USE OF A LACTASE FOR IMPROVING THE PREPARATION OF A STRAINED FERMENTED DAIRY PRODUCT

Abstract

The present invention relates to a method for manufacturing a strained fermented dairy product comprising the following successive steps: (a) providing a dairy product, (b) adding a lactase and a culture of bacteria comprising at least one strain of mesophilic lactic acid bacteria and at least one strain of thermophilic lactic acid bacteria and fermenting the dairy product to obtain a fermented dairy product, and (c) separating a liquid whey from the fermented dairy product to obtain a strained fermented dairy product. The present invention relates also to the use of a lactase for preventing the clogging of the separating device used in the preparation of a strained fermented dairy product.

Claims

1. A method for manufacturing a strained fermented dairy product comprising the following successive steps: (a) providing a dairy product, (b) adding a lactase and a culture of bacteria comprising at least one strain of thermophilic lactic acid bacteria and at least one strain of mesophilic lactic acid bacteria and fermenting the dairy product to obtain a fermented dairy product, and (c) separating a liquid whey from the fermented dairy product to obtain a strained fermented dairy product.

2. The method according to claim 1, wherein the dairy product provided in step (a) has a total protein content comprised between 2.8 and 4.6%.

3. The method according to claim 1, wherein the strained fermented dairy product obtained has a total protein content comprised between 6 and 16%.

4. The method according to claim 1, wherein the strain of mesophilic lactic acid bacteria is selected from Lactococcus sp.

5. The method according to claim 4, wherein the strain of mesophilic lactic acid bacteria is Lactococcus lactis subsp. lactis.

6. The method according to claim 1, wherein the strain of thermophilic lactic acid bacteria is selected from Streptococcus sp., Lactobacillus sp., Bifidobacterium sp. and combinations thereof.

7. The method according to claim 1, wherein the strain of thermophilic lactic acid bacteria is selected from Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Bifidobacterium animalis subsp. lactis and combinations thereof.

8. The method according to claim 1, wherein the culture of bacteria is a combination of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Lactococcus lactis subsp. lactis and Bifidobacterium animalis subsp. lactis.

9. The method according to claim 1, wherein the lactase is added before the culture of bacteria.

10. The method according to claim 9, wherein the lactase is added 10 to 40 min before the culture of bacteria.

11. The method according to claim 1, wherein the lactase is added in an amount of 0.005 wt % to 0.20 wt % based on the total weight of the dairy product.

12. The method according to claim 1, wherein the dairy product is fermented at a temperature between 25 C. and 44 C., for 3 to 25 hours.

13. The method according to claim 1, wherein step (c) is performed by centrifugation.

14. The method according to claim 1, comprising an additional step (e) after step (c) of cooling the strained fermented dairy product to a temperature of between 1 and 10 C.

15. (canceled)

16. The method according to claim 2, wherein the dairy product provided in step (a) has a total protein content comprised between 3.1 and 4.0%.

17. The method according to claim 3, wherein the strained fermented dairy product obtained has a total protein content comprised between 7 and 12%.

18. The method according to claim 4, wherein the strain of mesophilic lactic acid bacteria is selected from Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and combinations thereof.

19. The method according to claim 6, wherein the strain of thermophilic lactic acid bacteria is selected from Lactobacillus bulgaricus, Lactobacillus acidophilus, Lactobacillus paracasei, Lactobacillus casei, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus reuteri, Lactobacillus plantarum, Lactobacillus bifidus, Bifidobacterium bifidum, Bifidobacterium infantis, Bifidobacterium animalis, Bifidobacterium breve, Bifidobacterium longum, Streptococcus thermophilus, Streptococcus lactis, Streptococcus raffinolactis, Streptococcus cremoris and combinations thereof.

20. The method according to claim 11, wherein the lactase is added in an amount of 0.01 wt % to 0.15 wt % based on the total weight of the dairy product.

21. A method for preventing the clogging of a separating device during the preparation of a strained fermented dairy product comprising the addition of a lactase during the preparation of said strained fermented dairy product.

Description

FIGURES

[0138] FIG. 1 presents photographs of disks clogging occurred in a method of manufacture of a strained fermented dairy product using no lactase.

[0139] FIG. 2 represents the graphs of total protein content in the obtained strained fermented dairy product (strained mass) and the separated whey in function of time, as well as the inlet flow in the separator device in function of time, during 6 hours and 30 minutes production with a centrifugal separator device at industrial scale.

