Rheological and optical properties of commercial chocolate milk beverages

Journal of Food Engineering 51 (2002) 229±234

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Rheological and optical properties of commercial chocolate milk beverages Mario Yanes, Luis Dur an, Elvira Costell

*

Instituto de Agroquõmica y Tecnologõa de Alimentos (CSIC), P.O. Box 73, 46100 Burjassot, Valencia, Spain Received 29 September 2000; accepted 7 March 2001

Abstract Flow behaviour and colour of nine commercial samples from three di€erent lots of chocolate ¯avoured milk beverages were analysed. Experimental shear stress±shear rate relationships, obtained at 25°C, ®tted mostly to the Newton model, as for plain milk, though some samples ®tted better to Ostwald-de Waale and Bingham models. Newtonian viscosity values ranged from 2.67 to 18.68 mPa s for samples of one lot. At 5°C, as expected, Newtonian viscosity of samples was higher and pseudoplasticity increased (n values were lower). Six of the nine samples showed consistent viscosity values through the lots. Main di€erences in colour of samples were detected for parameter L (brightness), ranging from very light …L ˆ 53:5† to dark …L ˆ 18:3† samples. Except for two samples brightness values were consistent through the lots. Hue …h † values were consistent for all samples. However, chromaticity …C  † values di€ered from one lot to the other, except for two other samples, showing the diculty in controlling this attribute in industry. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Rheology; Colour; Milk beverages

1. Introduction Milk beverages of di€erent ¯avours for direct consumption are common in Spain and other countries. Their nutritional and sensory characteristics as well as their convenience, mainly when presented in individual packs, favour their consumption by several groups of consumers like young and elder people. Chocolate ¯avoured products are the most popular ones. Basically, they are formulated with milk, sucrose, cocoa powder and some hydrocolloids, added to improve consistency and prevent sedimentation of cocoa particles. Dairy solids are sometimes included. The particular characteristics of the di€erent ingredients ± fat content of milk, alcalinity and colour of cocoa powder, type and concentration of hydrocolloid ± should produce noticeable di€erences in the ®nal composition and in the speci®c physical and sensory properties of the formulated products. Some literature references can be found reporting on the dependance of the sensory properties of these products or of those obtained by dilution of instant powdered chocolate milk in water on some com-

*

Corresponding author. Tel.: +34-963-900022; fax: +34-963-636301. E-mail address: [email protected] (E. Costell).

positional factors, such as milk fat content (Raats & Shepherd, 1992), hydrocolloid, sucrose, and cocoa powder contents (Folkenberg, Bredie, & Martens, 1999; Hough & Sanchez, 1998). In¯uence of composition on consumer acceptance of these products has also been reported (Hough, Sanchez, Barbieri, & Martinez, 1997; Pangborn, 1988; Scriven & Petty, 1990). There is practically no information on physical properties of ¯avoured milk beverages, particularly on colour and ¯ow behaviour, despite their evident dependence on initial formulation and their considerable in¯uence on consumer acceptance. The e€ects of fat content on colour and on viscosity (Kristensen, Jensen, Madsen, & Birdi, 1997; Phillips, McGi€, Barbano, & Lawless, 1995; Wayne & Shoemaker, 1988), the relations existing between physicochemical characteristics of casein micelles and ¯ow behaviour (Kristensen et al., 1997; Prentice, 1992) and the e€ect of hydrocolloids on ¯ow behaviour (Langendor€ et al., 2000; Oakenfull, Miyoshi, Nishinari, & Scott, 1999; Schmidt & Smith, 1992) have been studied on milk, the major component of these beverages. It is to be expected that ingredients like sucrose, cocoa, and hydrocolloids may exert their in¯uence on both optical and rheological properties of milk beverages.

0260-8774/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 1 ) 0 0 0 6 1 - 9

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The aims of this work were to analyse ¯ow behaviour and colour of commercial chocolate milk beverages, to study di€erences between brands and lots and the e€ect of consumption temperature (5°C or 25°C) on their ¯ow behaviour.

