Composition and Physical Properties of North American Stick Margarines

Cfl/I. Inst. Food Se;. Teehnol. J. Vol. 22, No. 5, pp. 481·486, 1989

RESEARCH

Composition and Physical Properties of North American Stick Margarines E. Postmus, L. deMan 1 and J .M. deMan Department of Food Science University of Guelph Guelph, Ontario NI G 2W I

Abstract A number of commercial stick margarines were obtained from retail outlets in eastern and western Canada and the United States in order to compare their composition and physical properties. The fatty acid composition and trans isomer level in the fat was determined. The liquid portion of the margarine fats was obtained by absorption in filter paper and was also analyzed for fatty acid composition. The rate of absorption of the liquid fat in filter paper was termed oil mobility. There was an inverse relationship between oil mobility and hardness. The liquid portion of the margarine fats contained lower levels of palmitic acid then the original samples indicating that the solid portion of the fat contained high levels of palmitic acid. This fact is related to polymorphic stability of the margarines. Polymorphic behaviour was determined by X-ray diffraction analysis. Canola based margarines had a greater tendency to occur in the {3 modification than soybean based margarines. Crystallization temperatures of the separated fats were higher for Canola based margarines than for any of the other margarines. The difference between softening point of product and dropping point of separated fat was greater for margarines in the {3 form than those in the {3' form.

Resume Une certaine quantite de margarines en pain fut obtenue d'epiceries de l'est et de l'ouest canadien et des Etats-Unis dans le but de comparer leur composition et leurs proprietes physiques. Elles furent analysees pour leur composition en acides gras et pour leur teneur en isomeres trans. La fraction liquide des graisses de margarine fut extraite par absorption sur papier filtre et fut ensuite analysee pour sa composition en acides gras. Le taux d'absorption de la fraction liquide sur papier filtre fut designe mobilite de l'huile. Une relation inverse fut observee entre la mobilite de l'huile et la durete. La fraction liquide des graisses de margarine fut moins riche en acide palmitique que les echantillons originaux, indiquant ainsi que la fraction solide de la graisse etait plus riche en acide palmitique. Cette observation est reliee a la stabilite polymorphique des margarines. Le comportement polymorphique fut determine par diffraction aux rayons X. La modification fut plus apparente dans les margarines a base de canola que dans celles a base de soja. Les temperatures de cristallisation des graisses extraites furent plus elevees chez les margarine a base de canola que chez les autres. La difference entre le point de ramollissement du produit et le point d'egouttement de la graisse separee fut plus grande chez les margarines du type {3 que chez celles du type {3' .

Introduction Stick margarines are still very important products in both the U .S.A. and Canada, although they have

IdeMan Food Technology Services Inc., Guelph, NIH 6B5

been replaced partially by soft (tub) margarine. Canada is a major producer of canola oil while the U.S.A. is a major producer of soybean oil. The fats used in margarines in these countries reflect the availability of these oils. Margarine is a water in fat emulsion. The oil phase contains crystals, which form a three dimensional network. This network is important for the consistency and smoothness of the margarine (Haighton, 1976). The amount of crystals or solids and the size of crystals determine the hardness or firmness of the margarine. The size of crystals also effects the smoothness and mouthfeel of the margarine (deMan et al., 1979). For good mouth feel the crystals should melt at body temperature. Polymorphic transition of 13' (beta prime) crystals to l3(beta) results in slightly higher melting temperatures of the crystals. Coupled with larger crystals, margarines consisting of 13 crystals will have a sandy mouthfeel (Haighton, 1976; Chrysam, 1985). At high solids content, 13 crystals can form a very strong crystal network, resulting in a brittle and hard margarine. At low solid content large crystals cannot incorporate liquid oil as well as the small crystals, then the product becomes oily (Chrysam, 1985). Wiedermann (1978) has classified different fats and oils according to their polymorphic crystal tendency. He classified hydrogenated canola, soybean, corn and sunflower to be 13 tending, and tallow, butter and palm to be 13' tending. It is thought that the uniformity of the fatty acid chain length promotes beta crystallinity (deMan, 1978; Chrysam, 1985). For instance canola and sunflower contain only 4-7070 of 16 carbon fatty acid while palm oil contains 45%. The remaining fatty acids have 18 carbons. Therefore, palm oil is more diversified, as far as fatty acid chain length is concerned, than canola oil. However, the position of the fatty acid on the glyceride molecule is equally important. Timms (1984) has reviewed the various structures of triglycerides as to their polymorphic behaviour. In mixed saturated/unsaturated acid triglycerides, the 13' polymorph is usually found when the triglyceride is "asymmetric" meaning that two saturated or two unsaturated acids

