J. Dairy Sci. 2009. 92:2468-2476. doi:10.3168/jds.2008-1849
© 2009 American Dairy Science Association ®
Fermentation characteristics and transit tolerance of probiotic Lactobacillus casei Zhang in soymilk and bovine milk during storage
J. Wang*,
Z. Guo*,
Q. Zhang*,
L. Yan*,
W. Chen
,
X.-M. Liu,1 and
H.-P. Zhang*,1
* Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education, Inner Mongolia Agricultural University, Huhhot, Inner Mongolia 010018, P. R. China
School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122, P. R. China
1 Corresponding authors: hepingdd{at}vip.sina.com and liuxm{at}jiangnan.edu.cn
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ABSTRACT
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Lactobacillus casei Zhang is a novel strain that was screened out of koumiss collected in Inner Mongolia, and our previous research showed that L. casei Zhang has health benefits such as cholesterol-reducing and immunomodulating effects. The fermentation characteristics of L. casei Zhang in soymilk and bovine milk and the transit tolerance of L. casei Zhang in fermented milk products during refrigerated storage for 28 d were assessed. A faster decrease in pH and faster growth of L. casei Zhang during fermentation were observed in soymilk compared with bovine milk at various inoculation rates, probably because of the low pH buffering capacity of soymilk. The fermented bovine milk samples had much higher final titratable acidity (TA) values (between 0.80 and 0.93%) than the soymilk samples (between 0.40 and 0.46%). Dramatic increases in TA values in the fermented soymilk samples during storage were observed, and the TA values of the fermented soymilk samples changed from <0.56% to values between 0.86 and 0.98%. On the other hand, only slight increases in TA were observed in the bovine milk samples during the 28 d of storage. The survival rates of freshly prepared cultures of L. casei Zhang in simulated gastric juice at pH 2.0 and 2.5 were 31 and 69%, respectively, and the delivery of L. casei Zhang through fermented soymilk and bovine milk significantly improved the viability of L. casei Zhang in simulated gastric transit. Lactobacillus casei Zhang showed good tolerance to simulated gastric juice and intestinal juice in the fermented soymilk and bovine milk samples, and maintained high viability (>108 cfu/g) during storage at 4°C for 28 d. Our results indicated that both soymilk and bovine milk could serve as vehicles for delivery of probiotic L. casei Zhang, and further research is needed to elucidate the mechanism of the change in pH and TA of L. casei Zhang in fermented milk samples during fermentation and storage and to understand the difference between soy- and milk-based systems.
Key Words: Lactobacillus casei • soymilk • bovine milk • fermentation characteristic
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INTRODUCTION
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Koumiss is a traditional fermented alcoholic beverage prepared from mare’s milk by the people of the Central Asia steppes, including the Turks, Bashkirs, Kazakhs, Mongols, Yakuts, and Uzbeks, and has been reported to have therapeutic effects in hepatitis, chronic ulcer, and tuberculosis (Park et al., 2006). Lactobacillus casei Zhang was a novel strain screened from koumiss collected from Inner Mongolia, and our research has shown that L. casei Zhang has health benefits such as cholesterol-reducing and immunomodulating effects (Tuoya et al., 2006) as well as antagonism to Escherichia coli in mice (Zhang et al., 2007). In vitro tests indicated that L. casei Zhang showed high tolerance to simulated gastric juice, intestine juice, and bile salts, and it exhibited higher viable counts during storage in fermented bovine milk than commercial probiotics such as Lactobacillus acidophilus NCFM, Lactobacillus rhamnosus GG, Lactobacillus casei Shirota, and Bifidobacterium animalis Bb12 (our unpublished data) at the same inoculation rate.
