Healthy Oils and Fats san-trans for the Present Millennium

S.H. Goh* and T.S. Tang

Forest Research Institute of Malaysia,* Kuala Lumpur, Malaysia, and Malaysian Oil Palm Board, Bangi, Malaysia

Introduction

The controversies, embarrassments and even polemics resulting from dietary recommendations for oils and fats in nutrition of the past half century, only demonstrate the lack of present scientific understanding of the multifactors in the diet-health relationship apart from the need that scientific studies be free from socio-economic and geopolitical bias [Hu and Willett, 2002;Ravnskov, 1998, 2002, 2005; Kotte, 2003; Fallon et al, 2005; Ordovas, 2005]. That the health problems caused by trans-fats (raising bad LDL-cholesterol, lowering good HDL-cholesterol, interference with various metabolic pathways and ultimately cardiovascular diseases) from partial hydrogenation of soft oils could be swept under the carpet for so long until the recent FDA ruling for mandatory labelling by 2006, is typical of the tremendous influence of big business not unlike the previous issue of the dangers of cigarette smoking. While the economic waste was profound, the possible damage to the mental and physical health for misled and unsuspecting consumers can be incalculable. There is a need to be proactive yet responsible in response to a general concern to provide healthy foods rather than be driven by emotive consumer or capitalistic concerns. The manufacturer has to make informed and healthier choices in their products while consumers want to enjoy and even indulge in their food if they are assured of nutritional safety. Dietary products catering to extreme consumer demands, e.g. very low-fat diets, may have already done unintended harm (metabolic syndrome, type-II diabetes and obesity) to segments of the population even if the majority may not be adversely affected [Sanders, 2003; Weinberg, 2004;Lefevre et al, 2005].

All types of oils and fats serve to enrich human nutritional and culinary needs and it is unreasonable to expect one group of oils and fats to dominate and cater to the innumerable functionalities of food diversity. Fortunately there is increasing awareness of marked variations in dietary responses to health among individuals with different lifestyles and genetic backgrounds [Lefevre et al, 2005]. Furthermore with the detection of serious flaws in the diet-heart hypothesis, it is hoped that consumers and the food manufacturers will not be slavish in adherence to presumptions/prejudices on certain fats or cholesterol in the pursuit for healthy and enjoyable products as well as profits [Ravnskov, 1998, 2002, 2005]. Fundamentally, dietary oils and fats provide the human body with a most concentrated caloric source, material for cellular structure, fat-soluble vitamins, essential fatty acids and cholesterol, and the human being can have a choice to fulfil his/her physiological needs. As man desires more than nutrition, culinary delights must be in place for him to further enjoy/indulge his food by the use of cooking oils/fats that provide or create useful properties such as good heat transfer medium, texture, mouth-feel, lubricity, palatability and imparting taste/flavour.

As expected oils and fats can be invisible in the variety of available foods but what is used visibly has been the result of man’s requirements plus inventions in tandem with his social and environmental evolution. Thus, dietary oils and fats have become increasingly complex and sophisticated when man needs to enjoy a wide variety of cuisines. The current practice is that natural fat systems are modified and manipulated to offer functionality such as consistency in polymorphic crystalline networks, different melting ranges, oxidative stability, added taste/flavour and many other characteristics. In addition to the focus on physical, chemical and ease-of-processing characteristics, there have been considerable efforts to supplement in manufactured products nutritional values either real or just perceived. While there have been considerable success in adding value to processing for better oils and their useful constituents, claims of specific oils to be of better nutritional value especially in a diet-heart relationship have been controversial and in many instances been proven false [Gardner et al, 2005; Hu and Willett, 2002; Jenkins et al, 2005: Ravnskov, 2005; Kotte, 2003; Fallon et al, 2005; Ordovas, 2005].

The types and uses of oils and fats are numerous but the major uses can be summarised in Table 1.

