FERMENTED MILK PRODUCT

Abstract

The present invention relates to a fermented milk product with improved gel strength and/or serum viscosity.

Claims

1. A process for production of a fermented milk product, optionally yogurt, comprising fermenting milk using a composition comprising one or more bacterial strains selected from the group consisting of Streptococcus thermophilus DS71579 (Strain A), Streptococcus thermophilus D571586 (Strain B), Streptococcus thermophilus DS71584 (Strain C), Streptococcus thermophilus DS71585 (Strain D) and wherein the gel strength and/or the serum viscosity of the fermented milk product obtained, optionally yogurt, has been improved compared to the gel strength of a fermented milk product that has not been produced using the composition comprising one or more bacterial strains selected from the group consisting of Streptococcus thermophilus DS71579 (Strain A), Streptococcus thermophilus DS71586 (Strain B), Streptococcus thermophilus DS71584 (Strain C), Streptococcus thermophilus DS71585 (Strain D).

2. A process according to claim 1 wherein the composition is comprising Streptococcus thermophilus DS71586 (strain A).

3. A process according to claim 1 wherein the composition is comprising Streptococcus thermophilus DS71585 (strain B).

4. A process according to claim 1, wherein the composition is comprising Streptococcus thermophilus DS71586 (strain C).

5. A process according to claim 1, wherein the composition is comprising Streptococcus thermophilus DS71585 (strain D).

6. A process according to claim 1, wherein the composition further comprises one or more lactic acid bacteria selected from the group consisting of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. Bulgaricus.

7. A process according to claim 1, wherein the composition further comprises a Lactobacillus delbrueckii ssp. bulgaricus strain.

8. A process according to claim 7, wherein the Lactobacillus delbrueckii ssp. Bulgaricus strain is Lactobacillus delbrueckii ssp. bulgaricus DS71836 (strain E).

9. A process claim 7, wherein the composition comprises Streptococcus thermophilus DS71579 (strain A) and Streptococcus thermophilus DS71586 (strain B) and Streptococcus thermophilus DS71584 (strain C) and Streptococcus thermophilus DS71585 (strain D) and Lactobacillus delbrueckii ssp. bulgaricus DS71836 (strain E).

10. A process according to claim 1, wherein the composition comprises Streptococcus thermophilus DS71586 (strain B) and Streptococcus thermophilus DS71585 (strain D) and preferably optionally Lactobacillus delbrueckii ssp. bulgaricus DS71836 (strain E).

11. A process according to claim 7 wherein the gel strength is improved.

12. A process according to claim 7 wherein the serum viscosity is improved.

13. A process according to claim 7 wherein the gel strength and the serum viscosity is improved.

14. A fermented milk product, optionally yogurt, obtainable by the process of claim 1, wherein the fermented milk product, optionally yogurt, has an improved gel strength and/or an improved serum viscosity compared to a fermented milk product, optionally yogurt, that has not been produced by said process.

15. A composition comprising one or more bacterial strains selected from the group consisting of Streptococcus thermophilus DS71579 (Strain A), Streptococcus thermophilus DS71586 (Strain B), Streptococcus thermophilus DS71584 (Strain C), Streptococcus thermophilus DS71585 (Strain D) for the production of the fermented milk product, optionally yogurt as defined in claim 14, having an improved gel strength and/or an improved serum viscosity compared to a fermented milk product, optionally yogurt, that has not been produced by said composition.

16. A composition for production of a fermented milk product, optionally yogurt, said composition comprising one or more bacterial strains selected from the group consisting of Streptococcus thermophilus DS71579 (Strain A), Streptococcus thermophilus DS71586 (Strain B), Streptococcus thermophilus DS71584 (Strain C), Streptococcus thermophilus DS71585 (Strain D), wherein the time to reach pH 4.6 is reduced compared to a fermented milk product, yogurt, that has not been produced by said composition.

Description

FIGURES

[0075] FIG. 1 is a graph showing the shear stress at a shear rate of 215 s-1 for four different lactic acid blends in yogurt of three different protein levels.

