COMPARISON OF SENSORY QUALITIES OF ICE CREAM FROM RHEOLOGICAL
CHARACTERIZATION
DANIEL IKHU-OMOREGBE
Department of Chemical Engineering, Cape Peninsula University of Technology,
Cape Town, South Africa.
ABSTRACT
The relative sensorial impression and quality of different brands of commercial ice creams
were compared by carrying out oscillatory thermo-rheometry measurements. A temperature
sweep in the temperature range of -120C and 50C was performed on the four brands in order
to compare the scoopability, a feel of coldness when consumed and creaminess. The results
obtained suggested that the Ola brand was the easiest to scoop, the least sensorial coldness
was displayed by the Spar brand and the Country Fresh was the creamiest as it had the
highest G’ value when the ice cream has melted. This paper demonstrates the usefulness of
rheological information in assessing sensorial qualities of food products.
Keywords: rheology, ice-cream, sensorial quality, scoopability,coldness, creaminess.
1.
INTRODUCTION
Rheology is the science of deformation and flow behavior of materials. Knowledge of the rheological characteristics
of fluids and semisolid food materials is important in the design of flow process, quality control, storage and
processing stability (Davis, 1973). Rheology can also be useful in assessing the sensory characteristics of food based
materials (Chhabra, 2006). Conventionally ice cream is produced by rapidly cooling a homogenized mix of milk,
nonfat solids, stabilizers and emulsifiers in freezers to below -250C. The addition of air during the cooling process
contributes to the lightness or denseness of the ice cream (Wildmoser et al, 2004).
The study of rheological properties of ice-cream is useful for control of quality, texture, processing and the selection
of proper equipment in ice cream manufacture (Lal et al, 2006). Furthermore, the characterization of the
temperature-dependent rheological properties of ice cream is important to establish the relationship between
structure and flow and to correlate physical parameters with sensory evaluation (Muse and Hartel, 2004). Thus
oscillatory thermo-rheometry can effectively be used as a tool for assessing the sensory quality of ice creams
(Mezger, 2006).
Ice cream can be classified in terms of sensory quality characteristics such as rigidity, scoopability, creaminess and
sensorial impression of coldness. A particular ice cream should display low rigidity at low temperatures to ensure
good scoopability, whilst maintaining its creaminess after melting at higher temperatures for good mouth feeling. In
the intermediate melting range, a consumer does not like to sense feeling of coldness.
The sensory qualities can be illustrated using a temperature sweep as shown in figure 1. At temperatures less than 100C, the ice crystal microstructure dominates the rheological behavior. The levels of the storage modulus, G’ and
loss modulus, G” corresponds to the rigidity and scoopability of the ice cream (Adapa, 2000; Wildmoser, 2004). At
temperatures of between -100C and 00C, the ice crystals are melting. The steeper the slope of G’ and G”, the faster
the melting, that is a more pronounced sensorial impression of coldness. At temperatures above 0 0C, all the ice
crystals have melted and value of G” correlates the sensorial impression of creaminess. The higher the loss modulus,
G”, the creamier the sensorial impression of the ice cream felt by the consumer.
In this paper rheometry is used to assess and compare sensory qualities of four brands of ice cream in terms of
scoopability, coldness and creaminess. The ice cream brands were obtained from a supermarket in South Africa.
Figure 1: Temperature sweep illustration of for ice cream (Anton Paar manual)
2.
MATERIALS AND METHOD
The rheological measurements (temperature sweep) of four brands of ice cream were made using an Anton Paar
MC51 rheometer (Anton Paar GmbH, Ostfilden, Germany). The measurement system used for this work consists of
a conical plate 50mm in diameter with a cone angle of 2 degrees and a plate which is the base of the test section. The
gap between the two plates is 0.049 mm. A constant temperature circulator (Viscotherm VT2, Anton Paar GmbH)
with a temperature range of -20 ºC and 180 ºC (± 0.1 ºC) was used to control measurement temperature. All
measurements were carried out in duplicates and a third run was made if the pattern differs greatly otherwise one
with the least slope less feel of coldness was used for each brand.
