Effect of carbohydrates on the emulsifying, foaming and freezing properties of whey protein suspensions

Journal of Food Engineering 79 (2007) 279–286 www.elsevier.com/locate/jfoodeng

Effect of carbohydrates on the emulsifying, foaming and freezing properties of whey protein suspensions Zoran Herceg b

a,*

, Anet Rezˇek a, Vesna Lelas a, Greta Kresˇic´ b, Mila Franetovic´

c

a Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, 10000 Zagreb, Croatia Faculty of Tourism and Hospitality Management in Opatija, University of Rijeka, Primorska 42, 51410 Opatija, Croatia c Pliva d.d., Baruna Filipovic´a 79, 10000 Zagreb, Croatia

Received 14 June 2005; accepted 25 January 2006 Available online 10 March 2006

Abstract The aim of this study was to examine interactions between whey proteins (whey protein isolate (WPI), whey protein concentrate (WPC) and b-lactoglobulin) and carbohydrates (glucose, sucrose, starch and inulin) on some physical and functional properties of whey proteins and carbohydrates suspensions (10% dry matter (w/v)). Model systems were therefore investigated related to their foam expansion and foam stability. Carbohydrate addition in model suspensions of whey proteins resulted in significantly (P < 0.05) enhanced foam stability of protein suspensions (FSI; MFS). Model systems were also analyzed for emulsion activity index (EAI) and emulsion stability index (ESI) by the turbidometric technique. EAI and ESI values increased significantly (P < 0.05) in model suspensions prepared with WPI and b-lactoglobulin in combination with mono and disaccharides, while significant decrease (P < 0.05) were remarked in model suspensions prepared with inulin and starch addition. The phase-transition temperatures of investigated model systems were determined using differential thermal analysis with continuous scanning. In all model suspensions, significant lowering (P < 0.05) of initial freezing temperature has occurred. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Whey proteins; Carbohydrates; Freezing temperature; Emulsifying properties; Foaming properties

1. Introduction Whey proteins are used as food ingredients because of their unique functional characteristics like emulsifying, gelling, thickening, foaming and water binding capacity (Kinsella & Whitehead, 1989). As foodstuffs they are applied not only because of their functional properties, but also because of their high nutritive value and GRAS status (Bryant & McClements, 1998; Harper, 2000; Hudson, Daubert, & Foegeding, 2000). Proteins and polysaccharides found in food products, both contribute to food stability, texture and shelf life. Since most of the foodstuffs contain both polymers, interactions between proteins and polysaccharides that can pro*

Corresponding author. Tel.: +385 1 4605 035; fax: +385 1 4605 072. E-mail address: [email protected] (Z. Herceg).

0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.01.055

duce significant effect on stability of the entire system are of special interest (Dickinson & Stainsby, 1982). These interactions between macromolecules can be grouped as follows: either attractive (i.e. hydrophobic, hydrogen bonds, Van der Waals, disulfide bonds) or repulsive (i.e. electrostatic, hydration, steric repulsions); either strong (i.e. hydrophobic, hydration, steric repulsions) or weak (i.e. hydrogen bonds, Van der Waals, disulfide bonds), and non-specific or specific (Bryant & McClements, 1998). Former researches have shown that specific interactions between proteins and polysaccharides may result in formation of complex with substantially improved emulsifying characteristic (Akhtar & Dickinson, 2003; Dickinson & Galazka, 1991; Einhorn-Stoll, Ulbrich, Sever, & Kunzek, 2005; Mishra, Mann, & Joshi, 2001; Nagasawa, Ohgata, Takahashi, & Hattori, 1996; Neirynck, Van der Meeren, Bayarri Gorbe, Dierckx, & Dewettinck, 2004; Tesch, Gerhards, &