[0076] FIG. 2 is a graph showing the shear stress for four different lactic acid blends over the shear rate of 10 to 1000 s-1 in a yogurt with 3.4% protein.

[0077] FIG. 3 is a graph showing the shear stress for four different lactic acid blends over the shear rate of 10 to 1000 s-1 in a yogurt with 3.8% protein.

[0078] FIG. 4 is a graph showing the shear stress for four different lactic acid blends over the shear rate of 10 to 1000 s-1 in a yogurt with 4.2% protein.

[0079] FIG. 5 is an overview of stirring the yogurt before measuring the shear stress.

MATERIALS AND METHODS

1. Bacterial Strains.

[0080]

TABLE-US-00001 TABLE 1 Bacterial strains Strain CBS number Strain A CBS134831 Streptococcus thermophilus DS71579 B CBS134834 Streptococcus thermophilus DS71586 C CBS134832 Streptococcus thermophilus DS71584 D CBS134833 Streptococcus thermophilus DS71585 E CBS134835 Lactobacillus delbrueckii ssp. bulgaricus DS71836
All strains A-E were deposited on 9 Apr. 2013 at the Centraalbureau voor Schimmelcultures (Fungal Biodiversity Centre), Uppsalalaan 8, 3584 CT Utrecht, The Netherlands under the provisions of the Budapest Treaty.

2. Compositions Comprising Bacterial Strains

[0081] The following compositions were used in the Examples. The percentages relate to the cfu's (colony forming units)see Table 2.

TABLE-US-00002 TABLE 2 Compositions comprising bacterial strains - the % values relate to the cfu's of the respective strain in the composition. Composition Strain A Strain B Strain C Strain D Strain E ABCDE 24.75% 24.75% 24.75% 24.75% 1% AE 99.0% 1% BE 99.0% 1% CE 99.0% 1% DE 99.0% 1% BDE 49.5% 49.5% 1% BD 50% 50%
The Reference culture (Ref) used in the examples is a commercially available yogurt starter culture and does not contain any of strains A-E.

3. Yogurt Preparation (All Examples)

[0082] The fermented milk used is obtained by supplementing pasteurized skimmed milk (Campina, The Netherlands) with skimmed milk powder and cream (containing 39% fat). The final recipe is described in the different examples. The milk mixture is pasteurized at 92 C. for 6 minutes. In line homogenization takes place in the heating part of the pasteurizer at 60 C., in two stages of 80 and 40 bar. The homogenized, pasteurized milk is cooled back to the fermentation temperature (38 C.) and inoculated with the culture to be tested at a rate of 0.02% (w/w) Once a pH of 4.60 is reached, the yogurt is smoothened by pumping the yogurt through a sieve (poresize 500 m). The yogurt is then filled out into suitable containers. The yogurt cups are then stored at 4 C.

4. Yogurt Recipes

[0083] The following recipes were used in the Examples. All additions are wt % of the total milk recipe.

TABLE-US-00003 TABLE 3 Yogurt recipes Recipe Ingredient (%) A B C D E F G Skimmed Milk 96.0 81.6 82.2 87.7 0 0 0 Semi skimmed Milk 0 0 0 0 91.4 90.1 88.7 Skimmed Milk 0.4 0.0 6.3 1.0 0.9 2.2 3.6 Powder Cream (39% fat) 3.6 3.8 3.8 3.6 0 0 0 Sucrose 0.0 7.7 7.7 7.7 7.7 7.7 7.7 Demineralized water 0.0 6.9 0.0 0.0 0 0 0 Fat concentration 1.4 1.5 1.5 1.4 1.4 1.4 1.4 Protein 3.5 2.9 5.1 3.5 3.4 3.8 4.2 concentration