According to the Food and Agricultural Organisation (FAO), probiotic bacteria are defined as "live microorganisms that when administered in adequate amounts confer a health benefit on the host" (FAO, 2001). Therefore, in the development of probiotic foods, research is required to select the right vehicle for the delivery of the probiotics to ensure that probiotics are viable throughout the shelf life and overcome the physical and chemical barriers in the gastrointestinal (GI) tract (Samona and Robinson, 1991; Vinderola et al., 2000; Piano et al., 2006). Although yogurt produced from bovine milk is the most popular yogurt in the world, the demand for alternatives to bovine milk products is growing because of bovine milk allergenicity and the unique health benefits provided by other products such as soy products. Soy-based foods could provide unique health benefits to the consumers because of their hypolipidemic, anticholesterolemic, and antiatherogenic properties; they could also reduce the risk of hormone-associated health disorders (Favaro Trindade et al., 2001). Therefore, it would be desirable to evaluate how probiotic bacteria perform in various fermented milk products during fermentation and storage.
The objective of the present study was to investigate the fermentation characteristics and transit tolerance of L. casei Zhang in soymilk and bovine milk during refrigerated storage and to investigate the possibility of using fermented milk from various sources as vehicles for delivery of probiotic L. casei Zhang.
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MATERIALS AND METHODS
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Bacterial Strains and Reagents
Lactobacillus casei Zhang was isolated from koumiss collected in Xilin Guole of Inner Mongolia (Menghe et al., 2004), and a direct vat-set culture containing 2 x 1011 cfu/g of L. casei Zhang was prepared in our laboratory. Nonfat soymilk powder and nonfat dry bovine milk powder were purchased from Wandefu Food Co. Ltd. (Shandong, China) and NZMP Ltd. (Wellington, New Zealand), respectively. Nonfat soymilk powder contained 55 g of protein and 34 g of carbohydrate per 100 g, and nonfat bovine milk powder contained 33 g of protein and 51 g of lactose per 100 g.
Fermented Milk Manufacture
Nonfat soymilk powder or nonfat bovine milk powder was blended with water at 50°C to a total solids content of 6.0 and 11.0 g/100 g, respectively. Each of the hydrated solutions was supplemented with 1.5 g/100 g of glucose, and heated at 85°C for 30 min. Subsequently, the samples were cooled to the incubation temperature (37°C), inoculated with 2 x 106, 5 x 106, 1 x 107, or 2 x 107 cfu/g of L. casei Zhang. Fermentation was carried out until the samples with the highest inoculation rate (2 x 107 cfu/g) achieved a pH of 4.5. Then, the samples were cooled to 4°C and stored for 28 d. The pH value, titratable acidity (TA), and viable counts were determined at 0, 6, 12, 16, and 18 h during fermentation and at 0, 7, 14, 21, and 28 d during refrigerated storage. The transit tolerance was analyzed at 0, 1, 14, and 28 d during refrigerated storage. All analyses were performed in triplicate.
Fermentation Characteristics
The pH value was measured using a pHSJ-3F pH meter (Leici, Shanghai, China) with a combined glass electrode and temperature probe. Titratable acidity (% lactic acid) was determined by titration with NaOH using phenolphthalein as the indicator (National Standards of the People's Republic of China, 1996). The viable counts of L. casei Zhang were enumerated according to the description of Tharmaraj and Shah (2003).
Transit Tolerance
Preparation of Simulated Gastrointestinal Juices.
Phosphate buffered saline was prepared with 0.8 g of NaCl, 0.02 g of KH2PO4, and 0.115 g of Na2HPO4/100 g (Makras et al., 2006). The pH of PBS was adjusted to 2.0, 2.5, or 8.0, respectively, and PBS was sterilized by autoclaving at 121°C for 15 min. The simulated gastric juice was prepared by supplementing PBS (pH 2.0 and 2.5) with pepsin (1:10,000, Sigma Chemical Co., St. Louis, MO). Simulated intestinal juice was prepared by supplementing PBS (pH 8.0) with trypsin (1:250, Sigma Chemical Co.).
Transit Tolerance of L. casei Zhang.