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Schubert, 2002), together with significantly improved foaming and rheological properties (Giroux & Britten, 2004; Herceg, Lelas, Brncˇic´, Tripalo, & Jezˇek, 2004; Mishra et al., 2001; Paraskevopouloua et al., 2003; Pelegrine & Gasparetto, 2005; Sa´nchez, Rodrı´guez Nino˜, Caro, & Rodrı´guez Patino, 2005; Tavares & Lopes da Silva, 2003). However, some researches have shown that effect which arises from attractive interactions may have negative influence on protein–polysaccharide system stability, in dependence of proportion and variety of present polysaccharides (Schmitt, Janchez, Desobry Banon, & Hardy, 1998; Shim & Mulvaney, 2001; Rao, 1999; Zasypkin, Braudo, & Tolstoguzov, 1997). Thermophysical properties of foodstuffs (freezing and thawing) are result of a complex structure and chemical composition, and possible interactions of basic food substances. During phase change there are appearance of some interactions between collateral amino acid chains and basic polypeptide chain, and proteins reach maximal degree of polar group exposure which results in protein globule unfolding (Franks, Hatley, & Friedman, 1988; Graziano, Catanzano, Riccio, & Barone, 1997; Koseki, Kitabatake, & Doi, 1990). Cryoprotectants have significant impact on thermodynamic stability and protection of globular proteins from unfolding during freezing. This group include different alcohols, sugars and polysaccharides capable to induce changes of nucleation and freezing characteristic (Arakawa & Timasheff, 1982; Jou & Harper, 1996; Phillips, Whitehead, & Kinsella, 1994). The purpose of this study was to examine interactions between whey proteins (whey protein isolate (WPI), whey protein concentrate (WPC) and b-lactoglobulin) and carbohydrates (glucose, sucrose, starch and inulin) on some physical and functional properties of the mixture of proteins and carbohydrates (10% dry matter (w/v)). 2. Materials and methods 2.1. Materials Investigations were carried out using powdered whey protein isolate (WPI) and b-lactoglobulin produced by

Davisco Food International, whey protein concentrate (WPC) produced by MILEI GmbH and glucose, sucrose, starch and inulin produced by Ljubljanske mlekare d.d. The chemical composition of the WPC (proteins: 60.8%, water: 3.1%, ash: 4.2%, lactose: 25.0%, fat: 6.9%), wpi (proteins: 92.8%, water: 5.0%, fat: 0.5%, ash: 1.7%) and b-lactoglobulin (b-lactoglobulin : 88.55%, other proteins: 4.65%, water: 4.3%, fat: 0.2%, ash: 2.3%) were declared by the producer. 2.2. Model systems preparation The model systems marked as WPI, WPC or BETA were aqueous dispersions of powdered whey protein isolate, whey protein concentrate and b-lactoglobulin containing 10.0% of dry matter. For this purpose appropriate amount of WPI, b-lactoglobulin and WPC (Table 1) were dispersed in distilled water by vigorous hand mixing until homogenous dispersions were obtained at 25 °C. pH of investigated model systems were determined (Table 1). The model systems with carbohydrates addition (WPIG–WPI-I; WPC-G–WPC-I; BETA-G BETA-I) were prepared as follows: WPI, WPC and b-lactoglobulin were dispersed in appropriate amount of distilled water at 25 °C. After 30 s of vigorous hand mixing 1 g of glucose, sucrose, starch or inulin were added and the mixing continued until homogenous dispersions were obtained. 2.3. Foaming properties Dispersions were whipped at room temperature with blender (TIP 3228, Gorenje, Slovenia) equipped with a wire whip beater at speed setting 6 for up to 15 min to determine maximum foam expansion. Whipping was interrupted after 5 min intervals to determine foam expansion. Foam expansion was determined by level-filling a 100 ml plastic weighing boat with foam and weighing to ±0.01 g. Foam expansion was calculated using the expression:

Table 1 Composition and pH of model systems prepared with whey proteins (WPI, WPC, b-lactoglobulin) and carbohydrates (glucose, sucrose, starch and inulin) Samples

Protein (g)

WPI WPI-G WPI-S WPI-St WPI-I WPC WPC-G WPC-S WPC-St WPC-I BETA BETA-G BETA-S BETA-St BETA-I

10.50 9.25 9.25 9.25 9.25 10.31 9.15 9.15 9.15 9.15 10.43 9.21 9.21 9.21 9.21

Glucose (G) (g)

Sucrose (S) (g)

Starch (St) (g)

Inulin (I) (g)

1 1 1 1 1 1 1 1 1 1 1 1

Water (g)

pH

89.50 89.75 89.75 89.75 89.75 89.69 89.85 89.85 89.85 89.85 89.57 89.79 89.79 89.79 89.79

