Production of lactic acid in milk powder medium.METHOD & DISCUSSION

❰❰go to introduction

Bacteria in fermented milk products, like lactobacilli and lactococci produce lactic acid in anaerobic environments. Therefor I chose a bottle with tight cap for the expeiment. The tolerated temperature range vary a lot between different species and subspecies. Lactococcus lactis subsp. cremoris has a temperature growth range 10°–42°C (50°–108° F), and seems be to a good choice for room temperature. The bacteria along with others can be found in crème fraîche. By the use of crème fraîche in my experiment I ensure that at least one species of bacteria grow. All my equipment were decontaminated by washing and drying, thus not sterilezed. The procedure was as follows, in a cup I stirred together:

• 15 ml non-fat milk powder
• 150 ml water
• 15 ml crème fraîche

Then I filled the bottle with the mixture, screwed on the cap and put it into my thigh pocket. I kept it there in order for the liquid to be shaken. In step with the increasing amount of lactic acid, more and more milk casein coagulated and the milk became thicker and thicker. Now and then I checked the consistency by turning the bottle up-side-down while watching how fast the air bubble moved.

The air bubble.

After 18 hours the fermented milk appeared to be done and I opened the bottle. The top layer of the milk was very thick. Beneath this layer the milk hadn't become that very thick. It smelled a combination of yogurt and milk powder.

I poured up the fermented milk in a cup, blended and had it for snack. The image below on the left shows the stripes of the coagulated casein on the wall of the cup. It tasted similar to yogurt. Even though it was tasty, it could have been much tastier if it would have contained fat. Of course it's never guaranteed risk free to eat a product from an experiment. No gastro-intestinal symptoms were detected, that could be affiliated with the consumption of the fermented milk. The experiment shows that media based on milk powder can work very well. This knowledge will probably be very useful in future experiments.

References

• Wikipedia article about crème fraîche
• Toqeer Ahmed, Rashida Kanwal and Najma Ayub; Influence of Temperature on Growth Pattern of Lactococcus lactis, Streptococcus cremoris and Lactobacillus acidophilus Isolated from Camel Milk
• http://aem.asm.org/content/64/5/1950.full
• http://www.dairyconnection.com/Page3.html
• http://en.wikipedia.org/wiki/Lactic_acid_fermentation

Production of lactic acid in milk powder medium.INTRODUCTION

In my experience, it's complicated to make yogurt. Milk that has been heated to 60 °C in the process of pasteurization still contains, among others yeast, that can spoil the product. In order to avoid contamination one should either acquire HTST-milk or boil the milk. The milk should then be kept in 37–40 °C and a starter culture/yogurt is added. After about 18–36 hours, depending on temperature and species of microorganisms the fermented milk is done. Wouldn't it be better if one could just put some ingredients together in a bottle and after 18 hours the mixture would had become yogurt? Perhaps a solution of milk powder and water could be a good medium for lactic acid production, provided that there are not too many spores in the powder. Since milk powder is dry, then not many microorganisms should be able to grow there.

go to method and discussion ❯❯