The functional properties of fats and oils-A richness of diversity

A part of the importance of fats and oils derives from the functional properties that they confer to the foods. This is a consequence of their chemical nature and structural features. Lipids are relatively insoluble in water because their large non-polar region. However, they also contain groups with some degree of polarity. The combination of these polar and non-polar groups and their variations is what gives the range of functional properties observed and what made them so valuable. This issue of Grasas y Aceites reviews some of the functional properties of fats and oils. The Editors hope that the studies included will provide an state of the art reference volume of present knowledge and applications in these areas.


FATS AND OILS-A MAJOR INDUSTRY
The importance of fats and oils originates in the functionality that they can confer, this in turn arises from their chemical nature and the common structural features that exist in all fats and oils.In the context of this review, the term fats and oils specifically excludes mineral products and applies to what are normally called lipids.Lipids are defined by The Condensed Chemical Dictionary (1) as: « An inclusive term for fats and fat derived materials.Includes all substances which: 1. are relatively insoluble in water but soluble in organic solvents..., 2. related either actually or potentially to fatty acid esters, fatty alcohols, sterols, waxes etc..., and 3. utilisable by the animal organism.»Fats and oils cover a huge range of materials produced in vast tonnage every year.Table I gives world production figures for some major fats and oils.A more up to date analysis for the USA is given in Table II.The scale of consumption is huge and attests to the enormous importance of fats and oils to the global economy as well as the role that they play in our every day lives.Table III gives a further analysis of the data from the US for edible and inedible fats and oils.The total consumption of edible products is two and a half times that of inedible products attesting to the role of the food industry as consumers of fats and oils and their overall importance in food products.

FUNCTIONALITY
The origins of the functionality of fats and oils lies in the chemical constitution.As the definition given above implies a key feature of lipids is their relative insolubility in water, this arises because all lipid molecules have a common feature of containing a large non-polar region.This is highly variable and may itself contain a wide range of chemical species.However the second common feature of lipids is that they all contain a functional group or groups which have some degree of polarity.It is the combination of the polar and non-polar and the variations that are possible within these that give the range of functional properties that are observed and are of such value.
In order to try to classify this diversity it is useful to define a general formula for a lipid.A suitable one might be:

R (n) P (m)
In this representation R represents the hydrophobic entity and P the more polar entity.There are in general n hydrophobic species attached m polar species.Where n is greater than 1.It is not a necessary requirement that R 1 =R 2 =R 3 , a similar consideration applies for P and m.There is no implication of stereochemistry in this formula and this is, of course, another source of the diversity of lipid functionality.
In the simplest case of a fatty acid n=1 and m=1, even here there is enormous variation possible in R. In the important case of a tryglyceride P remains fixed but the number of possible combinations of R is very great.Variations in R 1 , R 2 and R 3 result in variations in melting temperatures of solids and in the general case where R contains sufficient carbon atoms to give alkyl chain flexibility a number of crystal habits are possible.Examples of the effects of changes in R on melting point and crystal habit are given in Table IV.In most commercially available fats and oils there is a range of R n .Examples of these are shown in chart 1 and illustrate the diversity of properties that will be available from different fats and oils.It is important to realise that the useful functionalities such as mouth feel derive not the presence of a single compound but from the variety of chemical and physical properties present.These will control such features as the solid liquid ratio at room temperature and the subsequent changes on exposure to body temperature in the mouth.Thus in this and many other cases, such a spreadability, important functionality comes from the mixture of materials present.
When R contains some chemical functionality that confers stiffness on the chain stereochemical effects start to become important.These can effect the packing of the chains and also will effect the chemical reactivity of the lipid.An example of this can be seen in the unsaturated chains.Cis -trans isomerism is very important in determining the nutritional value of lipids and the presence of double bonds in the alkyl chain restricts the ability to fit into membrane structures and increases fluidity.The interactions of macromolecules with the lipid may also be affected by the nature of R. The degree of stiffness of R and the nature of the chemical entity causing the stiffness will determine the restrictions on the interactions and in the some circumstances can give rise to highly stereospecific recognition.
The nature of the polar group is of vital importance in the interaction of the lipid with water: highly polar or charged groups will tend to be hydrophilic in nature and thus will tend to orient towards water whilst the hydrophobic groups will tend to orient towards non polar regions.These competing effects give rise to the surface activity that is often observed in lipids and to the formation of complex structures such as micelles and bilayers such as occur in membranes.Further complex liquid crystalline structures may also be formed giving rise to yet another range of diversity.

THE LITERATURE
It is not surprising that given the importance of fats and oils that there is a vast literature covering both the academic and commercial aspects of the subject.
The range of periodicals alone is enormous.Table V gives a partial list of some the periodicals dealing with lipid and lipid related research.
It is clear from the list that lipids and their wide variety of functions impinge on almost all aspects of human life and that importance of lipids at the national level is reflected by the number of national periodicals covering particular aspects of lipid science and technology.

CONCLUSIONS
Fats and oils are commercially and scientifically of great importance.In the following volume of Grasas y Aceites we review some of the functional properties of fats and oils.As must be clear from the foregoing any such review must be incomplete and partial.Nevertheless the editorial group hopes that this special edition of the Journal will provide a useful and up to date reference volume of current thinking and applications in the areas selected.

ACKNOWLEDGEMENT
The Author would like to thank Rebecca Sweet for help in the preparation of Table V.

2
Grasas y AceitesTable IV Melting points of various crystal habits of triglycerides.Melting points are given in degrees Celsius.Data from Ref.

1
The variation in fatty acid content of lipids from various sources