Eur. J. Lipid Sci. Technol.

102 (2000) 539–541 539

Bernd Brinkmann Quality criteria of industrial frying oils and fats

Fried food is very popular all around the world and comprises a wide variety of differ-
Walter Rau Neusser ent products. Each of them demands special attention to make them a success. Fac-
Öl und Fett AG, tors such as the melting point and the solid fat content may contribute to the palatabil-
Neuss, Germany
ity and appearance of fried food. Major characteristics of products, processing and
quality issues are related to the fatty acid composition of shortenings. Important points
to be considered for choosing a suitable oil for a specific product are highlighted and a
simple statistical method of value analysis is proposed to put the choice of a shorten-
ing on a better basis.

Keywords: Industrial frying, shortening, functionality of fat, quality criteria, value

analysis.

1 Introduction Tab. 2. Fatty acid composition of selected oils and fats.

Fried food is enjoying an ever-increasing popularity Fatty acids [ %] Palm Tallow Soy- Rape-
world-wide. There are a large variety of different types of oil bean oil seed oil
food that are fried (Tab. 1). The quality of fried food de- Saturated 51 55 15 7
pends in part on the oil or fat used in its production. Due Monounsaturated 39 40 21 58
to the absorption of up to 40 % fat during frying of some
Polyunsaturated 10 5 64 31
products, the shortening is an integral part of the food pre-
pared. Nevertheless, it is important not to ignore other
factors affecting fried food quality, like fryer design, nature Tab. 3. Key factors affected by the oil composition.
of fried food, frying conditions, and monitoring the frying Key factors
oil quality during use. The chemistry of frying as well as
many technological details are well described [1–3]. This Appearance Solidification
paper focuses on functional characteristics in their rela- Aroma Product shelf life
tion to the major constituents of frying fats. A method for Taste Product handling
selection of the right oil for a specific application is provid- Texture Oil storage
ed and may help to improve the overall quality of fried
food.
partly the fatty acid composition (Tab. 2) and their distri-
Tab. 1. Examples of popular fried food.
bution in the glycerides of the frying shortening which is

Review Article
Fried food responsible for sensory and functional properties of the
frying shortenings and the products prepared (Tab. 3).
French fries Cheese
Chicken Potato chips
2.1.1 Influence of saturated fatty acids (SAFA)
Fish Tortilla chips
From a functional standpoint, saturated fatty acids, such
Meat Extrusion snacks
as palmitic or stearic acid, are very stable against oxida-
Spring rolls Doughnuts
tion and polymerisation. They add structure to certain
Puff pastry Nuts products because of their high melting point. Without a
certain amount of saturated fatty acids for example, par-
fried products passing through a freezer will not solidify
2 Quality factors of frying oils and fats properly, causing trouble with greasy deposits on the
2.1 Fatty acid composition process equipment after the freezer. Handling a high
melting point shortening makes special care necessary.
Frying shortenings are edible fats or oils of plant and/or
For proper storage, insulated and heated tanks with agi-
animal origin. Their main components are triglycerides,
tators are a necessity to avoid partial crystallisation during
molecules built of glycerol esterified with fatty acids. It is
storage. Solid fats are even more difficult to handle, espe-
cially in smaller operations such as restaurants. Special
Correspondence: Bernd Brinkmann, Walter Rau Neusser Öl
und Fett AG, Industriestraße 36–40, 41460 Neuss, Germany.
care is needed during the start up of fryers. The initial
Phone: +49-2131-208118, Fax: +49-2131-208240; e-mail: melting of commercially common fat blocks has to be
BerndBrinkmann@WalterRauAG.de done very slowly and carefully. If the heating elements are

© WILEY-VCH Verlag GmbH, 69451 Weinheim, 2000 0931-5985/2000/0809-0539 $17.50+.50/0

