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ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 21, 2013

Thermal Influence on Rheological Characteristics of Butter and during Distribution, Storage and Use

Elling- Olav Rukke1, Carlos Salas-Bringas2, Roger K. Abrahamsen1, Ellen Skuterud1 and Reidar Barfod Schüller1 1Dept. of Chemistry, Biotechnology and , Norwegian University of Life Sciences, P.O.Box 5003, N-1432 Ås, Norway. 2Dept. of Mathematical Sciences and Technology, Norwegian University of Life Sciences, P.O.Box 5003, N-1432 Ås, Norway.

ABSTRACT margarine (80% and ) and Investigation of thermal behavior of spreads (40% ) became firmer by systems are essential in order to repeated ”heating and cooling” in a understand changes when the systems are temperature range between 4°C and 20°C exposed to different temperature cycles 1,2. during storage and use. In fat , From a theoretical point of view it was like butter and margarine, the amount of expected that the firmness of butter, would crystallized fat is greatly dependent on increase considerably beyond the original temperature, and so is the firmness. Even at level, due to temperature increase followed constant temperature, a slow recrystalization by subsequent cooling to original may occur since the fat crystals in such temperature3. This was not confirmed in the products seldom are in thermodynamic previous studies, partly related to the equilibrium. A slight temperature increase holding time at 20 oC. fat is partially often causes some melting of the fat solid at temperatures between approximately crystals. Upon subsequent slight cooling, 5 and 25oC, and its consistency is caused by newly formed crystals will deposit on the presence of a network of fat crystals in existing crystals, often referred to as liquid fat4. In another study5, the solid fat “sintering”. Consequently, the fat product contents of butter at different temperatures may markedly increase in firmness due to between 0 to 35°C were determined by small temperature fluctuations during pulsed nuclear magnetic resonance. Table 1 storage. summarize these findings for salted types of A Texture Profile Analyzer (Stable Micro butter5,6 and for a typical soft table Systems, UK, 1998) was used to measure margarine. rheological changes in firmness of the tested spreads caused by changes of the storage Table 1. Solid fat content (%) of butter*5 temperatures. The measurement equipment and soft table margarine**6 at different was feasible for the purpose. temperatures. 5°C 10°C 15°C 20°C 25°C 30°C INTRODUCTION 63* 56* 40* 22* 12* 5* In two previous studies, it was 28** 14** 3** investigated if butter (80 % milk fat),

179 In general the structure of products with migration of small crystals are ongoing. a continuous face of fat or , such as butter Crystal growth during post-crystallization and margarine, is based on a network of may sometimes lead to formation of solid crystalline particles. The nature of this bridges (sintering) in narrow gaps of fat crystal network can be dramatically altered crystal networks. Such fat crystal bonds are by changes in crystallization conditions7 ; divided into primary bonds (solid bridges), for example by changes in the temperature which are very strong and dissociate up on of the product. Accurate data for thermal mechanical work. Secondary bonds are properties of butter is a prerequisite for the much weaker12. Such sintering has been prediction of thermal behavior of food under mentioned in the literature, but less studied industrial conditions. extensively. Crystallization of water-in-oil emulsions A model that can be used to describe the is a complex process which is influenced formation and interaction among structural for instance by composition of the emulsion, elements that affect the macroscopic temperature treatment and state of properties of fat crystal network, is shown in dispersion of the fat. The fact that lipids Fig. 1. exhibit polymorphism8 is another incident that contributes to the complexity of fat crystals and their rheological behaviour. Crystal polymorphism is of fundamental importance for final product consistency and acceptability. By cooling anhydrous milk fat at different cooling rates from 60 oC to - 10 oC, it was found that the crystallized in 4 different polymorphic subcell types; sub-α, α, β´, and β with some reversible and some irreversible transitions9. Regarding butter, both polymorphism and rheology are largely determined by the treatment of the prior to the butter manufacturing. Slow and fast cooling of the Figure 1. Model describing factors with cream may result in similar rheological strong- and potential influence, properties and polymorphic forms, α,- and 10 affecting macroscopic properties of fat β´-crystals , but different microstructure . crystal network13. In addition this is further complicated by formation of mixed crystals. Mixed crystals This model suggests that lipid form when different kind of molecules are 11 composition, directly under influence of incorporated into the lattice of one crystal . storage conditions, will affect the solid fat After production, different content, polymorphism and microstructure crystallization processes proceed in semi- of a fat crystal network13. The model also solid fat products that consist of solid suggest that interactions among these factors crystals dispersed in a liquid oil. These post- play an important role, since they affect the crystallization processes include nucleation structure of the fat crystal network, and in of new crystals and crystal growth; so-called turn influence physical properties and Ostwald ripening which mean dissolution of sensory perception of the fat product. small crystals and growth of big ones. In composition of fats and addition polymorphic transformation (a their solubility has also been studied. property that gives rise to various Solubility of fats in has for aggregation of lipids), migration of oil, and

