesterification of selected edible oils did not significantly affect lipidemia (Zock and others 1995; Lee and others 2007a; Kim and others 2008). Indeed, a 3-wk diet study in humans comparing the effects of an enzymatically interesterified test fat containing 66.9% 16 : 0 on the position sn-2 with a noninteresterified test fat (6.4% 16 : 0 on the same position) did not alter fasting blood lipids (for example, HDL-c/LDL-c and TGs) in spite of very high intakes (Zock and others 1995). Further, TFAs-free margarines obtained by lipase-catalyzed interesterification and prepared with different weight ratios of canola oil, PS, and palm-kernel oil-based structured lipids caused low atherogenicity while displaying desirable textural properties (Kim and others 2008).
Eventually, a recent randomized crossover study investigating the acute metabolic effects of chemical and enzymatic interesterified stearic-acid-rich fat spreads in obese compared with nonobese men permitted to conclude that: (i) chemical or enzymatic interesterifications do not significantly affect blood parameters such as the postprandial glycemia, insulinemia, or cholesterolemia in both groups of patients; and (ii) the postprandial TG concentrations in obese subjects were, however, drastically increased by chemical interesterification, suggesting that the use of interesterified stearic-rich fat spread shall depend on the consumer´s health (Robinson and others 2009).
Genetically modified fatty acids composition
The better understanding of plant genetics and genomics (for example, modern mutation and transgenic technologies, unraveling of enzymatic pathways involved in the TG synthesis) is offering a great opportunity for the plant breeders to incorporate a range of FA profiles into oilseed crops (Wilson 1991; Röbbelen 1994; Davies 1996; Napier and Graham 2010; Wilson and Hildebrand 2010; Wilson 2012a). Interestingly, genetic modification of seed composition using sophisticated biotechnological tools would represent the most promising strategy to increase, in a long-term basis, the overall supply of high-oleic oil crops (Wilson 2012a), offering high-quality products containing both low-SFAs and low-TFAs content.
Thereby, the expression of FAD2 genes, which encode ∆12 (ω6) FA desaturases involved in the oleic acid (18 : 1) biosynthesis (Wilson and others 1980), can be inhibited in order to significantly increase oleic acid concentrations (often >50% of the total FAs) in seed oil (Hitz and others 1995; Wilson 2004). Further, the breeders can select favorable combinations of FAD2 alleles to increase the quality of edible oils (that is, nutritive value, oxidative, thermal, and environmental stabilities) (Lee and others 2007b; Wilson and Hildebrand 2010). For instance, the soybean oil quality has been improved by creating a very high-oleic acid trait after identification and combination of mutations in 2 FAD2 (that is, FAD-1A and FAD2-1B) (Pham and others 2010). Also, direct mutagenesis can be used to confer enhanced properties to fat foods (Liu and others 2002; Flickinger and Huth 2004), and possibly reducing the risk of CVDs associated with deleterious TFAs. It is the case of the low-oxygen-labile linolenic/high-oleic soybean oil that displayed high stability to oxidation as demonstrated by its longer shelf life and better performance in deep-frying applications (Hammond and Fehr 1984; Mount and others 1994; Wang 2002).
Up-to-date, only few private companies have received USDA regulatory approval to launch commercial production of oilseed varieties with genetically enhanced oleic acid concentration. Examples include Clear Valley™ and Odyssey™ mid-to-high-oleic canola oils and high-oleic sunflower oils (Cargill Inc 2005), Nexera™ Omega-9 canola and Omega-9 sunflower oils (Dow AgroSciences LLC 2005), Plenish™ high-oleic soybeans from E. I. du Pont de Nemours and Co. (Wilmington, DE, USA) (Butzen and Schnebly 2007; Sebastian and others 2012), and Vistive-Gold™ low saturated high-oleic soybeans from the Monsanto Co. (St. Louis, MO, USA) (Voelker and Wilkes 2011). Interestingly, Vistive-Gold™ soybean oil features more than 74% oleic acid in addition to about 3% palmitic acid, reducing total SFA and TFA concentrations while preserving the overall performance of a partially hydrogenated frying shortening (that is, fry life extension/oxidation stability improvement, sensory acceptability, and polymer buildup reduction during frying) (Voelker and Wilkes 2011; Ulmasov and others 2012). For these reasons, it is predicted that genetically enhanced high-oleic vegetable oils—led by soybean—may capture greater than 40% of the domestic consumption of vegetable oils in the United States by 2020 (Wilson 2012b).