5. Shear Stress of Yogurt

[0084] The samples were measured using a Physica MCR501 rheometer equipped with a concentric cylinder measurement system (CC-27). A solvent trap was used to prevent evaporation of water as much as possible. Yogurt samples are stored at 4 C. and are taken out of storage just prior to measuring in the rheometer, with the containers having to be handled with extreme care (as any sudden movements might damage the yogurt microstructure and thus lead to differences in results). As shown in FIG. 5, the closed container is turned from an upright position to a tilted one with an angle of 100, so that the container lid is now the lowest point. At this point, one has to turn the container 3 times around its axis (3360, 4 seconds per revolution), to slightly stir the yogurt without really damaging its structure. Subsequently the container is turned back into a normal upright position and can be opened. Once opened, one has to ascertain that there is no dried in material at the top of the container: if that is the case, this dried in material needs to be removed on one side (the side along which the yogurt will be poured). The container can then be slightly turned again to its side till the yogurt level reaches the top of the container at which time the yogurt can be gently spooned out of and over the top of the container into the measuring cup. Once filled the measuring cup is placed into the Physica Rheometer and superfluous material is removed by using a pipette. The procedure to load the yogurts takes about two minutes. Care needs to be taken to treat all different samples in exactly the same way, since difference in loading conditions can cause differences in the relative ranking of the yogurts. Before measurement the samples were allowed to rest and heat/cool to the measuring temperature (25 C.) for 5 minutes.

[0085] A standard experimental protocol was applied consisting out of the following two measuring sequences: [0086] 1. A strain sweep to determine the initial gel strength (dynamic shear modulus): this is an oscillatory test where at a fixed angular frequency (omega=10 rad/s) an increasing amplitude is applied: on a logarithmic scale the amplitude is increased from 0.01 to 100% with 5 measuring points per decade. [0087] 2. After the strain sweep the yogurts are allowed to rest for 30 seconds in the rheometer and subsequently a shear rate sweep is applied to determine the shear stress in mouth: This consists of applying an increasing shear rate to the yogurts ranging from 0.001 to 1000 s-1 on a logarithmic scale with 3 measuring points per decade (no fixed time setting: the rheometer software determines the required shearing time per measuring point).
This experiment gives a flow curve whereby the measured stress is plotted as a function of the applied shear rate. This curve can then be combined with literature data to determine the relevant shear stress in the mouth as explained in the following.

[0088] By sensory panelling of various food products Shama and Sherman identified windows of instrumental shear stresses and shear rates corresponding to products with similar thickness ratings but different shear-thinning behavior. These windows correspond to the rheological regimes applied in the mouth during thickness rating. The governing shear rate was shown to be dependent on the viscosity of the product itself. (see FIG. 1 from Shama, F. and Sherman, P. Journal of Texture Studies, 4, 111-118. (1973), Identification of stimuli controlling the sensory evaluation of viscosity II oral methods).

[0089] For the yogurts of the examples below the (predicted) shear stress in the mouth is determined by plotting the experimentally measured flow curves (measured shear stress in function of applied shear rate of the shear rate sweep experiment described above) onto the aforementioned FIG. 1 from Shama and Sherman. The predicted shear stress in the mouth is defined as the cross-over between the measured flow curves and the upper bound of the shear rate shear stress windows of FIG. 1 of Shama and Sherman. In FIG. 2 the authors give examples for various food stuffs. The thus derived shear stress gave a good correlation with the sensory perception of thickness in the mouth.

6. Brookfield

[0090] Viscosity measurement were performed using a Brookfield RVDVII+ Viscometer, which allows viscosity measurement on an undisturbed product (directly in the pot). The Brookfield Viscometer determines viscosity by measuring the force required to turn the spindle into the product at a given rate. The Helipath system with a T-C spindle was used as it is designed for non-flowing thixotropic material (gels, cream). It slowly lowers or raises a rotating T-bar spindle into the sample so that not always the same region of the sample is sheared (helical path). Thus, the viscometer measures constantly the viscosity in fresh material, and is thus thought to be the most suitable for measuring stirred yogurt viscosity. A speed of 30 rpm was used for 31 measuring points, at an interval of 3 sec. The average of the values between 60 and 90 seconds are reported.