Table 1. Varieties of Oils and Fats Products

Type of Fat/Oil Application / Functions and Properties
Frying Oils / Good heat transfer, crispiness, texture, flavour stability, oxidative stability, high smoke point
Margarine (soft, table, baking, pastry, reduced-fat, etc) / Emulsification, texture, plasticity, spreadability, miscibility, stability, uniformity, aeration, water content, colour, vitamin & flavour carrier
Various Types of Shortenings / Emulsification, texture, plasticity, miscibility, stability, uniformity, aeration, creaminess, pumpable/pour-able, flavour, colour
Vanaspati / Texture, uniformity, palatability
Confectionery / Melting mouthfeel, texture, stability, uniformity
Salads, Soups, Gravies / Liquid, emulsification, stability, flavour carrier, flavour development

Frying Oils

General. Deep frying is an important way for food preparation as oil is not only a good heat-transfer medium but also endows fried food with delightful organoleptic and sensory characteristics, such as flavour, texture, mouth-feel, crunchiness and golden brown appearance. The rise in importance of frying fats is synonymous with the rapid adoption of fast foods all over the world. Modern man does not just depend on the caloric nutrients from oils and fats that are generally now abundantly available but he is much conditioned to savour his fried food indulgently. Importantly, frying oil can be retained in the food after frying and depending on the food product and the type of frying oil, the fat content can reach up to 50% so that nutritional quality needs to be emphasized. Apart from this, frying demands many chemical quality characteristics in the oil, since frying causes hydrolysis, oxidation, degradation and oligomerisation/polymerization. Quality performance characteristics require that frying oils must be stable to harsh conditions of normally high frying temperatures (180˚C), which limit most oils to highly monounsaturated/saturated, especially to be made up of mainly long chain fatty acids and preferably contain high levels of antioxidants. Such constitutional requirements ensure high flash/smoke-points, low oxidation, low hydrolysis and polymerisation, the same qualities that minimize flammability, rancid odours, acidity, residues remaining in equipment and sticky kitchen deposits. Furthermore, thermo-oxidized oils are known to have deleterious physiological effects, e.g. when fed to rats they cause conditions such as necrosis of the liver, enlargement of kidney and liver, retarded growth, hair loss and dermatitis [Sulzle et al, 2004].

Techno-economically useful frying oils. Soft oils with high polyunsaturation are unsuitable as heavy-duty frying medium as they undergo extensive polymerisation and oxidation and leave unhealthy residues (oligomers/polymers and polar materials) in fried food and equipment, while ready oxidation means short shelf lives and also promotion of rancid odours due to breakdown of polyunsaturated oil molecules. Various limits have been placed on frying oils because of such undesirable properties: polymer formation, 10-12% (cooking equipment fouling, foaming and bitter taste); linolenic acid, <2% (off flavours); free fatty acids, 2.0-2.5% (decreased smoke and flash points); and polar compounds, 25-27% (excessive oxidation, adverse nutritional effects). Because of these requirements, especially for industrial use, several oils have been preferred as liquid frying oils, e.g. palmolein, palm oil fractions, peanut oil, cottonseed oil and high-oleic sunflower oil. High linoleic and linolenic oils are usually hydrogenated to monounsaturated, trans- and saturated fats to increase their oxidative stability but hydrogenation (unless it is total hydrogenation to obtain saturated oils) inevitably gives rise to undesirable trans-fats. In the previous years partially hydrogenated soy oil used for deep-frying have trans content that reach a high of 50%. While trans-fats had been useful for fat processors they have been well known to be unhealthy, strictly to be avoided because of the lack of a defined safe-limit and now governed internationally by set limits (e.g. <2%) such as standards or guidelines or mandatory labelling of content (FDA). Measures taken to avoid trans-fats in processing include use of complete hydrogenation and subsequent interesterifications with unhydrogenated oils but these may provide new oils with unknown and untested quality with respect to nutrition while the extra processing requirements incur higher costs [Juttelstad A, 2004]. Total hydrogenation provide stearic-rich fats that give rise to exaggerated postprandial lipaemia and so may increase the risk of CHD by contributing to both thrombotic and atherogenic processes [Berry and Sanders, 2005].

