CC BY
20
Jacek Domagala, Marek Sady, Ilona Wieteska, Maria Czernicka ©
Department of Animal Product Technology, Food Technology Faculty, University of
Agriculture in Krakow, Poland
THE COMPARISON OF SELECTED METHODS USED TO CREATING THE TEXTURE OF SET-YOGHURT PREPARED FROM GOAT MILK
Abstract
Set-type yoghurts from goat milk from middle lactation period modified by different methods were produced. As milk modification methods were chosen: concentration by ultrafiltration, addition of goat milk powder, addition of texture improver, addition of stabilizer and cross-linking of milk protein by transglutaminase.. The control yoghurt was prepared from non-modified goat milk. Yoghurts from modified milks were characterized by higher overall sensory quality, higher apparent viscosity, hardness, adhesiveness and lower syneresis than yoghurt from control milk. Yoghurts from ultrafiltrated milk was characterized by highest sensory quality and apparent viscosity. The highest values of hardness and adhesiveness were found for yoghurts from milk with addition of texture improver and stabilizer. Addition of stabilizer caused also the highest reduction of syneresis.
Key words: goat milk yoghurt, stabilizers, texture, texture improver, transglutaminase, ultrafiltration
Introduction
The composition of milk is one of the most important factor influencing yoghurt quality. Enrichment of milk in dry matter components can reduce seasonal fluctuations in its composition and allow to obtain of proper physical properties of yoghurt. The increase of total solids in milk for yoghurt cause an increase in viscosity and better consistency of final product and reduce syneresis in comparison with the product from milk with low content of total solids. Optimal level of total solids in milk for yogurt, giving the best textural properties of the product ranged from 14-16% [23,24].
Goat milk yoghurt, especially from middle lactation period contains lower amount of total solids and total protein, than in initial and final lactation period, and also than cow milk and needs modifications to obtain yoghurt with proper textural and rheological properties [11].
Addition of skimmed or whole milk powder, evaporation, ultrafiltration, addition of stabilizer are the methods often used for yoghurt milk enrichment. Addition of texture improver (special protein preparations), ultra high pressure of the milk of yoghurt, and modification of milk protein by microbial transglutaminase (TGase) (enzyme, that catalyses the formation of covalent cross-links between glutamine and lysine residues in many food proteins e.g. in casein) are the relatively new method of creating of physical properties of yoghurt [6,23]
© Jacek Domagala, Marek Sady, Ilona Wieteska, Maria Czernicka, 2008
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The aim of presented work is to compare selected methods of composition and properties of goat milk modification on the quality properties of yoghurt.
Material and methods
Raw milk collected from an Improved Polish White breed in middle lactation period was modified by following methods:
- concentration by UF technique to 1,5-fold (v/v) concentration degree using UF concentrator CH-2A from Amicon (Switzerland),
- addition of goat milk powder (Danmis, Poland) in the amount of 4%,
- addition of stabilizer JO 752 (Rhodia Food Biolacta, Poland) in the amount of 1%,
- addition of texture improver DSE 6693 (NZMP, New Zealand) in the amount of 2%,
- cross-linking of milk protein by microbial transglutaminase (Ajinomoto, Japan), added to milk in the amount of 2u/g protein and incubated with enzyme by 16 h in the temperature of 5°C. The type and amount of stabilizer and texture improver were chosen according to results of previous research [8,9], and the addition level and incubation condition of milk with transglutaminase were selected from the general information about transglutaminase [2]. The control milk was the milk without any modification. Milk for yoghurt preparation (control and modified) was pasteurized at 85°C for 15 min., cooled down to incubation temperature and inoculated with starter culture YC-180 (Chr. Hansen, Denmark). The culture was added at 2% converted into the batch starter culture. The yoghurts were incubated at 44°C until the cut of point of pH was reached. Then the products were cooled down to 5°C, stored at this temperature for 14 h and then analyzed.
In control and modified milk used for yoghurt preparations the following parameters were analyzed: total solids, total protein, fat, lactose, ash, density, acidity and pH. [3,21]. For yoghurts the following analysis were done: sensory evaluation, pH, apparent viscosity using rotary viscometer Rheotest RY2 (VEB MLW Medingen, Germany), hardness and adhesiveness using texture analyser TA-XT2 (Stable Micro Systems, UK) and syneresis using drainage method [16] and centrifugal method [20].
The experiment was repeated in 3 independent tests. Results were evaluated statistically. One factor analysis of variance was carried out and the significance of the difference among means were assessed with the Duncan Test.