Copyright'<: 1989 Canadian Institute of Food Science and Technology

481

occupy the 1, 2 or 2, 3 position and the remaining position is occupied by an unsaturated or saturated acid, respectively. The {3 polymorph is prevalent in "symmetrical" triglycerides where the saturated or unsaturated acids occupy the 1, 3 position and the 2 position is occupied by an unsaturated or saturated acid, respectively. An exception to the rule of symmetry is the triglyceride PStP where the stearic acid is in the 2 position, which is longer in chain length than the palmitic acid in the 1, 3 positions. PStP is {3' stable. Since canola oil has very strong {3 tendency, palm oil is incorporated to stabilize the {3 structure. Ward (1988) has made recommendations as to the solid contents and processing conditions for canola stick margarines. Storage conditions are crucial in preserving the {3 crystallinity. For example, exposing margarine to temperatures where melting and recrystallization of the fat can occur promotes the formation of {3 crystals (Chrysam, 1985). This study was undertaken to determine the chemical composition and some physical characteristics of 24 North American stick margarines as well as 3 butters. Special attention was given to a comparison between canola margarine from Canada and soybean margarines from the U.S.A.

Materials and Methods

100/120 Chromosorb WAW (Supelco) and operated at 170°C.

Trans fatty acids Methyl esters were made from the separated fats according to AOCS (1981) for the preparation of methyl esters (Method Ce 2-66). The trans fatty acid content of the methyl esters was determined by IR-spectrophotometry (AOCS Cd 14-16) using a Beckman model 4300 IR spectrophotometer.

Fat crystal structure The polymorphic forms of the fat crystals in the products were established by X-ray diffraction using a 601 Diffractis X-ray generator and a Guiner X-ray diffraction camera, Model FR 552 (Enraf-Nonius, Delft, The Netherlands) which was operated at 21°C (Naguib-Mostafa and deMan, 1985). An Enraf-Nonius Guinier viewer was used to measure the distance between diffraction lines on the film. Crystal size was visualized by polarized light microscopy using an Olympus model BH polarizing microscope with a PM-6 camera attachment. The polarized light photomicrographs were taken at 400x magnification on Kodak Panatomic-X film at 5°C. Fat crystal structure was established within two weeks of purchase of the samples.

Samples were purchased from supermarkets in Saskatchewan (Sask.), Manitoba (Man) and Ontario (Ont) in Canada and California (CA) and New York (NY) in the United States. All samples were transported in coolers containing ice and stored at refrigerator temperatures (4°C) thereafter. The samples were coded with a letter and a number. Samples labeled with the same letter but a different number have the same brandname but come from different areas. The fat was obtained by melting part of the margarine in the oven. After removal of the water layer the fat was dried and filtered. Oil mobility was estimated at WOC and 21°C by inserting five strips (length, 11.5 cm) of Whatman no. 1 chromatography paper 1.5 cm into the product and letting the oil rise for exactly 24 h. The height of the oil that had risen up the paper was then measured. The bottom part of the paper that had been in contact with the product was cut off and the part that contained the oil was extracted with petroleum ether. Samples were conditioned at the appropriate temperatures 24 h before testing.

Differential Scanning Calorimetry (DSC) was used to determine the crystallization behaviour of the separated fats using a model 900 Du Pont Thermal Analyzer. The fats were cooled from 60°C to 30°C/min at 5°C/min followed by cooling to 15°C/min at 3°C/min. The temperature of crystallization was taken as the temperature at the start of the exothermic crystallization deflection of the curve.