7. Serum Viscosity

[0091] A yogurt can be seen as a two-phase system: a protein rich phase embedded into a water-rich serum phase. The viscosity of such a system will be determined by the collective contribution of the two phases. In order to determine the contribution of the serum phase, the latter has been isolated by centrifugation of tubes filled with 40 g yogurt each in a BHG Hermle Z320 centrifuge (1 h at 4000 RPM/2500 g). The clear serum phase is decanted. This serum viscosity is measured using a Physica MCR 300 Rheometer. After loading, a shear rate sweep is applied to the samples: This consists of applying an increasing shear rate to the yogurts ranging from 40 s.sup.1 to 1000 s.sup.1 on a logarithmic scale with 5 measuring points per decade. The serum viscosity is defined as the measured viscosity at 100 s.sup.1.

8. Gel Strength

[0092] The samples were measured using a Physica MCR501 rheometer equipped with a concentric cylinder measurement system (CC-27). A solvent trap was used to prevent evaporation of water as much as possible. The samples were slightly stirred with a spoon before loading into the rheometer. Before measuring, the samples were allowed to rest and brought to the measuring temperature (25 C.) and maintained at that temperature for 5 minutes. In order to determine the gel strength (i.e. the dynamic shear modulus G (Pa)), a strain sweep is applied to the sample: this is an oscillatory test where at a fixed angular frequency (omega=10 rad/s) an increasing amplitude is applied: on a logarithmic scale the amplitude is increased from 0.01 to 100% with 5 measuring points per decade. The gel strength of a material is defined as the average of the measured moduli between the strain of 0.01% to 0.25% (so in the linear regime).

9. Sensory Analysis

[0093] In a sensory analysis the attributes thickness of mouth feel and ropiness are analysed. Thickness of mouth feel is the degree in which the product feels thick in the mouth. This sensation can be best perceived between tongue and palate. Ropiness is the degree in which the yogurt runs from the spoon.

[0094] The method used to perform the sensory analysis for the ropy structure and thickness in mouth feel was a ranking test. The panelists received the four products simultaneously in random order. The assessors were asked to rank the samples according to the specified attribute from least to most. The two attributes were assessed separately using new three digit codes to avoid any bias. The results were obtained by using the software FIZZ acquisition (Biosystemes, France, Couternon). Hereafter the results were computed by using the Friedman test (analysis of variance by ranks). As four products per recipe have to be measured, three sessions were held, resulting in 22 observations per measurement. The sum of ranks is calculated by measuring the total allocated 1, 2, 3 or 4 points, wherein 1 point is allocated for the lowest rank and 4 points for the highest rank.

EXAMPLES

Example 1

Effect of Lactic Acid Bacterial Strains on the Gel Strength and the Serum Viscosity of a Yogurt

[0095] Yogurt was made according to recipe A as defined in Table 3 and according to the method described in the Materials and Methods.

TABLE-US-00004 TABLE 4 Composition (see Table 3) Attribute Reference ABCDE BE DE BDE Time to reach 470 445 445 515 479 pH = 4.6 (min) Brookfield (Pa * s) 6 7 9 7 10 Shear stress (Pa) 17 21 23 17 27 Gel strength 58 70 64 75 80 dynamic modulus G* (Pa) Serum viscosity 1.42 1.46 1.58 1.48 1.62 (mPa * s)

[0096] The results show that all compositions BE, DE, BDE and ABCDE improve the gel strength and serum viscosity compared to the Reference composition.

Example 2

Effect of Lactic Acid Bacterial Strains on the Gel Strength of a Yogurt

[0097] Yogurt was made according to recipe D as defined in Table 3 and according to the method described in the Materials and Methods.

TABLE-US-00005 TABLE 5 Composition (see Table 3) Attribute Reference ABCDE AE BE CE DE BDE Time to reach pH = 4.6 495 468 1102 434 853 1094 343 (min) Brookfield (Pa * s) 6.5 8.6 5.5 7.8 5.1 8.1 14 Shear stress (Pa) 20 23 16 24 15 18 39 Gel strength 71 74 76 84 80 75 111 dynamic modulus G* (Pa)

[0098] The results show that all composition AE, BE, CE, DE, BDE and ABCDE improve the gel strength compared to the Reference composition.