2. Materials and methods 2.1. Samples Samples of nine di€erent brands, covering the commercial range in the Spanish market, were selected and acquired on three di€erent dates (lots): September 1999 (lot 1), December 1999 (lot 2), and March 2000 (lot 3). Their main characteristics are given in Table 1. 2.2. Soluble solids and pH Soluble solids were determined in a digital refractometer (ATAGO RX-100) at room temperature and the results expressed as degrees Brix at 20°C. A digital potentiometer (CRISON 2001) was used to measure pH at room temperature. Both measurements were done in quadruplicate.

2.4. Measurement of colour Colour of samples was measured in a Hunter colorimeter, Labscan II model, using 6 cm diameter and 3.8 cm height cells and a 0.5 in. diaphragm. Translucency of samples was previously checked by measuring di€used re¯ection of a 3.5 cm layer thickness on both black and white (X ˆ 78.5, Y ˆ 83.32, Z ˆ 87.94) backgrounds, according to Judd and Wyszecki (1967). Re¯ection spectra were registered and CIELAB colour parameters for 10° vision angle and D65 illuminant (L : brigthness, a : redness, b : yellowness, C  : saturation, and h : hue) were calculated. Measurements were done in triplicate on each of two subsamples. 2.5. Statistical analysis Analysis of variance of two factors and interactions were applied to the di€erent sets of data. Least signi®cant di€erences were calculated by the Fisher's test (a 6 0:05). These analyses were performed using the Statgraphics Plus 3.1 software.

3. Results and discussion

2.3. Rheological measurements

3.1. Characterization of ¯ow. In¯uence of temperature

A coaxial cylinders viscosimeter (Haake VT 550) with a NV double gap cell, monitored by a Rheowin Job Manager V. 2.5, Haake Software OS 550, was used. Shear stress values were measured at shear rates from 1.00 to 300 s 1 with a 120 s ramp, holding the samples in a thermostated bath at 25  0:1°C or at 5  0:1°C. Measurements were done in duplicate in each of two subsamples. Experimental data were ®tted to Newton _ Ostwald …r ˆ K c_ n † and Bingham …r ˆ r0 ‡ …r ˆ gc†, 0 _ models. Values of r and c_ were obtained and ®tted g c† to the di€erent models by using the Rheowin Data Manager V. 2.5 software.

The variation of shear stress (r) values with shear rate _ determined at two temperatures (25°C and 5°C) on (c), samples of the ®rst lot, were ®tted to Newton, Ostwaldde Waale, and Bingham models (Table 2). At 25°C, the ¯ow of samples 1, 2, and 3 was practically Newtonian with n values higher than 0.925 while that of samples 5, 6, 7, and 8 ®tted better to Ostwald-de Waale model with ¯ow indices ranging between 0.747 and 0.849. The latter samples also showed a good ®tting to the Bingham model with yield stress values higher than 100 mPa (150:20 < r0 < 503:80 mPa). Samples 4 and 9 showed an intermediate behaviour. In general, ¯ow behaviour of

Table 1 Soluble solids, pH values and price levels of chocolate milk beverage samples

a

Sample

Milk typea

Hydrocolloida

Soluble solids (°Brix)b

pHb

1 2 3 4 5 6 7 8 9

Non-fat & whole Non-fat & whole Low-fat Non-fat & dairy solids Low-fat Low-fat Low-fat Whole & dairy solids Non-fat

Alginate Alginate Carrageenan Alginate Carrageenan Carrageenan & CMC Carrageenan & MCC Carrageenan Carrageenan

16.25 16.30 18.17 17.75 18.02 17.60 17.77 18.40 17.50

7.35 7.20 6.71 6.79 6.86 6.83 6.98 6.87 7.05

(0.22) (0.21) (0.25) (0.13) (0.36) (0.21) (0.12) (0.38) (0.08)