Fatty acid composition

Hardness

The fatty acid composition of the margarines and the liquid oil that was extracted from the chromatography paper at lOoC and 21°C were determined by transesterification and analysis of the methyl esters by gas liquid chromatography (GLC) (Shehata et al., 1970) using a Shimadzu GC-8A gas chromatograph with a 2 m column packed with 10070 SP-2330 on

A cone penetrometer was used for measuring the hardness of the samples after the samples were conditioned for 24 h at WOC or 21°C (AOCS method Cc 16-60). Penetration readings in 0.1 mm units were taken after the cone was allowed to penetrate into the samples for 5 s. The hardness index (g/mm) was calculated as follows (Hayakawa and deMan, 1982):

482 / Postmus et al.

Softening point and dropping point The softening points of the products and the dropping points of the separated fats were determined with the Mettler FP80 Central processor, using a heating rate of 1°C/min. For the determination of the dropping points, the fats were melted and then solidified in the cups at -woC for 1 h (Mertens and deMan, 1972).

Crystallization and melting characteristics

J. Inst.

CUll.

Sci. Technol. Alil1lelll. Vo!. 22, No. 5, 1989

Mass of cone assembly (= 92.5 g) (I)

H.I·

penetration depth (mm)

Statistical analysis To calculate significant differences between two rows of unpaired values, the Wilcoxon's signed rank test was used. Linear regression was carried out to calculate correlations between paired values (Steel and Torrie, 1980).

Results and Discussion Table 1 lists the fatty acid composition of the unhydrogenated oils and fats that were listed as ingredients on the labels of the margarines. In Canada, oils do not have to be specified except to indicate whether they are of animal or vegetable origin. Palm oil, coconut oil and cocoa butter at present have to be declared separately. Table 2 shows the 16:0, trans, total 16:0 + 18:0 + trans, and 18:2

Table I. Fatty acid composition of vegetable oils and animal fats used in samples (0J0). 16:0 18:0 18:1 18:2 18:3 58 26 10 Canola 4 2 Soybean 1I 4 24 54 7 Corn II 2 25 61 I 69 0 Sunflower 7 4 20 25 2 19 54 0 Cottonseed Palm 45 6 39 10 0 26 22 44 3 I Beef tallow I 26 13 28 2 2 Butter' I Also contain shorter chain fatty acids

content of the margarine fats. Saturated and trans fatty acids are listed together because the report of the ad hoc committee on the composition of special margarines of the Health Protection Branch (Davignon et al., 1980) has placed these fatty acids in the same category. The content of palmitoleic acid (16: 1) is very low in vegetable oils, therefore the 16:0 content does not change upon hydrogenation. For this reason oils in margarines can be identified by their 16:0 content. Since many canola margarines

Table 2. Saturated, Irans and 18:2 fatty acids in the original margarines and in the liquid oil at 10°C (0J0). Original margarine Sample 16:0 Irans 16:0 + 18:0 18:2 No. + Trans Canola 7.9 34.7 54.3 5.3 Al I. Man. 2.0 2. A2 Sask. 7.4 34.2 52.3 Man. 60.6 6.8 3. BI 8.9 45.0 4. B2 Sask. 7.5 33.1 50.5 2.9 4.0 5. Cl Sask. 9.0 44.1 59.4 6. DI Man. 5.7 34.9 50.4 2.4 48.0 3.1 7. El Ont. 4.6 35.2 8. FI Ont. 4.9 35.7 48.3 3.0 Soybean 9. 10. 11. 12. 13. 14. 15. 16.