6.98 6.97 6.99 6.98 6.98 6.01 5.99 6.00 6.01 6.01 7.11 7.10 7.10 7.09 7.10

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Foam expansionð%Þ Unwhipped dispersion wt(g)  foam wt(g)  100 ¼ Unwhipped dispersion wt(g) ð1Þ Foam stability was determined by transferring 100 ml of maximum expansion foam into a pyrex filter funnel with dimensions of 7.5 cm inner top diameter, 0.4 cm inner stem diameter and 7.0 cm stem length. A small plug of glass wool was placed in the top of the funnel stem to retain the foam but allow drainage of the liquid. The time required for the first drop of liquid to drain from the funnel was determined as an index of foam stability. Also, the time (min) for drainage of the entire foam was determined for low stability foams (Morr & Foegeding, 1990).

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continuously scanning the temperature as well as the temperature difference between sample and reference material (quartz sand) during cooling (from 20 °C to 40 °C) and heating (from 40 °C to 10 °C) process. As the results of the measurements, DTA freezing or DTA thawing curves were obtained using software (STEP 7/WIN 32; Siemens, Energy and Automatisation, Inc.). 2.6. Statistical analysis Each experiment had three replications. To determine statistically significant differences between samples (P < 0.05), the data were subjected to analysis of variance and appropriate means separation was conducted using Duncan’s multiple range test using a statistical software program (SPSS for Windows Version 7.0).

2.4. Emulsifying properties 3. Results and discussion Protein dispersions and suspensions were analyzed by the turbidometric technique for emulsion activity index (EAI) and emulsion stability index (ESI) as previously described (Webb, Naeem, & Schmidt, 2002). Emulsions were prepared with 3% protein dispersions (w/v) using 10 ml of sunflower oil (Zvijezda d.o.o., Zagreb, Croatia), by mixing for 90 sec in a blender (Philips, model HR 2304). The absorbance of the diluted emulsions was measured by spectrophotometer (Helios-b, Pye Unicam Ltd, Cambridge, UK) at 500 nm in 1 cm path length cuvettes. The absorbance was read initially, after what turbidity and EAI were calculated using the following formula: T ¼ 2:303A=I

ð2Þ

where T = turbidity, A = absorbance at 500 nm and I = path length of cuvette (m). The emulsion activity index (EAI) was then calculated as EAI ¼ 2ðT Þ=/C

ð3Þ

where T = turbidity (calculated from above equation), / = oil volume fraction of the emulsion, C = the weight of protein per unit volume (g ml  1) of the protein aqueous phase before emulsion formation. Emulsion stability: The emulsion were held at 4 °C for 24 h and reanalyzed for emulsion activity as described previously. An emulsion stability index was calculated using the following formula: ESI ¼ ðT  DtÞ=DT

ð4Þ

where T = turbidity value at 0 h, DT = change in turbidity during 24 h period, Dt = time interval (24 h). 2.5. Phase changes temperatures determination using differential thermal analysis—DTA The freezing and thawing temperatures of investigated model systems were determined by differential thermal analysis using the apparatus ‘‘Elektron’’ (Croatia) by

3.1. Effect of carbohydrates on foam development and stability Among model systems prepared without carbohydrate addition the best foaming properties exhibited b-lactoglobulin with the greatest value for foam expansion and foam stability, respectively. On contrary, in WPC model system, foam formation was the least efficient, characterised with the smallest value for foam stability. Possible explanation lies in difference of total proteins share in sample’s dry matter (b-lactoglobulin 93%, and WPC 60.8%), accompanied with the ability of b-lactoglobulin to diffuse on liquid–air interface, unfold and stabilize the surface (Adebowale & Lawal, 2003; Chau & Cheung, 1998). During foam formation b-lactoglobulin undergoes through conformation changes after adsorption on air–water interface, with conformation changes occurring in tertiary, and sometimes in secondary protein structure (Clarkson, Cui, Darton, Clarkson, & Coll, 1999). Carbohydrate addition in model solutions of whey proteins (WPI, WPC, b-lactoglobulin) significantly affect (P < 0.05) foaming properties of all protein suspensions. The greatest increase in foam volume, and the highest foam stability were indicated for samples of WPI and b-lactoglobulin (Tables 2 and 4) prepared with addition of monoand disaccharides, respectively. The positive effect of carbohydrate addition on foam stability was the most evident in b-lactoglobulin model systems, in which glucose and sucrose significantly (P < 0.05) enhanced foam stability. In b-lactoglobulin samples, there is high protein share (more than 90%), and because of its high molecular flexibility it is capable for significantly faster propagation at air–water interface (Chau & Cheung, 1998). Addition of low molecular weight molecules stabilizes foam additionally (Murray, 1997), resulting in greater foam stability. Whey protein concentrate model systems due to the small protein share developed brittle and porous foam,