Besides, other studies showed that high-oleic acid concentration in soybean oil can be quantitatively inherited (Wilson and others 1981; Burton and others 1983; Hawkins and others 1983; Burton and others 2006), suggesting the possibility to produce nongenetically modified lines with high-oleic acid content based on controlled environmental conditions. Indeed, it is known that high temperatures generally increase linoleic and linolenic acids and reduce the oleic acid content in soybean seeds (Wilson 2004; Hou and others 2006), strongly suggesting that the culture of soybean oil crops at low temperatures could favor the opposite phenotype. Thereby, the germplasm line N78-2245 was perhaps the first soybean developed with higher levels (51%) of oleic acid by recurrent environmental selection (Wilson and others 1981).
Although the goal of most plant breeders was to obtain high-oleic acid trait in oils, others preferred to reduce SFA levels. This choice is explained by the facts that SFAs confer low nutritional value and would cause deleterious health effects (for example, contribution to atherosclerosis), in spite of their suitable functional properties (for example, desirable flavor, oxidation resistance, melting point, and SFC) necessary for the production of some fat foods (for example, margarines and shortenings) (Wang 2002). Thereby, soybean lines with low palmitic acid, a predominant SFA in soybean oil, were developed by chemical mutagenesis, recurrent selection, and hybridization (Erickson and others 1988; Bubeck and others 1989; Wilcox and Cavins 1990; Burton and others 1994). At least 3 recessive genes at the Fap locus are responsible for palmitic acid content in soybean oil and so can be used as selective markers (Pantalone and others 2004; Wilson 2004).
Further, other plant breeders have decided to decrease PUFAs content in oils because of their oxidative instability that may compromise the oil flavor, in spite of their health benefits (for example, participation in lowering atherosclerosis). For instance, linolenic acid was identified as an unstable component of soybean oil (Liu and White 1992) across various growing conditions (Oliva and others 2006), although its content in soybean oil is much lower than linoleic acid (Wilson 2004). Therefore, several low-linolenic acid soybean lines (for example, N79-2245) were developed by recurrent selection, mutagenesis, and germplasm screening (Wilson and others 1981). At least 3 independent genetic loci (for example, fan, fan2, fanb, and fanx) are associated with seed linolenic acid levels, which can be used as selective markers (Wilcox and others 1984; Wilcox and Cavins 1985; Rennie and Tanner 1991; Fehr and others 1992; Rahman and others 1996; Rahman and others 1998; Stojsin and others 1998). Moreover, the content reduction of PUFAs 18 : 2 and 18 : 3 in soybeans could be a good strategy to enhance their oleic acid content, owing to the consideration that oleic acid content negatively correlates with the PUFAs one (Lee and others 2007b).
Conclusion and Perspectives
Hydrogenation was developed several decades ago and used by the food industry to replace animal fat and tropical oils in food supply, naturally enriched in SFAs. Indeed, PCH was beneficial for the preparation of featured solid or semisolid fat products (for example, shortenings and margarines). However, the increasing public health concerns generated by PCH-induced deleterious TFAs (for example, contribution to CVDs) are stimulating the search of efficient and safe alternative technologies and methods (Figure 3).
Three valuable strategies are available to the food industry for producing commercial low-SFAs and low-TFAs products (that is, healthier sustainable edible oils): (i) fat replacement/reformulation. Selected fat replacers represent suitable ingredients to mimic the functionality (for example, melting point) and sensory properties (for example, lubricity, smooth texture, and mouth feel) while contributing to fewer calories. In many cases, a blend of ingredients offers the best solution for fat reduction; (ii) fat interesterifications (that is, chemical or enzymatic). Structured lipids produced by interesterification can be used in fat emulsions for total parenteral nutrition and enteral administration. They can be designed to contain a desirable balance of short-, medium-, and long-chain FAs that meet a certain nutritional requirement. Reduced calorie fats can also be produced because of differences in the absorption and physiological response of the TGs chain length. Interestingly, interesterifications do not significantly affect main blood lipid parameters; (iii) genetic modification of FAs composition. Genetic engineering (for example, mutation, hybridization, and gene expression regulation) enables to reduce TFAs and control the UFAs content (for example, increase of oleic acid and decrease of linolenic acid) necessary to produce of high-quality edible oils. Nevertheless, longitudinal studies are still required to determine their possible consequences on health.
Eventually, other food processes for potential future use by the food industry (for example, membrane technology, electrochemical approaches, enzymatic hydrogenation, and intrusion) may constitute new hopes.
Although the global agroindustry has made considerable progress to reduce TFAs in many food products, it is striving to bring forward zero or low trans-fat solutions for all of them in all concerned countries. The remaining challenges are surmountable with, but not limited to: (i) learning, thinking, and ethical actions for greatest decisions; (ii) financial investment and time to perform all necessary randomized international studies; and (iii) total transparency to the consumers (that is, information for prevention).
Conflict of Interests
The authors declare that there is no conflict of interest.
Silver nitrate thin-layer chromatography
Cis fatty acid
Conjugated linoleic acid
Fourier transform infrared spectroscopy-attenuated total reflection