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Effects of selected properties of ultrafiltered spray-dried milk powders on some properties of chocolate
ARTICLE IN PRESS
International Dairy Journal 13 (2003) 719–726
Effects of selected properties of ultrafiltered spray-dried milk powders on some properties of chocolate M. Kieran Keogh*, Cathriona A. Murray, Brendan T. O’Kennedy Teagasc, Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Ireland Received 6 January 2003; accepted 14 April 2003
Abstract The effects of selected properties of spray-dried milk fat powders on chocolate were determined. Milk powders produced from control or ultrafiltered (UF) milks with various levels of fat were blended with skim milk powder to give a standard 26 g fat 100 g1 powder. Particle size of the chocolate mixes after refining decreased as the fat content and free-fat content of the powders increased. Despite this, increasing fat and free-fat contents of powders reduced the Casson viscosity of the subsequent molten chocolates. Casson viscosities using powders from control or UF milks were similar, but decreased as the particle size of powders increased and particle size after refining the chocolate mix decreased. Casson yield value and hardness decreased as fat content of powders increased. Casson yield value increased with vacuole volume of powders. It is possible to alter important properties of chocolates using milk powders of varying fat contents, free-fat contents and particle sizes. r 2003 Elsevier Ltd. All rights reserved. Keywords: Milk powder properties; Chocolate particle size; Rheology; Hardness; Snap
1. Introduction Manufacturers of milk chocolate prefer to use milk powder produced by roller-drying rather than by spraydrying, because roller-dried powders have properties such as high free-fat content, large particle size and low vacuole volume which have positive effects on the properties of chocolate (Dewettinck, De Moor, & Huyghebaert, 1996). Previous research (Twomey, Keogh, O’Kennedy, & Mulvihill, 2002) defined the extent to which seasonal variations in the properties of spray-dried powders containing 56 g fat 100 g1 powder blended with skim milk powders affected the rheology of molten chocolate at the end of the conching stage and the final hardness of the chocolate. In subsequent work (Keogh, Murray, & O’Kennedy, 2003), spray-dried milk powders were prepared from control and ultrafiltered milks. These powders had a range of fat, free-fat, protein, moisture, vacuole volume contents, particle sizes and related properties. This paper deals with the effects of these powders on important properties of *Corresponding author. Tel.: +353-24-42235; fax: +353-25-42228. E-mail address: [email protected] (M. Kieran Keogh). 0958-6946/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0958-6946(03)00124-9
chocolate. In addition to the molten chocolate rheology and final hardness, the particle size after refining the chocolate ingredient mix and the particle size, snap and gloss of the final chocolates were studied in the current work. This should give greater insights into milk powder functionality, highlight certain powder properties beneficial to specific types of chocolate and bring nearer the goal of replacing roller-dried powder with spray-dried powder in chocolate. Milk powder properties that affect chocolate properties have been studied. These include free-fat (Zurcher, . 1976; de Koster, 1989a; Vendeville, 1995; Dewettinck et al., 1996; Twomey et al., 2000), specific fat pore surface (Scheruhn, Franke, & Tscheuschner, 2000), milk fat fractions (Hartel, 1996), milk fat hardness (Twomey et al., 2000), particle size (Chevalley, 1994; Twomey et al., 2000), particle size distribution (Mongia & Ziegler, 2000), particle structure (Verhey, 1986), particle density (Scheruhn et al., 2000), vacuole volume (Dodson, Lewis, Holgate, & Richards, 1984; Twomey et al., 2002), milk protein content and type (de Koster, 1989a, b), denaturation state (Anon., 1996; Hansen & Hansen, 1990; de Koster, 1989b); lactose content (Aguilar & Ziegler, 1994a), lactose crystallisation state (Bohren, Kuypers, & Meister, 1987; Aguilar & Ziegler,
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1994b) and moisture content (Heiss & Bartusch, 1957). Other minor components of milk fat such as mono- and di-glycerides (Tietz & Hartel, 2000) and phospholipids (Parsons & Keeney, 1969) may also have effects, but milk salts have been reported only to affect chocolate taste (de Koster, 1989a). However, convincing demonstrations of relationships between some of these milk powder and chocolate properties are frequently absent from the literature. One reason is that many workers use purchased powders, which provide qualitative rather than quantitative data. The processing of chocolate also has major effects on its properties, especially the refining conditions (gap width and roller pressure) and conching time. However, for the current work, the chocolate-making recipe, refining and conching conditions used before for 56 g fat 100 g1 powders (Twomey et al., 2002) were retained. The main objective of the current work was to determine the effects of variations in powder properties made from control and ultrafiltered milks on the properties of milk chocolate.
2. Materials and methods The milk chocolate recipe used (Twomey et al., 2000) had a 25 g 100 g1 incorporation rate of milk powder, a particle size after refining (by micrometer) of 26 mm (using a 56 g fat 100 g1 powder/skim milk powder blend), mean total fat content of 30.4 g 100 g1 and moisture content of 1.3 g 100 g1. 2.1. Preparation of milk chocolates Milk chocolates were manufactured using 21 of the spray-dried milk powders already made (Keogh et al., 2003). The powders had five fat contents (nominally 26, 30, 40 and 50–59 g 100 g1), free-fat contents (8–95 g 100 g1 fat), median particle sizes (56–121 mm), moisture contents (2.2–6.7 g 100 g1) and vacuole volumes (0.9–12.5 mL 100 g1). Standard powders containing 26 g fat 100 g1 were not blended, but powders with higher fat contents were blended with a commercial skim-milk powder to give a powder blend containing 26 g fat 100 g1 for use in chocolate. As the powders were made under constant processing conditions, the variations in the properties of the spray-dried powders (Table 1) were due mainly to differences in composition due to the fat content and level of ultrafiltration of the milks and total solids of the concentrates. The powders were stored in sealed bags at a constant temperature of 15 C until evaluated in chocolate. 2.2. Ingredients The following ingredients were used in the manufacture of milk chocolates as previously described (Twomey