Liquid oil at 10°C 16:0

18:2

6.0 5.3 6.8 6.4 6.6 5.5 4.1 4.2

6.7 6.4 8.8 6.2 9.8 5.7 5.3 10.5

10.4 10.6 10.4 10.2 10.1 11.5 10.7 10.5

25.2 29.1 28.3 27.9 23.2 30.1 28.5 22.4

43.9 46.9 46.2 45.9 41.8 49.0 46.7 41.6

22.0 19.2 18.3 19.6 28.0 16.4 19.5 29.3

8.8 9.3 8.4 8.5 9.3 8.4 6.9 8.5

28.4 25.6 26.5 27.4 36.7 17.6 19.0 39.8

Canola and/or Soybean 17. G3 Om. 18. H3 Om. 19. J2 Om.

10.7 9.9 8.6

41.6 31.9 31.4

57.2 49.0 46.8

4.6 15.3 12.5

7.4 8.3 6.2

13.4 17.4 17.4

Corn or Sunflower 20. MI' Nil 21. 22. 01 2

11.2 11.3 10.3

26.7 19.5 20.2

43.6 36.7 37.1

30.2 34.3 40.0

9.2 10.8 7.9

40.5 33.3 52.3

19.3 23.8

12.8 4.3

40.5 42.0

23.2 11.3

13.7 21.0

25.1 13.6

29.8 28.1 20.0

2.5 2.5 2.9

43.5 42.7 42.7

2.3 2.4 2.2

27.0 24.6 25.7

2.8 2.6 2.2

GI G2 HI H2 II JI KI Ll

CA NY CA NY CA NY NY NY

Ont. NY CA

Vegetable and Animal Fats 23. PI 3 NY Q4 24. NY Butter 25. RI Om. 26. SI Ont. 27. TI Ont. I corn 2sunflower and soybean 3butter and corn 4beef and cottonseed Call. 1J1!il. Food Sd. Tedmol. 1. Vol. 22, No. 5. 1989

Postmus

el

al. / 483

Fig. I. Polarized light photomicrographs of fat crystals in margarine with {3' polymorphic form (left) and {3 polymorphic form (right). One scale division = lO"m.

contain palm oil to stabilize their {3' crystallinity, the 16:0 content is increased from the original 4.5070 (Table 1). Usually the level of 16:0 in Canola margarines is not so high that it cannot be distinguished from soybean margarines which have 16:0 content of around 10.5%. However, on occasion this was not possible, therefore the margarines were divided as follows: canola (1 to 8); soybean (9 to 16); possible mixtures of canola and soybean (17 to 19); corn (20 and 21) and sunflower/soybean (22); and mixtures of vegetable and animal: butter and corn (23); and beef oil and cottonseed (24). Three samples of butter were included for comparison (25 to 27). The composition of the fatty acids of the canola margarines showed it to be the lowest in 16:0 and 18:2 content, the highest in trans and total 16:0, 18:0 plus trans (Table 2). The 16:0 content showed that with the exception of no. 7 and no. 8, canola margarines contained palm oil, because the 16:0 content was more than 4.5%. Taking palm oil to contain 45% of 16:0 (Table 1) the calculated additions of palm oil ranged from 3% in no. 6 to 11 % in no. 5. The labels of the soybean margarines indicated that no. 9, 10 and 15 might contain cottonseed oil, the remainder of the soybean margarines were labeled to contain liquid soybean oil. Judging again from the 16:0 content (Table 2), it is doubtful that any of the soybean margarines contained cottonseed oil (Table 1). As far as the addition of unhydrogenated soybean oil is concerned, only no. 16 contained appreciable amounts of 18:3 in the liquid part of the fat (4.0%). Lightly-hydrogenated oil, where the 18:3 has been reduced for oxidative stability reasons, can perhaps still be considered liquid. Although the 18:2 content of the soybean margarines was higher than that of the canola margarines, enzymatic analysis is required to establish the amount of essential fatty acids of the cis-cis-methylene interrupted 18:2 type. There is also a possibility that elevated quantities of trans-trans 18:2 fatty acids are present which have been reported as having negative health effects (Davignon et al., 1980). The trans determination by IR only measures 484 / Postmus et al.