Refined olive, high oleic sunflower/safflower and palmolein (including other palm oil fractions and blends with other oils such as canola, soy, corn and sunflower) are particularly suited for frying because of some or all of the following properties: high flash points, high monounsaturation or good amounts of saturated long chain fatty acids, high unsaturation at the nutritionally desirable sn2-position of the oil molecules, and the presence of natural antioxidants (vitamin E including tocotrienols). Attempts to obtain new genetically modified (GM) temperate crops with high oxidative stability to imitate olive, high-oleic sunflower or more highly saturated oils can cause anxiety on health and environmental concerns associated with GM in the long term. While blending of oils with high monounsaturation or slightly higher saturation, e.g. high-oleic oils, palmolein, peanut and cottonseed oils, are commonly practiced, the present world’s needs for trans-free frying oils are vast. So these have to be provided by commodity oils such as soy and canola that can be optimally blended with palmolein or palm oil apart from resorting to total hydrogenation. However, from economic and quality reasons, palmolein alone can fulfil the needs for healthy oils with high oxidative stability and which does not require hydrogenation; in fact it is the preferred choice for industrial frying applications. Also there are further advantages in techno-economic considerations in its consistent quality, low cost and ready availability. If for socio-political reasons there is a need to use locally produced crop oils, direct blends, fractionated blends or interesterified (chemical or enzymatic) blends with palmolein can be readily formulated even for temperate climates. Blends of other oils such as those of rapeseed or canola, soybean, corn, sunflower, peanut and cotton seed with 20-40% of palmolein, depending on the climatic conditions and seasons, will be suitable for use as cooking oil in temperate countries. There are other economically available liquid oils from the palm oil industry that include superoleins and red palmolein (enriched in natural vitamins and carotenes), the latter being a virgin palm oil preparation minimally processed at lower temperatures. The widespread consumption of instant noodles also requires palmolein or palm oil for industrial frying because of its good qualities especially for ensuring long shelf life against oxidation.

Home cooking oils that have palmolein blends to provide popular flavours may contain peanut oil and small amounts of sesame oil. It is noted that for home or gourmet cooking culinary preferences may override techno-quality considerations as the food is consumed immediately or the oils are discarded after a single use, e.g. sauté, pan-frying, stir-frying and baking with oils/fats such as almond, avocardo, butter, coconut, corn, safflower, sesame, soybean, sunflower, virgin olive, virgin palmolein and walnut.

Attempts have been made to produce suitable frying oils by growing GM soy with low linolenic acid or high oleic with low linolenic acids. However thermo-oxidative stability of linolenic acid (18:3) and linoleic acid (18:2) are not widely different but odour and organoleptic properties showed unexpected results. High linoleic soy and corn oils still show high degrees of oligomerisation/polymerisation on frying. Also, there is apparently a need to maintain a level of linoleic acid greater than linolenic acid (and not just having high oleic acid) to provide for good odour and flavour; oils with linoleic acid levels lower than linolenic acid curiously give rise to fishy flavours while oleic acid levels of around 60% (mid-oleic rather than high-oleic oils) provide optimal deep-frying flavours [Warner and Gupta, 2005]. Apart from organoleptic properties, major concerns for potato crisps (US chips) are in the oxidative stability during frying and storage. Palm olein and heated palm oil (mp. 36oC) directly or in blends with low-volume oils such as peanut and cottonseed oil are suitable. Too liquid oils can give crisps a wet look while solid fats tend to create a waxy appearance. Suitably introduced red palmolein by a continuous process into industrial frying of potato crisps enhance the consistent golden brown colour. Likewise industrial frying of other extruded snacks and nuts need palmolein, peanut and cottonseed or other stable oils including blends of fully hydrogenated soy or canola oils.