180 instance been calculated as a function of MATERIALS AND METHODS temperature12: Butter and margarine samples HM 11  (  ) Butter and margarine were purchased TmTR M  eX (1) from a local retailer in 500 grams wrapped packages according to Table 1. The samples where XM is the dissolved mole fraction, of each type of were from the same ∆HM the enthalpy, R the gas constant, Tm lot of production. Butter was produced by the of the pure fat, and T the TINE, Norwegian Association, temperature. The equation is valid for ideal Norway. Margarine based on vegetable fats solutions. and oils, mainly soy bean oil, were produced Both margarine and butter are examples by Mills, Norway. The samples were stored of food systems that are rather complex at +4 ºC until rheological measurements regarding measuring rheological properties. were carried out as measurements of “fresh During processing they are made from products”. Thereafter the samples were liquids with different viscosity, which may tempered 5 hours to 20, 25 and 30oC or may not exhibit elasticity. In addition respectively; three packages at each these products are quite heterogeneous, temperature. After 5 hours extension at the consisting of two or more phases as mentioned temperatures the samples were 14 emulsions . stored at 4oC for 48 hours until the next The objectives of this work are divided in rheological measurement. three main parts; Four replicate measurements in each 1. Theoretical approaches and package were carried out for each product understanding of mechanisms examined. All three replicates were taken appearing during temperature from inside the same package. These fluctuations in fat emulsions measurements were compared with caused by storage of fat measurements on butter and margarine emulsions. samples from the same lots kept 2. Simulation of the effect of continuously at 4oC. variation in storage temperature on the firmness of butter and Table 2. Name of spread, fat source and fat using a transient content in butter and margarine investigated temperature calculation program in this study. based on a finite element Spread Fat source Fat content(w%) modeling system. Butter milkfat 81 3. Experimental documentation to Soft veg. fats & oils 80 validate both the simulation, and the theoretical understanding of the phenomenon of firmness Instrumental analysis development in fat emulsions Penetration tests of the fat samples were during storage at fluctuating performed with the Texture Profile Analyser temperature and use. TA-HDi TPA (Stable Micro Systems, , 1998). The measurements were carried out on one surface of the 500 grams rectangular butter and margarine packages at +4oC.

