CC BY
13
Jacek Domagala, Marek Sady, Maria Czernicka, Ilona Wieteska ©
Department of Animal Product Technology, Food Technology Faculty, University of
Agriculture in Krakow, Poland
HARDNESS AND AHESIVENESS OF SET-YOGHURT PREPARED FROM GOATS MILK MEASURED USING CONICAL AND CYLINDRICAL PROBE
Abstract
Set-yoghurts from non-concentrated goat milk in initial, middle and final lactation periods were produced. The milk from middle lactation period was concentrated by ultrafiltration to different concentration degree and also used for yoghurt preparation. In milk for yoghurts the main physicochemical properties were analyzed. In yoghurts sensory evaluation and instrumental hardness and adhesiveness using conical and cylindrical probe and penetrometric test were determined. Generally hardness and adhesiveness of all yoghurts measured using cylindrical probe were significantly higher than the values of these parameters measured using conical probe. In the measurements with cylindrical probe the differences in hardness and adhesiveness between yoghurts from initial, middle and final lactation period and between yoghurts from non-concentrated and concentrated to different degree goat milk were higher and more significant than in the measurements with conical probe. It can suggest that cylindrical probe is more suitable for instrumental texture measurements of set-yoghurt than conical probe.
Key words: goat milk yoghurt, texture, hardness, adhesiveness
Introduction
Texture is one of the most important quality properties of yoghurt. The defects of texture properties such like too liquid consistency and too low viscosity may limit consumer acceptance of these products [1,11]. Texture is defined as physical properties of the product that come from its structural elements, which can be perceptible by human senses. Yoghurt texture may be evaluated sensorial or/and instrumental. The main instrumental texture parameters of yoghurt are hardness and adhesiveness. Hardness is defined as force, which is necessary for obtaining the precise deformation of the sample. Adhesiveness is work necessary for obtaining the force of attraction between area of foodstuff and other solids coming into contact with them. In order to obtain suitable texture parameters in instrumental measurements it is very important to use correct tests and probes [11,12]. According to Tamime and Robinson [14] penetrometric test is the most suitable for proper measurements of texture of set-type yoghurt.
The aim of presented work is the comparison of hardness and adhesiveness of goat milk yoghurt measured using conical and cylindrical probe.
© Jacek Domagala, Marek Sady, Maria Czernicka, Ilona Wieteska, 2008
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Material and methods
Goat milk for yoghurt preparations was obtained directly from the farm in the initial, middle and final lactation period. The milk from middle lactation period was concentrated using ultrafiltration technique to 1,5-fold, 2-fold and 2,5-fold (v/v) concentration degree and used for yoghurt preparation. In non-concentrated and concentrated raw milk the following parameters were analysed: total solids, total protein, fat, lactose, ash, non-protein nitrogen, density, viscosity potential acidity and pH [2,10]. Milk for yoghurt was pasteurized at 85°C for 15 min., cooled down to incubation temperature and inoculated with starter culture YC-180 from Chr. Hansen, Denmark. The culture was added at 2% converted into the batch starter culture. The yoghurts were incubated at 44°C until the pH 4,8 was reached. Than the products were cooled down to 5°C, stored at this temperature for 14 h and than analysed. For yoghurt the sensory evaluation and texture analysis using texture analyser TA-XT2 (Stable Micro Systems, UK) were carried out. In texture analysis the penetrometric test was done using plastic cylinder type SMS P/20 of 20 mm diameter and plastic cone type SMS P/60c. The depth of penetration was 25 mm, and the penetration rate was 1 mm/s. Diagrams of the dependence of force to time obtained in the test were analyzed using the computer program Texture Expert for Windows v. 1.05 (Stable Micro Systems, UK) with algorithm Fracture TPA. The texture parameters that were assessed included hardness and adhesiveness.
The experiment was repeated in 3 independent test. Results were evaluated statistically. One factor ANOVA was carried out and the significance of the difference among means was assessed with Duncan test.
Results and discussion
Physicochemical properties of non-concentrated goat milk from initial, middle and final lactation period used for yoghurt preparation are presented in Table 1, and non-concentrated and concentrated to different degree by ultrafiltration goat milk from middle lactation period in Table 2. Milk from middle lactation period contained significantly lower amount of total solids, total protein and fat than milk from initial and final lactation period. Density of milk from the middle lactation period was also lower than density of milk from initial and final lactation periods. Similar result for goat milk from different lactation periods obtained Domagala and Wszolek [6]. According to Guo et al. [8] the composition of goat milk from different breeds in the middle lactation period was similar to these obtained in presented work.
Concentration of milk using ultrafiltration technique caused significant increase in total solids, total protein, fat, ash and NPN content, and decrease in lactose content in comparison to the content of these components in non-concentrated milk. The differences in the amount of these components between concentrated to different degree milk was also significant. Similar changes in cow and goat milk components after ultrafiltration observed Biliaderis et.al. [3] and Abrahamsen and Holmen [1].
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Table 1.
