Food Structure

Volume 7 Number 2 Article 8

1988

Microstructure of Shortenings, Margarine and Butter - A Review

A. C. Juriaanse

I. Heertje

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Recommended Citation Juriaanse, A. C. and Heertje, I. (1988) "Microstructure of Shortenings, Margarine and Butter - A Review," Food Structure: Vol. 7 : No. 2 , Article 8. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol7/iss2/8

This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Food Structure by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. FOOD MICROSTRUCTURE, Vol. 7 (1988), pp. 181 - 188 0 730 - 5419/8 8$3.0 0+. 00 Scanning Mic roscopy International, Chic ago (AMF O'Hare). IL 60666 USA

MICROSTRUCTURE OF SHORTEN INGS, MARGARI NE AND BUTTER - A REVIEW

A.C. Juriaanse and I. Heertje

Unilever Research Laboratorium P . O. Box 114 3130 AC Vlaardingen, The Netherlands

Abstract Introduction

Fat spreads are composed of liquid oil, fat Microstructural studies in the area of fats and c rystals and water. The fat crystals in these prod­ fat- based spreads are becoming increasingly impor­ uc ts give the product the requi red consist ency and t ant. Both the dairy and margarine industries are stab ilize the water droplets. Shortenings are water­ r ealizing the import ance of these studies, since with free produc ts, the rheology of whic h depends on the the knowle dge of the produc t microstructure, a be t ­ solid fat content and interactions between fat crys­ ter understanding of the produc t properties and ways tals. Size and interaction between c rystals i s influ ­ to influence these can be obtained. Initial researc h enced by both composition and processing. Crystals focussed on properties lik e crystal modification and form a three- dimensional network. Recrystallization overall product properties, such as product rheology . phenomena, especially formation of large beta- crys­ More recently, the use of new techniques such as tals , can create product defects like sandiness. Mar­ electron microscopy (EM) in combination with well garines and halvarines are water- in - oil emulsions and established knowledge of margarines and butter has have a relatively simple product s truc ture. Because led t o a signifi cant improved understanding of of the wettability of fat crystals, part of the solids s tructures and their effect on produc t properties . are present in the water/ oil interface, and influence From a microstructural point of view, essential ­ the s t ability of the emulsion. Depe nding on the type ly three different structure- t ypes can be distin ­ of a pplication, tr·opical margarines, table margarines, gu ished: s hortenings (100 % fat) , margarines and halv­ halvarines, puff- pastry, c ream ing margarines, etc. , ar ines (80 and 60 % fat r espectively), and butter (80% the ratio of solidlliquid and water content c an be fat). Both composition and processing can be u sed varied. No essential differences exist in the micro­ to influe nce the product microstructure. Margarine structure of products for different applications. But­ and s hortenings not only can be composed of a rela­ ter differs in its microstructure from margarines be­ tively wide range of triacylglycerols but also the cause of different processing and raw materials. aqueous phase may contain different ingredients. Butter still contains a number of fat globules (de­ The composition of butter is much less subject to rived from the cream) in its final product structure. change: the only compositional changes result from These globules are dispersed in a ma trix of fat c rys ­ c hanges in the milk composition due to, e.g. , barn I tals and oil desce nding from fat globules that were pasture feeding, level of underfeeding, s tage of lac ­ broken during c hurning. Also the moisture is pre­ tation , breed of cattle, e t c. Consequently differences sent in different forms ranging from droplets to in butter microstruc ture often r esult from changes in "free moisture". Differences in microstruc ture can processing. For margarines and shortenings the be introduced by different processing regimes. many degrees of freedom has le d to a diversification of p roducts of 100 to 40 % fat, from soft high poly ­ unsaturated fa tty acids to hard puff- pastry products . The present paper reviews the literature on the microstructure of fat spreads. Micrographs used to illustrate the microstructure of fat spreads have been obtained from the investigations by the authors. Initial paper received September 20, 1988 Manuscript received November 30, 1988 Structural element s Direct inquiries to I. Heertje Telephone number: 31 10 4605513 Fat c rystals The formation of texture in spreads is the re­ sult of crystallization of triacylglycerols with high melting points. The crystals do not behave as single Key words: Fat s preads, short ening, butter, fat crystals, but show different types of aggregation crystals, crystal network , fat globule, water dropl et, with formation of a three- dimensional fat crystal air, microstructure, electron microscopy network. The strength of this network is influenced by many compositional and processing parameters (6) . Triacylglycerols crystallize in four different modifications: sub-a , a , 6 1 and B (8). The first two