et al., 2002): cocoa butter (Cadbury Ireland Ltd, Dublin), cocoa liquor (Nestle! Rowntree, Mallow, Co. Cork), sucrose (Irish Sugar Company, Mallow, Co. Cork), milk powders (prepared as described in Keogh et al., 2003) and lecithin (Topcithin 300, Lucas Meyer, Hamburg, Germany). 2.3. Process A Lipp conche (Lipp Mischtechnik, Mannheim, Germany) for 7 kg batches was used in the current work rather than the larger Frisse conche used previously. Cocoa liquor (0.831 kg) and 60% of the cocoa butter (0.810kg of 1.350 kg) were melted at 60 C . in a Stephan mixer (Stephan Sohne Gmbh, Hameln, Germany). Sugar (2.904 kg) and milk powder (1.653 kg) were then added to the melted fat and mixed for 5 min. The mixture was refined in two passes, with the gap sizes/pressure between the rollers of a three-roll refiner (Buhler, . New Barnet, Herts., UK) reduced in the second pass from 0.560 and 0.280 mm/1.0 MPa to 0.184 and 0.138 mm/0.7 MPa. These settings gave a particle size of 26 mm in the chocolate after refining when a 56 g fat 100 g1 powder/skim-milk powder blend was used. The refined mix was then conched in the Lipp conch for 7 h at 60 C. Lecithin (0.2 g 100 g1) and the remaining cocoa butter were added during the final stages of conching. A sample of molten chocolate was taken for rheological assessment at the end of the conching process and the remaining chocolate was stored in an incubator overnight at 50 C. On the following day, two 2 kg portions of the chocolate were tempered in a Hillard Chocolate System (Jimsan Enterprises, Inc., West Bridgewater, MA, USA) which was located in a controlled environment (21 C and 50% RH). The stored chocolate (50 C) was cooled to 45 C and held for 30 min; it was then tempered by cooling to 28 C in 20–25 min, holding for 10 min, heating to 30 C and holding for 5 min before moulding into plastic moulds. The moulded chocolate was placed in a temperature-controlled room at 15 C for 30 min before de-moulding and the finished bars were wrapped in aluminium foil and stored at 15 C until analysed. 2.4. Rheological properties of milk chocolate Samples of each chocolate were taken at the end of conching for rheological evaluation in a strain-controlled rheometer (Bohlin VOR) with concentric cylinder geometry. All measurements were taken at 40 C. Samples were pre-sheared for 2.5 min at 18.5 s1 followed by a shear rate sweep from 60 to 1 s1 in 3.5 min. The data were then used to calculate the Casson viscosity (ZCV ) and Casson yield value (sCA )
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Table 1 Selected properties of milk powders used in chocolate (n ¼ 21) Trial no.-fat content control or ultrafiltered
Fat (g 100 g1)
Protein (g 100 g1)
Free fat (g 100 g1)
Particle size (D(v; 0.5)) (mm)
Moisture (g 100 g1)
Vacuole volume (mL 100 g1)
1-26 Ca 1-26 UF1b 1-26 UF2 2-26 C 2-26 UF1 2-26 UF2 9-26 C 10-26 C 11-26 C 12-26 C 12-26 CRc 13-30 C 8-40 C 8-40 UF1 09-40 C 10-40 UF2 13-50 C 20-54 C 19-50 C 18-50 C 18-60 C Skim milk powder
25.1 25.5 25.6 24.5 25.2 25.1 26.1 29.2 29.3 25.6 25.7 31.9 39.6 42.9 40.4 40.2 51.7 53.8 51.4 51.7 59.2 0.8
28.6 32.2 34.1 29.7 32.9 35.1 25.7 30.3 30.1 26.7 26.8 35.3 27.0 32.2 20.7 26.9 17.4 17.5 18.3 18.3 15.3 —
12.6 21.2 57.1 25.7 49.3 74.2 13.2 13.6 9.3 8.4 7.8 20.6 45.0 63.1 49.4 73.9 78.4 91.2 74.9 90.4 95.5 —
82.6 75.5 121.3 55.7 63.7 68.3 59.3 83.7 69.7 69.9 64.9 63.7 57.1 67.9 81.9 78.8 104.1 67.4 93.7 70.5 91.6 61.6
4.5 4.2 6.7 2.3 2.9 3.8 3.7 2.6 2.6 2.2 3.2 2.9 2.7 2.3 3.0 3.8 2.3 3.2 2.8 3.0 2.8 5.0
12.5 8.3 9.6 7.4 6.6 5.7 4.1 8.4 7.4 7.3 6.4 7.3 3.7 2.7 3.1 4.0 3.3 2.0 2.5 2.5 0.9 22.2
a
C: control. UF: ultrafiltered milk. c R: replicate. b
(OICC, 1973) using the following equation: pffiffiffi pffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffipffiffiffi s ¼ sCA þ ZCA g’ ; where s is the shear stress (Pa), sCA is the Casson yield value (Pa), ZCV is the Casson viscosity (Pa s) and g’ is the shear rate (s1). 2.5. Hardness of moulded chocolate The maximum force (N) required to penetrate the moulded chocolate at 20 C for a distance of 5 mm with a 10 stainless-steel cone travelling at a velocity of 0.5 mm s1 was measured using an Instron Universal Testing Machine (Full, Yella Reddy, Dimick, & Ziegler, 1996). 2.6. Snap and gloss values of chocolate The snap and gloss values of the chocolates were assessed sensorially on a scale of 1=poor; 2=medium and 3=good by a panel of the same three technical people and the mean value recorded.
3. Results and discussion Twenty-one milk powders (26–60 g 100 g1 nominal fat content), including six prepared from UF milks, were
selected from a range of powders already produced (Keogh et al., 2003) for evaluation in chocolate. The properties of the milk powders used and the skim milk powder used for blending with the high-fat powders (fat content, free-fat content, particle size, moisture and vacuole volume) are outlined in Table 1. The effects of the powder properties on the particle size of the chocolate mix after refining, the viscosity and yield value of the molten chocolates at the end of conching and the hardness, snap and gloss of the finished chocolates are shown in Table 2. 3.1. Particle size after refining The particle size (by micrometer) of the chocolate mixes after refining increased curvilinearly from 26 to a mean of 43 mm as the fat content of the powders used decreased from 59 to 26 g 100 g1 (n ¼ 21; r ¼ 0:859; Po0:001; Fig. 1). However, the correlation coefficient was lower (r ¼ 0:817; Po0:001; Fig. 2) for the relationship between the particle size after refining and free-fat content of the powders. This is because the six powders produced from UF milks had higher protein and free-fat contents (codes UF1 and UF2, Table 1), but had almost the same mean particle size after refining as control powders (42 vs. 41 mm, Table 2). This shows that chocolate mixes containing powders with higher contents of fat (even though blended with skim milk
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Table 2 Properties of milk chocolates (n ¼ 21) Trial no.-fat content control or ultrafiltered
Particle size after refining (mm) (%)
Viscosity (Pa s)
Yield value (Pa)
Hardness (N)
Snap score (range 1–3)
Gloss score (range 1–3)
1-26 Ca 1-26 UF1b 1-26 UF2 2-26 C 2-26 UF1 2-26 UF2 9-26 C 11-26 11-26 12-26 C 12-26 CRc 13-30 C 8-40 C 8-40 UF1 09-40 C 10-40 UF2 13-50 C 20-54 C 19-50 C 18-50 C 18-60 C
46 41 43 42 45 42 40 44 44 40 41 44 40 37 37 45 38 28 39 28 26
1.55 1.57 1.46 1.57 1.58 1.59 1.65 1.61 1.55 1.63 1.63 1.58 1.33 1.31 1.43 1.45 1.28 1.42 1.39 1.39 1.32
10.1 12.1 11.7 13.0 11.2 14.6 13.8 11.5 15.6 14.2 14.3 10.7 6.4 6.5 10.8 10.2 7.7 6.1 7.5 6.2 6.5
2.81 3.42 2.65 3.54 3.23 3.20 2.93 3.21 3.21 3.06 3.15 2.73 2.30 2.27 2.56 2.50 1.97 2.49 2.69 2.75 2.80
3.0 2.0 2.0 3.0 3.0 2.5 3.0 3.0 2.5 2.5 3.0 2.5 2.0 2.0 2.5 2.0 2.5 2.0 2.0 2.7 2.6
2.7 3.0 2.0 2.0 2.0 2.5 3.0 3.0 3.0 3.0 3.0 3.0 2.0 2.3 3.0 2.0 3.0 2.0 2.0 2.7 2.6
a b
C: control. UF: ultrafiltered milk.