181 -3 Rheometer experimental set-up the relative density [kgm ] and cp is specific The Texture Profile Analyser (TPA) heat capacity at temperature T [Jkg-1K-1]. TA-HDi equipped with Texture Expert Exceed data computing programme was Statistical treatment programmed to measure compression and One-way ANOVA (Minitab 16) and penetration force. The probe PO 5R ½” 95% Tuckey simultaneous confidence Delrin BS 757 was used in all the intervals, pair-wise comparisons, was used experiments. The TPA - test settings were; to determine if statistically significant Pre-test speed: 2.0 mm/s, test speed:1.0 differences were observed after mm/s, post-test speed: 2.0 mm/s, distance: measurements. 5.0 mm, time: 5.0 s, force: 0.98 N, Load Cell: 25.0 kg, trigger type: Auto, data RESULTS acquisition rate: 200 pps. Table 3 reports the average per capita consumption of margarine and butter within Temperature calculations EU and Norway during the period from Temperature calculations is based on 1979 to 2010. The table gives at least three * Comsol Multiphysics version 4.3a. important informations; Comsol Multiphysics is an engineering, - Butter and margarine are essential design, and finite element analysis software food products in the diet both in EU for modeling and simulation of any and in Norway. physicbased system. This study used - The European pr. capita transient temperature calculations made on a consumption of these crystallized 3D model of butter in the tray as shown in emulsions is less than the Fig. 2. Account was made for the nonlinear consumption in Norway. temperature dependent thermal properties of - The consumption of margarine butter in the calculations. seems to decrease in Norway, while the butter consumption seems to

increase in EU. The thermal properties, in SI units, of butter 5 were taken as: Table 3. Average per capita consumption (kg) of butter (B) and margarine (M) in Tt  15.273 C (2) EU15 and Norway16 from 1979-2010. Year EU Norway k 0025.0183.0  t (3) B M B M 1979-80 2.0 5.0 5.0 15.0  7.08.949  t (4) 1989-90 2.0 4.9 3.0 13.0 1999 2.2 3.6 3.0 12.0 2007 2.4* 3.3* 3.0 9.0 c p   t0.0611+(1.61000 2010 3.6* 5.0* 3.0 9.0 6.75

+ 2 (5)  6.32)+(t0.1+1 *Estimates based on Statistics from IFMA 3.42 and IMACE14. + )  17)-(t0.0269+1 2 Fig. 2 show the calculated meshed 3D model of butter in container with lid where T is temperature [K], k is the thermal -1 -1 removed. The grid is relatively tight. The conductivity of the material [Wm K ], ρ is calculated heat transfer follows the connecting lines between the many nodes. * www.comsol.no

182 20 19 18 17 16 15 14 13  C) 12 11 10 9 8 7 Temperature ( 6 5 4 3 Figure 2. Comsol Multiphysics meshed 3D 2 Measured data 5 W/m2K (all surfaces) model of butter in container with lid 1 10 W/m2K (bottom) and 7 W/m2K (other surfaces) 0 removed. 0 25 50 75 100 125 150 175 200 225 250 Time (min) The temperature versus time Figure 3. Butter center temperature versus development in a butter container is shown time for different external heat transfer in Fig. 3. As illustrated in the figure, coefficients. Surrounding temperature was measured data are compared with calculated 20 °C. 88 data. The two set of calculated data are ButterMargarine dataMaximum data Minimum 75% based on heat transfer from the surroundings 80 o 25% at 20 C into the butter center according to Median two different external heat transfer 72 2 coefficients ( 5 W/m K through all surfaces, 64 and 10 W/m2K through the bottom with 7 W/m2K through other surfaces – numbers 56

48 selected to match real heat transfer). Force (N) To obtain the rate of heating of butter 40 when left in room temperature, a container of butter from TINE was taken out from a 32 at 1 °C and left on a wooden 24 table located in closed room at 21.5 °C. 16 Temperature was measured by a B New B20 B25 B30 M New M20 M25 M30 thermocouple type K inserted at the center of the container. The same pot was drawn at Figure 4. TPA boxplot highlighting scale for the FEM analysis and it is shown firmness (N) in butter (B) and margarine on Fig. 2 Temperature was measured in (M). The samples were measured at 4oC as fuction of time and it was used to estimate fresh (new), and after 5 hours extension of the heat transfer coefficients shown on Fig. the samples at 20, 25 and 30oC stored at 3. 4oC for 48 hours.