Declared in the label. Mean values of four measurements at 20°C, Standard deviations within parentheses. c H: High ; M: Medium; L: Low. b

Price levelc (0.05) (0.31) (0.03) (0.07) (0.04) (0.04) (0.06) (0.03) (0.06)

L M H M H H H H L

M. Yanes et al. / Journal of Food Engineering 51 (2002) 229±234

231

Table 2 Flow behaviour of chocolate milk beveragesa Sampleb

Temperature (°C)

Newton

Ostwald

g (mPa s)

r

Bingham

K (mPa sn )

n

r

r0 (mPa)

g0 (mPa s)

r

1 2 3 4 5 6 7 8 9

25 25 25 25 25 25 25 25 25

2.70 3.76 4.52 4.44 8.63 9.55 16.90 10.92 5.02

0.965 0.982 0.984 0.943 0.986 0.985 0.972 0.975 0.978

3.24 3.45 6.76 13.59 19.45 24.48 65.61 39.14 11.63

0.966 0.990 0.925 0.792 0.849 0.825 0.747 0.762 0.843

0.966 0.982 0.986 0.957 0.993 0.995 0.997 0.996 0.985

9.69 ±c 40.48 100.30 150.20 182.40 503.80 314.50 87.13

2.65 ± 4.33 3.94 7.88 8.65 14.40 9.37 4.59

0.966 ± 0.985 0.953 0.992 0.993 0.992 0.993 0.984

1 2 3 4 5 6 7 8 9

5 5 5 5 5 5 5 5 5

6.44 8.89 9.40 8.21 17.59 19.62 24.76 29.61 10.21

0.991 0.996 0.996 0.996 0.995 0.992 0.984 0.970 0.996

3.69 7.59 5.98 7.84 31.73 43.36 73.64 126.90 7.52

0.999 0.999 0.999 0.999 0.890 0.853 0.797 0.729 0.999

0.993 0.996 0.997 0.996 0.998 0.998 0.998 0.999 0.997

± ± ± ± 211.80 322.00 558.60 952.20 ±

± ± ± ± 16.54 18.03 21.99 24.91 ±

± ± ± ± 0.998 0.997 0.995 0.993 ±

a

Fitting of values of shear stress versus shear rate for samples of lot 1, measured at two temperatures (5°C and 25°C), to di€erent models. Flow parameters values and correlation coecients. b Identi®cation of samples in Table 1. c Not ®tting to model.

these products was qualitatively similar to that of milk. Although for most practical purposes milk is a nearly Newtonian ¯uid with viscosity values between 2.2 and 2.5 mPa s (Prentice, 1992), its ¯ow behaviour is complex Table 3 Viscosity of chocolate milk beverages from di€erent lots, at 250:1°Ca Sampleb

Lot 1

1 2 3 4 5 6 7 8 9

2.67 3.77 4.59 4.27 8.40 9.64 18.68 10.85 4.81

Lot 2 (0.05) (0.02) (0.09) (0.21) (0.87) (0.12) (1.7) (0.09) (0.28)

3.99 3.83 4.74 5.98 8.32 6.08 13.01 5.58 6.07

Lot 3 (0.18) (0.01) (0.68) (0.33) (0.27) (0.05) (1.19) (0.21) (0.02)

4.10 3.72 4.94 5.33 8.38 5.24 15.84 11.87 5.83

(0.06) (0.24) (0.16) (0.46) (0.39) (0.03) (1.14) (0.13) (0.01)

a

Mean values (n ˆ 4) in mPa s and standard deviations within parentheses. b Identi®cation of samples in Table 1.

