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Effects of high pressure homogenisation of ice cream mix on the physical and structural properties of ice cream
International Dairy Journal 32 (2013) 40e45
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Effects of high pressure homogenisation of ice cream mix on the physical and structural properties of ice cream Marialuisa Biasutti*, Elena Venir, Marilena Marino, Michela Maifreni, Nadia Innocente Department of Food Science, University of Udine, Via Sondrio 2/A, 33100 Udine, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 July 2012 Received in revised form 11 March 2013 Accepted 12 March 2013
This study investigated the effect of high pressure homogenisation (HPH) on the physical and structural properties of ice cream. Samples were produced from mixes differing in fat content (5% and 8%) and subjected to different homogenisation pressures (15/3 MPa and 97/3 MPa). Ice creams were compared for fat globule size distribution, overrun, melting behaviour, and hardness. No influence of HPH on fat structure destabilisation with respect to the conventional homogenisation (CH) was observed. The HPH ice cream samples with high fat content were characterised by the lowest overrun, the highest hardness and improved resistance to melting; the HPH ice creams with low fat content showed higher resistance to meltdown, but were not clearly differentiated for hardness with respect to the CH samples. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Ice cream is a multiphase system consisting of dispersed air bubbles, partially-coalesced fat globules, ice crystals and a continuous aqueous phase with dissolved solutes (sugars and salts) and suspended macromolecules (polysaccharides and proteins) (Goff, 1997; Marshall & Arbuckle, 1996). Each of these elements determines the structure of ice cream, which, in turn, affects its physical properties, such as resistance to melting and hardness, and viscoelastic behaviour, as well as the sensorial characteristics of the final product. Different factors contribute to the ice cream structure, such as ingredients used and the manufacturing process, which includes the homogenisation step. The main purpose of homogenisation is the reduction in size of fat globules to less than about 2 mm, resulting in a greater stability of fat globules during mix ageing. Moreover, the risk of churning of fat in the freezer is also reduced (Goff, 1997; Marshall & Arbuckle, 1996). Homogenisation also causes the formation of a new fat globule membrane. In fact, the passage through the homogeniser valve causes the rupture of the native membrane of fat globules and the subsequent change in its composition. Firstly, the adsorption of milk proteins and then their partial displacement by emulsifiers occurs during mix ageing process. This rearrangement weakens the newly formed membrane, which becomes less stable to shear forces and more susceptible to
* Corresponding author. Tel.: þ39 0432 558137. E-mail address: [email protected] (M. Biasutti). 0958-6946/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.idairyj.2013.03.007
partial coalescence. As a consequence, a network of partially agglomerated globules is achieved. This network surrounds the air cells, leading to a more stable foam structure (Goff, 1997; Marshall & Arbuckle, 1996). Homogenisation pressures ranging between 6 and 20 MPa are generally employed in ice cream mix processing (Marshall & Arbuckle, 1996). Various studies have been published with respect to the effect of conventional pressure homogenisation on ice cream characteristics, such as fat destabilisation, melting behaviour, hardness and ice crystal growth (Campbell & Pelan, 1998; Koxholt, Eisenmann, & Hinrichs, 2001; Olson, White, & Watson, 2003; Ranjan & Baer, 2005; Ruger, Baer, & Kasperson, 2002; Schmidt & Smith, 1989; Smet et al., 2010; Thomsen & Holstborg, 1998; Tosaki, Kitamura, Satake, & Tsurutani, 2009). Ice cream properties as affected by microfluidisation process have been investigated by Morgan, Hosken, and Davis (2000) and Olson et al. (2003). Studies have been published also on the effect of high-pressure homogenisation (HPH, ranging from 80 up to 200 MPa) on mix and ice cream properties (Gray & Turan, 2002; Hayes, Lefrancois, Waldron, Goff, & Kelly, 2003; Innocente, Biasutti, Venir, Spaziani, & Marchesini, 2009). Gray and Turan (2002) reported that homogenisation at 160 MPa caused a reduction in size of oil droplets compared to conventional homogenisation (CH) treatment, leading to a larger air:water interface and the best performance on creaminess for the ice cream. Hayes et al. (2003) did not observed a clear relationship between the degree of fat flocculation in mixes and fat globule coalescence and the melting properties of ice creams as a function of homogenisation pressure applied. They also reported that the apparent viscosity of mixes and
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the textural characteristics (hardness and gumminess) of ice creams with 5% fat and homogenised at 100 MPa were found to be similar to 8% fat ice creams homogenised at 18 MPa. Further investigations (Innocente et al., 2009) proved that HPH caused only a slight decrease in fat globule size compared with CH treatment, but a strong enhancement of the viscoelastic properties and the apparent viscosity of mixes. In fact, rheological results indicated that unhomogenised and CH mixes behaved as weak gels, whereas HPH treatment led to stronger gels. These results would be of interest since it is known that colloidal properties of mixes are essential in the development of ice cream body and texture, since they affect overrun, melting resistance, hardness and iciness (Goff, 1997; Marshall & Arbuckle, 1996). The aim of this study was to complete the previous study (Innocente et al., 2009) performed on ice cream mixes to evaluate the physical and structural properties of ice cream as affected by HPH of mixes. For this purpose, ice creams with different fat content (5% and 8%) were produced from mixes homogenised at 15/3 MPa and 97/3 MPa. Ice creams were also produced from unhomogenised mixes. All the ice cream samples were analysed for overrun, fat globule size distribution, melting behaviour, and hardness. 2. Materials and methods 2.1. Ingredients and ice cream mix formulation The following ingredients were used: commercial homogenised and pasteurised whole milk and milk cream (35% fat), and sucrose (all purchased in a local store), 5 Dextrose Equivalent maltodextrin (MaltrinÒ M040, Natural World s.r.l., Ravenna, Italy), spray-dried glucose syrup (C*Dry GL 01924, Cerestar France, Haubourdin Cedex, France), skim milk powder (Bayerische Milchindustrie, Landshut, Germany), whey protein concentrate (Hiprotal 880, Borculo Domo Ingredients, Zwolle, The Netherlands), mono- and diglycerides of fatty acids (E471, Natural World s.r.l., Ravenna, Italy), lactic acid esters of mono- and diglycerides of fatty acids (E472b, Natural World s.r.l.), carboxymethylcellulose (Walocel CRT-PA, Comiel s.r.l., Milan, Italy), guar gum (Indian Gum Industries Ltd., Mumbai, India), and locust bean gum (Seedgum A-175, LBG Sicilia s.r.l., Ragusa, Italy). Two formulations were prepared, containing 5% and 8% fat, respectively. Both formulations consisted of 19% carbohydrate, 10% non-fat milk solids, 0.5% emulsifiers and 0.25% stabilisers. Full details of the two formulations have been reported by Innocente et al. (2009). 2.2. Ice cream processing For each processing trial, a 9 kg batch of ice cream mix was prepared by mixing all ingredients at 65 C. After pasteurisation (82 C for 8 min) the mix batch was divided into three equal samples: the first portion was not homogenised (unhomogenised mix, UNH), the second portion was homogenised at 15 MPa (first stage) and 3 MPa (second stage) (conventional-pressure homogenised mix, CH), and the third portion was homogenised at 97/3 MPa (high-pressure homogenised mix, HPH). A 2-stage mode homogeniser (mod. Panda 2K, Niro Soavi s.p.a., Parma, Italy) was used. For CH treatments, inlet temperature of mixes ranged from 65 to 68 C and outlet temperature was 48 C. For HPH treatments, mix inlet temperature varied from 45 to 48 C and outlet temperature was 65 C (Innocente et al., 2009). All mixes were cooled in an ice bath to 4 C and aged at this temperature for 24 h without stirring. The mixes were then frozen using a horizontal batch ice cream freezer (3 L capacity, mod.
