Understanding the Temperature Dependence of Bifidobacterium lactis
As a vital inhabitant of the human gastrointestinal tract, Bifidobacterium lactis is a well-regarded probiotic with numerous health benefits, including supporting digestion, enhancing immune function, and easing conditions like constipation. Like all living microorganisms, its growth and metabolic activity are profoundly affected by environmental factors, with temperature being one of the most critical. Understanding the optimum temperature for the growth of Bifidobacterium lactis is not only a matter of academic interest but is also a cornerstone of producing effective probiotic supplements and fermented foods.
The Optimal Thermal Range
For many human-isolated strains of Bifidobacterium lactis, the optimal growth temperature is between 37°C and 38°C, which closely mirrors normal human body temperature. However, other studies, particularly those involving animal-derived strains or specific industrial applications like cheese-making, have shown optimal growth at slightly higher temperatures, sometimes ranging up to 43°C. The exact optimal temperature can be strain-dependent, meaning specific culture conditions must be tailored to the particular strain being propagated to achieve maximum biomass and activity. This flexibility within the broader optimal range allows for targeted manufacturing processes.
For example, studies have demonstrated that while certain Bifidobacterium species grow best at 37°C, other species can show improved acidification activity and cell concentration at 42°C. This illustrates the importance of not generalizing the optimal temperature across the entire species but rather optimizing conditions for each specific strain, such as BB-12 or HN019.
Factors Influencing Growth Beyond Temperature
While temperature is a primary driver, other conditions are equally important for robust B. lactis growth. The search results highlight several key factors:
- pH Level: Bifidobacteria generally thrive in a near-neutral pH range, typically between 6.5 and 7.0. During milk fermentation, however, the pH decreases due to the production of lactic and acetic acid, which can inhibit further growth if not managed. Some strains show greater acid tolerance than others, an important trait for survival in fermented dairy products and the digestive system.
- Oxygen Level: Most Bifidobacteria species are strict anaerobes, meaning they grow in the absence of oxygen. However, B. lactis is known for its impressive oxygen tolerance, which gives it a survival advantage in various food products and environments, including the gastrointestinal tract where oxygen levels vary. Oxygen-sensitive species, in contrast, require strict anaerobic conditions for cultivation.
- Nutrient Availability: The culture medium's composition, including carbohydrate sources like lactulose and other nutrients, significantly impacts growth. Studies have shown that adding prebiotics like lactulose can stimulate B. lactis growth in milk, although excessive concentrations can have inhibitory effects.
The Role of Temperature in Product Viability
Beyond fermentation, temperature is a critical factor for maintaining the viability of B. lactis in consumer products. High temperatures, such as those used in pasteurization, will rapidly kill probiotic bacteria. For this reason, probiotic products require careful handling and storage to ensure the live cultures remain viable. Refrigeration is a common method for prolonging the shelf life of probiotic products, significantly slowing down metabolic activity and cell death.
Impact of Temperature on Fermented Foods vs. Supplements
The table below outlines how temperature affects Bifidobacterium lactis in different contexts:
| Condition / Factor | Fermentation for Production | Storage of Fermented Foods (e.g., Yogurt) | Storage of Probiotic Supplements | In-Vivo (Gut Transit) |
|---|---|---|---|---|
| Optimal Temperature | ~37–43°C (Strain Dependent) | ~4°C (Refrigeration) | Cool, dry conditions (~4°C) | ~37°C (Body Temperature) |
| Effect | Maximizes growth and cell count for commercial production. | Greatly slows down metabolic activity to preserve viability over time. | Minimizes cell death and degradation over the product's shelf life. | Tolerates diverse conditions (acid, bile) to colonize the gut. |
| Goal | High cell density and efficient biomass production. | Stable product with consistent probiotic count. | Long-term viability of the freeze-dried cultures. | Survive passage and establish a beneficial presence. |
| Result of Suboptimal Temp | Slower growth, lower cell yield. | Reduced viable cell count over time. | Increased rate of cell death, reduced efficacy. | Reduced survival rate, lower therapeutic effect. |
The Importance of Storage Temperature
For finished products, low temperatures are preferable to preserve probiotic viability. During storage in refrigerated dairy products, for example, temperatures of around 4°C are used to slow down bacterial metabolism and prevent viability from dropping below therapeutic levels. Studies have compared storage at refrigerated temperatures with room temperature, consistently finding that lower temperatures are superior for maintaining cell counts over time. This is a key consideration for consumers who want to ensure they are receiving the stated dose of live bacteria from their probiotic product. Even for freeze-dried supplements, which are more resilient, storage in a cool environment is recommended.
Conclusion
The optimum temperature for growth of Bifidobacterium lactis is a dynamic and strain-dependent factor, generally ranging from 37°C to 43°C. For industrial fermentation, selecting and controlling the specific optimal temperature for a given strain is essential for maximizing biomass. In the final consumer product, maintaining a low temperature, typically via refrigeration, is paramount for preserving the viability of the live cultures. This careful temperature management, combined with other factors like pH and oxygen control, ensures that probiotic supplements and functional foods containing B. lactis deliver their intended health benefits to the consumer. For more information on factors affecting probiotic viability, the following research provides additional insight: Probiotics in Food Systems: Significance and Emerging Aspects.