and strongly dependent on temperature, on the applied shear rate and on both concentration and physical state of the dispersed phase, the latter being mainly due to the hydrodynamic volume of the casein micelles and to fat content (Van Vliet & Walstra, 1980). Depending on the conditions of measurement (shear strain rates and temperature) and on the type of viscosimeter used (capillary tube, rotational steady shear or controlled stress), the ¯ow of milk has been characterised by di€erent authors as Newtonian, shear thinning or Bingham plastic (Kristensen et al., 1997; Phillips et al., 1995; Wayne & Shoemaker, 1988). Quantitative di€erences in the rheological parameters between milk and the analysed milk beverages are due to the addition of sucrose and hydrocolloids to the latter. Qualitative di€erences could be

Table 4 Viscosity of chocolate milk beverages from di€erent lots at 5  0:1°Ca

a

Fig. 1. Viscosity of samples from all lots at 25  0:1°C.

Sampleb

Lot 1

1 2 3 4 5 6 7 8 9

6.89 8.51 9.86 8.45 18.19 20.41 32.13 30.07 9.99

Lot 2 (0.66) (0.53) (0.65) (0.33) (0.91) (1.12) (2.21) (0.65) (0.30)

7.27 6.65 8.72 10.22 19.13 11.82 21.61 10.38 11.19

Lot 3 (0.12) (0.10) (0.59) (0.47) (2.33) (1.21) (1.65) (0.97) (0.01)

8.37 6.96 9.40 10.28 14.02 10.63 23.70 20.11 9.45

(0.48) (0.11) (0.30) (0.32) (1.71) (0.65) (2.76) (0.53) (0.04)

Mean values …n ˆ 4† in mPa s and standard deviations within parentheses. b Identi®cation of samples in Table 1.

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M. Yanes et al. / Journal of Food Engineering 51 (2002) 229±234

attributed mainly to the di€erent types of milk used in their formulation (Table 1), to the concentration and type of hydrocolloid and to the possible interactions between them and the casein micelles. These beverages are frequently consumed cool. On decreasing the temperature from 25°C to 5°C (Table

Table 5 Opacity evaluationa Sampleb

L on black platec

L on white platec

t valued

1 2 3 4 5 6 7 8 9

33.65 37.20 31.63 25.67 41.28 46.60 53.54 45.78 36.17

33.68 37.48 31.76 25.50 41.29 46.46 53.55 45.45 35.71

0.9534 1.686 0.638 1.417 0.329 0.799 0.144 0.876 0.210

(0.12) (0.14) (0.61) (0.11) (0.09) (0.18) (0.02) (0.09) (0.44)

(0.09) (0.16) (0.27) (0.13) (0.13) (0.06) (0.14) (0.57) (1.52)

a

L values of samples, measured on black and on white background, and experimental Student t values. b Identi®cation of samples in Table 1. c Mean values of four measurements. Standard deviations in parentheses. d Student t value from tables (a ˆ 0:05) ˆ 2.353.

2), an increase in Newtonian viscosity was clearly observed, as expected, in all samples. Also consistency …K† values of pseudoplastic or shear thinning samples and both yield stress and plastic viscosity of samples ®tted to the Bingham model were higher. Fitting of rheograms obtained at 5°C to the three considered models con®rmed that samples 5, 6, 7, and 8 were less Newtonian than the rest. Without knowing the exact composition of the analysed samples it is dicult to interpret the detected di€erences in rheological behaviour. However, it can be assumed that the plasticity detected in samples 5, 6, 7, and 8 could be due to the formation a carrageenan/casein micelle network (Langendor€ et al., 2000) and that addition of carrageenan or alginate to the rest of samples simply produced an increase in viscosity of the whole system without contributing to the formation of network structures. 3.2. Rheological properties of samples. E€ects of sample and lot Rheological data obtained at 25°C for samples of lots 2 and 3 showed slight variations compared to the results for lot 1. In order to facilitate comparison and based on

Table 6 Colour of chocolate milk beveragesa

a b

Lot

Sampleb

L

a

1 1 1 1 1 1 1 1 1

1 2 3 4 5 6 7 8 9

33.68 37.48 31.76 25.50 43.72 46.46 53.00 45.45 35.71

(0.09) (0.16) (0.27) (0.13) (0.03) (0.06) (0.08) (0.57) (1.51)