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Table 2 Volume expansion and foam stability of model systems prepared with WPI and carbohydrates (glucose, sucrose, starch and inulin) Samples

Foam expansion %

Foam stability (min)

Time of mixing

WPI WPI-G WPI-S WPI-St WPI-I

5 min

10 min

15 min

286.23b 298.64a 306.59a 280.18c 287.35b

398.10b 426.32a 411.86a 390.20c 395.70b

469.11b 486.17a 483.21a 434.44c 460.28b

Foam stability index FSI

Maximum foam stability MFS

5.83c 6.21a 6.35a 6.01b 6.12b

114.87c 142.91a 140.87a 135.15b 136.67b

Within each column, mean values are significantly different (P < 0.05), if they do not share the same letter (Duncan’s multiple range test).

Table 3 Volume expansion and foam stability of model systems prepared with WPC and carbohydrates (glucose, sucrose, starch and inulin) Samples

Foam expansion %

Foam stability (min)

Time of mixing

WPC WPC-G WPC-S WPC-St WPC-I

5 min

10 min

15 min

280.64b 293.96a 284.55b 271.63c 277.89c

311.86c 314.03b 329.92a 306.22d 310.75c

360.24c 378.45a 370.68b 360.18c 353.46d

Foam stability index FSI

Maximum foam stability MFS

1.37c 1.99a 2.03a 1.31c 1.42b

61.17c 88.16a 89.38a 61.19c 65.28b

Means in column with different letters are significantly different (P < 0.05) according to Duncan’s multiple range test.

Table 4 Volume expansion and foam stability of model systems prepared with b-lactoglobulin and carbohydrates (glucose, sucrose, starch and inulin) Samples

BETA BETA-G BETA-S BETA-St BETA-I

Foam expansion %

Foam stability (min)

Time of mixing

Foam stability index FSI

Maximum foam stability MFS

6.87c 7.34a 7.13b 6.88c 6.93c

176.13c 189.24a 187.36b 176.15c 177.34c

5 min

10 min

15 min

354.45b 361.03a 368.28a 337.42c 332.26c

455.48b 469.91a 461.53a 348.86c 345.72c

520.64b 576.51a 522.05b 459.13d 493.22c

Within each column, mean values are significantly different (P < 0.05), if they do not share the same letter (Duncan’s multiple range test).

characterised with large lamellas pore. Starch addition caused slight but statistically insignificant (P > 0.05) decrease in the foam stability (Table 3). Changes cited above occurred because of increased solubility and molecular flexibility of protein, as a result of space orientation of proteins, their interactions, and extensions at liquid–air interface together with formation of thicker and more viscous film (Mishra et al., 2001). It is well known that sugars and polysaccharides have no affinity for air–water interface (Bos & van Vliet, 2001), but they encourage protein–protein interactions, which leads to development of multilayer cohesive protein film at interface, which prevents foam collapse and enables formation of more stable foam (Adebowale & Lawal, 2003). 3.2. Influence of carbohydrates addition on emulsifying properties The highest value for emulsion activity index (EAI), the interface area which could be stabilized with unit weight of

protein among model systems prepared without carbohydrate addition showed b-lactoglobulin, and the lowest was measured in WPC sample (Table 5). b-Laktoglobulin propagates on water-oil interface surface, changes the conformation at interface and consequently succeeds to stabilize larger surface area than isolates and concentrates (Klemaszewski, Das, & Kinsella, 1992). Significant amount of lactose present in WPC prevents protein propagation on interface surface resulting in decreased value of emulsion activity index (Zayas, 1997). For emulsions prepared with WPC, WPI and b-lactoglobulin, after carbohydrate addition increased turbidity (data not shown) was observed, as a result of difference in refractive index between oil droplets and water phase (Blijdenstein, Zoet, van Vliet, van der Linden, & van Aken, 2004). Emulsion activity index have decreased significantly (P < 0.05) for all model systems prepared with addition of inulin and starch, respectively, compared to model systems prepared without carbohydrate addition (Table 5). Bearing in mind that EAI is a value which shows protein capacity