181 A .C. Ju rioanse and I. Heertje modifications, sub-o. and a , are unstable and there­ i.e . , do re- form after rupture. fOI'e do not ex ist in spreads. The 8' modification is Prima r y bonds are c onsidered to be res ponsible stable but its crystal lattice is less well ordered than for the hardness of p1·oducts, whereas secondary the 8 modification. Of all modifications the 8 bonds contribute little to con sis tency . modification has the highest ordering and conse­ In other works (21) such a distinction between quently the highest melting point. In mos t spreads primary and secondary bonds is consider ed to be ar­ d iffe r ent r aw materials are blended to arrive at the bit,•ary and it is suggested that a t1'U e characteriza­ desit•ed overall crystallization and me lting behaviour. tion s hould be based on the concept of a spectrum As a conseque nce the triacylglycerol composition of of bond s tre ngths. In margarine, weak bonds form the blends is rather complicated. This implies that only a minor proportion of the bond s tre ng th spec­ in spreads the 8 modification does not occur very trum, s trong bonds form the major• part . Butter on often; the 8' modification is the predomina nt one. the other hand c ontains a small proportion of s trong Put cryst als can be e ither needles (Fig. 1) or pl a te ­ bonds. lets. The 8 modification is frequently correl a ted Microstruc tural observations of ne twork s truc ­ with structural defects: large 8 crystals are perceived tures substantiate suc h a concept ( 7 , this work). as sandiness (1) (Fig. 2). Water droplets Fat globules Margarmes and butter roughly contain 16 - 20% Fat globules as found in butter (Fig. 3) (14) water, which i s present in the structure as finely originate from the cream. Prior to the churn ing dispersed droplets. An impression of t he s t atus of process, the cream is physically ripened (i.e., the the water droplets in spreads can be obtained by cream is cooled to such an extent that fat crystalli ­ u s ing freeze- fracture as the sample preparation zation in the oil droplets occurs). Depending on t echnique for EM observation. their s trength these fat globules will survive the Fig. 6 shows the result of this technique for a churning process ( 19) _ fa t s pread, indicating tha t the sample fractures ei­ The fat g lobule in cream i s covered with a fat ther over the surface of the water droplets, or that g lobule membrane, whereas in butter parts of the cross frac ture of the droplet occurs. Because of membrane may be removed as a result of churning. the ir wettability fat crystals can b e found in the The outside of this membrane i s a hydrophilic, prote ­ 0 / W interface, which s tabilizes the water droplets inaceous layer of complex composition (14) (Fig. 4)_ (17). This stabilizing action of the fat crystals The periphery of the globule is formed by an appro­ s trongly depends on the presence of surface- active ximately 0. 1 - 0.5 \J ill thic k c rys tall ine s he ll (15). ingredients like monoacylglycerol s , phospholipids and Different opinions ex is t about whether this c rys tal ­ proteins ( 9) . line s hel l is com posed of high melting 8 c rys tal s (15, Emul s ify ing systems a pplie d in spreads usually 18), whic h concentra te in the oil / water (0 / W) int et•­ are based on monoacylg lycerols and lecithins (11). face as u t·c sult of ripe ning conditions and cryst al ­ Only in produc t s for other (e.g. bakery) applications lizatio n at the interface (2). Alte rnatively a s hell sometimes other s urfoc tants are u sed. Milk protein would rcsul t cryst al s tha t a re formed r andomly in (0 / W emulsifiers), as present in the aqueou s phase of the oil droplet during ripening and s ubsequently spreads, t e nd to destabilize the emulsion. Water transported to the 0 / W interface as a result of droplets in spreads should be kept small (preferably deformation during churning (24). The overage < 5 ~ m) to reduce microbiolog ical risks (22, 23)­ diameter of globules in butter i s 3 IJ m. Small droplets induce a g reasy t aste (see ref. 8, page Ne twork s 22 1). ----v8tSpreads derive their c onsist e ncy from inter­ Air action s between fat crystal s which form a three di ­ In some products (shortenings and margarines) men s ional network (Fig. Sa and 5b). The nature of air is introduced to influence eithe1• con sist ency ( 4, the interactions between the fat crystals determines 12} or appearance. Air usually is e ntrapped in the the t ype of network s truc ture and the rheology of liquid oil phase of a spread. Small c r yst als have the product. Quite a number of publications deal been described to orientate tangentially to the sur­ with rheological properties of fat spreads (for a face {1). It is not c lear whether t hese fat cryst als r eview see reference 3). have a stabilizing effec t on the a ir bubbles. After Many aspects are related to the amount and the c hurning, a similar type of arrangement is observed nature of the inte raction between fat c rystals (6): in fa t globules of butter (14). Under polarized light - the hardness of a spread depen ds on the amount a b it·efringent layer is observe d , also ascribed to of fat crystals; tangent ially oriented fat c rys tals in the outer layers - b lend compos ition wil l influence the molecular arrangement in c rystals and thus the strength Fig. 1. Typical example of fat crystals (freeze­ of interactions between crystals; frac ture). - s lowly c rystallizing blends will continue to Fig._2. Spherulites in S-cryst al modification, i solated c rys tallize aft er packaging, which favors the rroffia fat spread, induc ing sandiness. forma tion of a strong network; 3 1 - hig h cryst allization speeds give rise to soft and i~f· TheE~;::~ersy~~a~l{~! ~ ~~~r :t::ci:;:ei~ t i~~~~~~ ovcn'Jorked produc t s . by r emoving the oil from the ins ide of the g lobule Two types of bonds are assumed for crystal - during t he preparation procedure (reference 7). cryst al interaction s (5): Fig. 4 . Example of a cross- fractured butter globule. primary bonds, which result from crystals grow ­ Orientation of fat crystals parallel to the droplet ing together at some points. These bonds ar e surface (arrow 1); traces of r ema ining water around "irreversible", i.e . , do not re- form after rupture; the droplet (arrow 2). - secondary bonds , which are (w eak ) London­ ~- · Three dimensional n etworks of fat crystals Van der Wa lls forces, which are "rever s ible", m a shortening at (a) low and (b) high magnification.