Example 3

Effect of Lactic Acid Bacterial Strains on the Gel Strength of a Yogurt with Different Protein Contents

[0099] Yogurt was made according to recipe B, C and D as defined in Table 3 and according to the method described in the Materials and Methods.

TABLE-US-00006 TABLE 6 Time to reach Gel Shear Protein pH 4.6 Strength Stress Brookfield Composition Recipe (%) (min) (Pa) (Pa) (Pa * s) ABCDE B 2.9 370 39 20 7.4 ABCDE C 5.1 450 179 40 22.7 ABCDE D 3.5 466 74 23 8.6 BDE D 3.5 450 111 38 13.8 Reference D 3.5 495 71 19.6 6.4

[0100] The results in table 6 clearly show that increasing the protein content of a yogurt (2.9-3.5-5.1%), increases the gel strength (39-74-179 Pa respectively), the shear stress (20-23-40 Pa respectively) as well as the Brookfield of the yogurt (7.4-8.6-22.7 Pa*s respectively).

[0101] The results in table 6 also show that ABCDE and BDE are increasing the gel strength, the shear stress as well as the Brookfield of the yogurt when compared with the Reference composition.

[0102] The results in in table 6 furthermore show that composition BDE, compared to ABCDE, even further increases the gel strength, the shear stress as well as the Brookfield of the yogurt with a protein content of 3.5% (recipe D).

[0103] In particular, composition BDE increases the gel strength of the yogurt with 3.5% protein made with ABCDE (74 Pa) to the gel strength of a yogurt with 4.5% protein (made with ABCDE), This can be deduced by interpolation of the data obtained with ABCDE as the 3 protein levels (not shown). Similarly, composition BDE increases the shear stress of the yogurt with 3.5% protein made with ABCDE (23 Pa) to the shear stress of a yogurt with 5.0% protein (made with ABCDE). Finally, composition BDE increases the Brookfield of the yogurt with 3.5% protein made with ABCDE (8.6 Pa*s) to the Brookfield of a yogurt with 5.0% protein.

Example 4

Effect of Lactic Acid Bacterial Strains on the Time to Reach pH 4.6, Shear Stress and Viscosity of a Yogurt with Different Protein Contents, in Comparison with Commercially Available Strains

[0104] Yogurt was made according to recipe E, F and G as defined in Table 3 and according to the method described in the Materials and Methods. Additionally starter culture TA40 and YO-MIX 883 were used to inoculate the recipe E, F and G. TA40 and YO-MIX 883 are both commercially available from Danisco A/S and comprise Streptococcus thermophilus and Lactobacillus delbrueckii strains. Both cultures are known for providing thickness, as is exemplified for TA40 for example in FIG. 1 of US2009/0226567.

TABLE-US-00007 TABLE 7 Time to reach Shear Protein pH 4.6 Stress Brookfield Composition Recipe (%) (min) (Pa) (Pa * s) BD E 3.4 318 59 8.2 BDE E 3.4 356 56 7.1 TA40 E 3.4 467 44 5.4 YO-MIX 883 E 3.4 n.a. 44 5.6 BD F 3.8 339 62 10.3 BDE F 3.8 368 58 8.3 TA40 F 3.8 443 50 6.8 YO-MIX 883 F 3.8 861 52 6.4 BD G 4.2 366 68 12.1 BDE G 4.2 412 66 10.9 TA40 G 4.2 523 58 8.6 YO-MIX 883 G 4.2 838 58 8.7

[0105] The results in Table 7 clearly show that BD and BDE increase the shear stress as well as the Brookfield of the yogurt when compared with the TA40 and YO-MIX 883. Furthermore, Table 7 clearly shows that the time to reach pH 4.6 is lower for BD and BDE at all protein levels.