41
Mantematic K20/S, Cattabriga, Anzola Emilia, Italy) for a fixed time of 13 min. Ice creams were collected in 4 L containers and stored at 10 C (consumption temperature of ice cream) for 24 h before further testing was performed. For hardness determination, aliquots of extruded ice cream samples (0.5 L) were taken and stored separately at 18 C for 24 h. The overall experimental procedure was performed three times. 2.3. Fat particle size analysis The fat particle size distributions of ice cream mixes and melted ice creams were measured by dynamic light scattering, using a Nicomp 380 ZLS analyser (Particle Sizing System Nicomp, Santa Barbara, CA, USA). For size analysing, the Nicomp volume-weighted distribution was used and the volume-weighted mean diameters (D4,3) were recorded. The mix samples (unfrozen and aged at 4 C for 24 h) were diluted 1:1000 both in water and in an aqueous solution of 1% w/v of sodium dodecyl sulphate (SDS) (SigmaeAldrich, Steinheim, Germany) as dissociation medium (Gelin, Poyen, Courthaudon, Le Meste, & Lorient, 1994; Granger, Leger, Barey, Langendorff, & Cansell, 2005; Sourdet, Relkin, & César, 2003; Tomas, Paquet, Courthaudon, & Lorient, 1994). The measurement parameters were set as follows: temperature at 25 C (2 C), refractive index at 1.333, viscosity at 0.89 mPa s, 3 min for data integration time, scattering angle at 90 for UNH and CH mix samples and 170 for HPH samples (Innocente et al., 2009). As regards the ice creams, prior to analysis the samples (50 g; 10 C) were melted in a controlled temperature chamber (FTC 90I, Velp Scientifica srl, Usmate, Italy) at 25 C (2 C) for 30 min and were then ultrasonicated at power level 5 for 10 min (USCP00D, VWRÔ, Leuven, Belgium) at room temperature to ensure the absence of air bubbles (Gelin et al., 1994; Granger et al., 2005). Preliminary tests were performed to check that ultrasonication conditions adopted did not affect particle size. Images by microscope were taken to prove the absence of air bubbles in the ultrasonicated samples. The melted ice cream samples were analysed under the same operating conditions adopted for the mix samples (dilution, temperature, refractive index and data integration time). Scattering angle was set at 90 for all the ice cream samples. For each sample (mix and ice cream), measurements were carried out at least five times. 2.4. Overrun Mix and ice cream samples were weighed in a cup with a fixed volume of 125 mL and the overrun was calculated according to the following equation: Overrun (%) ¼ [(weight of ice cream mixweight of ice cream)/(weight of ice cream)]*100 (1) For each sample (mix and ice cream), measurements were carried out three times. 2.5. Melting behaviour The meltdown tests were carried out in a controlled temperature chamber at 25 C (2 C) (FTC 90I, Velp Scientifica srl, Usmate, Italy. The ice cream samples (truncated cone shape, initial weight of about 130 g, initial temperature at 10 C) were placed on a wire mesh (with 2 mm square openings) and the amount of melted ice cream passing through the wire mesh was collected and weighed every 2.5 min for 30 min. The percentage of melted ice cream was plotted against time. The melting behaviour of the ice cream samples was expressed as the time required to melt a known amount of ice cream. For each ice cream sample, measurements were carried out in triplicate.
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2.6. Hardness analysis The ice cream samples were transferred from a 18 C freezer to a 10 C freezer 24 h prior to analysis. Hardness measurements were carried out at room temperature. Nevertheless, the following criteria were adopted in order to minimise the melting effects: cups (72 mL capacity, 36 mm in height, 50 mm in diameter, with perforated bottom to avoid entrapping air during filling) were filled with and were then placed in the 10 C freezer for 20 min to stabilise the ice cream sample; hardness measurements were carried out immediately after removing the cup from the freezer; the probe was conditioned at 10 C before testing. Hardness was determined using an Instron Universal Testing Machine (mod. 4301, Instron Ltd., High Wycombe, UK) equipped with a 100 N load cell and a stainless steel cylindrical probe (8 mm diameter). The plunger was allowed to penetrate to the geometrical centre of the sample for 18 mm, with a crosshead speed of 50 mm min1. Hardness was expressed as the maximum load (N) corresponding to the ice cream resistance to penetration. For each ice cream sample, at least five measurements were carried out. 2.7. Statistical analyses One-way analysis of variance (F-test) and Tukey’s HSD test were used for multiple comparisons of the means. The differences were considered statistically significant for P 0.05. All statistical analyses were conducted using Statistical Discovery JMP 3.0 for Windows (SAS Institute Inc., Cary, NC). 3. Results and discussion 3.1. Fat particle size For both 5% and 8% fat content samples, mixes and ice creams were analysed in terms of particle (fat globule or aggregates) size distribution. Measurements were carried out dispersing samples both in water and in a dissociating medium (aqueous solution of 1%, w/v, SDS) to investigate the state of fat globule dispersion and, hence, sort out the fat destabilisation processes which may occur
among flocculation, coalescence or partial coalescence (Gelin et al., 1994; McClements, 2007; Méndez-Velasco & Goff, 2012; Sourdet et al., 2003). As an example, representative volume-weighted distributions in SDS (A) and in water (B) are reported for mix (Fig. 1) and ice cream (Fig. 2) samples with 8% fat content, but similar behaviours were also found for the systems with 5% fat content. In the mixes (Fig. 1) the fat globule distribution changed with the dispersing medium used. In fact, it can be noted that the particle size distribution in SDS of the UNH sample was characterised by a bimodal distribution with a main group of particles at about 1000 nm and a second group at about 200 nm. On the other hand, monomodal distributions were observed in the CH and HPH samples. Similar behaviour in SDS were also observed and discussed in a previous paper (Innocente et al., 2009). In the UNH samples the main group was attributed to the fat globules derived from milk and milk cream, and the second group to casein micelles. The latter was suggested to disappear in the CH and HPH mix samples as a result of disaggregation by the homogenisation treatment and/or of adsorption to the newly formed fat globule membrane (Innocente et al., 2009). Moreover, all the mixes (UNH, CH and HPH) showed monomodal distributions when diluted in water and a shift of the peak towards higher diameter values with respect to the corresponding samples dispersed in SDS. In the ice cream samples (Fig. 2) the particle size distribution of the homogenised systems (CH and HPH) became bimodal and did not differ between the samples dispersed in dissociating medium (Fig. 2A) and in water (Fig. 2B). In fact, they were characterised by a main group at about 1000 nm and a second group ranging from 100 to 300 nm both in SDS and in water. Similarly to that previously discussed for the mix samples, these groups refer to fat globule aggregates and to casein micelles, respectively. The casein micelles would be desadsorbed from the fat globule membrane by the freezing process. The particle size distribution of the ice cream sample produced from the unhomogenised mix (UNH) was found to differ with the dispersing medium used. In fact, it showed a bimodal distribution similar to that of the homogenised ice creams when diluted in SDS, whereas it was characterised by a monomodal distribution when diluted in water. Moreover, a shift of the peak
Fig. 1. Representative volume-weighted distributions of ice cream mix samples (8% fat content) subjected to different homogenisation pressures (UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa). Samples dispersed in either (upper set) sodium dodecyl sulphate solution as dissociating medium or (lower set) water.