Results and discussion
The composition and physicochemical properties of control goat milk and goat milk after different modifications used for yoghurt preparation are presented in Table 1.
Similar composition of goat bulk milk from from different breeds in the middle lactation period was found by Guo et al. [14] and from Improved Polish White breed by Domagala and Wszolek [11]. Ultrafiltration of the milk, addition of goat milk powder and texture improver increased significantly the amount of total solids, total protein, fat, lactose and ash and in the consequence density of modified milk in comparison to the values of these parameters in non-modified milk. Only the lactose content in UF milk was lower than in control and other modified milks, and the fat
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content in control milk and in the milk with addition of texture improver were similar. The addition of texture improver caused also an increase in acidity of the milk. Similar changes in composition of ultrafiltrated goat milk observed Abrahamsen and Holmen [1] and Karademir et al. [15].
Table 1.
Composition and physicochemical properties of goat milk (control and modified _by different methods) used for yoghurt preparations_
Control milk Milk after Milk with Milk with
Feature (used also for ultrafiltration addition of addition of
modification by goat milk texture
TGase or by powder improver
stabilizer
addition)
Total solids 11,45a'b'c 14,43a 15,53b,d 13,23c,d
[%] ± 0,41 ± 0,03 ± 1,66 ± 0,03
Total protein 2,71a'b'c 4,47a'd'e 3,65b,d,f 4,18c,e,f
[%] ± 0,06 ± 0,23 ± 0,34 ± 0,04
Fat [%] 3,2a'b 4,4a,c 4,2b,d 3,3C,D
± 0,1 ± 0,1 ± 0,1 ± 0,1
Lactose [%] 4,70a'b 4,02b'c'd 6,10A'C,E 4,76d,e
± 0,25 ± 0,05 ± 0,07 ± 0,08
Ash [%] 0,77a'b'c 0,93a'd 0,91B,a 0,86a,C,D
± 0,17 ± 0,11 ± 0,02 ± 0,02
Density 1,0267aac 1,0312a'd 1,0332b,d,e 1,0312c,e
[g/cm3] ± 0,0001 ± 0,0005 ± 0,0005 ± 0,002
Acidity 7,0a 7,4 7,8 8,1a
[°SH] ± 0,1 ± 0,1 ± 0,2 ± 0,4
pH 6,70 6,61 6,55 6,65
± 0,05 ± 0,34 ± 0,04 ± 0,05
A-F - statistically highly significantly differences between means (p < 0,01) marked with the same letters a-c - statistically significantly differences between means (p < 0,05) marked with the same letters
The results of sensory evaluation, pH, apparent viscosity, texture parameters and syneresis of analyzed yoghurts are presented in Table 2. Generally it was found significant differences in the mean values of determined parameters among all types of yoghurts. All yoghurts from modified milks were characterized by higher overall sensory quality, higher apparent viscosity, hardness, adhesiveness and lower syneresis than yoghurt from control milk. Among yoghurts from modified milks the highest sensory quality had yoghurts from ultrafiltrated milk and from milk with addition of texture improver. The lowest sensory quality caused yoghurt with addition of milk powder. The differences in pH were found only in the case of yoghurt from milk with addition of milk powder and yoghurts from milk with addition of texture improver and stabilizer.
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Table 2.
Properties of yoghurt prepared from goat mi k modified by different methods
Feature Control UF MP TI ST TGM
Sensory evaluation [points] 3,50^3,^ ± 0,18 4,68A,E,b ± 0,07 4,02a,E,°,d ± 0,06 4,51B,c ± 0,18 4,47c,d ± 0,13 4,27D,b ± 0,06
pH 4,49 ± 0,03 4,49 ± 0,06 4,40a,b ± 0,05 4,56a ± 0,03 4,60b ± 0,03 4,53 ± 0,04
Apparent viscosity [Pas] 0,50a,b,c ± 0,10 5 54a,d,e,f,g ± 0,68 3,33B,D,H,' ± 0,38 3,17c,e,j,k ± 0,75 0,67f,h,j ± 0,03 0,90g,i,k ± 0,02
Hardness [G] 15 77a,b,c,d ± 0,78 30,76A,EF,a ± 2,78 20,35E,G,H,b ± 0,63 67,44b,f,g,i,j ± 2,61 38,33c,a,H,I,K ± 0,80 27,05D,b,J,K ± 3,20
Adhesiveness [|Gs|] 4,66^^ ± 0,69 34,03a,e,f ± 0,95 22,09aAH ± 1,19 164,67b,e,g,1 ± 8,28 168,08C,f,h,j ± 3,08 27,10d,i,j ± 4,19
Syneresis I* [%] 32a,b,c ± 7 14a,d ± 3 34d,e,f,a ± 5 8b,e,b ± 0 3c,p,G ± 1 21a,b,G ± 2
Syneresis II** [%] 43a,b,c,d ± 2 14a,e,f,g ± 3 29b,e,h,i ±5 15c,h,j,k ± 2 1d,f,i,j,l ± 0 35g,k,l ± 3
*- drainage method, "-centrifugal method; UF - ultrafiltration, MP - addition of goat milk powder, TI -addition of texture improver
ST - addition of stabilizer, TGM - modification of milk by transglutaminase;
A-L - statistically highly significant differences between means (p < 0,01) marked with the same letter in the rows;
a-d - statistically significant differences between means (p < 0,05) marked with the same letter in the rows.
