End of Project ReportHigh free-fat, spray-dried powders were successfully
produced at a lower fat content (40% rather than 56%) using
ultrafiltration. Chocolates made from these powders had
improved flow properties and superior quality.
The stability, viscosity and firmness of toffees were improved
by optimising the casein, whey protein and lactose levels of
skim milk powders used in their manufacture.Department of Agriculture, Food and the Marin

Auty, Mark

Kelleher, Colin T

Kennedy, R.

Keogh, M.K.

O'Keeffe, James

O'Kennedy, Brendan

Twomey, Myra

T-Stór

DAIRY PRODUCTS RESEARCH CENTREMOOREPARKEND OF PROJECT REPORT 2000     DPRC No. 36M.K. Keogh and M. TwomeyDairy Ingredients for Chocolate andConfectioneryHigh free-fat, spray-dried powders were successfullyproduced at a lower fat content (40% rather than 56%) usingultrafiltration.  Chocolates made from these powders hadimproved flow properties and superior quality.The stability, viscosity and firmness of toffees were improvedby optimising the casein, whey protein and lactose levels ofskim milk powders used in their manufacture.Dairy Ingredients for Chocolate and ConfectioneryProducts(Dairy Ingredients for Chocolate and Confectionery)Armis No. 4519Project Team: Dr. M.K. Keogh (Leader)Ms. M. TwomeyDr. B.T. O' KennedyMr. M. AutyMr. R. KennedyMr. J. O'KeeffeMs. C. KelleherThe Dairy Products Research CentreMoorepark, Fermoy, Co. Cork.Teagasc acknowledges with gratitude grant aid under the Food Sub-programme(Sub-Measure 3 (ii) - Institutional R&D) of the Operational Programme forIndustrial Development.  The Programme is managed by the Department ofAgriculture and Food supported by EU and national funds.ISBN  1 84170 180 7DPRC No.  36© Teagasc, May 2001Teagasc 19 Sandymount Avenue EUROPEAN UNIONBallsbridge Dublin 4 European Regional Development Fund2Summary and ConclusionsChocolatePowders produced by spray-drying have been found not to performas well in chocolate manufacture as roller-dried powders.  This isattributed mainly to the free-fat levels of roller dried powders whichhave up to 90% free-fat, compared to less than 10% in regular spray-dried powder.  In a previous study (DPRC No. 13) it was shown thathigh fat spray-dried powders had the necessary free-fat level (up to95%) for chocolate, although free-fat levels were lower in powdersproduced in the January - March period. It was also shown that theproperties of the high fat powders important for chocolate wereaffected by milk composition. The effects of the powder properties onthe flow properties and hardness of chocolate were also clarified andquantified. The key objectives of these studies were:* to produce high free-fat spray-dried powders for chocolate at alower fat content (40% fat) and to reduce the flowability problemsassociated with high free-fat powders. * to determine the predictive ability of raw milk composition (milkprotein and solid fat content at 10ºC) to control the functionalproperties of spray-dried milk powders (free-fat, particle size andvacuole volume) important for chocolate. *  to determine the ability of the milk powder properties to predict thechocolate properties.* to make recombined powders using milk fats of varying solid fatcontent in order to quantify the effects of solid fat content on the flowproperties of the chocolate.3ToffeeReconstituted milk powder or sweetened condensed milk is used inconfectionery products such as toffees, caramels and fudges, but theirrole is poorly understood. Because of the high solids contents of theseconfectionery products, the concentration of ingredients in theavailable moisture is very high. The functionality of milk proteiningredients, in particular in a high-solids product is unknown.  Abetter knowledge of the role of each ingredient component could leadto development of specific ingredients to meet individual customerrequirements.  Hence, the key objective of this study was to evaluate the effects ofmilk powder composition on the processability, flow properties andfirmness of low moisture confectionery using toffee as an example.Main Conclusions and AchievementsMilk Powder for Chocolate- By using ultrafiltration to raise the protein content of the powders, itwas possible to produce high free-fat powders at a lower fat contentthan previously (40% rather than 56% fat).