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Fig. 2. Representative volume-weighted distributions of ice cream samples (8% fat content) subjected to different homogenisation pressures (UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/ 3 MPa). Samples dispersed in either (upper set) sodium dodecyl sulphate solution as dissociating medium or (lower set) water.
towards lower diameter values was observed in the sample diluted in water with respect to the sample dispersed in SDS. Tables 1 and 2 report the mean values of the volume-weighted diameters (D4,3) in SDS and in water obtained from the particle size distribution curves of the mix and the ice cream for the 5% and 8% fat content samples, respectively. In all the mix samples (UNH, CH and HPH) the mean fat globule diameters measured in SDS were found to be always lower than the values observed for the same samples dispersed in water. As a consequence, it can be inferred that, regardless of the homogenisation treatment applied, in the mixes flocculation appears to be the main aggregation process involving the fat globules. As regards the ice creams, different behaviours were observed between the homogenised (CH and HPH) and the unhomogenised samples. Firstly, it is worthy to note that in the UNH ice cream the volume-weighted diameters in water were found to be markedly lower than those measured in the corresponding mix, whereas no significant differences were observed in the mean values measured in SDS. As already mentioned, this would suggest a dissociation of aggregates, which may be attributed to casein micelles, by the freezing process. Secondly, it can be seen that in the UNH ice cream samples the mean particle diameter measured in SDS was found to be markedly higher than the value
measured in water. Since the mean diameters in SDS did not differ between the UNH ice cream and the corresponding mix, it can be deduced that coalescence is the main fat destabilisation process in the UNH ice cream sample. Coalesced globules would be detectable in the mix (both in SDS and in water) and in the ice cream when diluted in SDS, whereas they would not be measurable in the ice cream dispersed in water. The measured particles would be fat aggregates of smaller dimensions remained in the aqueous phase. As regards the homogenised ice creams (CH and HPH), in both these samples no significant differences were observed between the mean diameter values measured in SDS and in water. Moreover, these samples always showed higher mean diameters (in SDS) with respect to the corresponding mix samples. Therefore, it can be inferred that in the CH and HPH ice creams partial coalescence may be the fat destabilisation process occurred and no influence by increasing homogenisation pressure seems to be evident. The effect of the homogenisation treatment on the particle size of these three systems will be discussed solely based on particle sizes determined in SDS. For both 5% and 8% fat content samples, the mean diameters of the fat globules in the mix samples were found to markedly decrease from the unhomogenised (UNH) to the CH samples, while only a small further decrease from CH to HPH was
Table 1 Mean values (standard deviations) of volume-weighted diameters (D4,3) of fat globules in mixes and fat aggregates in ice creams with 5% fat content and subjected to different homogenisation pressures.a
Table 2 Mean values (standard deviations) of volume-weighted diameters (D4,3) of fat globules in mixes and fat aggregates in ice creams with 8% fat content and subjected to different homogenisation pressures.a
Sample
Homogenisation treatment
Mix
UNH CH HPH UNH CH HPH
Ice cream
D4,3 (nm)
D4,3 (nm)
Dissociating medium
Water
1066 94b,A 261 15b,C 220 16b,D 1033 66a,A 835 106a,B 843 74a,B
1456 452 741 365 761 824
120a 19a 128a 4b 61a 181a
a Homogenisation treatments were: UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa. Dissociating medium was an aqueous solution of 1%, w/v, sodium dodecyl sulphate. Different lowercase superscript letters in the same row and different uppercase superscript letters in a column refer to statistically significant differences (Student’s t-test, P 0.05).
Sample
Homogenisation treatment
Mix
UNH CH HPH UNH CH HPH
Ice cream
D4,3 (nm)
D4,3 (nm)
Dissociating medium
Water
980 85b,A 363 35b,B 246 7b,C 1128 63a,A 983 204a,A 1091 196a,A
1683 600 746 406 857 976
107a 53a 39a 22b 159a 179a
a Homogenisation treatments were: UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa. Dissociating medium was an aqueous solution of 1%, w/v, sodium dodecyl sulphate. Different lowercase superscript letters in the same row and different uppercase superscript letters in a column refer to statistically significant differences (Student’s t-test, P 0.05).
M. Biasutti et al. / International Dairy Journal 32 (2013) 40e45
3.2. Overrun Fig. 3 shows the average of the overrun values determined in the ice cream samples. A batch freezer was used and it is well known that in this freezing system air is incorporated at atmospheric pressure by direct entrainment from the agitator blades (Chang & Hartel, 2002). As a consequence, overrun may be affected by freezer operating parameters (such as dasher speed or freezing time) or mix properties (such as composition and methods of processing, which, in turn, influence the viscosity of the ice cream mix) (Marshall & Arbuckle, 1996; Sofjan & Hartel, 2004). The freezing process was carried out using the same operating parameters for all the mix samples, hence the overrun values of the ice creams will be discussed with reference to fat content or homogenisation pressure applied. It can be seen that fat content did not influence the overrun of the ice cream samples (Fig. 3). Similarly, also Chang and Hartel (2002) did not observe significant differences in the overrun values between non-fat (0%) and 14% fat ice creams. On the other hand, overrun of the ice cream samples appeared to be affected by the homogenisation treatment applied to the mixes. In fact, regardless of the fat content, the CH ice cream samples were found to have the highest overrun values, whereas the HPH samples had the lowest overrun values. These behaviours can be expected if it is considered that the previous study (Innocente et al., 2009) showed that the apparent viscosity values of the ice cream mixes have always been reported to be lower for the CH samples and higher for the HPH samples, compared with the UNH samples for both 5% and 8% fat content. In fact, it is well known that the whipping ability of ice cream is affected by its viscosity (Adapa, Dingeldein, Schmidt, & Herald, 2000; Marshall & Arbuckle, 1996) and ice cream mixes
Overrun (%)
60
b
c
b
c
50
3.3. Melting behaviour The melting behaviour of the ice cream samples is summarised in Fig. 4. It is expressed as the time required to melt a known amount of ice cream (5% of thawed ice cream in Fig. 4A, 10% of thawed ice cream in Fig. 4B). The samples can be grouped into two main sets: the lowest melting times were found for the CH ice creams, whereas higher resistance to meltdown were measured for the UNH and HPH samples (with HPH_8% characterised by the highest mean values). It is believed that these behaviours may be explained by taking into account the apparent viscosities of the mixes. In fact, the lowest melting times were determined in the ice creams (Fig. 4) produced from the CH mixes characterised by the lowest apparent viscosity, as previously reported (Innocente et al., 2009). On the other hand, the ice cream samples with intermediate melting time (meaning all the UNH samples and the HPH_5% sample, Fig. 4) may be associated to mixes with intermediate apparent viscosity values (Innocente et al., 2009). Finally, the HPH_8% system was characterised by the highest mean values of resistance to meltdown in ice cream (Fig. 4) and the highest apparent viscosity in the corresponding mix (Innocente et al., 2009).