50 Particle size after refining (µm)
Particle size after refining (µm)
50 45 40 35 30
45 40 35 30 25 0
25 24
30
36
42
48
54
60
20
40
60
80
100
Free-fat content (g100g-1 powder)
-1
Fat content (g100g powder)
Fig. 1. Effect of fat content of control and UF milk powders on the particle size of chocolate mixes after refining. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
powder) rather than higher free-fat and protein contents are more easily refined. This is probably because powder particles containing higher contents of fat are softer and respond better to refining. A particle size of 26 mm or lower after refining usually gives a grittiness score of zero in the final chocolate. The grittiness scores of these chocolates were not measured, but it is common experience that grittiness becomes increasingly detectable in finished chocolates as the particle size exceeds 26 mm.
Fig. 2. Effect of free fat content of control and UF milk powders on the particle size of chocolate mixes after refining. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
3.2. Casson viscosity of chocolate When the control powders containing 26–60 g fat 100 g1 were used to make chocolates, the Casson viscosity of the molten chocolates decreased linearly from 1.63 to 1.32 Pa s as the free-fat content of the powders increased from 8 to 95 g 100 g1 fat (r ¼ 0:870; n ¼ 15; Po0:001; Fig. 3). A similar correlation (r ¼ 0:886) was found between the Casson viscosity and fat content of the same powders (not
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1.7 Casson viscosity (Pas)
Casson viscosity (Pas)
1.7
723
1.6 1.5 1.4 1.3 1.2
1.6 1.5 1.4 1.3 1.2
0
20
40
60
80
100
-1
Free-fat content (g100g fat)
50
70
90
110
Powder particle size D(v, 0.5) µm
Fig. 3. Effect of the free-fat content of control powders on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
Fig. 4. Effect of the median particle size of control powders on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
shown). This provides further evidence that the effects of fat and free-fat contents of milk powders on the Casson viscosity are highly inter-related. However, when all powders (control and UF-treated) were evaluated, the correlation coefficient between the Casson viscosity of the chocolates and free-fat content of the powders was lower (0.783, n ¼ 21; Po0:001). The free-fat content of the six UF powders increased with increasing protein content (Table 1), but the mean Casson viscosity of the chocolates made with these powders was almost the same as the control powders (1.49 vs. 1.50 Pa s). This shows that the increased protein in the UF powders counteracted the viscosity-lowering effect in the chocolates of increased free-fat in the powders. Even though increasing powder protein content reduced the powder solids density (r ¼ 0:419; Po0:1), the particle density was not significantly reduced (Keogh et al., 2003), because the vacuole volume of the powders did not increase with powder protein as was found elsewhere (Aguilar et al., 1994a). Increasing protein content also increases the porosity of the powder structure (Mistry, Hassan, & Robison, 1992; Moreau & Rosenberg, 1993; Aguilar et al., 1994a), leading to increased absorption of fat into the powder particles (Scheruhn et al., 2000). There was also a significant correlation (r ¼ 0:658; n ¼ 21; Po0:01) between the vacuole volume of all the powders and the viscosity of the chocolates, because the vacuole volume of the powders was inversely related to the fat content (r ¼ 0:823; Po0:001) and the free-fat content (r ¼ 0:717; Po0:001). This confirms that increasing fat or free-fat depressed foaming and vacuole formation (Verhey, 1986). The vacuole volume of powders has been found to be related to the viscosity (Dodson et al., 1984) or the yield value of chocolates (Twomey et al., 2002). This is because powders with high vacuole volumes occupy a larger volume of the continuous fat phase or in extreme cases may have a greater tendency to shatter during refining and produce fines (Aguilar & Ziegler, 1995).
There was also a significant correlation (r ¼ 0:516; n ¼ 15; Po0:05; Fig. 4) between the particle size of the control powders and the Casson viscosity of the chocolates. The Casson viscosity decreased from 1.57 to 1.28 Pa s as the powder particle size increased from 57 to 104 mm. The decrease in Casson viscosity might have been greater, had not the increase in particle size been mainly due to the increased moisture content of the powders (Keogh et al., 2003). This suggests that the increased powder moisture mainly counteracted the benefits of increased particle size. Even if the decrease in Casson viscosity was not large in commercial terms, the effects of the particle size of powders with the same moisture content will be investigated in a future paper. As has been already stated (Twomey et al., 2002), larger particle size powders have lower specific surface area, less fat from the continuous phase is required to coat the powder particles and as a result, the Casson viscosity decreases. The Casson viscosity of the chocolates was related to the particle size of chocolate mixes after refining but contrary to the way anticipated. In principle, Casson viscosity and even more so the yield value are expected to decrease with increasing particle size after refining (Aguilar et al., 1995), but Fig. 5 shows that viscosity increased as the particle size after refining increased (r ¼ 0:586; n ¼ 21; Po0:01). This is because the reduction in viscosity of chocolates caused by increasing powder free-fat contents far outweighed the effect of the decrease in particle size after refining the higher-fat powders. Taking all factors together, high-fat powders and properties associated with high-fat powders (high free-fat and low vacuole volume) reduced the viscosity of molten chocolate at the end of conching. 3.3. Casson yield value of chocolate The Casson yield value of the chocolates decreased curvilinearly (r ¼ 0:873; n ¼ 21; sig. o0.001, Fig. 6) from a mean of 12.8 Pa for powders containing 26 g fat
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724
16
Casson yield value (Pa)
Casson viscosity (Pas)
1.7 1.6 1.5 1.4 1.3
14 12 10 8 6
1.2 25
30 35 40 45 Particle size after refining (µm)
0
50
Fig. 5. Effect of the particle size after refining of chocolate mixes on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
10
Fig. 7. Effect of the vacuole volume of milk powders on the Casson yield value of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
16
3.6
Chocolate hardness (N)
Casson yield value (Pa)
2 4 6 8 Vacuole volume (mL100g-1)
14 12 10 8 6
3.2 2.8 2.4 2.0 1.6
4 20
30
40
50
60
-1
Powder fat content (g100g )
24
30
36
42
48
54
60
Powder fat content (g100g-1)
Fig. 6. Effect of the fat content of milk powders on the Casson yield value of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
Fig. 8. Effect of the fat content of milk powders on the hardness of chocolates. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
100 g1 to 6.5 Pa for a powder containing 59 g fat 100 g1. The yield value was also similarly related to the free-fat content (r ¼ 0:709; n ¼ 21; Po0:001). Since the vacuole volume of the powders decreased as the fat and free-fat contents of the powders increased (Keogh et al., 2003), the yield value of the chocolates increased as the vacuole volume of the same powders increased (r ¼ 0:737; n ¼ 20; Po0:001; Fig. 7). As with the Casson viscosity previously, high-fat powders and properties associated with high-fat powders (high free-fat and low vacuole volume) reduced the Casson yield value of molten chocolates at the end of conching.
present in the continuous phase of the chocolate (Aguilar, Hollender, & Ziegler, 1994; Twomey et al., 2002). As a result, the hardness of the finished chocolate decreased. Two chocolates made with roller dried powders and two retail bar chocolates had hardness values in the range 2.3–2.6 N, whereas milk powders with fat contents of 39–52 g 100 g1 had hardness values in the range 2.0–2.8 N.
3.4. Hardness of finished chocolate The hardness of the finished chocolates decreased curvilinearly from a mean of 3.1 N for powders containing 26 g fat 100 g1 powder to 2.5 N for powders containing 39–59 g fat 100 g1 powder (Fig. 8, r ¼ 0:786; n ¼ 21; Po0:001). The free-fat content of the powders was less strongly related to chocolate hardness (r ¼ 0:569; n ¼ 21; Po0:01). As the powder fat content increased, free-fat increased and more milk fat was
3.5. Snap score of chocolates The snap scores (scale 1–3) of the chocolates ranged from 2.0 to 3.0, but were not related to any property of the powders. The snap score of two retail bar chocolates and two chocolates made with roller dried powders achieved the highest score of 3.0. 3.6. Gloss score of chocolates The gloss scores (scale 1–3) of the chocolates also ranged from 2.0 to 3.0, but were not related to any property of the powders. The gloss scores of two retail
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bar chocolates and two chocolates made with roller dried powders achieved the highest score of 3.0.