- The flow properties of high fat powders (40% and 56% fat) werepoorer than commercial whole milk powders (26% fat). There was nosignificant effect of fat content (40 - 56%) and free-fat content (39%- 100%) on the flow properties. The flow properties disimproved asthe temperature increased from 5 to 25ºC. - Confirmatory trials showed that the free-fat of the milk powders was4predicted well by the protein and solid fat content at 10ºC of themilks. However, the size of the powder particles was predicted lesswell. The vacuole volume of the powders was not related to milkcomposition.- It was possible to predict the viscosity and final hardness of thechocolates from the free-fat and particle size of the powders but theyield value of the chocolates was predicted less well from the solid fatat 10ºC and vacuole volume of the powders. - The free-fat level of recombined powders was unaffected by thesolid fat content of the fat. There were no differences in the flowproperties of chocolates made with recombined powders with milkfats of different solid fat content, that is, the expected decrease in yieldvalue did not occur with increasing solid fat content.Milk Powder for Low Moisture Confectionery (Toffee)- The firmness of cooked toffee at 90ºC was increased by the caseincontent and decreased by the lactose content of the skim milkpowders.- The hardness of the final toffees was increased both by the caseincontent and the lactose content of the skim milk powders.- Toffee firmness, hardness and colour were affected by thecasein:whey protein ratio of milk powders. Pre-heat treatment of thereconstituted milk at low milk solids concentration was necessary forthe production of toffees stable to heat.- Microscopic examination of the toffees showed that the casein:wheyprotein ratio affected the size of the fat pools and protein aggregatesin the toffees and that the degree of whey protein denaturation wasresponsible for toffee structure.5Research and ResultsConfirmatory trials for powders in chocolateA previous project was very successful in understanding and definingthe effect of the selected milk components (milk protein and solid fatcontent at 10ºC) on the functional properties of  high fat (56%) spray-dried milk powders (free-fat, particle size and vacuole volume)important for chocolate (see DPRC No. 13). In the current project, five trial powders made for confirmatorypurposes showed that the properties of the milk powders werepredicted by the protein and solid fat content at 10ºC of the milks.Five chocolates were then made to demonstrate that it was possibleto predict the chocolate properties from those of the milk powdersused.High free-fat powders (40% fat)The previous studies were carried out using 56% fat powders, whichhad high free-fat contents.  Free-fat levels were then raised in powders containing anintermediate fat content of 40%.   These powders were prepared:- from a control milk, - by ultrafiltration of the skim milk followed by addition of cream toincrease the protein:lactose ratio from 0.64 (control) to 0.94 and - by adding lactose to reduce the protein:lactose ratio to 0.58. 6As the protein:lactose ratio increased, the free-fat of the powdersincreased from 40 (control) to 75%.  Two series of 26 and 40% fat powders were produced by treatingmilk with plasmin or phospholipase or a combination of bothenzymes (40% fat powder only) and compared to control powders.The free-fat and particle size of these powders were not significantlydifferent from untreated powders. No differences were found in theflow properties of the chocolates made from these powders, but anobjectionable rancid off-flavour was found in the combined-enzymetreated chocolates.Flow properties of high free-fat powdersThe flow properties of the high fat powders (40 and 56% fat)produced were poorer than commercial whole milk powders (26%fat). There was no significant effect of fat content (41.5% - 56%) andfree-fat content (39% - 100%) on the flow properties of the high fatpowders. The flow properties were reduced as the temperatureincreased from 5 to 25ºC.Effect of solid fat content of powders on chocolateThe influence of the solid fat content of milk powders on chocolatewas then studied. Recombined milk powders (40% fat) wereprepared from reconstituted skim milk powder and milk fats with solidfat contents at 10ºC of 41, 51 and 61%. In contrast to results obtained for high fat powders made in theprevious project from creams ranging in solid fat content from 39 to56%, the free-fat level of the recombined powders was unaffected by7the solid fat content of the fat. There were no differences in the flowproperties of the chocolates made with these powders, that is, theexpected decrease in yield value did not occur. Thus, changes foundin powders made