the isolated trans acids. The fatty acids of the liquid fraction of the fat of the samples that were extracted from the chromatography paper at 10°C are also listed in Table 2. Statistical analyses indicated that the 16:0 content was significantly lower and the 18:2 content significantly higher in the liquid fraction as compared to that of the whole fat. This indicates that the 16:0 fatty acid is concentrated in the solid fraction. The diversity of fatty acid chain lengths is therefore greater in the solid fraction than in the liquid fraction of the original fat. There was no significant difference between the fatty acid composition of the liquid oil at 10°C and 21°C. X- ray diffraction showed the crystals of 4 of the 8 canola margarines to be in the {3 form (no. 1, 2, 7 and 8). As already mentioned, no. 7 and 8 did not contain any palm oil. Although both no. 1 and 2 contained palm oil, this did not prevent the polymorphic transition to the {3 form. Processing conditions, storage conditions and/or the addition of palm oil in the unhydrogenated form, which has been shown to be less effective than when palm oil is hydrogenated with the canola oil (Yap, 1988), may have caused the {3 crystal formation. Sorbitan tristearate which is also an inhibitor of polymorphic transition (Lee and deMan, 1984)~ was indicated on the labels of A, Band D as a possible ingredient. The presence of this substance was not investigated. Margarine no. 18 contained a mixture of {3 and {3' crystals. Figure 1 illustrates the difference in crystal size between a margarine containing {3' and one containing {3 crystals. Softening points of margarines, dropping points of the separated fat and the difference between the two are listed in Table 3. Softening points were higher than dropping points. Canola margarines that were in the {3 form showed the greatest difference between softening and dropping point (no 1, 2, 7 and 8) which ranged from 2.2 to 3.3°C. No. 24 consisted partly of a beef fat which often shows a mixture of {3 and {3' crystals (Timms, 1984). In the dropping point determination the fat is solidified at -10°C and consists of mixed crystals which are most likely to be in the {3' form. In the scraped surface heat exchanger during the processing of margarines, mixed crystals formed on the very cold surfaces are partially melted when mixed with the rest of the fat with the result that the higher melting portion of the mixed crystal is left. When {3' crystals after manufacture transform into {3 crystals the melting point rises again. A difference of more than 2.2°C between a softening and a dropping point would point to a potential polymorphic transition. Crystallization temperatures as determined by DSC (Table 3) indicated that those of canola margarines were significantly higher than those of all other margarines including those of butter. The higher crystallization temperature of canola margarines is undoubtedly related to their higher trans content. According to Ward (1988) this requires different parameters during manufacture than soybean margarines. J. Inst. Can. Sci. Technol. Alimellf. Vo!. 22, No. 5, 1989

Table 3. Softening points of products, dropping points and crystallation temperatures of separated fat (0C). Dropping Sample Softening Softening point point point minus dropping point

-No.

Canola I. 2. 3. 4. 5. 6. 7. 8.

Crystallization point

AI A2 BI B2 Cl DI El fl

Man. Sask. Man. Sask. Sask. Man. ant. ant.

36.8 37.0 34.1 36.3 35.4 35.1 36.7 36.0

34.6 34.5 32.3 34.5 33.2 34.2 33.7 32.7

2.2 2.5 1.8 1.8 2.2 .9 3.0 3.3

20.8 21.5 21.2 20.5 20.5 21.5 20.3 18.5

GI G2 HI H2 II Jl KI

CA NY CA NY CA NY NY NY

34.5 34.0 33.6 35.3 35.8 34.0 34.3 34.8

33.1 32.7 32.7 33.3 35.0 33.8 32.6 33.4

1.4 1.3 .9 2.0 .8 .2 1.7 1.4

18.7 16.3 17.7 17.0 19.0 18.4 15.5 15.3

ant. ant. ant.

32.2 34.2 34.9

31.5 33.5 34.3

.7 .7 .5

14.1 18.9 16.6

ant. NY CA

34.0 34.8 34.0

32.9 34.0 33.1

1.1 .8 .9

15.7 17.0 17.0

32.6 34.1

31.5 31.9

1.1 2.2

18.8 18.0

31.0 33.6 34.1

33.2 33.2 33.4

-2.2 .4 1.0

18.7 18.8 19.0

Soybean 9. 10. 11. 12. 13. 14. 15. 16.