Lactobacillus casei Zhang was grown in de Man, Rogosa, and Sharpe (MRS) broth at 37°C for 18 h and centrifuged at 2,500 x g at 4°C for 10 min. The collected cells were resuspended in sterile saline and inoculated into the simulated gastric juice (pH 2.0 or 2.5) at 108 cfu/mL. Because the pH in the human stomach ranges from 1 (during fasting) to 4.5 (after a meal) and food ingestion can take up to 3 h, tolerance was assayed by determining the total viable count of L. casei Zhang after a 3-h incubation in simulated gastric juice (pH 2.0 or 2.5). Then, 1.0 mL of the solution was taken and added to 9.0 mL of simulated intestinal juice (pH 8.0) and incubated at 37°C for 8 h. The small intestine transit tolerance of L. casei Zhang was assayed by determining the total viable count after incubation for 4 and 8 h.
Transit Tolerance of L. casei Zhang in the Fermented Soymilk and Bovine Milk Samples.
One gram of the fermented soymilk or bovine milk sample was mixed with 9.0 mL of simulated gastric juice (pH 2.0 or 2.5) and incubated at 37°C for 3 h. Then, 1.0 mL of the solution was taken and added to 9.0 mL of simulated intestinal juice (pH 8.0), and the sample was incubated at 37°C for 8 h for the transit tolerance analysis. During the process, the resistance of L. casei Zhang to simulated gastric juice was analyzed after 3 h of incubation in simulated gastric juice, and transit tolerance was analyzed after 4- and 8-h incubations in simulated intestinal juice as described above.
Determination of Total Viable Count and Survival Rate
Total viable counts of L. casei Zhang were determined by a pour-plate method using MRS agar after serial dilution in maximum recovery. The MRS agar plates were incubated anaerobically at 37°C for 48 h, and survival rate was calculated according to the following equation:
where N1 = the total viable count of L. casei Zhang after treatment by simulated gastrointestinal juices, and N0 = the total viable count of L. casei Zhang before treatment.
Statistical Analysis
Data were analyzed by ANOVA using Proc Mixed (SAS Institute Inc., Cary NC). Significant differences between means were determined using Fisher’s protected least significant difference test. Significant differences were determined at 
= 0.05. All analyses were conducted in triplicate.
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RESULTS AND DISCUSSION
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Fermentation Characteristics and Viability of L. casei Zhang During Fermentation
pH and TA.
The changes in pH and TA of the soymilk and bovine milk samples inoculated with 4 levels of L. casei Zhang are shown in Table 1. During fermentation, gradual decreases in pH and increases in TA were observed in both the fermented soymilk and bovine milk samples, and the higher inoculation levels generally resulted in higher acidification rates. A faster drop in pH during fermentation was observed in the soymilk samples compared with the bovine milk samples at all inoculation rates. The pH values of the soymilk and bovine milk samples generally reached 4.5 within 16 and 18 h of fermentation, respectively. The fermented bovine milk samples had much higher final TA values (between 0.80 and 0.93%) than the soymilk samples (between 0.40 and 0.46%).
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Table 1. Changes in pH and titratable acidity (TA) values in fermented soymilk and bovine milk samples inoculated with Lactobacillus casei Zhang during fermentation at 37°C1
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Sugar utilization tests indicate that L. casei Zhang can metabolize ribose, glucose, mannose, fructose, galactose, sucrose, maltose, and sorbitol, but it cannot or has limited ability to use arabinose, xylose, melibiose, raffinose, and lactose (Menghe et al., 2004). Although bovine milk contains high lactose content and soymilk contains raffinose and stachyose, glucose should be the main carbon source for L. casei Zhang in the 2 fermented milk products because of the lack of ability of L. casei Zhang to metabolize lactose, raffinose, and stachyose (Menghe et al., 2004). In the present study, the same amounts of glucose were added to the soymilk and bovine milk samples before fermentation. However, besides glucose, L. casei Zhang might utilize the sucrose present in soymilk as well, which could be one of the reasons for the faster decrease in pH and faster growth of L. casei Zhang in soymilk.