[0140] FIG. 3 represents the percent of whey release from the fermented dairy products of example 2 (relative to the influence of the culture of bacteria) in comparison to the Reference product (product a)).

[0141] FIG. 4 represents microscopy confocal photos of a) a dairy product fermented with only thermophilic lactic acid bacteria (on the left) and b) a dairy product fermented with a culture of thermophilic and mesophilic lactic acid bacteria (on the right).

[0142] FIG. 5 represents the percent of whey release from the fermented dairy products of example 3 (relative to the impact of lactase addition) in comparison to the Reference product (product a)).

[0143] FIG. 6 represents the percent of whey release from the fermented dairy products of example 4 (relative to the impact of dosage and time of addition of the lactase) in comparison to the Reference product (product a)).

[0144] FIG. 7 represents the total protein content of the strained fermented dairy products obtained in example 4 (relative to the impact of dosage and time of addition of the lactase).

EXAMPLES

[0145] 1. Evolution of Total Protein Content at the Outlet of the Separator Device During Separation Before and after Disk Clogging Appears

[0146] A strained fermented dairy product was prepared by fermenting a heat-treated skimmed dairy mix (prepared from skimmed milk and skimmed milk powder in proportions so as to obtain a total protein content of about 3.5%) with a culture of lactic acid bacteria consisting of a mix of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Lactococcus lactis subsp. lactis and Bifidobacterium animalis subsp. lactis.

[0147] The heat-treatment was performed according to the following steps: [0148] a first pre heat-treatment step to reach a temperature of about 60 C., followed by [0149] an homogenisation step at a pressure of about 50 bars (2 stages), followed by [0150] a second heat-treatment step at a temperature of about 92 C. for about 5 min.

[0151] The heat-treated dairy mix was fermented at 37 C. and went into lactic acidification until reaching a targeted pH of 4.60.

[0152] The fermented dairy product was then re-heated to an appropriate separation temperature, around 41 C., and then separated by a 12 nozzles centrifugal separation device to produce around of a strained fermented dairy product reaching a total protein content of about 10% and of whey.

[0153] After some hours of production, the total protein content in the strained fermented product at the outlet of the device suddenly decreases (below 9.3% total protein content) whereas the total protein content recovered in the whey increases the other way around (above 0.50%), without observing any fluctuation on the flows neither of the whey nor on the strained fermented mass outlet (see FIG. 2), due to a disk clogging of the centrifugal separation device (see FIG. 1).

[0154] When this effect appears, we observe a degradation of the main separation performance parameters: protein recovery rate decreases significantly (2% versus the starting phase of the production and getting worse when going ahead with the production) and the yield was increasing in the same way.

2. Impact of the Culture of Bacteria on Disk Clogging of the Centrifugal Separator

[0155] A heat-treated dairy mix was prepared as in example 1. The heat-treated dairy mix was then divided in 3 batches, to be inoculated with 3 different cultures of bacteria: [0156] a) a culture of only thermophilic lactic acid bacteria strains: Lactobacillus Bulgaricus and Streptococcus thermophilus, [0157] b) a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis), [0158] c) a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus and Streptococcus thermophilus) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis).

[0159] The three heat-treated dairy mixes were then fermented as indicated in example 1. The fermented dairy products were then re-heated to the appropriate separation temperature, around 41 C., and then separated at laboratory spin centrifuge: 4 samples of 40 g of each fermented dairy product, at 4000 rpm during 4 min. Then, the whey separated was weighted with a precision weighting device. The results obtained are presented on FIG. 3 as a percent of whey release in comparison to the product a) taken as the Reference product.

[0160] These results demonstrate that the quantity of whey released by each fermented dairy product is fully dependent on the type of bacteria used for the fermentation step: in all the products where a combination of thermophilic and mesophilic lactic acid bacteria strains (products b) and c)) were used for the fermentation step, a decrease of whey releasing capacity was observed.

[0161] Without wishing to be bound by any theory, the inventors are of the opinion that depending upon the type of bacteria used to performed the fermentation step, the secondary compounds resulting from the standard lactic acid fermentation may vary, producing differences in the permeability of the coagulum, therefore, producing differences in the way the curd is able to separate the liquid phase (whey) from the solid phase.