using cream were not reproduced with recombinedpowders. These changes were already considered to be due to factorsassociated with the solid fat, rather than to the effect of solid fat perse.The toffee process, evaluation methods and trialsThe equipment necessary for the toffee confectionery stage of theproject was installed and a standard method for the manufacture oftoffee confectionery at pilot scale was set up to evaluate the effects ofskim milk powder composition. Skim milk powder was firstreconstituted in water with sugar to the composition of sweetenedcondensed skim milk (Table 1). Table 1: Composition of reconstituted skim milk powder as sweetened condensed skim milkfor toffee.The powder and part of the sugar were dry mixed and stirred intowater at 60ºC.  The mix was stirred for 5 minutes and allowed tostand overnight at 4°C.  Hydrogenated palm kernel oil was melted at60ºC and added to the mixture of glucose syrup and reconstitutedsweetened skim milk powder (Table 2).8Ingredient %Skim milk powder 27.5Sugar 38.5Water 34.0Table 2: Composition of toffee.These ingredients were mixed using a Silverson mixer to disperse themelted fat into the aqueous syrup before the addition of the sugar.After the remainder of the sugar was added, the mix was stirred well.The mixture was then placed in the gas cooker (Savage Bros. Co.,1125 Lunt Ave., Elk Grove Village, IL. 60007, USA) and heated withcontinuous stirring until a temperature of 121ºC was reached.  At thistemperature, which represents the end of the cooking process, asample of the molten toffee was taken and cooled to 90ºC forviscosity measurement.Effect of Gross CompositionThe effect of the casein, whey protein and lactose levels of the skimmilk powders on the processability, flow properties andmicrostructure of the toffees was quantified in a statistically-designedseries of 23 trials (14 trials and 9 repeated). In 9 of the trials, lactosewas added to increase the protein:lactose ratio further. The firmness G' (Pa) of the cooked toffee after cooling from 121ºC to90ºC was increased by the casein content and decreased by thelactose content of the skim milk powders. The hardness (kg.m.s-2) ofthe final toffees was increased both by the casein content and lactosecontent of the skim milk powders. This means that lactose contributed9Ingredient %Glucose syrup 34.0Reconstituted sweetened condensed skim milk 32.0Sugar 22.5Hydrogenated palm kernel oil 11.5to the firmness of the toffee after crystallisation only. Microstructuraldifferences between toffees were observed using laser microscopy.Toffee samples containing powder with a high protein:lactose ratiohad more aggregated protein material, some of which was adsorbedat the surface of the fat globules. Samples with a low protein:lactoseratio had a thinner layer of protein surrounding the fat globules. Thenon-adsorbed protein material was less aggregated. Samples with a low protein:lactose ratio also exhibited proteinaggregation leading to processing difficulties due to burn-on. Anexplanation was sought for this instability/burn-on problem. Thisoccurred at a protein:lactose ratio in skim milk powders of 0.68 andbelow. The effects of the casein and whey proteins was less obvious,and further trials were carried out to clarify their role (Table 3). Effect of casein:whey protein ratioArtificial skim milk powders with specific casein:whey protein ratioswere prepared. Various ratios of phosphocasein and whey proteinisolate (Table 3) were reconstituted (total protein 3.2%) in a simulatedmilk salt solution with 4.5% lactose. These artificial milks were pre-heated at 97.5ºC x 2 min, concentrated by evaporation to 45% solidsand spray-dried. The powders were then evaluated in toffee.10Table 3: Flow properties of toffees made with artificial milk powders with various casein:wheyprotein ratios.Maximum toffee firmness, hardness and good colour were found atthe intermediate casein:whey protein ratio of 80:20. Milk powderswith casein:whey protein ratios between 100:0 and 70:30 producedtoffees which were stable to heat, but toffees containing a 0:100 ratio(whey protein alone) or an 80:20 ratio without pre-heat treatmentexhibited instability and burn-on to the sides of the cooker. In bothcases of instability/burn-on, the whey proteins were not bound to theheat-stable casein and were free to exhibit instability and burn-on.This demonstrates that the binding of the heat-sensitive whey proteinsto casein at low milk solids concentration is a necessary requirementfor the production of stable toffees.11Artificial