Sequencing the genomes of probiotics such as Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus johnsonii, and Lactobacillus plantarum reveals that they are remarkably deficient in biosynthetic capacities, which are compensated for by their abundant proteolytic systems and extensive capacity for uptake of macromolecules (Pfeiler and Klaenhammer, 2007). In our previous study, we have shown that L. casei Zhang has similar proteolytic activity to L. acidophilus NCFM (unpublished data), which was confirmed by the fact that L. casei Zhang grew well in different media. The variation in the rate of the acidification might indicate the difference in the proteolytic activity of L. casei Zhang in the 2 types of fermented milk products.
The pH buffering capacity of milk is an important determinant of the properties of fermented products, and the contribution of different constituents of milk to the pH buffering properties of various dairy products has been a subject of study for several decades (Whittier, 1929; Upreti et al., 2006; Ahmad et al., 2008). In general, besides weak acids, bases, and their complexes with metal cations, proteins and free amino acids are the major contributors to pH buffering in milk (Upreti et al., 2006). The low final TA values of soymilk indicated that soymilk had lower pH buffering capacity than bovine milk, which might be attributed to the variation in protein composition and physicochemical properties of soy proteins and milk proteins. Glycinin and β-conglycinin are the main proteins present in soybean, constituting about 40 g/100 g and 30 g/100 g of the total soy protein, respectively, whereas bovine milk mainly contains casein and whey proteins. Previous research (Farnworth et al., 2007) reported that soymilk had lower buffering capacity than bovine milk, which was consistent with our results.
Microbiological Analysis.
The changes in the viable counts of the fermented soymilk and bovine milk samples during fermentation are shown in Table 2. The fermented soymilk samples had higher viable counts than the fermented bovine milk samples at the end of fermentation. After 6 h of fermentation, L. casei Zhang displayed similar growth rates in soymilk and bovine milk regardless of inoculation rates. However, sharp increases in the viable counts of L. casei Zhang were observed in soymilk samples within the next 10 h of fermentation, unlike the slow growth of L. casei Zhang in bovine milk. Both the higher viable counts of L. casei Zhang and the higher acidification rate in fermented soymilk samples indicated that L. casei Zhang might have higher proteolytic activity in soymilk.
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Table 2. Changes in the viable counts of Lactobacillus casei Zhang in the fermented soymilk and bovine milk samples during fermentation at 37°C1
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Fermentation Characteristics and Viability of L. casei Zhang During Storage
pH and TA.
The changes in pH and TA of L. casei Zhang in the fermented soymilk and bovine milk samples during storage are shown in Table 3. During storage, gradual decreases in pH and increases in TA were observed in both the fermented soymilk and bovine milk samples regardless of the inoculation rates of L. casei Zhang. The fermented bovine milk samples had higher TA before storage, ranging from 0.85 to 0.96%, and only slight increases in TA were observed during the 28 d of storage; the final TA values of the samples were in the range of 1.00 to 1.08%. Dramatic increases in TA values in the fermented soymilk samples during storage were observed. The TA values of the fermented soymilk samples before storage were in the range of 0.44 to 0.56%, but the final TA values of the fermented soymilk samples after the 28 d of storage ranged from 0.86 to 0.98%. The continuous decrease in pH in the fermented soymilk and bovine milk during storage showed the occurrence of postacidification, which indicated that L. casei Zhang had acid-producing ability at refrigeration temperature. The final pH of the fermented soymilk after refrigerated storage for 28 d was lower than that of the fermented bovine milk.
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Table 3. Changes in pH and titratable acidity (TA) values in the fermented soymilk and bovine milk samples inoculated with Lactobacillus casei Zhang during storage at 4°C for 28 d1
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The sharp increases in TA values of the fermented soymilk samples indicated that there was dramatic change in buffering capacity during storage. As we pointed out earlier, the pH buffering capacity of milk comes mainly from proteins, free amino acids, weak acids, bases, and their complexes with metal cations (Upreti et al., 2006). Soymilk and bovine milk are unique systems that vary in many aspects such as protein and carbohydrate composition, which results in variation in buffering capacity and fermentation characteristics as observed in the present study. However, more research is needed to elucidate the mechanism of the change in pH and TA of L. casei Zhang in the fermented milk samples during fermentation and storage and understand the difference between soy- and milk-based systems.