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Table 5 Emulsifying properties and emulsion stability of model systems prepared with WPI, WPC, b-lactoglobulin and carbohydrates (glucose, sucrose, starch and inulin) Emulsion activity index EAI (m2/g)

WPI 395.52b WPC 267.30d BETA 441.73c

WPI-G 437.35a WPC-G 289.87a BETA-G 456.73a

WPI-S 438.16a WPC-S 277.06b BETA-S 447.99b

WPI-St 394.20c WPC-St 263.13e BETA-St 433.02d

WPI-I 394.80c WPC-I 272.53c BETA-I 328.93e

Emulsion stability index ESI (h)

WPI 167.34c WPC 111.28d BETA 190.24c

WPI-G 173.28a WPC-G 121.38a BETA-G 213.13a

WPI-S 170.14b WPC-S 122.67a BETA-S 211.48b

WPI-St 154.11d WPC-St 113.84c BETA-St 187.34d

WPI-I 109.32e WPC-I 119.84b BETA-I 140.20e

Values in row followed by a different superscript letters are significantly (P < 0.05) different (Duncan’s multiple range test).

for remaining at oil–water interface just after emulsion formation (Mangino, 1994), the reason of index decreasing lies in fact that addition of incompatible polysaccharides and saccharides which do not adsorb at emulsion droplet, can induce depletion interactions between emulsion droplets and increase viscosity of water phase (Cao, Dickinson, & Wedlock, 1990; Lekkerkerker, Poon, Pusey, Stroobants, & Warren, 1992; Vrij, 1976). Emulsion stability index (ESI) is evaluation of protein capacity for remaining at oil–water interface after emulsion storage or emulsion heating (Mohanty, Mulvihill, & Fox, 1988). The highest ESI were observed for model systems prepared with b-lactoglobulin, which acts as emulsifier (Dickinson & Galazka, 1991). Emulsions prepared with WPC (60% of protein in dry matter) are less stable, because as previously reported (Tesch et al., 2002), if surfactants (surface active agents that stabilize oil–water interface) are not applied, emulsion break-down occurs. For emulsions prepared with WPC, values of ESI have increased significantly (P < 0.05) after addition of all four carbohydrates. On contrary, ESI values for emulsions prepared with b-lactoglobulin and WPI, have decreased significantly (P < 0.05) after starch and inulin addition, because of partial aggregation of oil droplets (Dickinson & Galazka, 1991; Vanapalli, Palanuwech, & Coupland, 2002). Free, unadsorbed, polysaccharide, present in continuous emulsion phase, caused reversible depletion and flocculation leading to fast serum separation (Dickinson, 1996; Dickinson, Ma, & Povey, 1994) and consequently decreased emulsion stability. That effect can also be explained by the size of added molecules which obstruct protein propagation on oil–water interface (Kim, Decker, & McClements, 2003). Due to its hydrophility, inulin has the ability to form hydrogen bonding with b-lactoglobulin deducting its free groups, decreasing surface tension and causing emulsion destabilization (Lupano & Gonzalez, 1999). On the other hand, mono- and disaccharide addition caused emulsion stability to increase. After glucose and sucrose addition values of ESI and EAI (Table 5) have sig-