11.99 13.07 11.03 11.43 10.84 12.19 9.71 12.01 13.95

2 2 2 2 2 2 2 2 2

1 2 3 4 5 6 7 8 9

38.46 37.97 31.45 25.68 41.88 42.13 53.55 41.26 18.31

(0.37) (0.61) (0.33) (0.08) (0.13) (0.11) (0.14) (0.24) (0.29)

3 3 3 3 3 3 3 3 3

1 2 3 4 5 6 7 8 9

38.20 36.59 33.83 44.99 41.28 45.66 50.62 40.14 41.71

(0.52) (0.49) (0.12) (0.39) (0.09) (0.19) (0.09) (0.26) (0.90)

b (0.04) (0.17) (0.08) (0.25) (0.02) (0.05) (0.08) (0.31) (0.38)

h

(0.24) (0.33) (0.53) (0.74) (0.20) (0.13) (0.27) (0.07) (0.41)

18.87 19.96 18.83 19.68 19.62 22.57 17.96 21.53 22.14

(0.20) (0.18) (0.40) (0.61) (0.15) (0.08) (0.26) (0.19) (0.24)

50.56 49.10 54.11 54.35 54.59 57.32 57.29 56.12 50.91

(0.43) (0.90) (1.05) (1.5) (3.3) (0.28) (0.40) (0.70) (1.28)

11.59 (0.06) 13.3 (0.14) 11.01 (0.17) 11.71 (0.28) 10.93 (0.26) 11.72 (0.19) 9.89 (0.12) 12.71 (0.10) 11.97 (0.20)

16.0 (0.36) 14.76 (0.45) 17.23 (0.62) 15.62 (0.62) 14.73 (0.50) 17.81 (0.79) 14.72 (0.06) 17.39 (0.27) 18.10 (0.42)

19.81 19.76 20.45 19.52 18.34 21.32 17.73 21.37 21.70

(0.29) (0.26) (0.19) (0.37) (0.27) (0.56) (0.10) (0.13) (0.39)

54.22 47.47 57.30 53.13 53.40 56.62 56.10 53.83 56.52

(0.60) (0.35) (0.93) (1.6) (1.5) (1.55) (0.29) (0.41) (0.69)

11.08 11.51 10.85 12.31 10.85 12.59 11.28 13.93 14.28

14.08 14.13 18.28 15.62 14.70 18.00 16.24 20.70 18.79

17.91 18.22 21.26 19.89 18.27 21.97 19.77 24.95 23.60

(0.38) (0.15) (0.43) (0.32) (0.23) (0.49) (0.01) (0.23) (0.11)

51.80 50.82 59.76 52.12 53.56 54.99 55.21 56.04 52.70

(1.25) (0.68) (1.6) (1.46) (1.1) (1.4) (0.31) (0.60) (1.59)

(0.23) (0.18) (0.06) (0.26) (0.17) (0.19) (0.10) (0.19) (0.58)

14.58 15.09 15.26 15.95 16.35 19.00 15.12 17.86 17.19

C

(0.05) (0.19) (0.53) (0.44) (0.39) (0.73) (0.09) (0.29) (0.33)

L ; a ; b ; C  ; and h mean values (standard deviations within parentheses) of samples from three lots. Identi®cation of samples in Table 1.