A
40 30 20 10 0
20 15
a
a,b b,c
b
c
c
10 5 0 UNH
B
a
a
70
with high viscosities were found by Schmidt, Lundy, Reynolds, and Lee (1993) to incorporate less air during freezing. As previously mentioned, all mixes were frozen in a batch freezer. Nevertheless, the lack of air incorporation for the HPH samples may not be as pronounced in a continuous freezing system. In fact, it is known that incorporation of air is less dependent on viscosity of the mix if a continuous freezer is used because this allows to regulate the amount of air being introduced into the mix to produce ice cream with the desiderate overrun (Marshall & Arbuckle, 1996; Schmidt & Smith, 1989). Schmidt and Smith (1989) did not observe differences in the overrun values of ice creams produced from homogenised mixes (13.8 MPa versus 27.6 MPa) differing in viscosity. These authors attributed this result to the use of a continuous freezer.
Melting time (min)
observed. These behaviours confirmed the data reported in the previous study (Innocente et al., 2009). As regards the ice cream systems, aggregates similar in size were found between the CH and HPH ice creams. Therefore, it can be inferred that no differences in the extent of fat destabilisation in ice creams occurred as homogenisation pressure increased from 15/3 MPa to 97/3 MPa. This is probably due to the differences in the viscoelastic properties of these mixes previously observed (Innocente et al., 2009). In fact, comparing these two systems, the CH mixes were found to behave as a weak gel and the HPH mixes as a more structured gel-like system (Innocente et al., 2009). The latter has been suggested to derive from pressure-induced colloidal interactions, which led to a network rearrangement or interpenetrating network formation (Biasutti, Venir, Marchesini, & Innocente, 2010; Innocente et al., 2009; Venir, Marchesini, Biasutti, & Innocente, 2010). This network may not allow a different fat destabilisation during freezing process in the HPH systems with respect to the CH ice creams.
Melting time (min)
44
25
a
CH
HPH
a
a,b
b,c c
20
c
15 10 5 0
5% fat
8% fat
Fig. 3. Averages and standard deviations (error bars) of the overrun value (%) measured in mix and ice cream samples with different fat contents (5% and 8%) and subjected to homogenisation at different pressures ( :UNH, 0 MPa; :CH, 15/3 MPa; : HPH, 97/3 MPa). Different superscript letters refer to statistically significant differences (Tukey’s HSD test, P 0.05).
UNH
CH
HPH
Fig. 4. Averages and standard deviations (error bars) of the time (min) required to melt a known amount of ice cream. Panel A, time required to melt 5% of ice cream; panel B, time required to melt 10% of ice cream. ( : 5% fat content; : 8% fat content; UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa). In each graph, different superscript letters refer to statistically significant differences (Tukey’s HSD test, P 0.05).
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References
3
Max Load (N)
45
2
1
0 5% fat
8% fat
Fig. 5. Averages and standard deviations (error bars) of the hardness value (Max Load, N) measured in the ice cream samples with different fat contents (5% and 8%) and subjected to homogenisation at different pressures ( :UNH, 0 MPa; :CH, 15/3 MPa; : HPH, 97/3 MPa).
3.4. Hardness Fig. 5 reports the average hardness values of the ice cream samples. The HPH ice cream with 8% fat content showed the highest hardness value (1.773 N) and was clearly differentiated from all the other samples. The latter showed lower values of resistance to deformation, which ranged from 0.466 to 0.825 N. No clear relationship between hardness and homogenisation pressure was observed. This behaviour may be affected by the overrun values of ice creams and the apparent viscosity of mixes. In fact, lower overrun data were observed (Fig. 3) and higher viscosity values were reported (Innocente et al., 2009) for the HPH ice creams (higher hardness, Fig. 5), whereas higher overrun (Fig. 3) and lower apparent viscosities (Innocente et al., 2009) were found for the CH samples (lower hardness, Fig. 5). Hardness is reported to be affected by overrun as well as the rheological properties of the mix. Different studies showed an inverse relationship between hardness and overrun (Goff et al., 1995; Muse & Hartel, 2004; Sofjan & Hartel, 2004). According to Muse and Hartel (2004), air in ice cream behaves as a compressible dispersed phase, which opposes less resistance to a compression force when a greater amount is entrapped. These authors also observed that as the flow behaviour index and the consistency coefficient of mix increased, the ice cream hardness increased (Muse & Hartel, 2004). 4. Conclusions Flocculation appears to be the main aggregation process occurred in the mixes, regardless the homogenisation pressure applied. In the ice creams, coalescence and partial coalescence are the main fat destabilisation phenomena suggested for the UNH and both the homogenised (CH and HPH) systems, respectively. Therefore, it seems that in ice cream high pressure homogenisation did not cause a different structure of destabilised fat globules with respect to the conventional treatment. It is suggested that high pressure homogenisation may have a structuring effect on the proteins of the serum phase. These proteins may form a network rearrangement or interpenetrating network, which may not allow a different fat destabilisation between CH and HPH treatment. This appears to be confirmed by the overrun, melting rate and hardness behaviours. In fact, the HPH ice cream samples with high fat content were characterised by lower overrun, the highest hardness and an improvement in melting resistance. On the other hand, with respect to the CH samples, the HPH ice creams with low fat content showed higher resistance to meltdown, but were not clearly differentiated for hardness.
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Structural changes in oil-in-water emulsions during the manufacture of ice cream. Food Hydrocolloids, 8, 299e308. Goff, H. D. (1997). Colloidal aspects of ice creamea review. International Dairy Journal, 7, 363e373. Goff, H. D., Freslon, B., Sahagian, M. E., Hauber, T. D., Stone, A. P., & Stanley, D. W. (1995). Structural development in ice cream e dynamic rheological measurements. Journal of Texture Studies, 26, 517e536. Granger, C., Leger, A., Barey, P., Langendorff, V., & Cansell, M. (2005). Influence of formulation on the structural networks in ice cream. International Dairy Journal, 15, 255e262. Gray, S. J., & Turan, S. (2002). Method for the preparation of an aerated frozen product. Patent No. US 6,497,913 B1. Hayes, M. G., Lefrancois, A. C., Waldron, D. S., Goff, H. D., & Kelly, A. L. (2003). Influence of high pressure homogenisation on some characteristics of ice cream. Milchwissenschaft, 58, 519e523. Innocente, N., Biasutti, M., Venir, E., Spaziani, M., & Marchesini, G. (2009). Effect of high-pressure homogenization on droplet size distribution and rheological properties of ice cream mixes. Journal of Dairy Science, 92, 1864e1875. Koxholt, M. M. R., Eisenmann, B., & Hinrichs, J. (2001). Effect of the fat globule sizes on the meltdown of ice cream. Journal of Dairy Science, 84, 31e37. McClements, D. J. (2007). Critical review of techniques and methodologies for characterization of