nificantly increased (P < 0.05) because of interactions with proteins, resulted in formation of a system with improved emulsifying properties (Dickinson & Galazka, 1991; Nagasawa et al., 1996; Semenova, Antipova, & Belyakova, 2002). Biopolymer complexes (or conjugates) can cover entire surface of oil droplet through mechanism of cooperative adsorption and formation of thick macromolecular multilayer which electrostaticly and stericly contributes to stability (Dickinson & Eriksson, 1991). In this layer, proteins mainly stabilize emulsion droplets with electrostatic repulsive forces (McClements, 2001; Tesch et al., 2002). 3.3. Effect of carbohydrates on phase transition temperatures Significantly lowering of initial freezing temperature (P < 0.05) was observed for all model suspensions prepared with whey proteins and carbohydrates (Table 6). This phenomenon is well recognized (Goff & Sahagian, 1996; Hartel, 1998a, 1998b; Tolstoguzov, 2002), and could be explained with the fact that carbohydrate addition affect ice nucleation and ice-crystal growth. Direct contact of protein and water is thermodynamically unfavourable in the presence of sugar (Arakawa & Timasheff, 1982), and it is directly correlated with enhancement of hydrophobic interactions (Phillips et al., 1994). This change in systems can cause decrease of interaction between water–proteins (Barone, Del Vecchio, Giancola, & Notaro, 1992). Inulin addition lowered freezing temperature the most efficiently in system with high protein share (WPI), followed by WPC, and b-lactoglobulin (Table 6). Inulin can act to lower ice nucleation temperature due to its colligative characteristics and the ability to form bridges with hydrophilic amino acids on protein surface and hydrogen bonds with water (Lupano & Gonzalez, 1999). Thereby, lowering of freezing temperature can be referred to protein preferential hydration in the presence of inulin (Arakawa, Bhat, & Timasheff, 1990; Xie & Timasheff, 1997). It was also observed that the lowest freezing temperature in model systems prepared without carbohydrates, had whey protein concentrate, because of previously

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Table 6 Freezing and thawing temperatures of model systems prepared with WPI, WPC, b-lactoglobulin and carbohydrates (glucose, sucrose, starch and inulin) Freezing temperature Tf (°C)

WPI 0.98e WPC 1.08c BETA 0.87d

WPI-G 1.52b WPC-G 1.63a BETA-G 1.43a

WPI-S 1.30d WPC-S 1.21b BETA-S 1.32b

WPI-St 1.43c WPC-St 1.57a BETA-St 1.16c

WPI-I 1.69a WPC-I 1.62a BETA-I 1.48a

Peak of freezing curve Tfm (°C)

WPI 4.20c WPC 4.53c BETA 4.73b

WPI-G 6.47a WPC-G 6.38a BETA-G 5.95a

WPI-S 6.34a WPC-S 6.28a BETA-S 5.84a

WPI-St 5.78b WPC-St 5.74b BETA-St 5.35a

WPI-I 6.63a WPC-I 6.46a BETA-I 6.11a

Thawing temperature Tth (°C)

WPI 6.32c WPC 6.13b BETA 6.83c

WPI-G 7.24a WPC-G 7.17a BETA-G 7.53a

WPI-S 7.03b WPC-S 7.05a BETA-S 7.27b

WPI-St 7.12a WPC-St 6.33b BETA-St 7.12b

WPI-I 7.46a WPC-I 7.24a BETA-I 7.98a

Peak of thawing curve Tthm (°C)

WPI 1.09c WPC 1.31c BETA 1.63b

WPI-G 1.62a WPC-G 2.01a BETA-G 2.01a

WPI-S 1.36b WPC-S 2.09a BETA-S 1.90a

WPI-St 1.53a WPC-St 1.67b BETA-St 2.12a

WPI-I 1.59a WPC-I 1.92a BETA-I 1.92a

Mean values followed by the same letter in the same row are not significantly different (P < 0.05) (Duncan’s multiple range test).

discussed significant lactose share. Consequently, the highest freezing temperature was determined for b-lactoglobulin (Table 6). 4. Conclusions Specific interactions between proteins and polysaccharides in investigated model systems resulted in system with improved functional properties. The effect of formed system depends on the type of polysaccharides as well as the type of used whey proteins. Addition of carbohydrates in model whey protein solutions significantly improved foam stability (P < 0.05) of investigated suspensions. The highest value for foam volume expansion and the best foam stability were observed for systems prepared with whey protein isolate and b-lactoglobulin with addition of mono- and disaccharides, respectively. Addition of the same mono- and disaccharides in model system prepared with whey protein isolate and b-lactoglobulin, resulted in system with also significantly improved emulsifying properties (P < 0.05). Emulsion activity index and emulsion stability index have decreased significantly (P < 0.05) in model systems prepared with WPI and b-lactoglobulin, after starch and inulin addition, in comparison to systems prepared without carbohydrate addition. Lowering of initial freezing temperature was significant (P < 0.05) and was observed in all model systems prepared with whey proteins and carbohydrates, in contrast to protein suspensions without carbohydrates.

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