M. Yanes et al. / Journal of Food Engineering 51 (2002) 229±234

Fig. 2. Re¯ectance spectra of a light sample (a) and a dark one (b).

a

233

the slight di€erences of behaviour found, as outlined above, the viscosity of all samples were computed by ®tting to the Newton model (Table 3). Mean values showed quite a wide variation between samples, going from a very ¯uid beverage with similar viscosity to that of plain milk (2.67 mPa s for sample 1 from lot 1) to rather thick and creamy type of product (18.68 mPa s for sample 7 from lot 1). Two samples, 5 and 6, showed moderate viscosity (around 8±10 mPa s) and the rest were thinner (lower than 5 mPa s). An analysis of variance of viscosity data, considering samples and lots as sources of variation, showed that interaction between sample and lot e€ects was signi®cant (a 6 0:05) (F value ˆ 27.09, F from tables ˆ 2.03). Di€erences in viscosity between lots for samples 6, 7, and 8 were responsible for this, as can be observed in Fig. 1. The other six samples showed consistent viscosity values through lots, indicating an adequate rheological control of the commercial beverage. Viscosity data obtained at 5°C (Table 4) con®rmed the expected increase in viscosity for all samples. An analysis of variance considering sample and temperature e€ects as sources of variation showed that their interaction was not signi®cant (a 6 0:05) (F ˆ 2.33, F from tables ˆ 2.04), which means that the viscosity variation due to temperature was similar for all samples. 3.3. Opacity and colour

b

c Fig. 3. L versus a plots of colour of samples from lots 1 (a), 2 (b), and 3 (c).

Before measuring colour, the samples degree of opacity or translucency was checked by comparing the L values obtained on black and on white backgrounds. Results showed that no di€erences were detected between two such measurements (Table 5), which means that, for the sample thickness used (3.5 cm), they can be considered totally opaque. Consequently, all colour measurements were carried out on a white background using the instrument plate (X ˆ 78.5, Y ˆ 83.32, Z ˆ 87.94). Brightness …L †, redness …a †, yellowness …b †, saturation …C  †, and hue …h † values for the nine chocolate milk beverage samples from each of the three lots are given in Table 6. A wide range of brightness values was found going from very light coloured samples (L ˆ 53.5 for sample 7 from lot 2) to very dark ones (L ˆ 18.3 for

Table 7 In¯uence of samples and lots on chocolate milk beverages coloura

a

E€ect

L

C

h

Lot Sample Lot  sample

777.62b 2167.27b 469.45b

32.78b 253.53b 36.96b

1.01c 36.49b 6.85b

F values of two-way ANOVA of L ; C  ; and h data. Signi®cant at a ˆ 0:05. c Not signi®cant. b

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M. Yanes et al. / Journal of Food Engineering 51 (2002) 229±234

throughout the lots. Signi®cance of the interaction is due to some di€erences found for samples 1, 2, 3, and 9 (Fig. 4(c)). In spite of the above-mentioned di€erences, a rather acceptable uniformity in colour attributes through lots was observed in most samples.

Acknowledgements To CICyT of Spain for ®nancial support (Project AGL2000-1590) and to PROMEP-SEP and UJAT of Mexico for the fellowship awarded to author Yanes.

References

Fig. 4. L (a), C  (b), and h (c) values for samples from three lots.

sample 4 from lot 2). Re¯ection spectra of two representative colours that could be described as light brown or cream and dark chocolate, respectively, are shown in Fig. 2, where the typical distribution of re¯ectance values for brown coloured materials can be observed. On plotting L versus a values for samples from each lot (Fig. 3), it can be observed that variations in brightness of samples were di€erent between lots and that di€erences in redness (a values) were also important not only between samples but also between lots, showing lack of homogeneity probably due to a de®cient control of colour. An analysis of variance of two factors, lot and sample, and interactions, applied to the three main parameters representing colour attributes, L (brightness), C  (saturation), and h (hue) (Table 7), showed a signi®cant interaction for parameter L , mainly due to considerable di€erences among lots for samples 4 and 9 while for the rest of the samples L values were consistent throughout the lots (Fig. 4(a)). The lot±sample interaction was also signi®cant for C  values but in this case all samples except 4 and 6 showed variations between lots (Fig. 4(b)), which shows the diculty in monitoring colour saturation from batch to batch. The e€ect of lot on values of h was not signi®cant, the hue being rather constant

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