Microbiological Analysis.
The changes in viable counts in the fermented soymilk and bovine milk samples during storage are shown in Table 4. Generally, there were no significant changes in the viable counts of L. casei Zhang in the 2 types of fermented milk samples at the 4 inoculation rates. For probiotics to perform in vivo, it is essential that the carrier food contains at least 106 viable cells of the probiotic microorganism per gram (Vinderola et al., 2000). During the fermentation of soymilk and bovine milk, viable counts of L. casei Zhang increased above 108 cfu/g and maintained viability during storage at 4°C regardless of inoculation rate, which indicated the probiotic potential of L. casei Zhang in various fermented milk products.
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Table 4. Changes in the viable counts of Lactobacillus casei Zhang in the fermented soymilk and bovine milk samples during storage at 4°C for 28 d1
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Tolerance of L. casei Zhang in Various Samples to Simulated GI Tract During Storage
Effect of Storage of Fermented Milk Samples on Viability of L. casei Zhang in Simulated Gastric Juice.
The effects of storage of the fermented soymilk and bovine milk on the survival rates of L. casei Zhang (inoculated at 2 x 107 cfu/g) in simulated gastric juice were studied, and the results are shown in Figure 1. Food is the common delivery system for probiotic bacteria, and can protect probiotic bacteria from acidic conditions and enhance gastric survival due to the pH increase of the gastric contents resulting from the addition of the food (Huang and Adams, 2004). The survival rates of the control (freshly prepared culture of L. casei Zhang) in simulated gastric juice at pH 2.0 and 2.5 were 31 and 69%, respectively, and the delivery of L. casei Zhang through the fermented soymilk milk and bovine milk significantly improved the viability of L. casei Zhang in the simulated gastric transit to different extents (Figure 1).
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Figure 1. Survival of Lactobacillus casei Zhang in simulated gastric juice at a) pH 2.0 and b) pH 2.5 at 37°C for 3 h in fermented soymilk and bovine milk samples during storage at 4°C for 28 d. * = survival of pure L. casei Zhang in the simulated gastric juice.
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Lactobacillus casei Zhang in fermented soymilk and bovine milk samples showed better tolerance to the simulated gastric juice at pH 2.5 (>90%) than at pH 2.0 before and during storage. No significant changes in the viability of L. casei Zhang in the simulated gastric juice at pH 2.5 were observed in both the fermented milk samples during storage, and L. casei Zhang in the fermented bovine milk samples showed higher survival rate in simulated gastric juice at pH 2.0 than in the fermented soymilk samples. Gradual decreases in the survival rate of L. casei Zhang in the fermented bovine milk in simulated gastric juice of pH 2.0 were reported (from 95 to 71%) during refrigerated storage for 28 d, whereas in the fermented soymilk samples, L. casei Zhang showed a low survival rate between 50 and 60% during storage.
Effect of Storage in Various Samples on Viability of L. casei Zhang in Simulated Intestinal Juice.
Small intestine transit tolerance is essential for probiotic strains to colonize the small intestine. The results of the viability of L. casei Zhang after 4 and 8 h of incubation in simulated transit juices are shown in Figures 2 and 3, respectively. The incubation of the samples in simulated gastric juices at pH 2.0 adversely affected the viability of L. casei Zhang during the 4- and 8-h incubation in the intestinal juices, and survival rates of L. casei Zhang in the soymilk and bovine milk samples after 28 d of storage in the intestinal juices were around 32 and 63%, respectively. In contrast, samples incubated in the simulated transit juices at pH 2.5 showed better viability in both the fermented milk samples during the 4- and 8-h incubation in the intestinal juices (>91 and 75%, respectively), and higher survival rates of L. casei Zhang were observed in the bovine milk samples.