emulsion stability. Critical Reviews in Food Science and Nutrition, 47, 611e649. Marshall, R. T., & Arbuckle, W. S. (1996). Ice cream (5th ed.). New York, NY, USA: International Thomson Publishing. Méndez-Velasco, C., & Goff, H. D. (2012). Fat structure in ice cream: a study on the types of fat interactions. Food Hydrocolloids, 29, 152e159. Morgan, D., Hosken, B., & Davis, C. (2000). Microfluidised ice-cream emulsions. Australian Journal of Dairy Technology, 55, 93. Muse, M. R., & Hartel, R. W. (2004). Ice cream structural elements that affect melting rate and hardness. Journal of Dairy Science, 87, 1e10. Olson, D. W., White, C. H., & Watson, C. E. (2003). Properties of frozen dairy desserts processed by microfluidization of their mixes. Journal of Dairy Science, 86, 1157e 1162. Ranjan, S., & Baer, R. J. (2005). Effects of milk fat and homogenization on the texture of ice cream. Milchwissenschaft, 60, 189e192. Ruger, P. R., Baer, R. J., & Kasperson, K. M. (2002). Effect of double homogenization and whey protein concentrate on the texture of ice cream. Journal of Dairy Science, 85, 1684e1692. Schmidt, K., Lundy, A., Reynolds, J., & Yee, L. N. (1993). Carbohydrate or protein based fat mimicker effects on ice milk properties. Journal of Food Science, 58, 761e763/779. Schmidt, K. A., & Smith, D. E. (1989). Effects of varying homogenization pressure on the physical properties of vanilla ice cream. Journal of Dairy Science, 72, 378e384. Smet, K., De Block, J., Van Der Meeren, P., Raes, K., Dewettinck, K., & Couduzer, K. (2010). Influence of milk fatty acid composition and process parameters on the quality of ice cream. Dairy Science and Technology, 90, 431e447. Sofjan, R. P., & Hartel, R. W. (2004). Effects of overrun on structural and physical characteristics of ice cream. International Dairy Journal, 14, 255e262. Sourdet, S., Relkin, P., & César, B. (2003). Effects of milk protein type and pre-heating on physical stability of whipped and frozen emulsions. Colloids and Surfaces B: Biointerfaces, 31, 55e64. Thomsen, M., & Holstborg, J. (1998). The effect of homogenization pressure and emulsifier type on ice cream mix and finished ice cream. In W. Buchhein (Ed.). Proceedings of the international symposium held in Athens, Greece, 18e19 September 1997: Ice cream (pp. 105e111). Brussels, Belgium: International Dairy Federation. Tomas, A., Paquet, D., Courthaudon, J. L., & Lorient, D. (1994). Effect of fat and protein contents on droplet size and surface protein coverage in dairy emulsions. Journal of Dairy Science, 77, 413e417. Tosaki, M., Kitamura, Y., Satake, T., & Tsurutani, T. (2009). Effects of homogenisation conditions on the physical properties of high-fat ice cream. International Journal of Dairy Technology, 62, 577e583. Venir, E., Marchesini, G., Biasutti, M., & Innocente, I. (2010). Dynamic high pressureinduced gelation in milk protein model systems. Journal of Dairy Science, 93, 483e494.
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International Dairy Journal journal homepage: www.elsevier.com/locate/idairyj
Effects of high pressure homogenisation of ice cream mix on the physical and structural properties of ice cream Marialuisa Biasutti*, Elena Venir, Marilena Marino, Michela Maifreni, Nadia Innocente Department of Food Science, University of Udine, Via Sondrio 2/A, 33100 Udine, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 July 2012 Received in revised form 11 March 2013 Accepted 12 March 2013
This study investigated the effect of high pressure homogenisation (HPH) on the physical and structural properties of ice cream. Samples were produced from mixes differing in fat content (5% and 8%) and subjected to different homogenisation pressures (15/3 MPa and 97/3 MPa). Ice creams were compared for fat globule size distribution, overrun, melting behaviour, and hardness. No influence of HPH on fat structure destabilisation with respect to the conventional homogenisation (CH) was observed. The HPH ice cream samples with high fat content were characterised by the lowest overrun, the highest hardness and improved resistance to melting; the HPH ice creams with low fat content showed higher resistance to meltdown, but were not clearly differentiated for hardness with respect to the CH samples. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Ice cream is a multiphase system consisting of dispersed air bubbles, partially-coalesced fat globules, ice crystals and a continuous aqueous phase with dissolved solutes (sugars and salts) and suspended macromolecules (polysaccharides and proteins) (Goff, 1997; Marshall & Arbuckle, 1996). Each of these elements determines the structure of ice cream, which, in turn, affects its physical properties, such as resistance to melting and hardness, and viscoelastic behaviour, as well as the sensorial characteristics of the final product. Different factors contribute to the ice cream structure, such as ingredients used and the manufacturing process, which includes the homogenisation step. The main purpose of homogenisation is the reduction in size of fat globules to less than about 2 mm, resulting in a greater stability of fat globules during mix ageing. Moreover, the risk of churning of fat in the freezer is also reduced (Goff, 1997; Marshall & Arbuckle, 1996). Homogenisation also causes the formation of a new fat globule membrane. In fact, the passage through the homogeniser valve causes the rupture of the native membrane of fat globules and the subsequent change in its composition. Firstly, the adsorption of milk proteins and then their partial displacement by emulsifiers occurs during mix ageing process. This rearrangement weakens the newly formed membrane, which becomes less stable to shear forces and more susceptible to
* Corresponding author. Tel.: þ39 0432 558137. E-mail address: [email protected] (M. Biasutti). 0958-6946/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.idairyj.2013.03.007
partial coalescence. As a consequence, a network of partially agglomerated globules is achieved. This network surrounds the air cells, leading to a more stable foam structure (Goff, 1997; Marshall & Arbuckle, 1996). Homogenisation pressures ranging between 6 and 20 MPa are generally employed in ice cream mix processing (Marshall & Arbuckle, 1996). Various studies have been published with respect to the effect of conventional pressure homogenisation on ice cream characteristics, such as fat destabilisation, melting behaviour, hardness and ice crystal growth (Campbell & Pelan, 1998; Koxholt, Eisenmann, & Hinrichs, 2001; Olson, White, & Watson, 2003; Ranjan & Baer, 2005; Ruger, Baer, & Kasperson, 2002; Schmidt & Smith, 1989; Smet et al., 2010; Thomsen & Holstborg, 1998; Tosaki, Kitamura, Satake, & Tsurutani, 2009). Ice cream properties as affected by microfluidisation process have been investigated by Morgan, Hosken, and Davis (2000) and Olson et al. (2003). Studies have been published also on the effect of high-pressure homogenisation (HPH, ranging from 80 up to 200 MPa) on mix and ice cream properties (Gray & Turan, 2002; Hayes, Lefrancois, Waldron, Goff, & Kelly, 2003; Innocente, Biasutti, Venir, Spaziani, & Marchesini, 2009). Gray and Turan (2002) reported that homogenisation at 160 MPa caused a reduction in size of oil droplets compared to conventional homogenisation (CH) treatment, leading to a larger air:water interface and the best performance on creaminess for the ice cream. Hayes et al. (2003) did not observed a clear relationship between the degree of fat flocculation in mixes and fat globule coalescence and the melting properties of ice creams as a function of homogenisation pressure applied. They also reported that the apparent viscosity of mixes and