Physicochemical properties of non-concentrated goat milk from different _lactation periods used for yoghurt preparation_
Feature Lactation period
Initial Middle Final
Total silids [%] 12,61a ± 0,10 11,04ab ± 0,11 13,07B ± 0,21
Total protein [%] 3,37a ± 0,04 3,07a ± 0,04 3,70a,A ± 0,14
Fat [%] 4,0a ± 0,1 3,1A,B ± 0,2 4,2B ± 0,1
Lactose [%] 4,73 ± 0,18 4,61 ± 0,05 4,93 ± 0,03
Ash [%] 0,82 ± 0,04 0,73a ± 0,02 0,87a ± 0,02
NPN [%] 0,34a ± 0,01 0,28a ± 0,01 0,30 ± 0,00
Density [g/cm3] 1,0308a ± 0,0005 1,0289a,b ± 0,0003 1,0309B ± 0,0003
Viscosity [mPas] 1,67a ± 0,04 1,60B ± 0,00 1,94a'b ± 0,03
Acidity [°SH] 7,2 ± 0,1 6,9 ± 0,2 7,3 ± 0,4
pH 6,63 ± 0,02 6,68 ± 0,03 6,65 ± 0,03
A-B - highly significant differences between means (p < 0,01) marked with the same letter in the rows a - significant differences between means (p < 0,05) marked with the same letter in the rows
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Table 2.
Physicochemical properties of goat milk from middle lactation period, non-concentrated and concentrated to different degree by ultrafiltration, used for _yoghurt preparation_
Rodzaj mleka Non- Concentration degree
concentrated 1,5-fold 2,0-fold 2,5-fold
Total solids 11,04a,b,c 13,91a33 15,61B33 16,91cef
[%] ± 0,11 ± 0,31 ± 0,32 ± 0,03
Total protein 3,07a'b'c 4,08a33 5,46B33 7,08C3F
[%] ± 0,04 ± 0,07 ± 0,10 ± 0,26
Fat [%] 3,1A'B'C 4,4a3 5,1b,e 6,1C,D,E
± 0,2 ± 0,1 ± 0,2 ± 0,3
Lactose [%] 4,61a3 4,36a,C 3,50^" 2,71B,C,"
± 0,05 ± 0,06 ± 0,25 ± 0,32
Ash [%] 0,73^ 0,88 a33 1,02B,D,a 1,09C,E,a
± 0,02 ± 0,02 ± 0,01 ± 0,02
NPN [%] 0,28a3 0,33a,C 0,44a,",A 0,54B,C,"
± 0,01 ± 0,03 ± 0,02 ± 0,04
Density [%] 1,0289a,A,B 1,0306a,C,D 1,0343A,C,b 1,0360B,D,"
± 0,0003 ± 0,0006 ± 0,0004 ± 0,0006
Viscosity 1,60a3 1,91C 2,35A'a 2,85B,C,a
[mPas] ± 0,00 ± 0,06 ± 0,02 ± 0,28
Acidity [°SH] 6,9a 7,0 7,6 7,8a
± 0,2 ± 0,1 ± 0,2 ± 0,4
pH 6,68 6,69a 6,64 6,57a
± 0,03 ± 0,01 ± 0,03 ± 0,05
A-F - highly significant differences between means (p < 0,01) marked with the same letter in the rows a-b - significant differences between means (p < 0,05) marked with the same letter in the rows
On Figure 1 the results of sensory evaluation of goat milk yoghurt prepared from non-concentrated milk in different lactation periods and in middle lactation period from non-concentrated and concentrated milk to different degree using UF technique are presented. Yoghurt from non-concentrated milk from middle lactation period has significantly lower sensory quality than yoghurts from initial and final lactation periods. Among yoghurts from ultrafiltrated milk the 1,5-fold concentration degree caused the best sensory quality, and the 2-fold only slightly lower. 2,5-fold concentration degree was too high, and the quality of yoghurt from this milk was comparable with the quality of yoghurt from non-concentrated milk.
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highly significant differences between means (p < 0,01) marked with the same letter a-b - significant differences between means (p < 0,05) marked with the same letter
Figure 1. Sensory evaluation of goat milk yoghurt prepared from non-concentrated
milk in different lactation periods (A) and in middle lactation period from non-concentrated (N) and concentrated milk to different degree using UF technique (B)
The values of hardness and adhesiveness of prepared yoghurts measured by conical and cylindrical probe are presented in table 3 and table 4. The significance of differences between results obtained using conical and cylindrical probes in also marked in both tables. Hardness and adhesiveness measured using cylindrical probe were significantly higher than the values of these parameters obtained using conical probe. Only in the case of yoghurt prepared from 1,5-fold concentrated by UF milk, the difference between hardness measured using cylindrical and conical probe was not significant.
The differences in hardness and adhesiveness between yoghurts from initial, middle and final lactation period and between yoghurts from non-concentrated and concentrated to different degree was also observed, although in measurements with cylindrical probe these differences were higher and more significant. It can suggest that cylindrical probe is more suitable for instrumental texture measurements of setyoghurt than conical probe.
Table 3.