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Figure 2. Survival of Lactobacillus casei Zhang in simulated intestinal juice incubated at 37°C for 4 h in the fermented soymilk and bovine milk samples during storage at 4°C for 28 d. a) After 3 h of incubation in the simulated gastric juice (pH 2.0), L. casei Zhang was incubated in simulated intestinal juice for 4 h; b) after 3 h of incubation in simulated gastric juice (pH 2.5), L. casei Zhang was incubated in simulated intestinal juice for 4 h. * = survival of pure L. casei Zhang in simulated intestinal juice.
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Figure 3. Survival of Lactobacillus casei Zhang in simulated intestinal juice incubated at 37°C for 8 h in the fermented soymilk and bovine milk samples during storage at 4°C for 28 d. a) After 3 h of incubation in simulated gastric juice (pH 2.0), L. casei Zhang was incubated in simulated intestinal juice for 8 h; b) after 3 h of incubation in simulated gastric juice (pH 2.5), L. casei Zhang was incubated in simulated intestinal juice for 8 h. * = survival of pure L. casei Zhang in simulated intestinal juice.
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The sequenced genomes of intestinal lactobacilli have illustrated how these species adapted to the environment of the GI tract, including stress tolerance, uptake of nutrients, and adhesion to intestinal cells and mucus (Pfeiler and Klaenhammer, 2007). A 2-component regulatory system was identified, which functions in both acid tolerance and proteolysis, indicating an evolutionary link between growth of L. acidophilus in milk and acidification (Azcarate-Peril et al., 2005). Through our research, we showed that L. casei Zhang had good viability and transit tolerance in fermented milk samples during storage, but more research is needed before industrial production and application of the strain. We have been conducting research on the genomics and proteomics of L. casei Zhang, which would bring new insights in the fermentation characteristics and probiotic properties of L. casei Zhang.
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CONCLUSIONS
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The present study showed that L. casei Zhang could grow in various foods such as soymilk and bovine milk, and it maintained high viability during 28 d of storage at 4°C. During storage, L. casei Zhang showed high tolerance to simulated gastric juice and intestinal juice. Therefore, L. casei Zhang showed good probiotic properties and great potential for application in the development of probiotic food products. Variation in fermentation characteristics and transit tolerance of L. casei Zhang in fermented soymilk and bovine milk was observed, and further research is needed to understand the difference between soy- and milk-based systems.
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ACKNOWLEDGMENTS
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The authors acknowledge the support from Hi-tech Research and Development Program of China (863 Program; grant nos. 2006AA10Z345 and 2007AA10Z353) and New Century Excellent Talent Planning of Education Ministry of China (NCET-06–0269).
Received for publication October 29, 2008.
Accepted for publication February 17, 2009.
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REFERENCES
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|---|
Ahmad, S., Gaucher, I., Rousseau, F., Beaucher, E., Piot, M., Grongnet, J. F. and Gaucheron, F.. 2008. Effects of acidification on physico-chemical characteristics of buffalo milk: A comparison with cow’s milk. Food Chem. 106:11–17.[CrossRef]
Azcarate-Peril, M. A., McAuliffe, O., Altermann, E., Lick, S., Russell, W. M. and Klaenhammer, T. R.. 2005. Microarray analysis of a two-component regulatory system involved in acid resistance and proteolytic activity in Lactobacillus acidophilus. Appl. Environ. Microbiol. 71:5794–5804.[Abstract/Free Full Text]
FAO (Food and Agriculture Organization). 2001. Evaluation of health and nutritional properties of powdered milk and live lactic acid bacteria. FAO (Geneva, Switzerland) and Agriculture Organization of the United Nations and World Health Organization Expert Consultation Report; ftp//ftp.fao.org/docrep/fao/meeting/009/y6398e.pdf.