M. Biasutti et al. / International Dairy Journal 32 (2013) 40e45
the textural characteristics (hardness and gumminess) of ice creams with 5% fat and homogenised at 100 MPa were found to be similar to 8% fat ice creams homogenised at 18 MPa. Further investigations (Innocente et al., 2009) proved that HPH caused only a slight decrease in fat globule size compared with CH treatment, but a strong enhancement of the viscoelastic properties and the apparent viscosity of mixes. In fact, rheological results indicated that unhomogenised and CH mixes behaved as weak gels, whereas HPH treatment led to stronger gels. These results would be of interest since it is known that colloidal properties of mixes are essential in the development of ice cream body and texture, since they affect overrun, melting resistance, hardness and iciness (Goff, 1997; Marshall & Arbuckle, 1996). The aim of this study was to complete the previous study (Innocente et al., 2009) performed on ice cream mixes to evaluate the physical and structural properties of ice cream as affected by HPH of mixes. For this purpose, ice creams with different fat content (5% and 8%) were produced from mixes homogenised at 15/3 MPa and 97/3 MPa. Ice creams were also produced from unhomogenised mixes. All the ice cream samples were analysed for overrun, fat globule size distribution, melting behaviour, and hardness. 2. Materials and methods 2.1. Ingredients and ice cream mix formulation The following ingredients were used: commercial homogenised and pasteurised whole milk and milk cream (35% fat), and sucrose (all purchased in a local store), 5 Dextrose Equivalent maltodextrin (MaltrinÒ M040, Natural World s.r.l., Ravenna, Italy), spray-dried glucose syrup (C*Dry GL 01924, Cerestar France, Haubourdin Cedex, France), skim milk powder (Bayerische Milchindustrie, Landshut, Germany), whey protein concentrate (Hiprotal 880, Borculo Domo Ingredients, Zwolle, The Netherlands), mono- and diglycerides of fatty acids (E471, Natural World s.r.l., Ravenna, Italy), lactic acid esters of mono- and diglycerides of fatty acids (E472b, Natural World s.r.l.), carboxymethylcellulose (Walocel CRT-PA, Comiel s.r.l., Milan, Italy), guar gum (Indian Gum Industries Ltd., Mumbai, India), and locust bean gum (Seedgum A-175, LBG Sicilia s.r.l., Ragusa, Italy). Two formulations were prepared, containing 5% and 8% fat, respectively. Both formulations consisted of 19% carbohydrate, 10% non-fat milk solids, 0.5% emulsifiers and 0.25% stabilisers. Full details of the two formulations have been reported by Innocente et al. (2009). 2.2. Ice cream processing For each processing trial, a 9 kg batch of ice cream mix was prepared by mixing all ingredients at 65 C. After pasteurisation (82 C for 8 min) the mix batch was divided into three equal samples: the first portion was not homogenised (unhomogenised mix, UNH), the second portion was homogenised at 15 MPa (first stage) and 3 MPa (second stage) (conventional-pressure homogenised mix, CH), and the third portion was homogenised at 97/3 MPa (high-pressure homogenised mix, HPH). A 2-stage mode homogeniser (mod. Panda 2K, Niro Soavi s.p.a., Parma, Italy) was used. For CH treatments, inlet temperature of mixes ranged from 65 to 68 C and outlet temperature was 48 C. For HPH treatments, mix inlet temperature varied from 45 to 48 C and outlet temperature was 65 C (Innocente et al., 2009). All mixes were cooled in an ice bath to 4 C and aged at this temperature for 24 h without stirring. The mixes were then frozen using a horizontal batch ice cream freezer (3 L capacity, mod.
41
Mantematic K20/S, Cattabriga, Anzola Emilia, Italy) for a fixed time of 13 min. Ice creams were collected in 4 L containers and stored at 10 C (consumption temperature of ice cream) for 24 h before further testing was performed. For hardness determination, aliquots of extruded ice cream samples (0.5 L) were taken and stored separately at 18 C for 24 h. The overall experimental procedure was performed three times. 2.3. Fat particle size analysis The fat particle size distributions of ice cream mixes and melted ice creams were measured by dynamic light scattering, using a Nicomp 380 ZLS analyser (Particle Sizing System Nicomp, Santa Barbara, CA, USA). For size analysing, the Nicomp volume-weighted distribution was used and the volume-weighted mean diameters (D4,3) were recorded. The mix samples (unfrozen and aged at 4 C for 24 h) were diluted 1:1000 both in water and in an aqueous solution of 1% w/v of sodium dodecyl sulphate (SDS) (SigmaeAldrich, Steinheim, Germany) as dissociation medium (Gelin, Poyen, Courthaudon, Le Meste, & Lorient, 1994; Granger, Leger, Barey, Langendorff, & Cansell, 2005; Sourdet, Relkin, & César, 2003; Tomas, Paquet, Courthaudon, & Lorient, 1994). The measurement parameters were set as follows: temperature at 25 C (2 C), refractive index at 1.333, viscosity at 0.89 mPa s, 3 min for data integration time, scattering angle at 90 for UNH and CH mix samples and 170 for HPH samples (Innocente et al., 2009). As regards the ice creams, prior to analysis the samples (50 g; 10 C) were melted in a controlled temperature chamber (FTC 90I, Velp Scientifica srl, Usmate, Italy) at 25 C (2 C) for 30 min and were then ultrasonicated at power level 5 for 10 min (USCP00D, VWRÔ, Leuven, Belgium) at room temperature to ensure the absence of air bubbles (Gelin et al., 1994; Granger et al., 2005). Preliminary tests were performed to check that ultrasonication conditions adopted did not affect particle size. Images by microscope were taken to prove the absence of air bubbles in the ultrasonicated samples. The melted ice cream samples were analysed under the same operating conditions adopted for the mix samples (dilution, temperature, refractive index and data integration time). Scattering angle was set at 90 for all the ice cream samples. For each sample (mix and ice cream), measurements were carried out at least five times. 2.4. Overrun Mix and ice cream samples were weighed in a cup with a fixed volume of 125 mL and the overrun was calculated according to the following equation: Overrun (%) ¼ [(weight of ice cream mixweight of ice cream)/(weight of ice cream)]*100 (1) For each sample (mix and ice cream), measurements were carried out three times. 2.5. Melting behaviour The meltdown tests were carried out in a controlled temperature chamber at 25 C (2 C) (FTC 90I, Velp Scientifica srl, Usmate, Italy. The ice cream samples (truncated cone shape, initial weight of about 130 g, initial temperature at 10 C) were placed on a wire mesh (with 2 mm square openings) and the amount of melted ice cream passing through the wire mesh was collected and weighed every 2.5 min for 30 min. The percentage of melted ice cream was plotted against time. The melting behaviour of the ice cream samples was expressed as the time required to melt a known amount of ice cream. For each ice cream sample, measurements were carried out in triplicate.