Lt

Canola and Soybean 17. 18. 19.

G3 H3 J2

Corn or Sunflower 20. 21.

22.

MI I NIl 01 2

Vegetable and Animal fat PI 3 NY QI 4 NY

23. 24.

Butter 25. 26. 27. I

RI SI TI

ant. ant. ant.

corn

2sun flower

and soybean 3butter and corn -lbeef tallow and cottonseed

The rate at which the liquid oil rises in the filter paper (oil mobility) is listed in Table 4. The oil mobility was highest for the corn and sunflower/soybean margarines, most likely because of the incorporation of unhydrogenated oils. The animal fats showed the lowest oil mobility. Both the canola and soybean margarines exhibited a wide range. Results on oil mobility are very reproducible. Differences between five replicates are usually not more than I to 2 mm. Hardness index values at 10°C (Table 4) indicated that the corn and sunflower/soybean margarines were the softest. The hardness index values for the canola margarines ranged from 9.3 to 23.5 and those of the soybeans from 13.4 to 18.0. There was no significant difference between hardness index values of canola and soybean margarines. However, the range in hardness values for the canola margarines was much wider. Oil mobility and hardness index were also evaluated at 21°C. However, at this temperature the cone penetration test became unreliable because of Call. Ins!. Food Sci. TedlllOl. J. Vol. 22, No. 5, !9X9

the softness of the products. Some of the margarines oozed oil and therefore the oil mobility evaluation became unreliable. Testing at temperatures of 15°C instead of 21°C would have resulted in more meaningful values. The relationship between oil mobility and hardness index is plotted in Figure 2. The correlation between oil mobility and hardness for all samples was -.73. The same correlation for the vegetable oil margarines was -.80. The animal fat showed the greatest hardness index and lowest oil mobility. The consistency of butter no. 25 was exceptionally hard. Polarized light microscopy of butter 26 and 27 showed globular fat crystals, while those of no. 25 were needles with spherulites (deMan and Wood, 1959). Butter 25 was made by the Gold'n Flow process (Wood and deMan, 1958). Results of this study indicate that the quality of some canola stick margarines needs improvement. Greater stability of the crystal structure is required. Ward (1988) recommended incorporation of at least 10llJo palm oil in stick margarines. Higher amounts Postmus et al. / 485

..

Table 4. Oil Mobility and Hardness Index at 10 0 e. No.

Sample

Oil Mobility (mm)

Hardness Index (g/mm)

o o

•

sov4:>e ..n

•

corn

Canola I.

2. 3. 4. 5. 6. 7. 8.

Al A2 BI B2 Cl Dl El Fl

Man. Sask. Man. Sask. Sask. Man. Onto Ont.

22.3 13.9 8.1 14.9 14.0 8.7 11.4 13.4

9.3 23.5 18.1 19.7 16.6 15.2 20.0 14.6

GI G2 HI H2 11 11 KI L1

CA NY CA NY CA NY NY NY

15.8 20.0 12.7 13.2 16.7 9.2 22.8 23.4

14.3 15.9 18.0 17.3 15.4 17.9 13.4 12.7

11.4 13.6 20.7

14.8 14.4 10.7

26.8 32.0 25.0

10.1 10.5 11.7

o

,

.

'5

o

o

~

•

Soybean 9. 10. 11. 12. 13. 14. 15. 16.

Mixtures of Canola and Soybean 17. 18. 19.

G3 H3 J2

Ont. Ont. Onto

Corn or Sunflower 20. 21. 22

MI 1 Nil 01 2

Ont. NY CA

Mixtures of Vegetable and Animal Fats 23. 24.

PI 3 QI 4

NY NY

10.2 4.2

28.9 40.2

RI SI

Ont. Ont. Onto

5.7 4.4 6.5

43.8 25.8 29.9

Butters 25. 26. 27.