French fries are now usually marketed prefried and frozen, to be refried (or oven heated) to a crisp golden-brown at 180oC before consumption. Solid frying fats (mp 42-46oC) are available for this purpose and they are by necessity more saturated either from blends containing total hydrogenation of soft oils (soy, canola and corn) or using stearin fractions such as natural palm stearin. Frying in solid fats allows lower fat uptake and allow chips to be harder in texture and avoiding an oily appearance [Kita et al, 2005]. Solid animal fats are also possible for use but there are considerations such as of additional load of cholesterol, undesirable chemicals from the animals/animal feeds, potential hazard of animal diseases and in some cases religious preferences.

Semisolid Fat Resources for Margarines and Shortenings

Margarine has had a long history from what was introduced as a cheap replacement of butter or a poor man’s butter, then to move forward as a perceived healthy alternative (low-fat, polyunsaturated and later with added cholesterol-lowering stanols/sterols) but only to be downgraded again because of unhealthy trans-fats arising from partial hydrogenation of polyunsaturated oils [Timms, 2005]. As margarines and shortenings are solid or semisolid fats they had been made of either natural saturated or synthetic saturated and trans-fats by partial hydrogenation. To obtain the required functionalities without recourse tohydrogenation, many manufacturers have to reformulate for trans-freecompositions which necessarily require the inclusion of acceptable amounts of available sources of semisolid or solid fats such as cottonseed, cocoa butter, palm, tallow and lard. By far, palmolein and palm oil fractions are the most economic and widely available of raw materials and yet have healthy compositional and nutritional characteristics [Choudhury et al, 1995; Ong and Goh, 2002; Truswell, 2004; Goh et al, 2004]. Large sections of consumers, still having ingrained misconceptions of all saturated fats and cholesterol (e.g. deposits in arteries are saturated fats, which is untrue, but rather being due to unsaturated fats particularly polyunsaturates [Felton et al, 1994]), may need to be reassured that palmolein provides better blood lipid profiles than olive and sunflower oils in humans [Choudhury et al, 1995; Truswell, 2004] and non-human primates [van Jaarsveld et al, 2002]. Further, recent studies indicate that incorporating up to 20% palm oil with high linoleic or oleic oils in a high (38% en) fat diet do not significantly affect the lipid profiles of humans [Thijssen and Mensink, 2005]. Undesirable trans fats, although proven versatile for the manipulation as solid fats, can readily be replaced by palmitic-type oils and fats which can give rise to ’-prime fine crystals required in margarines and shortenings [deMan and deMan, 2001].

Recent nutritional data has re-emphasised the need for a balance of the variety of saturated, monounsaturated, polyunsaturated and long chain 3-fatty acids for the proper health and functioning of the body [Fallon et al, 2005; Lefevre et al, 2005; Ordovas, 2005; Ravnskov, 2005]. Despite the overly concern of saturated fats in nutrition, it may be noted that the body requires and biosynthesises up to 40% of saturated fatty acids mainly in the form of palmitic (16:0), stearic, myristic (14:0) and other saturated short/medium chain fatty acids, all of which play many other important biochemical functions for the body. Likewise human milk has these constituents and the total saturated fatty acids can be 50% or more. Palmitic acid has another beneficial aspect as unlike trans acids, it increases the good HDL-cholesterol. Of great concern is that “the results of four population studies suggest that the intake of trans fatty acids compared to saturated fatty acids per gram is associated with a 10-fold higher risk increment for the development of coronary heart disease. A negative effect of trans fatty acids on the human fetus and newborns has been further substantiated” [Stender and Dyerberg, 2003]. Data from studies gave rise to “justified suspicion that trans fatty acids increase the risk of Type 2 diabetes” and there are possible other effects such as insulin sensitivity, promotion of allergic disease in children and changes in body fat distribution.