4. Conclusions The properties of the chocolates were influenced by the properties of the spray-dried milk powders used in their manufacture. Chocolate mixes were more easily refined to a smaller particle size when blended high-fat powders were used rather than powders containing 26 g fat 100 g1. The smaller particle size after refining was related more to the fat content than to the free-fat content of the high-fat powders. The Casson viscosity of molten chocolates decreased with increasing free-fat or fat content of the control powders. However, the higher protein contents of UF powders counteracted the effect of their higher free-fat contents on the Casson viscosity in chocolates. Increasing the powder particle size mainly by increasing the moisture content reduced the Casson viscosity of the molten chocolates by a modest amount, indicating that increased powder moisture counteracted the benefits of increased particle size. The particle size after refining, which decreased as the fat content of the powder used increased, did not increase the viscosity of the chocolates at the end of conching. The effect of the particle size decrease was far outweighed by the increased free-fat contents of the higher fat powders and lead overall to a reduction in the viscosity of the chocolates. The Casson yield value also decreased as the fat and free-fat contents of the powders used increased. Because of the already-established effects of fat and freefat on the vacuole volume of powders (Keogh et al., 2003), the Casson yield value of the chocolates increased with increasing vacuole volume of the powders. The hardness of the chocolates also decreased with increasing fat and free-fat contents of the powders used, as more milk fat became available to the continuous cocoa butter phase. The snap and gloss scores of the chocolates were not related to any property of the powders.
Acknowledgements This project was part-funded by the Irish Government under the National Development Plan 2000–2006. The technical assistance of Mr. John O’Keeffe and Mr. Robert Kennedy is greatly appreciated.
References Aguilar, C. A., Hollender, R., & Ziegler, G. A. (1994). Sensory characteristics of milk chocolate with lactose from spray-dried milk powder. Journal of Food Science, 59(6), 1239–1243.
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Aguilar, C. A., & Ziegler, G. A. (1994a). Physical and microscopic characterization of dry whole milk with altered lactose content. 1. Effect of lactose concentration. Journal of Dairy Science, 77(5), 1189–1197. Aguilar, C. A., & Ziegler, G. A. (1994b). Physical and microscopic characterization of dry whole milk with altered lactose content. 2. Effect of lactose crystallization. Journal of Dairy Science, 77(5), 1198–1204. Aguilar, C. A., & Ziegler, G. R. (1995). Viscosity of molten milk chocolate with lactose from spray-dried whole-milk powders. Journal of Food Science, 60(1), 120–124. Anon. (1996). Spruhgetrocknetes . Vollmilchpulver, Eigenschaften und Functionen. Susswaren, 40(11), 20–21. . Bohren, H.-U., Kuypers, T. W., & Meister, N. (1987). A process for the production of a milk powder. UK Patent Application 2 183 135 A. Societ!e des Produits Nestl!e S.A., Vevey, Switzerland. Chevalley, J. (1994). Chocolate flow properties. In S. T. Beckett (Ed.), Industrial chocolate manufacture and use (2nd ed.) (pp. 150–151). London: Blackie Academic and Professional. De Koster, P. (1989a). Funktionalit.at von Milchprodukten in Schokolade (I). Zucker- und Susswaren Wirtscaft, 42(9), . 278–282. De Koster, P. (1989b). Funktionalit.at von Milchprodukten in Schokolade (II). Zucker- und Susswaren Wirtscaft, 42(10), . 326–330. Dewettinck, K., De Moor, H., & Huyghebaert, A. (1996). The free-fat content of dried milk products and flow properties of milk chocolate. Milchwissenschaft, 51(1), 25–28. Dodson, A. G., Lewis, D. F., Holgate, J. H., & Richards, S. P. (1984). Research Report 495. BFMIRA, Leatherhead, Surrey, UK. Full, N. A., Yella Reddy, S., Dimick, P. S., & Ziegler, G. R. (1996). Physical and sensory properties of milk chocolate formulated with anhydrous milk fat fractions. Journal of Food Science, 61(5), 1068–1084. Hansen, S. O., & Hansen, P. S. (1990). Spray dried whole milk powder for the manufacture of milk chocolate. Scandinavian Dairy Information, 2, 79–82. Hartel, R. (1996). Applications of milk-fat fractions in confectionery products. Journal of the American Oil Chemists’ Society, 73(8), 945–953. Heiss, R., & Bartusch, W. (1957). On the rheological properties of dark chocolate masses. Review of International Chocolate, 12, 312–315. Keogh, M. K., Murray, C. A., & O’Kennedy, B. T. (2003). Effects of ultrafiltration of whole milk on some properties of spray-dried milk powders. International Dairy Journal, in press. Mistry, V. V., Hassan, H. N., & Robison, D. J. (1992). Effect of lactose and protein on the microstructure of dried milk. Food Structure, 11(1), 73–82. Mongia, G., & Ziegler, G. R. (2000). The role of particle size distribution of suspended solids in defining the flow properties of milk chocolate. International Journal of Food Properties, 3(1), 137–147. Moreau, D. L., & Rosenberg, M. (1993). Microstructure and fat extractability in microcapsules based on whey proteins or mixtures of whey proteins and lactose. Food Structure, 12(4), 457–468. Parsons, J. G., & Keeney, P. G. (1969). Phospholipid concentration in cocoa butter and its relationship to viscosity in dark chocolate. Journal of the American Oil Chemists’ Society, 46(8), 425–427. Scheruhn, E., Franke, K., & Tscheuschner, H.-D. (2000). Einfluss der Milchpulverart auf das Verarbeitungsverhalten und die Fliesseigenschaften von Milchschokoladenmasse, Teil 2. Merkmale des Milchpulvers beeinflussen die Viskosit.at. Zucker- und Susswarenwirtschaft, 53(5), 131–136. .
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Tietz, R. A., & Hartel, R. W. (2000). Effects of minor lipids on crystallization of milk fat–cocoa butter blends and bloom formation in chocolate. Journal of the American Oil Chemists’ Society, 77(7), 763–771. Twomey, M., Keogh, M. K., O’Kennedy, B. T., & Mulvihill, D. M. (2000). Effect of milk composition on selected properties of spraydried high-fat and skim-milk powders. Irish Journal of Agricultural and Food Research, 39(1), 79–94. Twomey, M., Keogh, M. K., O’Kennedy, B. T., & Mulvihill, D. M. (2002). Seasonal effects of some milk powder characteristics on the
rheology of milk chocolate. Irish Journal of Agricultural and Food Research, 41(1), 105–116. Vendeville, J. E. (1995). Make milk work for you in your chocolate. Kennedy’s Confection, 2(10), 14–15, 17. Verhey, J. G. (1986). Physical properties of dried milk in relation to chocolate manufacture. Netherlands Milk and Dairy Journal, 40(2), 261–268. Zurcher, . K. (1976). Anforderungen an Milchpulver. International Review for Sugar and Confectionery, 29(3), 278–282.