Fig. 4 shows a TPA plot highlighting firmness (N) at 4oC for butter (B) and margarine (M). The samples were stored at +4 ºC until rheological measurements were carried out as reference measurements of “fresh products”; B New and M New. Then

183 the samples were tempered 5 hours at 20, between approximately 5 and 30oC, and its 25 and 30oC respectively; three packages at consistency is caused by the presence of a each temperature. After 5 hours extension at network of fat crystals in liquid fat17. the mentioned temperatures the samples Information about temperature versus were stored at 4oC for 48 hours until next time development in the spread container, TPA measurement. was calculated on a 3D model as shown in Four replicate measurements in each Fig. 2. Both measured- and calculated package were carried out for each product temperatures versus time in butter center for examined.Butter increased the firmness different external heat transfer coefficients extremely after 5 hours at 20, 25 and 30 oC are illustrated. Surrounding temperature was followed by 48 hours storage at 4 oC. This is 20 °C. Based on this documentation, 5 in intense contrast to the rheological hours was used as extension of the samples characteristics of margarine which seems at temperatures tested (20, 25 and 30oC ). more or less unaffected of the thermal The rheological characteristics of influence. margarine seemed to be more or less The results in Fig. 4 also show that unaffected of the thermal treatment in this butter is much firmer than margarine as study. This is also as expected. Modern fresh products. It is about two times firmer margarines are tailor-made products, which than margarine measured as fresh at 4 oC. differ significantly from classical margarine This ratio increase dramatically during for and butter regarding properties and fat instance consumers treatment of butter at composition. These new properties are in home when leaving butter on the table or line with present-day market requirements, outside the fridge for some hours. like spreadability from the refrigerator and high content of polyunsaturated fatty . DISCUSSION In the past, margarine was purely regarded Fig. 4 presents individual average TPA as a substitute for butter. Its physical measurements. The results show rheological properties were much like those of butter, characterics and differenent behaviour which is and spreadable at ambiente between butter and margarine when temperatures, but very hard under cooler simulating the consumers handling of these conditions. articles at extreme time and temperature Rheological characteristics of margarine combinations. But such temperature/time and butter are expressed in terms such as cycles happens from time to time at home consistency, texture, plasticity, hardness, during activities of daily living structure and spreadability18. These The TPA plot in Fig. 4 highlight characteristics are related to a number of firmness or force (N) at 4 oC for margarine variable factors; temperature, solid fat and butter. The measurements reported give content, crystal size, crystal size a clear trend for the two types of full fat distribution, crystal shape, interparticle spreads. Butter was much firmer than forces and mechanical treatment of the margarine both as fresh, and after thermal emulsion. The two dominating factors are treatment at 20, 25 and 30 oC followed by 48 the amount of solid triglycerides and the hours storage at 4 oC . processing conditions during production. From a theoretical point of view, it was But in this study, we just investigated the expected that the firmness of butter should storage conditions; Fig. 1. increase beyond the original level, due to The results prove the declared temperature increase followed by phenomenon related to setting of butter. An subsequent cooling to original increased temperature of butter and a temperature2,3. As pin pointed in Table 1, following cooling will re-crystallize the milk fat is partially solid at temperatures melted fat which make the crystal network