[0106] Similarly FIG. 1 shows the shear stress at 215 s-1 (PA) for compositions BD, BDE, TA40 and YO-MIX 883 for recipes E, F and G. FIG. 1 clearly shows a higher shear stress for compositions BD and BDE in comparison with TA40 and YO-MIX 883 for all three recipes E, F and G. Thus, BD and BDE increase the shear stress even in recipes with reduced amounts of protein, i.e. from 4.2 to 3.8 and 3.4% protein.

[0107] Moreover, BD is able to provide a shear stress/Brookfield in yogurt recipe E having 3.4% protein of 59 Pa, while TA40 and YO-MIX 883 provide a comparable shear stress of 58 in yogurt recipe G having 4.2% protein. Thus, by using BD the protein can be reduced with 0.8% of the yogurt while maintaining the shear stress. In other words, BD provides a reduction in protein level of 19%.

[0108] FIGS. 2 to 4 show the shear stress versus shear rate for compositions BD, BDE, TA40 and YO-MIX 883 for recipe E, F and G having 3.4, 3.8 and 4.2% protein, respectively. FIGS. 2 to 4 shows that the higher shear stress of composition BD and BDE when compared with TA40 and YO-MIX 883 is consistent over the shear rate of 10 to 300 s.sup.1, which is the relevant range for determination of shear stress in yogurts.

Example 5

Effect of Lactic Acid Bacterial Strains on Serum Viscosity of a Yogurt with Different Protein Contents, in Comparison with Commercially Available Strains

[0109] Similar to example 4, yogurt was prepared with recipes E, F and G with lactic acid bacteria BD, BDE, TA40 and YO-MIX 883. Table 8 below shows the results of the measured serum viscosity

TABLE-US-00008 TABLE 8 Protein Serum viscosity Composition Recipe (%) (mPa * s) BD E 3.4 2.19 BDE E 3.4 2.15 TA40 E 3.4 1.90 YO-MIX 883 E 3.4 2.12 BD F 3.8 2.37 BDE F 3.8 2.38 TA40 F 3.8 2.11 YO-MIX 883 F 3.8 2.35 BD G 4.2 2.50 BDE G 4.2 2.44 TA40 G 4.2 2.21 YO-MIX 883 G 4.2 2.43

[0110] As can be seen in Table 8, the serum viscosity of BD and BDE is improved if compared with the serum viscosity of TA40 and YO-MIX 883 for recipe E, F and G having 3.4, 3.8 and 4.2% protein. In comparison with TA40, BD is nearly able to provide the TA40 serum viscosity of 2.21 in yogurt with 4.2% protein, however in a yogurt having only 3.4% protein. Thus BD is able to improve serum viscosity and reduce the protein content of yogurt.

Example 6

Effect of Lactic Acid Bacterial Strains in a Sensory Panel Test of a Yogurt with Different Protein Contents, in Comparison with Commercially Available Strains

[0111] Similar to example 4, yogurt was prepared with recipes E, F and G with lactic acid bacteria BD, BDE, TA40 and YO-MIX 883. To study the perceived gel strength and serum viscosity by a sensory panel, a panel test is carried out as described in the materials and methods. The attribute ropiness is linked with serum viscosity, and the attribute thickness of mouth feel is linked with gel strength.

TABLE-US-00009 TABLE 9 Sum of ranks Protein Sum of ranks Thickness of mouth Composition Recipe (%) ropiness feel BD E 3.4 59 65 BDE E 3.4 63 62 TA40 E 3.4 59 36 YO-MIX 883 E 3.4 40 57 BD F 3.8 68 64 BDE F 3.8 57 54 TA40 F 3.8 55 57 YO-MIX 883 F 3.8 41 45 BD G 4.2 58 63 BDE G 4.2 72 48 TA40 G 4.2 57 54 YO-MIX 883 G 4.2 34 55

[0112] In Table 9 the highest sum of ranks per yogurt recipe are written in bold. Table 9 clearly shows that BD and BDE have the highest sum of ranks and are thus perceived as providing the most ropiness or providing the most thickness in the mouth.