International Dairy Journal 13 (2003) 719–726
Effects of selected properties of ultrafiltered spray-dried milk powders on some properties of chocolate M. Kieran Keogh*, Cathriona A. Murray, Brendan T. O’Kennedy Teagasc, Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Ireland Received 6 January 2003; accepted 14 April 2003
Abstract The effects of selected properties of spray-dried milk fat powders on chocolate were determined. Milk powders produced from control or ultrafiltered (UF) milks with various levels of fat were blended with skim milk powder to give a standard 26 g fat 100 g1 powder. Particle size of the chocolate mixes after refining decreased as the fat content and free-fat content of the powders increased. Despite this, increasing fat and free-fat contents of powders reduced the Casson viscosity of the subsequent molten chocolates. Casson viscosities using powders from control or UF milks were similar, but decreased as the particle size of powders increased and particle size after refining the chocolate mix decreased. Casson yield value and hardness decreased as fat content of powders increased. Casson yield value increased with vacuole volume of powders. It is possible to alter important properties of chocolates using milk powders of varying fat contents, free-fat contents and particle sizes. r 2003 Elsevier Ltd. All rights reserved. Keywords: Milk powder properties; Chocolate particle size; Rheology; Hardness; Snap
1. Introduction Manufacturers of milk chocolate prefer to use milk powder produced by roller-drying rather than by spraydrying, because roller-dried powders have properties such as high free-fat content, large particle size and low vacuole volume which have positive effects on the properties of chocolate (Dewettinck, De Moor, & Huyghebaert, 1996). Previous research (Twomey, Keogh, O’Kennedy, & Mulvihill, 2002) defined the extent to which seasonal variations in the properties of spray-dried powders containing 56 g fat 100 g1 powder blended with skim milk powders affected the rheology of molten chocolate at the end of the conching stage and the final hardness of the chocolate. In subsequent work (Keogh, Murray, & O’Kennedy, 2003), spray-dried milk powders were prepared from control and ultrafiltered milks. These powders had a range of fat, free-fat, protein, moisture, vacuole volume contents, particle sizes and related properties. This paper deals with the effects of these powders on important properties of *Corresponding author. Tel.: +353-24-42235; fax: +353-25-42228. E-mail address: [email protected] (M. Kieran Keogh). 0958-6946/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0958-6946(03)00124-9
chocolate. In addition to the molten chocolate rheology and final hardness, the particle size after refining the chocolate ingredient mix and the particle size, snap and gloss of the final chocolates were studied in the current work. This should give greater insights into milk powder functionality, highlight certain powder properties beneficial to specific types of chocolate and bring nearer the goal of replacing roller-dried powder with spray-dried powder in chocolate. Milk powder properties that affect chocolate properties have been studied. These include free-fat (Zurcher, . 1976; de Koster, 1989a; Vendeville, 1995; Dewettinck et al., 1996; Twomey et al., 2000), specific fat pore surface (Scheruhn, Franke, & Tscheuschner, 2000), milk fat fractions (Hartel, 1996), milk fat hardness (Twomey et al., 2000), particle size (Chevalley, 1994; Twomey et al., 2000), particle size distribution (Mongia & Ziegler, 2000), particle structure (Verhey, 1986), particle density (Scheruhn et al., 2000), vacuole volume (Dodson, Lewis, Holgate, & Richards, 1984; Twomey et al., 2002), milk protein content and type (de Koster, 1989a, b), denaturation state (Anon., 1996; Hansen & Hansen, 1990; de Koster, 1989b); lactose content (Aguilar & Ziegler, 1994a), lactose crystallisation state (Bohren, Kuypers, & Meister, 1987; Aguilar & Ziegler,
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1994b) and moisture content (Heiss & Bartusch, 1957). Other minor components of milk fat such as mono- and di-glycerides (Tietz & Hartel, 2000) and phospholipids (Parsons & Keeney, 1969) may also have effects, but milk salts have been reported only to affect chocolate taste (de Koster, 1989a). However, convincing demonstrations of relationships between some of these milk powder and chocolate properties are frequently absent from the literature. One reason is that many workers use purchased powders, which provide qualitative rather than quantitative data. The processing of chocolate also has major effects on its properties, especially the refining conditions (gap width and roller pressure) and conching time. However, for the current work, the chocolate-making recipe, refining and conching conditions used before for 56 g fat 100 g1 powders (Twomey et al., 2002) were retained. The main objective of the current work was to determine the effects of variations in powder properties made from control and ultrafiltered milks on the properties of milk chocolate.
2. Materials and methods The milk chocolate recipe used (Twomey et al., 2000) had a 25 g 100 g1 incorporation rate of milk powder, a particle size after refining (by micrometer) of 26 mm (using a 56 g fat 100 g1 powder/skim milk powder blend), mean total fat content of 30.4 g 100 g1 and moisture content of 1.3 g 100 g1. 2.1. Preparation of milk chocolates Milk chocolates were manufactured using 21 of the spray-dried milk powders already made (Keogh et al., 2003). The powders had five fat contents (nominally 26, 30, 40 and 50–59 g 100 g1), free-fat contents (8–95 g 100 g1 fat), median particle sizes (56–121 mm), moisture contents (2.2–6.7 g 100 g1) and vacuole volumes (0.9–12.5 mL 100 g1). Standard powders containing 26 g fat 100 g1 were not blended, but powders with higher fat contents were blended with a commercial skim-milk powder to give a powder blend containing 26 g fat 100 g1 for use in chocolate. As the powders were made under constant processing conditions, the variations in the properties of the spray-dried powders (Table 1) were due mainly to differences in composition due to the fat content and level of ultrafiltration of the milks and total solids of the concentrates. The powders were stored in sealed bags at a constant temperature of 15 C until evaluated in chocolate. 2.2. Ingredients The following ingredients were used in the manufacture of milk chocolates as previously described (Twomey