182 Mic rostruc ture of Shorte nings, Margarine and Butte r

183 A.C. Juriaanse and I. Heertje of the fat globules and induced by pressure exerted crystals. DP.pending on the type of product, more or by air during churning. less solids are applied. Over the last two decades Air is present in products in all shapes (Fig. 7), the fats industry has diversified the margarine area from round bubbles to strongly deformed areas, de­ into products aimed at specific applications such as pending on the way it has been introduced into the margarine for tropical countries, halvarines, and product. Smooth round air bubbles are found when products for bakery applications like creaming, cake­ introduc tion is done at low solids levels, e.g., during mak ing and puff- pastry products. whipping of margarines or shortenings in cake prepa­ In halvarines essentially the same microstruc­ ration. Strongly deformed a ir bubbles are found ture is found as in margarines: only the ratio water when high solid contents are present a t the moment droplets/fat/oil is different. In puff- pastry a finer of air introduction, e .g., during processing or churn ­ crystal structure is preferred to a coarse crystal ing. In butter some air (approximately 5 %) is still structure (10, 11). The finer crystal structure was present as a result of the churning process (14) (Fig. found to give a better performance in pastry prepar­ 8). ation while the pastry margarine itself showed less Product structure work softening. Butter Shortenings --In butter a limited number of milk fat globules Due to their composition s hortenings have the are still present in the final product. The number of simplest product s truc ture of all fat spr eads. These fat globules that survive processing strongly depends products are composed of liquid oil and fat crystals on the ripening procedure of the cream (19,20) and only . Blending different oil s offers a wide range of on the working condition s during and after proces­ solid/liquid ratios. Fat crystals usually take the s ing (20): Cold -warm-cold (CWC) ripening procedures shape of needles or platelets. give stable globules with thick surface crystal layers The existence of a three- dimensional network of of high melting triacylg lycerols, while the interior of fat c rys tal s has been postulated for many years (5). the globule contains crystal aggregates and liquid oil. but only recently sample preparation techniques have A large number of these globules sur-vive processing developed (7) that could demonstrate the existence of in contrast to globules formed during "cold-ripening" such a network. The nature of the network s truc­ (19) which are less stable and break during ture wiU depend on both composition and processing processing (Fig. 12). conditions . In particular, the extent to which indi­ Intensive working destroys fat globules r esulting vidual crystals aggregate, determines the character of in a more crystalline interglobular phase and conse­ the observed network. As an example of this, Fig. 9 quently a harder consistency. A combination of "C­ shows the microstructure of two shortenings of the ripening" and intensive working is applied in the same composition. The only difference is found in production of summer butter. Winter butter is pro­ the processing condition. duced by applying a ewe- ripening (20) . For some applications air- containing shortenings The interglobular phase in butter is a mixture are produced. The presence of air does not princi­ of liquid oil, crystal aggregates and membrane resi­ pally affect the cryst al-crystal interactions in the dues. In fresh butter the crystals are slightly crystal network but it does reduce the number of c urved and sometimes arrange in groups with parallel cryst als per unit of volume. The product hardness orientation . The liquid phase often contains ordered {g/cm2) decreases with increasing air contents (5). structures which are not as distinctly differentiated At higher levels of air, brittleness may occur (4). from amorphous areas as real crystals. Possibly they Tempering, i.e., storage above ambient for a few represent liquid crystals (16). After 10 days storage days (5) is sometimes applied for s hortenings. Dur­ of fresh butter an increase of uncurved newly formed ing this process recrystallization takes p lace in crystals is observed. This phenomenon is thought to whic h mixed crystals (as formed during fast c rystal ­ be related to the setting and hardening of butter lization in a votator) "demix" and form other more (16}. s table crystals. This generally leads to larger crystals and a slightly softer products. Fig. 6. Water droplets in fat spreads. The freeze f'riiCfUre technique gives r ise to two different images Marga{/:: s hortening, margarine derives its con s ist­ of water droplets depending on whether the sampl e ency from a fat crystal network. No essential dif­ breaks (S) over the surface of the droplet or (C) ferences in fat crystal network are found on compar­ whether cross- fracture occurs "through" the droplet. ing these two types of products. The most striking difference in s tructure is the presence of water ~-· Example of air cells in a shortening. Air droplets in margarine. Water droplet s of a few \.l ffi ~during votator processing. are formed during intensive mixing of fat and water phase during processing. In this process crystals can Fig. 8. Air cell in a churned product. (g) fat glob­ orientate at the water droplet surface. ule; (w) water. The air interface is covered with fat In margarines 11 shells" of fat crystals can be globules. found ( 7) (Fig. 10) that surround the water droplets. These "shells" seem to be interconnected with the Fig. 9. Partial c rystallization in rest shows a struc­ three- dimensional fat crystal network. ture of interconnected c r ystal clu s ters (a), whereas The water droplet size distribution can be in­ complete crystallization in a votatorline shows a fluenced by processing: intensive shear during pro­ structure of connected plate- like crystals (b). cessing results in a finer emulsion (Fig. 11). The main difference in microstructure found in all 80% Fig. 10. Fat crystalline network (f) and water drop­ fat products is the nature of the fat crystalline net­ let structure (w) showing a crystalline shell, in a work, e.g., the s ize, shape, and aggregation of fat margarine.