184 stiffer, resulting in firmer consistency19. In  The measurements may be used by contrast to butter, margarine is formulated the industry for instance to of oil blends which allow control of the contribute to aid more optimal solid fat content. This control is directly formulation of spreadable water-in- related to the consistency and type of oil emulsions. Spreadability of crystalline structure formed during butter and margarine can easily be processing, storage and use. assessed by measurement of its In this study only deformation rheology complex viscosity at different was used as method for characterization of temperatures. changes in the microstructure of butter and margarine caused by thermal influence. In REFERENCES further studies of this phenomenom, 1. Rukke, E.O., Kottage, D., Abrahamsen, polarized light microscopy will be utilized R.K., and Schüller, R.B. (2010), to analysis changes in fat crystal network as “Rheological studies of butter and a supplement to this rheological margarine exposed to repeated breaks in the investigation. cooling chain”, Annual Transactions of the Nordic Rheology Society, 18, 11-17. CONCLUSIONS This study investigated thermal influence 2. Rukke, E.O., Skuterud, E., Abrahamsen, in rheological characteristics of butter and R.K., and Schüller, R.B. (2011), margarine during simulated distribution, “Rheological characterization of crystallized storage and use. The conclusions can be water-in-oil emulsions during storage and summarized as follows: use”, Annual Transactions of the Nordic  The firmness of butter at 4 ⁰C Rheology Society, 19, 19-26. increased dramatically beyond the original level, due to temperature 3. Mulder, H. and Walstra, P. (1974) “The increase between 20 and 30 oC milk fat globule”, Commonwealth followed by subsequent cooling to Agricultural Bureaux, England, ISBN 0 original storage temperature at 4oC. 85198 289 1, pp. 272-274  Margarine remained unaffected of this treatment. 4. Van Aken, G.A. and Visser, K.A. (2000).  Theoretical temperature calculations ”Firmness and crystallization of milk fat in based on Comsol Multiphysics relation to processing conditions”, Journal Simulation of the effect of storage of Science, 83, 1919-1932 temperature of butter corresponded well with real temperature 5. Nahid, A. (2007). “Modeling heat transfer measurements. These findings were in butter products”. PhD Thesis in used to prove both the simulation, Bioprocess Engineering, Institute of and the theoretical understanding of Technology and Engineering, Masey the phenomenon of firmness University, Palmerston Nort, . development in fat emulsions during storage and use. 6. Trans free table margarine containing  The TPA-measurement instrument DHA (2012), White , SPX Flow was feasible giving objective Technology Hanse GMBH, www.spx.com rheological information about changes in firmness of fat spreads 7. Litwinenko, J.W., Rojas, A.M., Gerschen- when repeating a number of time and son, L.N., and Marangoni, A.G. temperature cycles. (2002),“Relationship between crystallization behaviour, microstructure and mechanical

185 properties in a -based ”, 16. Norwegian Directorate of Health (2011), Journal of the American Oil Chemists Utviklingen i norsk kosthold. Mat- Society (JAOCS), 79, 647-654. forsynings-statistikk og forbruks- 8. Borwankar, R.P., Frye, L.A., Blaurock, undersøkelser. IS-1943, p 8. A.E., and Sasevich, F.J. (1992) “Rheological characterization of melting of 17.Van Aken, G.A. and Visser, K.A. (2000). margarines and tablespreads”, Journal of ”Firmness and crystallization of milk fat in Food Engineering, 16, 55-74. relation to processing conditions”, Journal of Dairy Science, 83, 1919-1932. 9. Lopez, C., Lesieur, P., Bourgaux, C. and Ollivon, M. (2010), “Thermal and structural 18. Alexandersen, K.A. (2005), “Margarine behaviour of anhydrous milk fat. Influence Processing Plants and Equipment”, Bailey`s of cooling rate”, Journal of Dairy Science, Industrial Oil and Fat Products, Sixth 88, 511-526. Edition, Six Volume Set, ISBN: 978-0-471- 38460-1, 459-532. 10. Rønholt, S., Kirkensgaard, J.J., Bæk Pedersen, T., Mortensen, K. and Knudsen, 19. Mortensen, B.K. (2012), “Butter and J.C. (2012) “Polymorhism, microstructure related products – Product characteristics, and rheology of butter. Effects of cream production technology and quality aspects”, treatment”. Food Chemistry, 135, 1730- International Dairy Books, Mælkeritidende, 1739. www.dairybooks.dk, ISBN 978-87-995290- 0-1, 33 11. Mulder, H. and Walstra, P. (1974) “Mixed crystals”, The Milk fat globule, The Universitas Press, Belfast, ISBN 0 85198 289 1, 40-45.

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15. IFMA and IMACE statistics (2010) – International Federation of Margarine Association and International Federation of Countries of .

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