et al., 2002): cocoa butter (Cadbury Ireland Ltd, Dublin), cocoa liquor (Nestle! Rowntree, Mallow, Co. Cork), sucrose (Irish Sugar Company, Mallow, Co. Cork), milk powders (prepared as described in Keogh et al., 2003) and lecithin (Topcithin 300, Lucas Meyer, Hamburg, Germany). 2.3. Process A Lipp conche (Lipp Mischtechnik, Mannheim, Germany) for 7 kg batches was used in the current work rather than the larger Frisse conche used previously. Cocoa liquor (0.831 kg) and 60% of the cocoa butter (0.810kg of 1.350 kg) were melted at 60 C . in a Stephan mixer (Stephan Sohne Gmbh, Hameln, Germany). Sugar (2.904 kg) and milk powder (1.653 kg) were then added to the melted fat and mixed for 5 min. The mixture was refined in two passes, with the gap sizes/pressure between the rollers of a three-roll refiner (Buhler, . New Barnet, Herts., UK) reduced in the second pass from 0.560 and 0.280 mm/1.0 MPa to 0.184 and 0.138 mm/0.7 MPa. These settings gave a particle size of 26 mm in the chocolate after refining when a 56 g fat 100 g1 powder/skim-milk powder blend was used. The refined mix was then conched in the Lipp conch for 7 h at 60 C. Lecithin (0.2 g 100 g1) and the remaining cocoa butter were added during the final stages of conching. A sample of molten chocolate was taken for rheological assessment at the end of the conching process and the remaining chocolate was stored in an incubator overnight at 50 C. On the following day, two 2 kg portions of the chocolate were tempered in a Hillard Chocolate System (Jimsan Enterprises, Inc., West Bridgewater, MA, USA) which was located in a controlled environment (21 C and 50% RH). The stored chocolate (50 C) was cooled to 45 C and held for 30 min; it was then tempered by cooling to 28 C in 20–25 min, holding for 10 min, heating to 30 C and holding for 5 min before moulding into plastic moulds. The moulded chocolate was placed in a temperature-controlled room at 15 C for 30 min before de-moulding and the finished bars were wrapped in aluminium foil and stored at 15 C until analysed. 2.4. Rheological properties of milk chocolate Samples of each chocolate were taken at the end of conching for rheological evaluation in a strain-controlled rheometer (Bohlin VOR) with concentric cylinder geometry. All measurements were taken at 40 C. Samples were pre-sheared for 2.5 min at 18.5 s1 followed by a shear rate sweep from 60 to 1 s1 in 3.5 min. The data were then used to calculate the Casson viscosity (ZCV ) and Casson yield value (sCA )
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Table 1 Selected properties of milk powders used in chocolate (n ¼ 21) Trial no.-fat content control or ultrafiltered
Fat (g 100 g1)
Protein (g 100 g1)
Free fat (g 100 g1)
Particle size (D(v; 0.5)) (mm)
Moisture (g 100 g1)
Vacuole volume (mL 100 g1)
1-26 Ca 1-26 UF1b 1-26 UF2 2-26 C 2-26 UF1 2-26 UF2 9-26 C 10-26 C 11-26 C 12-26 C 12-26 CRc 13-30 C 8-40 C 8-40 UF1 09-40 C 10-40 UF2 13-50 C 20-54 C 19-50 C 18-50 C 18-60 C Skim milk powder
25.1 25.5 25.6 24.5 25.2 25.1 26.1 29.2 29.3 25.6 25.7 31.9 39.6 42.9 40.4 40.2 51.7 53.8 51.4 51.7 59.2 0.8
28.6 32.2 34.1 29.7 32.9 35.1 25.7 30.3 30.1 26.7 26.8 35.3 27.0 32.2 20.7 26.9 17.4 17.5 18.3 18.3 15.3 —
12.6 21.2 57.1 25.7 49.3 74.2 13.2 13.6 9.3 8.4 7.8 20.6 45.0 63.1 49.4 73.9 78.4 91.2 74.9 90.4 95.5 —
82.6 75.5 121.3 55.7 63.7 68.3 59.3 83.7 69.7 69.9 64.9 63.7 57.1 67.9 81.9 78.8 104.1 67.4 93.7 70.5 91.6 61.6
4.5 4.2 6.7 2.3 2.9 3.8 3.7 2.6 2.6 2.2 3.2 2.9 2.7 2.3 3.0 3.8 2.3 3.2 2.8 3.0 2.8 5.0
12.5 8.3 9.6 7.4 6.6 5.7 4.1 8.4 7.4 7.3 6.4 7.3 3.7 2.7 3.1 4.0 3.3 2.0 2.5 2.5 0.9 22.2
a
C: control. UF: ultrafiltered milk. c R: replicate. b
(OICC, 1973) using the following equation: pffiffiffi pffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffipffiffiffi s ¼ sCA þ ZCA g’ ; where s is the shear stress (Pa), sCA is the Casson yield value (Pa), ZCV is the Casson viscosity (Pa s) and g’ is the shear rate (s1). 2.5. Hardness of moulded chocolate The maximum force (N) required to penetrate the moulded chocolate at 20 C for a distance of 5 mm with a 10 stainless-steel cone travelling at a velocity of 0.5 mm s1 was measured using an Instron Universal Testing Machine (Full, Yella Reddy, Dimick, & Ziegler, 1996). 2.6. Snap and gloss values of chocolate The snap and gloss values of the chocolates were assessed sensorially on a scale of 1=poor; 2=medium and 3=good by a panel of the same three technical people and the mean value recorded.
3. Results and discussion Twenty-one milk powders (26–60 g 100 g1 nominal fat content), including six prepared from UF milks, were
selected from a range of powders already produced (Keogh et al., 2003) for evaluation in chocolate. The properties of the milk powders used and the skim milk powder used for blending with the high-fat powders (fat content, free-fat content, particle size, moisture and vacuole volume) are outlined in Table 1. The effects of the powder properties on the particle size of the chocolate mix after refining, the viscosity and yield value of the molten chocolates at the end of conching and the hardness, snap and gloss of the finished chocolates are shown in Table 2. 3.1. Particle size after refining The particle size (by micrometer) of the chocolate mixes after refining increased curvilinearly from 26 to a mean of 43 mm as the fat content of the powders used decreased from 59 to 26 g 100 g1 (n ¼ 21; r ¼ 0:859; Po0:001; Fig. 1). However, the correlation coefficient was lower (r ¼ 0:817; Po0:001; Fig. 2) for the relationship between the particle size after refining and free-fat content of the powders. This is because the six powders produced from UF milks had higher protein and free-fat contents (codes UF1 and UF2, Table 1), but had almost the same mean particle size after refining as control powders (42 vs. 41 mm, Table 2). This shows that chocolate mixes containing powders with higher contents of fat (even though blended with skim milk
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Table 2 Properties of milk chocolates (n ¼ 21) Trial no.-fat content control or ultrafiltered
Particle size after refining (mm) (%)
Viscosity (Pa s)
Yield value (Pa)
Hardness (N)
Snap score (range 1–3)
Gloss score (range 1–3)
1-26 Ca 1-26 UF1b 1-26 UF2 2-26 C 2-26 UF1 2-26 UF2 9-26 C 11-26 11-26 12-26 C 12-26 CRc 13-30 C 8-40 C 8-40 UF1 09-40 C 10-40 UF2 13-50 C 20-54 C 19-50 C 18-50 C 18-60 C
46 41 43 42 45 42 40 44 44 40 41 44 40 37 37 45 38 28 39 28 26
1.55 1.57 1.46 1.57 1.58 1.59 1.65 1.61 1.55 1.63 1.63 1.58 1.33 1.31 1.43 1.45 1.28 1.42 1.39 1.39 1.32
10.1 12.1 11.7 13.0 11.2 14.6 13.8 11.5 15.6 14.2 14.3 10.7 6.4 6.5 10.8 10.2 7.7 6.1 7.5 6.2 6.5
2.81 3.42 2.65 3.54 3.23 3.20 2.93 3.21 3.21 3.06 3.15 2.73 2.30 2.27 2.56 2.50 1.97 2.49 2.69 2.75 2.80
3.0 2.0 2.0 3.0 3.0 2.5 3.0 3.0 2.5 2.5 3.0 2.5 2.0 2.0 2.5 2.0 2.5 2.0 2.0 2.7 2.6
2.7 3.0 2.0 2.0 2.0 2.5 3.0 3.0 3.0 3.0 3.0 3.0 2.0 2.3 3.0 2.0 3.0 2.0 2.0 2.7 2.6
a b
C: control. UF: ultrafiltered milk.
50 Particle size after refining (µm)
Particle size after refining (µm)
50 45 40 35 30
45 40 35 30 25 0
25 24
30
36
42
48
54
60
20
40
60
80
100
Free-fat content (g100g-1 powder)
-1
Fat content (g100g powder)
Fig. 1. Effect of fat content of control and UF milk powders on the particle size of chocolate mixes after refining. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
powder) rather than higher free-fat and protein contents are more easily refined. This is probably because powder particles containing higher contents of fat are softer and respond better to refining. A particle size of 26 mm or lower after refining usually gives a grittiness score of zero in the final chocolate. The grittiness scores of these chocolates were not measured, but it is common experience that grittiness becomes increasingly detectable in finished chocolates as the particle size exceeds 26 mm.