milk powder Firmness G' Hardness Comments(Pa) (kg.m.s2)Casein:whey protein 100:0 518 1.3 Homogenous mix, dark colourCasein:whey protein 90:10 300 4.2 Smooth, pale colour, filled moulds wellCasein:whey protein 80:20 795 7.6 Smooth, good intermediate colourCasein:whey protein 70:30 612 4.6 Dark colourCasein:whey protein 0:100 - - No shape, dark areas, protein aggregation.80:20; no pre-heat treatment     423 8.0 Lumpy with dark patches, like caramelTable 4 summarises the microstructure of six toffee formulations asobserved by confocal scanning laser microscopy (CSLM). Eachtoffee sample was stained with a fluorescent dye for the fat andprotein, which highlighted their distribution in the toffees (seeFig.1).Table 4: CSLM observations of toffees made with sweetened condensed milk and artificialmilk powders with various casein:whey protein ratios.The microscope observations suggest that casein-whey proteininteractions play an important role in the physical structure oftoffee. Small fat globules with adsorbed small protein aggregateswere present in the acceptable toffees made with sweetenedcondensed milk and the powder with casein:whey protein ratio ofMilk Ingredient Microstructure ObservationsSweetened condensed milk Small fat globules adsorbing (control) small protein aggregates. Some pools of free-fat up to 20 µm.Casein:whey protein 100:0 Large pools of free-fat up to 30 µm. Protein highly aggregated and adsorbed to fat interface.Casein:whey protein 90:10 Some free-fat. Small fat globules with high level of adsorbed protein. Similar to control but with smaller fat pools.Casein:whey protein 80:20 Small fat globules with protein adsorbed. Similar to control.Casein:whey protein 70:30 Similar to control but with more free-fat. Casein:whey protein 0:100 Extensive free-fat with very large network of protein aggregates. Very little adsorbed protein.1280:20. The toffees made with powders with casein:whey proteinratios of 100:0 and 0:100 contained highly aggregated proteinmaterial.  However, their flow properties were quite different from thewhey protein-only toffee being much more viscous that thephosphocasein-only toffee.This suggests that denatured whey is largely responsible for thestructure-forming properties of toffee. The milk protein compositionalso influenced the size of the fat pools, which in turn would beexpected to influence sensory properties such as greasiness andflavour release. 13PublicationsAuty, M.A.E., Guinee, T.P., Fenelon, M., Twomey, M. and Mulvihill,D.M. (1998). Confocal microscopy methods for studying themicrostructure of dairy products and ingredients (Abstract). In:Scanning 98, Baltimore, Md. USA. 12 May 1998, 3pp. Keogh, M.K. (1998). Milk powder in chocolate manufacture.Workshop on 'Chocolate Manufacture and the Role of DairyIngredients' held at DPRC, Moorepark, Fermoy, Co. Cork.  25 March,1998.O'Kennedy, B.T. (1998). Functionality of dairy ingredients inchocolate. Same Workshop.Twomey, M. and Keogh, M.K. (1998). Milk powder in chocolate.Farm and Food, 8, 9 -11.Keogh, M.K. (1998). Dairy ingredients in chocolate. DPRC End-of-Project Report No. 13 (Armis No. 4223). Teagasc, Dublin, Sept.1998.Twomey, M., Keogh, M.K., O'Kennedy, B.T., Auty, M.A. and Mulvihill,D.M. (2000). Effect of milk composition on selected properties ofspray-dried high fat and skim-milk powders. Irish. Jnl. Ag. & FoodRes. 39, 79-94. Twomey, M., Keogh, M.K., O'Kennedy, B.T., Auty, M.A. and Mulvihill,D.M. (2000). Milk chocolate manufacture using spray-dried milkpowder.  Irish Jnl. Ag. & Food Res. (Submitted).Twomey, M., Keogh, M.K., Auty, M.A,, O'Kennedy, B.T. and Mulvihill,D.M. (2000). Effect of skim milk powder composition on therheological properties of toffee confectionery. Jnl. Texture Studies (InPreparation).14Auty, M.A., Twomey, M., Guinee, T.P. and Mulvihill, D.M. (2000). Thedevelopment and applications of confocal laser microscopy (CSLM)methods for studying the distribution of fat and protein in fat spreads,dairy products and chocolate. Jnl. Dairy Research (Submitted).Twomey, M., Keogh M.K. and Auty, M.A. (2000). The role of milkpowder composition in toffee consistency. Workshop on 'NewDevelopments in Applications and Quality of Dairy Ingredients' heldat DPRC, Moorepark, Fermoy, Co. Cork. 24 February 2000.For further information, please contact Dr. Kieran Keogh15DAIRY PRODUCTS RESEARCH CENTREMoorepark, Fermoy, Co. Cork, IrelandTel: +353 (0) 25 42222 - Fax: +353 (0) 25 42340E-Mail: reception@moorepark.teagasc.ieM.K. Keogh

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