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2.6. Hardness analysis The ice cream samples were transferred from a 18 C freezer to a 10 C freezer 24 h prior to analysis. Hardness measurements were carried out at room temperature. Nevertheless, the following criteria were adopted in order to minimise the melting effects: cups (72 mL capacity, 36 mm in height, 50 mm in diameter, with perforated bottom to avoid entrapping air during filling) were filled with and were then placed in the 10 C freezer for 20 min to stabilise the ice cream sample; hardness measurements were carried out immediately after removing the cup from the freezer; the probe was conditioned at 10 C before testing. Hardness was determined using an Instron Universal Testing Machine (mod. 4301, Instron Ltd., High Wycombe, UK) equipped with a 100 N load cell and a stainless steel cylindrical probe (8 mm diameter). The plunger was allowed to penetrate to the geometrical centre of the sample for 18 mm, with a crosshead speed of 50 mm min1. Hardness was expressed as the maximum load (N) corresponding to the ice cream resistance to penetration. For each ice cream sample, at least five measurements were carried out. 2.7. Statistical analyses One-way analysis of variance (F-test) and Tukey’s HSD test were used for multiple comparisons of the means. The differences were considered statistically significant for P 0.05. All statistical analyses were conducted using Statistical Discovery JMP 3.0 for Windows (SAS Institute Inc., Cary, NC). 3. Results and discussion 3.1. Fat particle size For both 5% and 8% fat content samples, mixes and ice creams were analysed in terms of particle (fat globule or aggregates) size distribution. Measurements were carried out dispersing samples both in water and in a dissociating medium (aqueous solution of 1%, w/v, SDS) to investigate the state of fat globule dispersion and, hence, sort out the fat destabilisation processes which may occur
among flocculation, coalescence or partial coalescence (Gelin et al., 1994; McClements, 2007; Méndez-Velasco & Goff, 2012; Sourdet et al., 2003). As an example, representative volume-weighted distributions in SDS (A) and in water (B) are reported for mix (Fig. 1) and ice cream (Fig. 2) samples with 8% fat content, but similar behaviours were also found for the systems with 5% fat content. In the mixes (Fig. 1) the fat globule distribution changed with the dispersing medium used. In fact, it can be noted that the particle size distribution in SDS of the UNH sample was characterised by a bimodal distribution with a main group of particles at about 1000 nm and a second group at about 200 nm. On the other hand, monomodal distributions were observed in the CH and HPH samples. Similar behaviour in SDS were also observed and discussed in a previous paper (Innocente et al., 2009). In the UNH samples the main group was attributed to the fat globules derived from milk and milk cream, and the second group to casein micelles. The latter was suggested to disappear in the CH and HPH mix samples as a result of disaggregation by the homogenisation treatment and/or of adsorption to the newly formed fat globule membrane (Innocente et al., 2009). Moreover, all the mixes (UNH, CH and HPH) showed monomodal distributions when diluted in water and a shift of the peak towards higher diameter values with respect to the corresponding samples dispersed in SDS. In the ice cream samples (Fig. 2) the particle size distribution of the homogenised systems (CH and HPH) became bimodal and did not differ between the samples dispersed in dissociating medium (Fig. 2A) and in water (Fig. 2B). In fact, they were characterised by a main group at about 1000 nm and a second group ranging from 100 to 300 nm both in SDS and in water. Similarly to that previously discussed for the mix samples, these groups refer to fat globule aggregates and to casein micelles, respectively. The casein micelles would be desadsorbed from the fat globule membrane by the freezing process. The particle size distribution of the ice cream sample produced from the unhomogenised mix (UNH) was found to differ with the dispersing medium used. In fact, it showed a bimodal distribution similar to that of the homogenised ice creams when diluted in SDS, whereas it was characterised by a monomodal distribution when diluted in water. Moreover, a shift of the peak
Fig. 1. Representative volume-weighted distributions of ice cream mix samples (8% fat content) subjected to different homogenisation pressures (UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa). Samples dispersed in either (upper set) sodium dodecyl sulphate solution as dissociating medium or (lower set) water.
M. Biasutti et al. / International Dairy Journal 32 (2013) 40e45
43
Fig. 2. Representative volume-weighted distributions of ice cream samples (8% fat content) subjected to different homogenisation pressures (UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/ 3 MPa). Samples dispersed in either (upper set) sodium dodecyl sulphate solution as dissociating medium or (lower set) water.
towards lower diameter values was observed in the sample diluted in water with respect to the sample dispersed in SDS. Tables 1 and 2 report the mean values of the volume-weighted diameters (D4,3) in SDS and in water obtained from the particle size distribution curves of the mix and the ice cream for the 5% and 8% fat content samples, respectively. In all the mix samples (UNH, CH and HPH) the mean fat globule diameters measured in SDS were found to be always lower than the values observed for the same samples dispersed in water. As a consequence, it can be inferred that, regardless of the homogenisation treatment applied, in the mixes flocculation appears to be the main aggregation process involving the fat globules. As regards the ice creams, different behaviours were observed between the homogenised (CH and HPH) and the unhomogenised samples. Firstly, it is worthy to note that in the UNH ice cream the volume-weighted diameters in water were found to be markedly lower than those measured in the corresponding mix, whereas no significant differences were observed in the mean values measured in SDS. As already mentioned, this would suggest a dissociation of aggregates, which may be attributed to casein micelles, by the freezing process. Secondly, it can be seen that in the UNH ice cream samples the mean particle diameter measured in SDS was found to be markedly higher than the value
measured in water. Since the mean diameters in SDS did not differ between the UNH ice cream and the corresponding mix, it can be deduced that coalescence is the main fat destabilisation process in the UNH ice cream sample. Coalesced globules would be detectable in the mix (both in SDS and in water) and in the ice cream when diluted in SDS, whereas they would not be measurable in the ice cream dispersed in water. The measured particles would be fat aggregates of smaller dimensions remained in the aqueous phase. As regards the homogenised ice creams (CH and HPH), in both these samples no significant differences were observed between the mean diameter values measured in SDS and in water. Moreover, these samples always showed higher mean diameters (in SDS) with respect to the corresponding mix samples. Therefore, it can be inferred that in the CH and HPH ice creams partial coalescence may be the fat destabilisation process occurred and no influence by increasing homogenisation pressure seems to be evident. The effect of the homogenisation treatment on the particle size of these three systems will be discussed solely based on particle sizes determined in SDS. For both 5% and 8% fat content samples, the mean diameters of the fat globules in the mix samples were found to markedly decrease from the unhomogenised (UNH) to the CH samples, while only a small further decrease from CH to HPH was
Table 1 Mean values (standard deviations) of volume-weighted diameters (D4,3) of fat globules in mixes and fat aggregates in ice creams with 5% fat content and subjected to different homogenisation pressures.a
Table 2 Mean values (standard deviations) of volume-weighted diameters (D4,3) of fat globules in mixes and fat aggregates in ice creams with 8% fat content and subjected to different homogenisation pressures.a
Sample
Homogenisation treatment
Mix
UNH CH HPH UNH CH HPH
Ice cream
D4,3 (nm)
D4,3 (nm)
Dissociating medium
Water
1066 94b,A 261 15b,C 220 16b,D 1033 66a,A 835 106a,B 843 74a,B
1456 452 741 365 761 824
120a 19a 128a 4b 61a 181a
a Homogenisation treatments were: UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa. Dissociating medium was an aqueous solution of 1%, w/v, sodium dodecyl sulphate. Different lowercase superscript letters in the same row and different uppercase superscript letters in a column refer to statistically significant differences (Student’s t-test, P 0.05).
Sample
Homogenisation treatment
Mix
UNH CH HPH UNH CH HPH
Ice cream
D4,3 (nm)
D4,3 (nm)
Dissociating medium
Water
980 85b,A 363 35b,B 246 7b,C 1128 63a,A 983 204a,A 1091 196a,A
1683 600 746 406 857 976
107a 53a 39a 22b 159a 179a
a Homogenisation treatments were: UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa. Dissociating medium was an aqueous solution of 1%, w/v, sodium dodecyl sulphate. Different lowercase superscript letters in the same row and different uppercase superscript letters in a column refer to statistically significant differences (Student’s t-test, P 0.05).