Tt

I

corn 2sun flower and soybean 3butter and corn 4beef and cotton seed

of palm oil, especially when slightly hydrogenated, may permit softer canola hardstocks that contain less saturated and more unsaturated fatty acids. The possibility exists that unhydrogenated canola oil could be incorporated. Chrysam (1985) has stated that {3 tendencies are related to the diversity of the highest melting portion of the fat and not necessarily to that of the whole fat. Our future research will therefore concentrate on the highest melting fraction of the solid fat. Attempts will be made to predict (3' stability of canola hardstocks by incorporation of a suitable palm oil with or without surfactants.

Acknowledgements Financial support was provided by the Natural Sciences and Engineering Research Council of Canada. B. Blackman performed the fatty acid analyses.

References AOCS. 1981. Official and Tentative Methods of the American Oil Chemists' Society. Vol. I. Champaign, IL.

486 / Postmus et al.

I

Oil

7 ~iJlty

<.-/24 ...... )

Fig. 2. Relationship between oil mobility and hardness index of margarines.

Chrysam, M. 1985. Table spreads and shortening. In: Bailey's Industrial Oil and Fat Products. Vol. 3. T. Applewhite, (Ed.). pp 54-86. Wiley Interscience, NY Davignon, J., Holub, B., Little, J.A., McDonald, B.E. and Spence, M. 1980. Report of the ad-hoc committee on the composition of special margarines. Minister of Supply and Services Canada Cat. no. H44-46/1980E. deMan, J.M. and Wood, F.W. 1959. Polarized light microscopy of butter fat crystallization. Proceedings of XV Intern. Dairy Congress 2: 1010. deMan, J .M. 1978. Crystallization behaviour of hydrogenated rapeseed oil. Can. Inst. Food Sci. Technol. J. 11:195. deMan, J.M., Dobbs, J.E. and Sherman, P. 1979. Spreadability of butter and margarine. In: Food Texture and Rheology. P. Sherman (Ed.). p. 45. Academic Press, London. Haighton, A.J. 1976. Blending, chilling and tempering of margarines and shortenings. J. Am. Oil Chem. Soc. 53:397. Hayakawa, M. and deMan, J.M. 1982. Interpretation of cone penetrometer consistency measurements of fats. J. Texture Stud. 13:201. Lee, S. and deMan, J .M. 1984. Effect of surfactants on the polymorphic behaviour of hydrogenated canola oil. Fette Seifen Anstrichm. 86:460. Mertens, W. and deMan, J.M. 1972. Automatic melting point determination of fats. J. Am. Oil Chem. Soc. 49:366. Naguib-Mostafa, A. and deMan, J.M. 1985. Polymorphism of hydrogenated canola oil. J. Am. Oil Chem. Soc. 62:756. Shehata, A.A.Y., deMan, J.M. and Alexander, J.e. 1970. A simple and rapid method for the preparation of methyl esters of fats in milligram amounts for gas chromatography. Can. Inst. Food Sci. Technol. J. 3:85. Steel, R.G.D. and Torrie, J.H. 1980. Principles and Procedures of Statistics: A biometrical approach. 2nd ed. McGrawHill, NY. Timms, R.E. 1984. Phase behaviour of fats and their mixtures. In: Progress in Lipid Research. 23:1-35. R.T. Holman (Ed.). Pergamon Press, Oxford. Ward, J. 1988. Processing canola oil products. J. Am. Oil Chem. Soc. 65:1731. Wiedermann, L.H. 1978. Margarine and margarine oil. Formulation and control. J. Am. Oil Chem. Soc. 55:823. Wood, F.W. and deMan, J.M. 1958. Some observations on the physical structure of butter manufactured by the Gold'n Flow process. Proc. of the XIV Int. Dairy Congress. 2:3. Yap, P.H. 1988. Polymorphism of palm oil and the effect of addition of palm oil on the polymorphic properties of hydrogenated canola oil. M.Sc. thesis. University of Guelph. Guelph, Ont. Submitted February 25, 1989 Revised July 14, 1989 Accepted July 14, 1989

1. Ins£. COli. Sci. Technol. Aliment. Vol. 22. No. 5. 1989