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Viability of Bifidobacteria strains in fermented and non-fermented milk
Food Biotechnology S. Bielecki, J. Tramper and J. Polak (Editors) 9 2000 Elsevier Science B.V. All rights reserved.
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Viability of Bifidobacteria strains in fermented and non-fermented milk I. Motyl and Z. Libudzisz Institute of Fermentation Technology and Microbiology, Technical University of L6dz, Stefanowskiego 4/10, 90-924 L6d~, Poland.
The subject of this study was a comparison of viability of bifidobacteria, during 21 day period under storage conditions (4-5~ in fermented and non-fermented milk. The viability was additionally tested in fermented milk at temperatures of 18~ and 30~ Tested material included 10 strains of Bifidobacterium species. High viability of bifidobacteria cells in non-fermented and fermented milk at different storage conditions resulted in least 21-day biological stability of milk product containing the bacteria of Bifidobacterium species. However, over-acidification of a product, especially stored at temperature 30~ significantly deteriorated its organoleptic properties.
1. INTRODUCTION High viability of bifidobacteria both in fermented and non-fermented milk, is a very important feature, which should be taken into account when choosing cultures for use in the production of milk products. To perform their therapeutic role, milk products should contain at least 106 living cells of Bifidobacterium/ml in the moment of consumption.
2. MATERIALS AND METHODS
The subject of this study was a comparison of viability of bifidobacteria under storage conditions (4-5~ in fermented and non-fermented milk during 21 days period. Tested material included 10 strains of Bifidobacterium species from the collection of the Institute of Animal Reproduction and Food Science of the Polish Academy of Sciences in Olsztyn, Poland (B42, KNA1, B36, Bif f2), Institute of Food Biotechnology, the Academy of Agriculture in Olsztyn (558, J/III, 100J), Department of Milk and Fat Technology, Prague Technical University, Prague, Czech Republic (BN, BD) and from the National Collection of Agricultural and Industrial Microorganisms, Hungary (B.bif). These strains were chosen from among 26 cultures as expressing the highest resistance to low pH (1.5) and bile salts (4%). After 2 hours of incubation at pH 1.5, their viability was about 102 CFU/ml. Tested strains were also resistant to 4% bile in the medium, and after 12 hours of incubation in such medium demonstrated viability at the level of about 106 CFU/ml. The initial level of bifidobacteria in those studies ranged from 10s to 109 CFU/ml.
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Figure 1. Number of living bacteria during storage: a) sweet milk stored at 4-5~ b) fermented bifidus milk stored at 4-5~ c) fermented bifidus milk stored at 18~ d) fermented bifidus milk stored at 30~
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Figure 2. Change in acidity ofbifidus milk during 12 and 21 days storage: a) sweet milk stored at 4-5~ b) fermented bifidus milk stored at 4-5~ c) fermented bifidus milk stored at 18~ d) fermented bifidus milk stored at 30~
268 UHT milk with 2% fat was inoculated with a bacterial suspension in NaC1 (10% inoculum (v/v)), and then either incubated at 37~ until acidified (fermented milk) or it was left under refrigerating conditions (non-fermented milk). In order to determine to what extent improper storage conditions might reduce the number of living bacteria, the viability of Bifidobacterium was also checked in fermented milk stored at 18~ and 30~ The viability of bacteria was controlled by the plate method (Garcha'e medium after 7, 12, 17, 19 and 21 days of storage. Total lactic acid was measured by titration with 0.1M NaOH. Results were expressed in ml of 0.1 M NaOH/10 ml of milk.
3. RESULTS As a result of these investigations it was found that all tested bacterial strains in fermented milk are characterised by high viability in refrigerating conditions. The number of living cells after 21 days of storage was almost at the initial level or slightly decreased 108-109 CFU/ml. Titration acidity of fermented milk stored at temperature 4-5~ after 21 days, irrespective of the strain, ranged from 8.1 to 11.2 ml 0.1M NaOH/10 ml of milk. The highest viability in fermented milk was expressed by strains: KNA1 and Bi36. In non-fermented milk, the level of living Bifidobacterium cells after 21 days of storage at 4-5~ decreased from 108 CFU/ml to 10 7 CFU/ml, and titration acidity increased from about 0.4 to 1.5 ml 0.1 M NaOH. The strains 100J and 558 showed the highest viability (Fig. 1). During storage at 18~ and 30~ the number of living bacteria was very high, and depending on the strain was recorded at the level of about 108-109 CFU/ml. Only strain BN expressed decrease in survival and the number of detected living cells at 30~ was about 10 7 CFU/ml. After 21 days of storage, depending on the strain, the acidity of fermented milk increased either to about 6.6-8.7 ml 0.1 M NaOH/10 ml milk, when stored at 18~ or to about 9.9-14.4 ml 0.1M NaOH/10 ml milk, when stored at 30~ (Fig. 2).
4. CONCLUSIONS Both non-fermented and fermented milk, containing bacteria of Bifidobacterium species, showed at 21-day long biological stability. Additionally, it was found that the choice of strains which could survive in model conditions at pH 1.5 guaranteed very good shelf life of both fermented and non-fermented milk. Moreover, it was observed that even improper storage of milk fermented with the tested Bifidobacterium resulted in survival of at least 106 CFU/ml, thus complying with the standard. However, over-acidification of a product, especially at temperature of 30~ significantly deteriorated its organoleptic properties.