M. Biasutti et al. / International Dairy Journal 32 (2013) 40e45
3.2. Overrun Fig. 3 shows the average of the overrun values determined in the ice cream samples. A batch freezer was used and it is well known that in this freezing system air is incorporated at atmospheric pressure by direct entrainment from the agitator blades (Chang & Hartel, 2002). As a consequence, overrun may be affected by freezer operating parameters (such as dasher speed or freezing time) or mix properties (such as composition and methods of processing, which, in turn, influence the viscosity of the ice cream mix) (Marshall & Arbuckle, 1996; Sofjan & Hartel, 2004). The freezing process was carried out using the same operating parameters for all the mix samples, hence the overrun values of the ice creams will be discussed with reference to fat content or homogenisation pressure applied. It can be seen that fat content did not influence the overrun of the ice cream samples (Fig. 3). Similarly, also Chang and Hartel (2002) did not observe significant differences in the overrun values between non-fat (0%) and 14% fat ice creams. On the other hand, overrun of the ice cream samples appeared to be affected by the homogenisation treatment applied to the mixes. In fact, regardless of the fat content, the CH ice cream samples were found to have the highest overrun values, whereas the HPH samples had the lowest overrun values. These behaviours can be expected if it is considered that the previous study (Innocente et al., 2009) showed that the apparent viscosity values of the ice cream mixes have always been reported to be lower for the CH samples and higher for the HPH samples, compared with the UNH samples for both 5% and 8% fat content. In fact, it is well known that the whipping ability of ice cream is affected by its viscosity (Adapa, Dingeldein, Schmidt, & Herald, 2000; Marshall & Arbuckle, 1996) and ice cream mixes
Overrun (%)
60
b
c
b
c
50
3.3. Melting behaviour The melting behaviour of the ice cream samples is summarised in Fig. 4. It is expressed as the time required to melt a known amount of ice cream (5% of thawed ice cream in Fig. 4A, 10% of thawed ice cream in Fig. 4B). The samples can be grouped into two main sets: the lowest melting times were found for the CH ice creams, whereas higher resistance to meltdown were measured for the UNH and HPH samples (with HPH_8% characterised by the highest mean values). It is believed that these behaviours may be explained by taking into account the apparent viscosities of the mixes. In fact, the lowest melting times were determined in the ice creams (Fig. 4) produced from the CH mixes characterised by the lowest apparent viscosity, as previously reported (Innocente et al., 2009). On the other hand, the ice cream samples with intermediate melting time (meaning all the UNH samples and the HPH_5% sample, Fig. 4) may be associated to mixes with intermediate apparent viscosity values (Innocente et al., 2009). Finally, the HPH_8% system was characterised by the highest mean values of resistance to meltdown in ice cream (Fig. 4) and the highest apparent viscosity in the corresponding mix (Innocente et al., 2009).
A
40 30 20 10 0
20 15
a
a,b b,c
b
c
c
10 5 0 UNH
B
a
a
70
with high viscosities were found by Schmidt, Lundy, Reynolds, and Lee (1993) to incorporate less air during freezing. As previously mentioned, all mixes were frozen in a batch freezer. Nevertheless, the lack of air incorporation for the HPH samples may not be as pronounced in a continuous freezing system. In fact, it is known that incorporation of air is less dependent on viscosity of the mix if a continuous freezer is used because this allows to regulate the amount of air being introduced into the mix to produce ice cream with the desiderate overrun (Marshall & Arbuckle, 1996; Schmidt & Smith, 1989). Schmidt and Smith (1989) did not observe differences in the overrun values of ice creams produced from homogenised mixes (13.8 MPa versus 27.6 MPa) differing in viscosity. These authors attributed this result to the use of a continuous freezer.
Melting time (min)
observed. These behaviours confirmed the data reported in the previous study (Innocente et al., 2009). As regards the ice cream systems, aggregates similar in size were found between the CH and HPH ice creams. Therefore, it can be inferred that no differences in the extent of fat destabilisation in ice creams occurred as homogenisation pressure increased from 15/3 MPa to 97/3 MPa. This is probably due to the differences in the viscoelastic properties of these mixes previously observed (Innocente et al., 2009). In fact, comparing these two systems, the CH mixes were found to behave as a weak gel and the HPH mixes as a more structured gel-like system (Innocente et al., 2009). The latter has been suggested to derive from pressure-induced colloidal interactions, which led to a network rearrangement or interpenetrating network formation (Biasutti, Venir, Marchesini, & Innocente, 2010; Innocente et al., 2009; Venir, Marchesini, Biasutti, & Innocente, 2010). This network may not allow a different fat destabilisation during freezing process in the HPH systems with respect to the CH ice creams.
Melting time (min)
44
25
a
CH
HPH
a
a,b
b,c c
20
c
15 10 5 0
5% fat
8% fat
Fig. 3. Averages and standard deviations (error bars) of the overrun value (%) measured in mix and ice cream samples with different fat contents (5% and 8%) and subjected to homogenisation at different pressures ( :UNH, 0 MPa; :CH, 15/3 MPa; : HPH, 97/3 MPa). Different superscript letters refer to statistically significant differences (Tukey’s HSD test, P 0.05).
UNH
CH
HPH
Fig. 4. Averages and standard deviations (error bars) of the time (min) required to melt a known amount of ice cream. Panel A, time required to melt 5% of ice cream; panel B, time required to melt 10% of ice cream. ( : 5% fat content; : 8% fat content; UNH, 0 MPa; CH, 15/3 MPa; HPH, 97/3 MPa). In each graph, different superscript letters refer to statistically significant differences (Tukey’s HSD test, P 0.05).
M. Biasutti et al. / International Dairy Journal 32 (2013) 40e45
References
3
Max Load (N)
45
2
1
0 5% fat
8% fat
Fig. 5. Averages and standard deviations (error bars) of the hardness value (Max Load, N) measured in the ice cream samples with different fat contents (5% and 8%) and subjected to homogenisation at different pressures ( :UNH, 0 MPa; :CH, 15/3 MPa; : HPH, 97/3 MPa).
3.4. Hardness Fig. 5 reports the average hardness values of the ice cream samples. The HPH ice cream with 8% fat content showed the highest hardness value (1.773 N) and was clearly differentiated from all the other samples. The latter showed lower values of resistance to deformation, which ranged from 0.466 to 0.825 N. No clear relationship between hardness and homogenisation pressure was observed. This behaviour may be affected by the overrun values of ice creams and the apparent viscosity of mixes. In fact, lower overrun data were observed (Fig. 3) and higher viscosity values were reported (Innocente et al., 2009) for the HPH ice creams (higher hardness, Fig. 5), whereas higher overrun (Fig. 3) and lower apparent viscosities (Innocente et al., 2009) were found for the CH samples (lower hardness, Fig. 5). Hardness is reported to be affected by overrun as well as the rheological properties of the mix. Different studies showed an inverse relationship between hardness and overrun (Goff et al., 1995; Muse & Hartel, 2004; Sofjan & Hartel, 2004). According to Muse and Hartel (2004), air in ice cream behaves as a compressible dispersed phase, which opposes less resistance to a compression force when a greater amount is entrapped. These authors also observed that as the flow behaviour index and the consistency coefficient of mix increased, the ice cream hardness increased (Muse & Hartel, 2004). 4. Conclusions Flocculation appears to be the main aggregation process occurred in the mixes, regardless the homogenisation pressure applied. In the ice creams, coalescence and partial coalescence are the main fat destabilisation phenomena suggested for the UNH and both the homogenised (CH and HPH) systems, respectively. Therefore, it seems that in ice cream high pressure homogenisation did not cause a different structure of destabilised fat globules with respect to the conventional treatment. It is suggested that high pressure homogenisation may have a structuring effect on the proteins of the serum phase. These proteins may form a network rearrangement or interpenetrating network, which may not allow a different fat destabilisation between CH and HPH treatment. This appears to be confirmed by the overrun, melting rate and hardness behaviours. In fact, the HPH ice cream samples with high fat content were characterised by lower overrun, the highest hardness and an improvement in melting resistance. On the other hand, with respect to the CH samples, the HPH ice creams with low fat content showed higher resistance to meltdown, but were not clearly differentiated for hardness.
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