184 Mic rostruc ture of Shortenings, Ma rgarine and Butte r

185 A.C. Juriaanse and I. Heertje

The e mul s ion structure of butter has been a (ed.). Academic Press, 471 - 497. subject of much debate, especially the water continu­ 2. Buchheim \Y, Prec ht 0 (1979). Elektronen­ ity of the product (13,14). At the start of butter mikroskopische Untersuchung der Kristallisations ­ production, water is the continuous phase. During vorgl!nge in den FettkiJgelchen w!l.hrend der Rahm­ churning and subsequent working, the fat phase b e ­ reifung. Milchwissenschaft 34, 657 - 662. comes the continuous phase. By more intensive 3. De Man JM (1983)-:- Consistency of fats: A working, the water becomes more finely dispersed in review . J . Am. Oil Chern. Soc. 60, 82 - 87. the product . Nevertheless, in contrast to margarine, 4. Gupta S, De Man JM (il85). Modification water continuity in butter i s s till observed. It has of rheological properties of butter. Milchwissenschaft been proposed by Mulder (13) that the water con ­ 40 , 321-325. taining membranes of many fat globules lie so c lose - 5. Haighton AJ ( 1963). Die Konsistenz von to water droplets that a pathway is offered for Margarine und Fetten. Fette Seifen Anstrichm . ~. transport of water molecules (water channels). This 479 - 482 . type of structural arrangement can indeed be ob­ 6. Haighton AJ (1976) . Blending, chilling, served by freeze fracture EM (Fig. 13), although and tempering of margarines and shortenings. J. Am. water, as such, cannot be detected. Oil Chern . Soc . 53, 397 - 399. Water droplets in the final products have sizes 7. Heertje I, Leunis M, van Ze ijl WJM, between 0.25 and 25 l! m. Occasionally small fat Berends E ( 1987) . Product morphology of fatty globul es are incorporated in the water phase (17) . products. Food Microstruct. 6, 1-8 . The presence of fat crystal s around the water drop­ 8. Larsson K (1986) . - Physical properties­ lets in butter is a matter of some debate. A dense s truc tural and physical characteristics. In Lipid surface coverage with high melting butterfat crystals Handbook , Gunstone FD, Harwood JL, Padley FB has been reported ( 17}. In other work such a s hell (eds . ). Chapman and Hall, London. formation was not observed (7). 9. Lu cassen-Reijnders EH, Tempel M van den (1963}. Stabilization of water- in-oil emulsions by Conclusions solid particles. J. Phys. Chern. 67, 731 - 734. 10 . Madsen J, Als G ( 1971). Konsistenz und Fat spreads have a microstructure composed of Kristalltechnische VerhH.Itnisse bei der Herstellung liquid oil, fat crystals, water droplets and sometimes von Ziehmargarine auf Druckkfihlern und air . A wide variety in ingredients and processes Ktlhltrommeln. Fette Seifen Anstrichm. 73, 405-410. influences the product s tructure: 11. Madsen J (1987). Emulsifiir"s u sed in - the fat composit ion determines the amount of margarine, low calorie spread, shortening, bakery fat crystals, the s peed of crystallization, as well compound and filling. Fett Wiss. Technol. Fat Sci. as the s ize, the s hape and the aggregation of Techno!. 89, 165-172. the individual crystals into a network. 