540 Brinkmann Eur. J. Lipid Sci. Technol. 102 (2000) 539–541

not well covered with molten fat, the whole vat may catch 2.1.4 Polyunsaturated fatty acids (PUFA)
fire due to local overheating.
Polyunsaturated fatty acids have a good nutritional im-
The appearance of a food may be adversely affected, if age. Oils with high levels of PUFAs are used in salad oils
products are fried in fats with a melting point above stor- and dressings, but they have distinct disadvantages when
age temperature. Partial solidification of triglycerides is used for industrial frying. Some countries, like France,
responsible for grey, pale, and dry looking surfaces of have even established legal limits for linolenic acid in
fried foods kept under cold storage conditions. frying oils. The formation of polymers, cyclic fatty acids,
and other undesirable degradation products during heat-
Too much saturated fatty acid in a cooking fat or oil, as in- ing is increased in frying oils having high concentrations
dicated by a melting point above body temperature, may of fatty acids like linoleic or linolenic acid. Linoleic acid
result in finished products that have an unpleasant waxy e.g. oxidises 100 times faster than oleic acid. Small quan-
mouth feel. tities of polyunsaturated fatty acids may be tolerated
for the development of specific flavour components. Oxi-
2.1.2 Monounsaturated fatty acids (MUFA) dation products formed from PUFAs, like aldehydes,
are dependent on the fatty acid structure and may vary
Monounsaturated fatty acids, mainly oleic acid, are still widely in their flavour type and intensity.
relatively stable against oxidation. Due to their low melt-
ing point, MUFAs do not add to the texture, which may be The shelf life of products fried in shortenings with higher
an advantage depending on the type of product. Frying concentrations of PUFAs is also shorter than those fried
oils, rich in oleic acid, are relatively neutral and provide a in other fats. To offset the development of undesirable
“light taste” to fried food compared e.g. to tallow or soy- flavours during storage, special care has to be taken in
bean oil. The appearance of fried products may be im- the choice of packaging material, packing conditions, and
proved in terms of richer colour and a glossier surface, if storage conditions.
fried in oils with a melting point below storage tempera-
The interaction between the foods being fried and the
ture. This is also valid for polyunsaturated fatty acids as
shortening is also important. The fat contained in meat,
well. In terms of nutritional value, oleic acid has the undis-
fish, or other products will be exchanged with the fat in the
puted position of being a heart healthy component in the
fryer and can adversely affect the quality of the fat in the
diet and is often cited as a major contributor to the suc-
fryer. Par-fried products will also influence the end prod-
cess of the Mediterranean diet.
uct by carrying over fat into the final fryer. Both sources
may contribute to a reduced oil life of the shortening, es-
2.1.3 Trans fatty acids (TFA) pecially if highly polyunsaturated fatty acids are entering
Trans fatty acids are geometrical isomers of their corre- the system.
sponding cis fatty acids.
2.2 Other quality related components
Cis double bond
H H There are other minor components like sesamol or
oryzanol, which will improve the performance of frying
I I oils, whereas copper and iron are serious pro-oxidants.
–C = C –
The presence of these materials will quickly lead to
Trans double bond products tasting badly and will destroy the cooking oil.
H Lecithin, a natural ingredient of many oil seeds, may
I cause excessive foaming because of its emulsifying prop-
–C = C – erties.
I Excess water, especially free water, is a safety risk and
H
may cause serious accidents, if spontaneous evaporation
TFAs naturally occur in certain animal fats like butter, but of the water takes place while refilling wet oil into hot fry-
are also formed during the hydrogenation of oils into high- ers.
er melting fats and during deodorisation of highly unsatu-
rated oils. TFAs are higher in their melting point than their 3 Guideline to choose the right oil
cis configured counterparts and show a behaviour similar
to SAFAs. The health impact of individual TFAs is still There is no ideal frying shortening that satisfies each and
under investigation, but it is generally agreed that TFAs every frying application. The reason lies in the different
have an adverse influence on the ratio of low and high types of products, frying conditions, further processing,
density lipoproteins. storage, and expected shelf life. In order to choose the
Eur. J. Lipid Sci. Technol. 102 (2000) 539–541 Quality criteria of industrial frying oils and fats 541

best product one should prepare a list of important attrib- Tab. 5. Value analysis.
utes. The following simple questionnaire, shown in Tab. 4,
Criterion ai–n fat 1 fat 1 fat 2 fat 2
may help in choosing the best match for the required
i–n bi–n (a × b)i–n bi–n (a × b)i–n
product profile. Functionality, nutritional concerns, or mar-
keting issues may sometimes contradict with the com- Cost 9 3 27 5 45
mercial view. Therefore, any oil that is selected may be a Taste 4 2 8 5 20
compromise of at least the three factors mentioned in SAFA 2 4 8 5 10
Fig. 1. Gloss 1 1 2 3 3
TFA 5 3 15 5 25
Functionality Sum 60 103

Tab. 6. Basic specification for frying shortenings.

Ideal fat? Criterion specification

Colour Light
Nutrition Cost Taste Bland
Flavour Bland
Fig. 1. Main factors for choosing a frying fat. Free fatty acids 0,1 Max
Peroxid value 1 meq O2/kg Max
Tab. 4. Questionnaire for the appropriate product. Smoke point 220 °C Min
Moisture 0.1 % Max
Area of concern Factors to be considered
Linolenic acid 2% Max
Nutrition Low SAFA content wanted?
Melting point Fitting the application
Level of TFA accepted?
Additives acceptable?
Process Type of product to be fried?
Frying temperature? mum requirements may be seen in Tab. 6. Beyond this, it
Continuous frying? may be useful to include the type of raw material used
Turnover rate? and to add the fatty acid composition, especially if trans
Oil storage facilities? fatty acids are to be limited for nutritional reasons.
Product Storage e.g. deep frozen?
Shelf life wanted? When specifications are established, it is also important
Sensory attributes? to agree on the method(s) of analysis. It is always best to
Commercial Cost? use officially recognised methods such as of the Interna-
Availability? tional Organization for Standardization (ISO), Internation-
Environmental Packaging? al Union of Pure and Applied Chemistry (IUPAC), Associ-
ation of Official Analytical Chemists (AOAC), American Oil
Chemists” Society (AOCS) or German Society for Fat
The choice of fat can be further supported by statistical Science (DGF)-methods.
methods like value analysis. Criteria to be fulfilled by the
wanted shortening are fixed and given points for impor- References (for further reading)
tance (ai–n) by an interdisciplinary team. The team then
determines by vote how each of the proposed products [1] E. G. Perkins, M. D. Erickson: Deep-Frying, AOCS-Press,
fulfills the single criteria (bi–n). The sum of (ai–n × bi–n) of Champaign IL (USA) 1996.
each shortening will lead to a ranking among the products [2] Y. H. Hui: Bailay’s Industrial Oil & Fat Products. 5 Edition,
as shown in Tab. 5. The highest score will be the best Volume 3, John Wiley & Sons Inc. New York (USA) 1996
product supported by views from different angles in an or- p. 409–482.
ganisation. [3] S. P. Kochhar: New Developments in Industrial Frying. PJ
Barnes & Associates, Bridgewater (UK) 1997.
4 Basic specification for frying oils and fats
When purchasing frying shortenings, like any other prod-
uct, it is essential to establish specifications. The mini- [Received: June 8, 2000; accepted: July 25, 2000]