Farnworth, E. R., Mainville, I., Desjardins, M. P., Gardner, N., Fliss, I. and Champagne, C.. 2007. Growth of probiotic bacteria and bifidobacteria in a soy yogurt formulation. Int. J. Food Microbiol. 116:174–181.[CrossRef][Medline]
Favaro Trindade, C. S., Terzi, S. C., Trugo, L. C., Della Modesta, R. C. and Couri, S.. 2001. Development and sensory evaluation of soymilk based yoghurt. Arch. Latinoam. Nutr. 51:100–104.[Medline]
Huang, Y. and Adams, M. C.. 2004. In vitro assessment of the upper gastrointestinal tolerance of potential probiotic dairy propionibacteria. Int. J. Food Microbiol. 91:253–260.[CrossRef][Medline]
Makras, L., Triantafyllou, V., Fayol-Messaoudi, D., Adriany, T., Zoumpopoulou, G., Tsakalidou, E., Servin, A. and De Vuyst, L.. 2006. Kinetic analysis of the antibacterial activity of probiotic lactobacilli towards Salmonella enterica serovar Typhimurium reveals a role for lactic acid and other inhibitory compounds. J. Res. Microbiol. 157:241–247.[CrossRef]
Menghe, B., Wu, R. N., Wang, L. P., Yang, X. J., Xu, J., Dong, Y., Sun, Z. H. and Zhang, H. P.. 2004. Isolation and identification of Lactobacillus from koumiss collected in Inner Mongolia and People's Republic of Mongolia. China Dairy Indust. 32:6–11.
National Standards of the People's Republic of China. 1996. Method for analysis of hygienic standard of milk and milk products. Bulletin 5009.46. CNS, Beijing, China.
Park, W. Y., H. Zhang, B. Zhang, and L. Zhang. 2006. Mare milk. Pages 275–296 in Handbook of Milk of Non-bovine Mammals. Blackwell Publishing, Ames, IA.
Pfeiler, A. E. and Klaenhammer, T. R.. 2007. The genomics of lactic acid bacteria. Trends Microbiol. 15:546–553.[CrossRef][Medline]
Piano, M. D., Morelli, L., Strozzi, G. P., Allesina, S., Barba, M., Deidda, F., Lorenzini, P., Ballare, M., Montino, F., Orsello, M., Sartori, M., Garello, E., Carmagnola, S., Pagliarulo, M. and Capurso, L.. 2006. Probiotics: From research to consumer. Dig. Liver Dis. 38(Suppl 2):S248–S255.[CrossRef][Medline]
Samona, A. and Robinson, R. K.. 1991. Enumeration of bifidobacteria in dairy products. J. Soc. Dairy Technol. 44:64–66.[CrossRef]
Tharmaraj, N. and Shah, N. P.. 2003. Selective enumeration of Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacteria, Lactobacillus casei, Lactobacillus rhamnosus, and Propionibacteria. J. Dairy Sci. 86:2288–2296.[Abstract/Free Full Text]
Tuoya, Suyalema and Zhang, H. P.. 2006. Effect of Lactobacillus casei Zhang on koumiss on the production of cytokines in sera of mouse. Food Sci. 27:488–491.
Upreti, P., Bühlmann, P. and Metzger, L. K.. 2006. Influence of calcium and phosphorus, lactose, and salt-to-moisture tatio on cheddar cheese quality: pH buffering properties of cheese. J. Dairy Sci. 89:938–950.[Abstract/Free Full Text]
Vinderola, C. G., Bailo, N. and Reinheimer, J. A.. 2000. Survival of probiotic microflora in a Argentinian yoghurts during refrigerated storage. Food Res. 33:97–102.[CrossRef]
Whittier, E. O. 1929. Buffer intensities of milk and milk constituents. I. The buffer action of casein in milk. J. Biol. Chem. 83:79–88.[Free Full Text]
Zhang, H. P., Zhang, Q. J., Ren, G. Q. and Bao, Q. H.. 2007. The antagonism of Lactobacillus casei Zhang to pathogenic Escherichia coli in mice and the influence on the microbial population in gut. Microbiology 34:447–450.
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ABSTRACT
INTRODUCTION