12. 1\iassiello FJ (1978) . Changing trends in - water and water- phase ingredients are emu lsi ­ con sumer margarines. J. Am. Oil Chern. Soc. 55, 262 - fi ed in the fat continuous matt•ix. Some of the 265. - water- soluble ingredient s, such as milk proteins 13 . Mulder M (1957). The presence of mois ­ (0 /W emulsifiers}. affect the emuls ion stability ture in butter. Neth. Milk Dairy J . 11 , 25-42. and consequently the efficiency of emulsifi ca­ 14. Mulder H, Walstra P (1974}.-Structure and tion of the water in the product; texture of butter. In: The milk fat globule. Emulsion - emulsifiers also affect the network s tructure science as applied to milk products and comparable a nd the emulsion s tability during and after foods. Pudoc, Wageningen, 246-287. processing; 15. Precht D, Buchheim W (L979). Elektronen­ - processing is another instrument to manipul at e mikroskopische Untersuchungen Ub e r die physikalische crystallization and emulsifi cation conditions such Struktur von Streichfetten. I. Di e l\1ikrostruktur der that the desired product properties are obtain­ Fettkfigelchen in Butter. Milchwissen schaft 34, 745- ed. It is c lear that these conditions stron gl y 749. - affect s tructural parameters, such as crystal 16. Precht D, Buchheim W (1980). Elektronen­ size, crystal-crystal interactions , network mikroskopische Untersuchungen fib er die physikalische formation, and emul sion stability; Struktur von Streichfetten. II. Die Mikrostruktur der - finally, storage can induce changes in product zwischenglobulliren Fe ttphase in Butter. Milchwissen­ structure, e.g., as a result of recrystallization . schaft 35, 393 -398. Recent developments, especially in the area of 11-:- Precht D, Buc hheim W (1980). Elektronen­ electron microscopy, have led to a major increase in mikroskopische Untersuchungen fib er die physikalische our understanding of the structure of fat spreads. Struktur von Streichfetten. 3. Die wllssrige phase in Hypotheses regarding network formation and distribu­ der Butter. Milchwissenschaft 35, 684 - 690. tion of water in various spreads, as they were postu­ 18. Precht D (1980). Untersuchungen fiber die la ted in the past. have b een subs tantiated. The Kristallstruktur und den molekularen Aufbau der chall enge for the future lies in relating composition Fe:tphase von Butter. Fe tte Seifen Anstrichm . 82, and processing variables to changes in product struc ­ 142 - 147. - ture. i.e. , network structure, fat c rys tals, cream 19. Precht D, Peters K- H (1981). Die Konsist­ globules, air cells, water droplets, and s hell struc­ enz der Butter. I. Elektronenmikroskopische Unter­ ture. suchungen zum EinOuss unterschiedlicher Rahmreif­ ungstemperaturen auf die H!l.ufigkeit bestimmter Fett­ References ki.lgelchentypen im Rahm. Milchwissenschaft 36, 616- UO. - 1. Berger KG, Jewell GG, Pollitt RJ M (1979). Oils and Fats. In: Food Microscopy, Vaughan JG

186 Mi c rostruc ture of Shortenings , Margarine and Butter

~- Differe nces in water droplet size distribu ­ tion m margarine as a result of: (a) low and, (b) high shear during processing.

