Improved medium of Lactobacillus -some research and thought
I have been fascinated with the L. Reuteri yogurt benefits, and learned a lot from redditers.
My perception now is : Due to the slow growing rate of Reuteri and potential contamination, it is not easy to maintain single strain over many generations.
PS: my L. Reuteri starter is still on the way, have not culture L. Reuteri before, but several years home-made yogurt experience.
If optimizing growth rate and achieve high CFU is the goal, Milk is not the optimal medium for L Reuteri.
Lactobacillus spp are known as fastidious microorganisms that cannot grow on simple mineral media supplemented only with a carbon source. In addition to carbohydrates (carbon source), culture media of LAB are usually supplemented with various free amino acids, peptides, nucleic acid derivatives, fatty acids esters, minerals, vitamins, and buffering agents.
Coconut milk and carrot mix is much better than milk, but may be far from optimal.
MRS or modified is the standard medium in research community, but has 10 components is expensive. But it helps to understand the functions of components
MRS Broth modified, Vegitone suitable for microbiology, NutriSelect® Plus | Sigma-Aldrich
Lactobacilli MRS Broth- Composition, Principle, Preparation, Results, Uses
Comparison of formulations with functions
| Component | Standard MRS, g/L | Modified Vegitone / selective MRS, g/L | Main function in medium |
|---|---|---|---|
| Proteose peptone | 10.0 | 10.0, vegetable source | Nitrogen, carbon, peptides, amino acids and growth factors for Lactobacillus growth. In the modified medium, vegetable peptone replaces animal-derived peptone. [himedialabs.com], [merckmillipore.com] |
| Beef extract | 10.0 | Not present | Additional nitrogenous compounds, amino acids, vitamins and growth nutrients. Removed in Vegitone formulation to make it non-animal derived. [documents....fisher.com], [merckmillipore.com] |
| Yeast extract | 5.0 | 5.0 | Source of B-complex vitamins, amino acids and growth-enhancing nutrients. [himedialabs.com], [assets.fishersci.com] |
| Dextrose / glucose | 20.0 | 20.0 | Fermentable carbohydrate and main energy source. Acid production from glucose fermentation can be tracked in the modified formula using bromocresol green. [himedialabs.com], [himedialabs.com] |
| Polysorbate 80 / Tween 80 | 1.0 | adds 1 mL/L separately | Supplies fatty acids, especially oleic esters, needed by Lactobacilli and can help nutrient uptake. In some modified MRS products, Tween 80 is added separately during preparation rather than listed as powder composition. [merckmillipore.com], [sigmaaldrich.com] |
| Ammonium citrate | 2.0 | 2.0 | Selective agent. Helps inhibit competing organisms such as streptococci, molds, gram-negative organisms and other background flora, while supporting Lactobacilli. [himedialabs.com], [himedialabs.com] |
| Sodium acetate | 5.0 | 5.0 | Selective agent. Suppresses many competing bacteria and contributes to selectivity for lactic acid bacteria. [en.wikipedia.org], [himedialabs.com] |
| Magnesium sulfate | 0.1 | 0.10 | Supplies Mg²⁺ ions required as enzyme cofactors and for bacterial metabolism. [himedialabs.com], [microbiolo...inique.com] |
| Manganese sulfate | 0.05 | 0.05 | Supplies Mn²⁺ ions important for Lactobacillus growth and metabolism. [himedialabs.com], [microbiolo...inique.com] |
| Dipotassium phosphate | 2.0 | 2.0 | Buffering agent and phosphate source. Helps maintain pH stability / osmotic balance during growth. [documents....fisher.com], [himedialabs.com] |
| Bromocresol green | Not present | 0.04 | pH indicator. Changes from green/blue-green toward yellow under acidic conditions, allowing visual detection of acid production from fermentation. [himedialabs.com], [pdf.benchchem.com] |
| Captan | Not present | 0.004 | Antifungal / selective agent. Used to suppress yeasts and molds in some modified MRS Vegitone formulations. [merckmillipore.com], [sigmaaldrich.com] |
| 2-Phenylethyl alcohol | Not present | 3.0 | Selective inhibitor. Helps suppress gram-negative organisms, molds and some gram-positive bacteria, improving selectivity for Lactobacilli. [merckmillipore.com], [himedialabs.com] |
Low cost MRS:
> the modified MRS contained only glucose, yeast extract, dipotassium phosphate, manganese sulfate monohydrate, Tween 80 and sodium acetate anhydrous.
>The estimated optimum amounts of the medium factors for the growth of L. plantarum JNU 2116 are as follows: soy-peptone 0.213%, glucose 1.232%, yeast extract 1.97%, and magnesium sulfate 0.08%.
promising is the Whey based alternative modified MRS broth for Lactobacillus
From AI: Typical Whey-Based Medium Formulation Optimized for L. reuteri
To match commercial MRS yields, supplement a sweet whey or Whey Protein Concentrate (WPC) matrix with a dedicated nitrogen and vitamin booster:
- Whey base: 10% to 15% (w/v) Sweet Whey Powder or a 5%–8% WPC80 solution (acts as primary lactose and protein scaffold).
- Nitrogen booster: 0.5% to 1.0% Yeast Extract (crucial for providing the specific amino acids and B-complex vitamins L. reuteri cannot synthesize). []
- Metabolic precursor: 1.5% to 2.0% Glycerol (required if your target is antimicrobial reuterin synthesis). []
- Carbon kicker: 0.5% Glucose (optional; accelerates the early log phase before the bacteria switch over to breaking down the whey's lactose). [1]
- Surfactant: 0.1% Tween 80 (protects cell membrane integrity during division).
- Mineral Salts & Buffers:
- 0.5% Sodium acetate
- 0.2% Dipotassium hydrogen phosphate (K₂HPO₄)
- 0.02% Magnesium sulfate (MgSO₄ ⋅ 7H₂O)
- 0.01% Manganese sulfate (MnSO₄ ⋅ H₂O) [1]
⚠️ Crucial Culturing & Processing Parameters
- Strict Temperature Ceiling (38°C / 100°F): Unlike standard lactobacilli that tolerate or prefer higher temperatures (42°C–45°C), L. reuteri peaks cleanly at 38°C. Pushing temperatures to standard yogurt incubation thresholds (above 41°C) can severely stall or kill the bacteria. [1, 2]
- pH Range Selection: Adjust the initial medium pH to 6.2–6.5 before sterilization. L. reuteri drops the culture pH rapidly via heterofermentative lactic and acetic acid generation. A higher initial starting buffer ensures it does not self-terminate prematurely from acute acid shock. [, 2, 3]
- The Reuterin Production Pathway: If you are harvesting reuterin (3-hydroxypropionaldehyde) as a biopreservative, L. reuteri requires the addition of glycerol to act as a hydrogen acceptor during carbohydrate fermentation. If you only want raw biomass for encapsulation or freeze-drying, you can completely omit the glycerol to save costs. [, 2]
- Gas Environment: L. reuteri prefers a anaerobic environment or a static, microaerophilic setup with high ambient CO₂ to hit maximum biomass densities.
next step:
1 verify the source about AI advice
2 source components to culture.