Fig. 2. Effect of free fat content of control and UF milk powders on the particle size of chocolate mixes after refining. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
3.2. Casson viscosity of chocolate When the control powders containing 26–60 g fat 100 g1 were used to make chocolates, the Casson viscosity of the molten chocolates decreased linearly from 1.63 to 1.32 Pa s as the free-fat content of the powders increased from 8 to 95 g 100 g1 fat (r ¼ 0:870; n ¼ 15; Po0:001; Fig. 3). A similar correlation (r ¼ 0:886) was found between the Casson viscosity and fat content of the same powders (not
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1.7 Casson viscosity (Pas)
Casson viscosity (Pas)
1.7
723
1.6 1.5 1.4 1.3 1.2
1.6 1.5 1.4 1.3 1.2
0
20
40
60
80
100
-1
Free-fat content (g100g fat)
50
70
90
110
Powder particle size D(v, 0.5) µm
Fig. 3. Effect of the free-fat content of control powders on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
Fig. 4. Effect of the median particle size of control powders on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
shown). This provides further evidence that the effects of fat and free-fat contents of milk powders on the Casson viscosity are highly inter-related. However, when all powders (control and UF-treated) were evaluated, the correlation coefficient between the Casson viscosity of the chocolates and free-fat content of the powders was lower (0.783, n ¼ 21; Po0:001). The free-fat content of the six UF powders increased with increasing protein content (Table 1), but the mean Casson viscosity of the chocolates made with these powders was almost the same as the control powders (1.49 vs. 1.50 Pa s). This shows that the increased protein in the UF powders counteracted the viscosity-lowering effect in the chocolates of increased free-fat in the powders. Even though increasing powder protein content reduced the powder solids density (r ¼ 0:419; Po0:1), the particle density was not significantly reduced (Keogh et al., 2003), because the vacuole volume of the powders did not increase with powder protein as was found elsewhere (Aguilar et al., 1994a). Increasing protein content also increases the porosity of the powder structure (Mistry, Hassan, & Robison, 1992; Moreau & Rosenberg, 1993; Aguilar et al., 1994a), leading to increased absorption of fat into the powder particles (Scheruhn et al., 2000). There was also a significant correlation (r ¼ 0:658; n ¼ 21; Po0:01) between the vacuole volume of all the powders and the viscosity of the chocolates, because the vacuole volume of the powders was inversely related to the fat content (r ¼ 0:823; Po0:001) and the free-fat content (r ¼ 0:717; Po0:001). This confirms that increasing fat or free-fat depressed foaming and vacuole formation (Verhey, 1986). The vacuole volume of powders has been found to be related to the viscosity (Dodson et al., 1984) or the yield value of chocolates (Twomey et al., 2002). This is because powders with high vacuole volumes occupy a larger volume of the continuous fat phase or in extreme cases may have a greater tendency to shatter during refining and produce fines (Aguilar & Ziegler, 1995).
There was also a significant correlation (r ¼ 0:516; n ¼ 15; Po0:05; Fig. 4) between the particle size of the control powders and the Casson viscosity of the chocolates. The Casson viscosity decreased from 1.57 to 1.28 Pa s as the powder particle size increased from 57 to 104 mm. The decrease in Casson viscosity might have been greater, had not the increase in particle size been mainly due to the increased moisture content of the powders (Keogh et al., 2003). This suggests that the increased powder moisture mainly counteracted the benefits of increased particle size. Even if the decrease in Casson viscosity was not large in commercial terms, the effects of the particle size of powders with the same moisture content will be investigated in a future paper. As has been already stated (Twomey et al., 2002), larger particle size powders have lower specific surface area, less fat from the continuous phase is required to coat the powder particles and as a result, the Casson viscosity decreases. The Casson viscosity of the chocolates was related to the particle size of chocolate mixes after refining but contrary to the way anticipated. In principle, Casson viscosity and even more so the yield value are expected to decrease with increasing particle size after refining (Aguilar et al., 1995), but Fig. 5 shows that viscosity increased as the particle size after refining increased (r ¼ 0:586; n ¼ 21; Po0:01). This is because the reduction in viscosity of chocolates caused by increasing powder free-fat contents far outweighed the effect of the decrease in particle size after refining the higher-fat powders. Taking all factors together, high-fat powders and properties associated with high-fat powders (high free-fat and low vacuole volume) reduced the viscosity of molten chocolate at the end of conching. 3.3. Casson yield value of chocolate The Casson yield value of the chocolates decreased curvilinearly (r ¼ 0:873; n ¼ 21; sig. o0.001, Fig. 6) from a mean of 12.8 Pa for powders containing 26 g fat
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724
16
Casson yield value (Pa)
Casson viscosity (Pas)
1.7 1.6 1.5 1.4 1.3
14 12 10 8 6
1.2 25
30 35 40 45 Particle size after refining (µm)
0
50
Fig. 5. Effect of the particle size after refining of chocolate mixes on the Casson viscosity of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
10
Fig. 7. Effect of the vacuole volume of milk powders on the Casson yield value of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
16
3.6
Chocolate hardness (N)
Casson yield value (Pa)
2 4 6 8 Vacuole volume (mL100g-1)
14 12 10 8 6
3.2 2.8 2.4 2.0 1.6
4 20
30
40
50
60
-1
Powder fat content (g100g )
24
30
36
42
48
54
60
Powder fat content (g100g-1)
Fig. 6. Effect of the fat content of milk powders on the Casson yield value of molten chocolates at the end of conching. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
Fig. 8. Effect of the fat content of milk powders on the hardness of chocolates. Regression line (—) is fitted to experimental values (K). See text for details of preparation of chocolates.
100 g1 to 6.5 Pa for a powder containing 59 g fat 100 g1. The yield value was also similarly related to the free-fat content (r ¼ 0:709; n ¼ 21; Po0:001). Since the vacuole volume of the powders decreased as the fat and free-fat contents of the powders increased (Keogh et al., 2003), the yield value of the chocolates increased as the vacuole volume of the same powders increased (r ¼ 0:737; n ¼ 20; Po0:001; Fig. 7). As with the Casson viscosity previously, high-fat powders and properties associated with high-fat powders (high free-fat and low vacuole volume) reduced the Casson yield value of molten chocolates at the end of conching.
present in the continuous phase of the chocolate (Aguilar, Hollender, & Ziegler, 1994; Twomey et al., 2002). As a result, the hardness of the finished chocolate decreased. Two chocolates made with roller dried powders and two retail bar chocolates had hardness values in the range 2.3–2.6 N, whereas milk powders with fat contents of 39–52 g 100 g1 had hardness values in the range 2.0–2.8 N.
3.4. Hardness of finished chocolate The hardness of the finished chocolates decreased curvilinearly from a mean of 3.1 N for powders containing 26 g fat 100 g1 powder to 2.5 N for powders containing 39–59 g fat 100 g1 powder (Fig. 8, r ¼ 0:786; n ¼ 21; Po0:001). The free-fat content of the powders was less strongly related to chocolate hardness (r ¼ 0:569; n ¼ 21; Po0:01). As the powder fat content increased, free-fat increased and more milk fat was
3.5. Snap score of chocolates The snap scores (scale 1–3) of the chocolates ranged from 2.0 to 3.0, but were not related to any property of the powders. The snap score of two retail bar chocolates and two chocolates made with roller dried powders achieved the highest score of 3.0. 3.6. Gloss score of chocolates The gloss scores (scale 1–3) of the chocolates also ranged from 2.0 to 3.0, but were not related to any property of the powders. The gloss scores of two retail
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bar chocolates and two chocolates made with roller dried powders achieved the highest score of 3.0.