Yoghurt from ultrafiltrated milk was characterized by highest apparent viscosity, while the lowest viscosity was observed in yoghurt with addition of stabilizer and in yoghurt from milk modified by transglutaminase. The highest values of hardness and adhesiveness were found for yoghurts from milk with addition of texture improver and stabilizer. The influence of ultrafiltration and modification of milk by transglutaminase on hardness and adhesiveness of yoghurts was comparable. The lowest values of these parameters was stated for yoghurt from milk with addition of milk powder. Addition of stabilizer caused also the highest reduction of syneresis determined by both methods. Addition of texture improver and ultrafiltration were only slight lower effective in reduction of syneresis. The lowest influence on syneresis had the modification of milk by transglutaminase and addition of milk powder.
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Pluta et al. [20] also found considerable limitation of syneresis for yoghurts with gelatin, guar gum and xantan addition. According to Domagala et al. [8] addition of stabilizers caused an increase in apparent viscosity, hardness and adhesivevess, a decrease in syneresis, but no effect on sensory quality of goat milk yoghurts.
Significant improvement of quality parameters of yoghurt coagulum produced from UF cow or goat milk reported many authors [1,4,5,7,17,22].
Elferink [12] found a positive effect of texture improver Domovictus, produced on the basis of whey proteins on the structure, viscosity and stability of yoghurts during storage. According to Domagala et al. [9] goat milk yoghurts with texture improvers had significantly better sensory quality, higher apparent viscosity, hardness and adhesiveness and reduced syneresis than control yoghurt. Tamime and Robinson [23] also indicate positive role of texture improvers (which may replace milk powder or stabilizer addition) in formation of the yoghurt's viscosity, texture, mouth feel and syneresis.
According to Faergemand et al. [13] addition of transglutaminase to cow milk enable the production of yoghurt with proper texture without addition of milk powder. Lauber et al. [18] and Lorenzen et al. [19] have found that cross-linking of casein in milk by microbial TGase increase hardness and viscosity of cow's milk yoghurt and reduce syneresis. Similar results for yoghurts from goat milk modified by TGase were obtained by Domagala et al. [10].
Conclusions
1. Yoghurts from modified goat milks were characterized by higher overall sensory quality, higher apparent viscosity, hardness, adhesiveness and lower syneresis than yoghurt from control milk.
2. Yoghurts from ultrafiltrated milk was characterized by highest sensory quality and apparent viscosity.
3. The highest values of hardness and adhesiveness were found for yoghurts from milk with addition of texture improver and stabilizer. The influence of ultrafiltration and modification of milk by transglutaminase on hardness and adhesiveness of yoghurts was comparable.
4. The highest reduction of syneresis caused addition of stabilizer. Addition of texture improver and ultrafiltration were only slight lower effective in reduction of syneresis.
References
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3. AOAC 1995. Official methods of analysis, Washington DC.
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Summary
Set-type yoghurts from goat milk from middle lactation period modified by different methods were produced. As milk modification methods were chosen: concentration by ultrafiltration, addition of goat milk powder, addition of texture improver, addition of stabilizer and cross-linking of milk protein by transglutaminase.. The control yoghurt was prepared from non-modified goat milk. Yoghurts from modified milks were characterized by higher overall sensory quality, higher apparent viscosity, hardness, adhesiveness and lower syneresis than yoghurt from control milk. Yoghurts from ultrafiltrated milk was characterized by highest sensory quality and apparent viscosity. The highest values of hardness and adhesiveness were found for yoghurts from milk with addition of texture improver and stabilizer. Addition of stabilizer caused also the highest reduction of syneresis
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