[0162] The fermented dairy products a) and b) were also observed in microscopy confocal (Confocal microscope Leica TC SP2fluorescent markers for proteins DyLight 488, .sub.abs=493 nm; .sub.emi=518 nm, 10 L in 500 L of fermented product40 water immersion at 20 C.). The corresponding photos are presented on FIG. 4 (on the left the fermented dairy product containing only thermophilic strains (product a)) and on the right the fermented dairy product containing a culture of thermophilic and mesophilic lactic acid bacteria strains (product b))). It can be observed that the density of the protein network is different between both fermented dairy products, the dairy product product b) being more granular, with bigger dark spaces between the proteins aggregates.

[0163] Without wishing to be bound by any theory, the inventors are of the opinion that the dark spaces in the proteins networks could contain different types and amounts of secondary metabolites of the fermentation (as for ex. exopolysaccharides), able to bind water, therefore, making the coagulum more impermeable and thus, more difficult to be separated.

3. Impact of the Addition of a Lactase on the Whey Releasing Capacity of a Dairy Product Fermented with a Culture of Thermophilic and Mesophilic Lactic Acid Bacteria Strains

[0164] A heat-treated dairy mix was prepared as in example 1. The heat-treated dairy mix was then divided in 3 batches, to be inoculated as follows: [0165] a) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis), [0166] b) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, (Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strains (Lactococcus lactis subsp. lactis) and a lactase (Ha-Lactase 5200 from Hansen at a dosage of 0.04%), [0167] c) with a culture of only thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus and Streptococcus thermophilus).

[0168] The three dairy mixes were fermented as detailed in example 1. The fermented dairy products were then re-heated to the appropriate separation temperature, around 41 C., and then separated at laboratory spin centrifuge: 4 samples of 40 g of each fermented dairy product, at 4000 rpm during 4 min. Then, the whey separated was weighted with a precision weighting device. The results obtained are presented on FIG. 5 as a percent of whey release in comparison to the product a) taken as the Reference product.

[0169] It was observed that the quantity of whey released by each fermented dairy product is fully dependent on the type of bacteria culture as mentioned in example 2 (product a) v. product c)). It was also observed that the addition of the lactase leads to a significant increase of the permeability of the curd (product a) v. product b)), close to the permeability of the curd of the dairy product fermented with only thermophilic strains (product c)).

4. Impact of the Dosage and Time of Addition of the Lactase on the Whey Releasing Capacity of a Dairy Product Fermented with a Culture of Thermophilic and Mesophilic Lactic Acid Bacteria Strains

[0170] A heat-treated dairy mix was prepared as in example 1. The heat-treated dairy mix was then divided in 5 batches, to be inoculated as follows: [0171] a) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of mesophilic strains (Lactococcus lactis subsp. lactis), [0172] b) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis) and a lactase (Maxilact LGi 5000 from DSM at a dosage of 0.06%), [0173] c) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis) and a lactase (Maxilact LGi 5000 from DSM at a dosage of 0.05%), [0174] d) with a culture of thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus, Streptococcus thermophilus and Bifidobacterium bifidum) and of a mesophilic lactic acid bacteria strain (Lactococcus lactis subsp. lactis) and a culture of a lactase (Maxilact LGi 5000 from DSM at a dosage of 0.05%) added 20 minutes before the innoculation of the culture of bacteria, [0175] e) with a culture of only thermophilic lactic acid bacteria strains (Lactobacillus Bulgaricus and Streptococcus thermophilus).

[0176] The five dairy products were then fermented as in example 1. The fermented dairy products were then re-heated to the appropriate separation temperature, around 41 C., and then separated at laboratory spin centrifuge: 4 samples of 40 g of each fermented dairy product, at 4000 rpm during 4 min. Then, the whey separated was weighted with a precision weighting device. The results obtained are presented on FIG. 6 as a percent of whey release in comparison to the product a) taken as the Reference product.

[0177] It was observed that the quantity of whey released by each coagulum is fully dependent on the type of bacteria culture (product a) v. product e)) as mentioned in examples 2 and 3. It was also observed that the addition of a lactase leads to a significant increase of the permeability of the curd (products b), c) and d) v. product a)). Moreover, it was observed that the time of addition of the lactase has an additional impact on the separation step (product c) v. product d)). When the lactase was added 20 minutes before the culture of bacteria, the impact on the whey releasing capacity was greater, allowing a slight decrease on the dosage of the lactase itself.

[0178] The total protein content of the strained fermented dairy products obtained in each case is presented on FIG. 7.