4. Conclusions The properties of the chocolates were influenced by the properties of the spray-dried milk powders used in their manufacture. Chocolate mixes were more easily refined to a smaller particle size when blended high-fat powders were used rather than powders containing 26 g fat 100 g1. The smaller particle size after refining was related more to the fat content than to the free-fat content of the high-fat powders. The Casson viscosity of molten chocolates decreased with increasing free-fat or fat content of the control powders. However, the higher protein contents of UF powders counteracted the effect of their higher free-fat contents on the Casson viscosity in chocolates. Increasing the powder particle size mainly by increasing the moisture content reduced the Casson viscosity of the molten chocolates by a modest amount, indicating that increased powder moisture counteracted the benefits of increased particle size. The particle size after refining, which decreased as the fat content of the powder used increased, did not increase the viscosity of the chocolates at the end of conching. The effect of the particle size decrease was far outweighed by the increased free-fat contents of the higher fat powders and lead overall to a reduction in the viscosity of the chocolates. The Casson yield value also decreased as the fat and free-fat contents of the powders used increased. Because of the already-established effects of fat and freefat on the vacuole volume of powders (Keogh et al., 2003), the Casson yield value of the chocolates increased with increasing vacuole volume of the powders. The hardness of the chocolates also decreased with increasing fat and free-fat contents of the powders used, as more milk fat became available to the continuous cocoa butter phase. The snap and gloss scores of the chocolates were not related to any property of the powders.
Acknowledgements This project was part-funded by the Irish Government under the National Development Plan 2000–2006. The technical assistance of Mr. John O’Keeffe and Mr. Robert Kennedy is greatly appreciated.
References Aguilar, C. A., Hollender, R., & Ziegler, G. A. (1994). Sensory characteristics of milk chocolate with lactose from spray-dried milk powder. Journal of Food Science, 59(6), 1239–1243.
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Aguilar, C. A., & Ziegler, G. A. (1994a). Physical and microscopic characterization of dry whole milk with altered lactose content. 1. Effect of lactose concentration. Journal of Dairy Science, 77(5), 1189–1197. Aguilar, C. A., & Ziegler, G. A. (1994b). Physical and microscopic characterization of dry whole milk with altered lactose content. 2. Effect of lactose crystallization. Journal of Dairy Science, 77(5), 1198–1204. Aguilar, C. A., & Ziegler, G. R. (1995). Viscosity of molten milk chocolate with lactose from spray-dried whole-milk powders. Journal of Food Science, 60(1), 120–124. Anon. (1996). Spruhgetrocknetes . Vollmilchpulver, Eigenschaften und Functionen. Susswaren, 40(11), 20–21. . Bohren, H.-U., Kuypers, T. W., & Meister, N. (1987). A process for the production of a milk powder. UK Patent Application 2 183 135 A. Societ!e des Produits Nestl!e S.A., Vevey, Switzerland. Chevalley, J. (1994). Chocolate flow properties. In S. T. Beckett (Ed.), Industrial chocolate manufacture and use (2nd ed.) (pp. 150–151). London: Blackie Academic and Professional. De Koster, P. (1989a). Funktionalit.at von Milchprodukten in Schokolade (I). Zucker- und Susswaren Wirtscaft, 42(9), . 278–282. De Koster, P. (1989b). Funktionalit.at von Milchprodukten in Schokolade (II). Zucker- und Susswaren Wirtscaft, 42(10), . 326–330. Dewettinck, K., De Moor, H., & Huyghebaert, A. (1996). The free-fat content of dried milk products and flow properties of milk chocolate. Milchwissenschaft, 51(1), 25–28. Dodson, A. G., Lewis, D. F., Holgate, J. H., & Richards, S. P. (1984). Research Report 495. BFMIRA, Leatherhead, Surrey, UK. Full, N. A., Yella Reddy, S., Dimick, P. S., & Ziegler, G. R. (1996). Physical and sensory properties of milk chocolate formulated with anhydrous milk fat fractions. Journal of Food Science, 61(5), 1068–1084. Hansen, S. O., & Hansen, P. S. (1990). Spray dried whole milk powder for the manufacture of milk chocolate. Scandinavian Dairy Information, 2, 79–82. Hartel, R. (1996). Applications of milk-fat fractions in confectionery products. Journal of the American Oil Chemists’ Society, 73(8), 945–953. Heiss, R., & Bartusch, W. (1957). On the rheological properties of dark chocolate masses. Review of International Chocolate, 12, 312–315. Keogh, M. K., Murray, C. A., & O’Kennedy, B. T. (2003). Effects of ultrafiltration of whole milk on some properties of spray-dried milk powders. International Dairy Journal, in press. Mistry, V. V., Hassan, H. N., & Robison, D. J. (1992). Effect of lactose and protein on the microstructure of dried milk. Food Structure, 11(1), 73–82. Mongia, G., & Ziegler, G. R. (2000). The role of particle size distribution of suspended solids in defining the flow properties of milk chocolate. International Journal of Food Properties, 3(1), 137–147. Moreau, D. L., & Rosenberg, M. (1993). Microstructure and fat extractability in microcapsules based on whey proteins or mixtures of whey proteins and lactose. Food Structure, 12(4), 457–468. Parsons, J. G., & Keeney, P. G. (1969). Phospholipid concentration in cocoa butter and its relationship to viscosity in dark chocolate. Journal of the American Oil Chemists’ Society, 46(8), 425–427. Scheruhn, E., Franke, K., & Tscheuschner, H.-D. (2000). Einfluss der Milchpulverart auf das Verarbeitungsverhalten und die Fliesseigenschaften von Milchschokoladenmasse, Teil 2. Merkmale des Milchpulvers beeinflussen die Viskosit.at. Zucker- und Susswarenwirtschaft, 53(5), 131–136. .
ARTICLE IN PRESS 726
M. Kieran Keogh et al. / International Dairy Journal 13 (2003) 719–726
Tietz, R. A., & Hartel, R. W. (2000). Effects of minor lipids on crystallization of milk fat–cocoa butter blends and bloom formation in chocolate. Journal of the American Oil Chemists’ Society, 77(7), 763–771. Twomey, M., Keogh, M. K., O’Kennedy, B. T., & Mulvihill, D. M. (2000). Effect of milk composition on selected properties of spraydried high-fat and skim-milk powders. Irish Journal of Agricultural and Food Research, 39(1), 79–94. Twomey, M., Keogh, M. K., O’Kennedy, B. T., & Mulvihill, D. M. (2002). Seasonal effects of some milk powder characteristics on the
rheology of milk chocolate. Irish Journal of Agricultural and Food Research, 41(1), 105–116. Vendeville, J. E. (1995). Make milk work for you in your chocolate. Kennedy’s Confection, 2(10), 14–15, 17. Verhey, J. G. (1986). Physical properties of dried milk in relation to chocolate manufacture. Netherlands Milk and Dairy Journal, 40(2), 261–268. Zurcher, . K. (1976). Anforderungen an Milchpulver. International Review for Sugar and Confectionery, 29(3), 278–282.