265
Viability of Bifidobacteria strains in fermented and non-fermented milk I. Motyl and Z. Libudzisz Institute of Fermentation Technology and Microbiology, Technical University of L6dz, Stefanowskiego 4/10, 90-924 L6d~, Poland.
The subject of this study was a comparison of viability of bifidobacteria, during 21 day period under storage conditions (4-5~ in fermented and non-fermented milk. The viability was additionally tested in fermented milk at temperatures of 18~ and 30~ Tested material included 10 strains of Bifidobacterium species. High viability of bifidobacteria cells in non-fermented and fermented milk at different storage conditions resulted in least 21-day biological stability of milk product containing the bacteria of Bifidobacterium species. However, over-acidification of a product, especially stored at temperature 30~ significantly deteriorated its organoleptic properties.
1. INTRODUCTION High viability of bifidobacteria both in fermented and non-fermented milk, is a very important feature, which should be taken into account when choosing cultures for use in the production of milk products. To perform their therapeutic role, milk products should contain at least 106 living cells of Bifidobacterium/ml in the moment of consumption.
2. MATERIALS AND METHODS
The subject of this study was a comparison of viability of bifidobacteria under storage conditions (4-5~ in fermented and non-fermented milk during 21 days period. Tested material included 10 strains of Bifidobacterium species from the collection of the Institute of Animal Reproduction and Food Science of the Polish Academy of Sciences in Olsztyn, Poland (B42, KNA1, B36, Bif f2), Institute of Food Biotechnology, the Academy of Agriculture in Olsztyn (558, J/III, 100J), Department of Milk and Fat Technology, Prague Technical University, Prague, Czech Republic (BN, BD) and from the National Collection of Agricultural and Industrial Microorganisms, Hungary (B.bif). These strains were chosen from among 26 cultures as expressing the highest resistance to low pH (1.5) and bile salts (4%). After 2 hours of incubation at pH 1.5, their viability was about 102 CFU/ml. Tested strains were also resistant to 4% bile in the medium, and after 12 hours of incubation in such medium demonstrated viability at the level of about 106 CFU/ml. The initial level of bifidobacteria in those studies ranged from 10s to 109 CFU/ml.
266
Figure 1. Number of living bacteria during storage: a) sweet milk stored at 4-5~ b) fermented bifidus milk stored at 4-5~ c) fermented bifidus milk stored at 18~ d) fermented bifidus milk stored at 30~
267
Figure 2. Change in acidity ofbifidus milk during 12 and 21 days storage: a) sweet milk stored at 4-5~ b) fermented bifidus milk stored at 4-5~ c) fermented bifidus milk stored at 18~ d) fermented bifidus milk stored at 30~
268 UHT milk with 2% fat was inoculated with a bacterial suspension in NaC1 (10% inoculum (v/v)), and then either incubated at 37~ until acidified (fermented milk) or it was left under refrigerating conditions (non-fermented milk). In order to determine to what extent improper storage conditions might reduce the number of living bacteria, the viability of Bifidobacterium was also checked in fermented milk stored at 18~ and 30~ The viability of bacteria was controlled by the plate method (Garcha'e medium after 7, 12, 17, 19 and 21 days of storage. Total lactic acid was measured by titration with 0.1M NaOH. Results were expressed in ml of 0.1 M NaOH/10 ml of milk.
3. RESULTS As a result of these investigations it was found that all tested bacterial strains in fermented milk are characterised by high viability in refrigerating conditions. The number of living cells after 21 days of storage was almost at the initial level or slightly decreased 108-109 CFU/ml. Titration acidity of fermented milk stored at temperature 4-5~ after 21 days, irrespective of the strain, ranged from 8.1 to 11.2 ml 0.1M NaOH/10 ml of milk. The highest viability in fermented milk was expressed by strains: KNA1 and Bi36. In non-fermented milk, the level of living Bifidobacterium cells after 21 days of storage at 4-5~ decreased from 108 CFU/ml to 10 7 CFU/ml, and titration acidity increased from about 0.4 to 1.5 ml 0.1 M NaOH. The strains 100J and 558 showed the highest viability (Fig. 1). During storage at 18~ and 30~ the number of living bacteria was very high, and depending on the strain was recorded at the level of about 108-109 CFU/ml. Only strain BN expressed decrease in survival and the number of detected living cells at 30~ was about 10 7 CFU/ml. After 21 days of storage, depending on the strain, the acidity of fermented milk increased either to about 6.6-8.7 ml 0.1 M NaOH/10 ml milk, when stored at 18~ or to about 9.9-14.4 ml 0.1M NaOH/10 ml milk, when stored at 30~ (Fig. 2).
4. CONCLUSIONS Both non-fermented and fermented milk, containing bacteria of Bifidobacterium species, showed at 21-day long biological stability. Additionally, it was found that the choice of strains which could survive in model conditions at pH 1.5 guaranteed very good shelf life of both fermented and non-fermented milk. Moreover, it was observed that even improper storage of milk fermented with the tested Bifidobacterium resulted in survival of at least 106 CFU/ml, thus complying with the standard. However, over-acidification of a product, especially at temperature of 30~ significantly deteriorated its organoleptic properties.