Four market brands of vanilla ice-cream were chosen randomly for the purpose of this study with the following
ingredients as state on the labels of the containers.
a. American parlour : milk solids, sugar, butter, vegetable fat, stabilisers, emulsifiers, floavouring and
colourants.
b. Country fresh: skimmed milk, cane sugar, whey powder (milk), vegetable fat, glucose syrup, cocoa
powder, emulsifiers, stabilisers, citric acid, flavourants, colourants and may contain traces of nuts.
c. Ola: milk solids, cane sugar, vegetable fat, whey solids (milk), glucose solids, emulsifiers, stabilizers,
flavourants, colourants and may contain traces of nuts.
d. Spar: cane sugar, glucose, butter vegetable fat, stabilisers, emulsifiers, flavouring, colourants and may also
contain traces of nuts.
RESULTS AND DISCUSSION
The results of the temperature sweep which are a plot of G’ and G” versus temperature are shown in Figure 2 (a – d)
for the four brands for a temperature range of -120C and 80C. The results show similar ‘S’ shaped characteristic
curves. The curves are characterized by a plateau from -120C to about -80C, a rapid drop in both the storage and
loss moduli and a flatten-out at temperatures above 00C. The value of G’ is observed to be consistently higher that
those of G’’ at both the upper and lower plateau sections of the plots. This suggests that these materials display a
more rigid structure as G’ is an indication of the rigidity of the material.
(a)
(b)
(b)
(d)
Figure 2: Temperature sweeps for (a) the Ola, (b) the Spar (c) the Country Fresh and (d) American Palour brands
In the region of -120C to -80C, the G’ values give an indication of the scoopability of the ice cream. The mean value
of G’ at the plateau are 1.05x105Pa for the Ola brand, 1.30x105Pa for the Spar brand, 1.46x105Pa for the American
Palour and 1.64x105 for the Country Fresh brand. These values are shown in Fig. 6a. Since these G’ values are
related to the scoopability of the ice cream, it can be suggested that the Country Fresh brand displays a much greater
rigidity compared to the other three brands. Thus in terms of scoopability, the Ola brand is of better quality as it the
easiest to scoop.
In the region of -80C and 00C there is a steep drop in both the storage and loss moduli for all the materials resulting
in gradients which are a reflection of sensorial feeling of coldness when consumed. The steeper the slope, the
sharper the feeling of coldness experienced. This is due the rapid drop in the storage and loss moduli. A gradual
decrease in these values is more appealing to the senses rather than a rapid rate of change. The sharp drop in the
values of the moduli is experienced by the senses as a sharp cold sensation. The coldness is related to the amount of
ice that is present within the structure of the ice cream (Granger, 2004). The gradients as obtained for these
materials, Fig. 6b are 4.19 for the American Palour, 3.70 for the Country Fresh, 3.07 for the Ola and 2.95 for the
Spar brand. These values suggest that the Spa brand has a better sensorial feel of coldness as it has the least gradient
compared to the three brands.
Figure 6: Comparison of sensorial qualities of the four brands
In the higher temperature region of 00C and 80C, the loss modulus, G” value gives indication of the creaminess of
the ice cream. The G” values are also indicators of the viscous behavior of the ice cream samples, hence the higher
the G’’ values the more creamy the sample (Wildmoser, 2004). In Fig. 6c, the values obtained were 54.4 Pa for the
Country Fresh brand, 36.68 Pa for the Ola brand, 34.62Pa for the Spar and 23.13 for the American Palour. Thus it
can be suggested that the American Palour is less creamy than the other three while the Country Fresh is the
creamiest product.
The results obtained in this work demonstrate the usefulness of rheology to assess and compare useful food quality
desirables such as sensorial impressions. It provides a scientific quantifiable data to assess properties that cannot be
quantified. By determining the scoopability, coldness experienced and creaminess, the ratio of the ingredients and
processing operations can be altered accordingly to produce a more appealing and satisfying product.
CONCLUSION
The sensory qualities of four brands of ice cream were compared using rheological principles. the data obtained
from oscillatory rheometry, temperature sweeps, were used to assess the relative sensorial impressions of these
products. The results obtained suggested that the Ola brand was the easiest to scoop, the least sensorial coldness was
displayed by the Spar brand and the Country Fresh was the creamiest as it had the highest G’ value when the ice
cream has melted. This paper demonstrates the usefulness of rheological information in assessing sensorial qualities
of food products.
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