Hardness and adhesiveness of yoghurt prepared from goat milk in different _lactation period measured by conical and cylindrical probe
Lactation Hardness [G] Level Adhesiveness [|Gs|] Level
period Conical Cylindrical of Conical Cylindrical of
probe probe signif. probe probe signif.
Initial 15,80aA 25,92a,b ** 6,87a 29,25A,a **
± 0,95 ± 1,88 ± 1,18 ± 2,20
Middle 11,23a,B 16,90a,c * 2,27a,b 15,66Ba **
± 0,79 ± 1,19 ± 0,55 ± 2,68
Final 36,68a,b 51,84B,C ** 7,08b 137,41a,b **
± 1,34 ± 0,96 ± 1,78 ± 2,78
A-C a-b
highly significant differences between means (p < 0,01) marked with the same letter in the columns - significant differences between means (p < 0,05) marked with the same letter in the columns ** - highly significant differences between results (p < 0,01) obtained using conical and cylindrical probe *- significant differences between results(p < 0,05) obtained using conical and cylindrical probe
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Table 4.
Hardness and adhesiveness of yoghurt prepared from non-concentrated and
from ultrafiltrated to different degree goat milk measured by conical and _cylindrical probe_
Type of milk Hardness [G] Level Adhesiveness [|Gs|] Level
Conical probe Cylindric al probe of signif. Conical probe Cylindrica l probe of signif.
Non- 11,23a'b'c 16,90a'b,c * 2,27aäc 15,66abc **
concentrated ± 0,79 ± 1,19 ± 0,55 ± 2,68
UF 1,5-fold 25,93A,a 29,49^ ns 16,19a'd 53,84aäe **
± 2,52 ± 1,32 ± 2,44 ± 2,50
UF 2-fold 34,02B 51,55b,d ** 21,94B,a 80,68bäf **
± 2,34 ± 1,20 ± 2,01 ± 5,11
UF 2,5-fold 40,20C,a 53,78c,e * 31,37CAa 145,01C3F **
± 1,30 ± 4,02 ± 4,01 ± 18,50
A-C - highly significant differences between means (p < 0,01) marked with the same letter in the columns a-b - significant differences between means (p < 0,05) marked with the same letter in the columns ** - highly significant differences between results (p < 0,01) obtained using conical and cylindrical probe *- significant differences between results(p < 0,05) obtained using conical and cylindrical probe ns - not significant
Istrumental texture analysis using texture analyser TA-XT2 and penetrometric test have used in their investigations among others Hess et al. [9], Fiszman and Salvador [7] and Salvador and Fiszman [13] for cow milk yoghurts, Bonczar et al. [4] for sheep milk yoghurts and Domagala and Kupiec [5] for goat milk yoghurts. Only Hess et al. [9] have used conical probe and the others authors cylindrical probe with 12,7 and 20 mm. The values of texture parameters obtained for cow milk yoghurts with stabilizers by Hess et al. [9] using conical probe were similar to the results obtained in this work for yoghurt from 2-fold and 2,5-fold concentrated goat milk and for goat milk from final lactation period. The results of hardness and adhesiveness for all assessed in presented work yoghurts using cylindrical probe were lower than obtained for cow milk yoghurt by Fiszman and Salvador [7] and Salvador and Fiszman [13] and for sheep milk yoghurt by Bonczar et al. [4]. The hardness and adhesiveness obtained in this work using cylindrical probe were similar to the hardness and adhesiveness of goat milk yoghurts form non-concentrated and 2-fold concentrated milk obtained by Domagala and Kupiec [5] using also cylindrical probe.
Conclusions
1. Hardness and adhesiveness of analysed yoghurts measured using cylindrical probe were significantly higher than the values of these parameters obtained using conical probe.
2. The differences in hardness and adhesiveness obtained using cylindrical probe were higher and more significant than those obtained using conical probe.
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3. Cylindrical probe is more suitable for instrumental texture measurements of set-yoghurt than conical probe.
References
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28. Bonczar G., Wszolek M., Siuta A. 2002. The effects of certain factors on the properties of yoghurt made from ewe's milk. Food Chem., 79, 85-91.
29. Domagala J., Kupiec B.E. 2003. Changes in texture of yoghurt from ultrafiltrated goat's milk as influenced by different membrane types. Electronic Journal of Polish Agricultural Universities, Food Science and Technology, 6, 1.
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Summary
Set-yoghurts from non-concentrated goat milk in initial, middle and final lactation periods were produced. The milk from middle lactation period was concentrated by ultrafiltration to different concentration degree and also used for yoghurt preparation. In milk for yoghurts the main physicochemical properties were analyzed. In yoghurts sensory evaluation and instrumental hardness and adhesiveness using conical and cylindrical probe and penetrometric test were determined. Generally hardness and adhesiveness of all yoghurts measured using cylindrical probe were significantly higher than the values of these parameters measured using conical probe. In the measurements with cylindrical probe the differences in hardness and adhesiveness between yoghurts from initial, middle and final lactation period and between yoghurts from non-concentrated and concentrated to different degree goat milk were higher and more significant than in the measurements with conical probe. It can suggest that cylindrical probe is more suitable for instrumental texture measurements of set-yoghurt than conical probe.
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