~ - Differences in the survival of fat globules m butter as a result of differences in the ripening procedure in the cream prior to churning. (a) ewe- ripened cram; (b) e - ripened cream.

~. Freeze- fracture micrograph of butter showmg membranes of fat globules in c lose contact with water droplets. Arrow indicates position of deformation of the globule surface. (w) Wat er droplet; (F) fat globule.

187 A.C. Juriaanse and I. Heertje

20. Precht D, Peters K- H {1981). Di e Konsist­ Authors: In our opinion s hell formation around enz d e r Butte r . II. Zusammenh!lnge zwischen der sub­ ~roplets is not the same in different products. mikros kopisc hen Struktur von Rahmfe ttk11ge lc hen It can vary between a c lear s hell and the mere en­ sowie Butte r und der Konsistenz in Abhltngigke it von trapment of the water in the c ontinuous fat matrix, spezie llen physikalischen Rahmreifungsverfahren. without a clear shell s tructure. In butter (text Milc hwissenschaft 36, 673 - 676. reference 7) , as well as in some other products. the 21. Shama F,Sherman P (1970). The influe nce latter structure is predominant. of work softe ning on the viscoelas tic properties of It cannot be excluded that freeze -fracture butter and margarine. J. Texture Stud. l, 196- 205 . techniques when applied to products conta ining oil, 22. Verrips CT , Zaalberg J (1980). The intrin­ may lead to e rroneous r e sults. Al so in fat systems, s ic microbial s tability of water- in-oil emuls ions. I. freezing v elocity appears to be very c ritical . We Theory. Eur. J. Appl. Mic robiol. Biotechnol. 10, 187- found that emul s ifiers play an important role in s hell 196. - formation, but certainly other aspects, such as pro­ 23. Verrips CT , Smid D, Kerkhof A (1980). cessing conditions, must also b e consider e d. Working The intrinsic microbial stability of water - in-oil may enhance the possibility for transport of fat emulsions. II. Experimental . Eur. J. Appl. Microbial. crystals to the oil / water interface (Heertje et al., Biotechnol. 10, 73 -85. this issue). Such a mec hanism would , however, not 24. Wrustra P (1974). High-melting triglyceri­ be valid during c hurning in the normal processing of des in the fat globule membrane: an artefact! Neth. butter by phase inversion. Also from this bac k ­ Milk Da iry J . ~· 3-9. ground prominent shell formation in butter is not very likely. Discussion with Reviewers D.P. Dylews ki: In your opinion how would a c lose D. Precht: Is the r e c lear evidence that only the S' ­ linkage of microscopy, rheology, and sensory help in and a - form s are present in spreads or could also less the formulation and processing of n ew oil-based s table forms like the o. - form exist due to certain products? temp erature treatments (e .g. , rapid c ooling)? Authors: Examples of how microstructure, rheology Authors : By X-ray diffraction techniques it i s s hown and product properties are related have been given that, under normal storage conditions, indeed only in this paper and other articles from our laboratory the S' - and a- modifications are present. During (e.g., see text r e ference 7; and Heertje et al., the processing, how ever, under c onditions of s trong article following this paper in this issue ). In this cooling, first the a - modification is formed, whic h is c ontext, it should be mentioned how: in general rapidly c onverted to the 6' - modification. - the nature of the network s truc ture (e .g., Preservation of a -modification would require the continuous ver su s granular) influences the use of low temperature and storage of the product hardness of a produc t; below the melting points of the mo s t abundant n­ - the emulsion s truc ture influences other sen sorial forms , i.e., below 0° C . prope rties. By delibe rately manipulating the s truc ture by D. Precht and W. Bu chheim: According to ou r own the applied processing, it will be possible to induce observattons the accumulations of fat crystal s around desired produc t properties. the water droplets of butter, margarine, and low- fat da iry and non- dairy spreads is s imila r , despite s trongly varying amounts of surface- active lipids in these products . Could there be another driving force be hind this separation process than the one t hat the authors have me ntioned?

188