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 ❯❯

Winogradsky column day 22

Winogradsky column
day 22

During the last week the rusty layer has become higher and the contrast to the transparent layer beneath has become more accentuated.

Winogradsky column day 15

Winogradsky column
day 15

After two weeks the water has become turbid. The entire sediment layer is now black, probably as a result of the processes mentioned in the previous blog post. Above the sediment one can see a thin red layer. I guess this is formed by anaerobic purple sulfur bacteria that get energy from H₂S. Further upwards is a break followed by a level with a rusty shade. I suppose this layer is made of non-sulfur purple bacteria, that uses H₂ as energy source. This type of bacteria do not tolerate sulfur as well as the sulfur bacteria, what should explain the gap between the layers, since the concentration of sulfur declines toward the top. At the water surface at the top of the column some lighter particles float.

Rhodopseudomonas palustris, the bacteria I want to isolate is a purple non-sulfur bacteria. Probably it's already possible to do that, even though I'd like to wait one or two more weeks till I try something new.

References

• Winogradsky column: perpetual life in a tube — Edinburgh University

Winogradsky column day 7

Winogradsky column
day 7

The lower part of the sediment has changed color to black. I suppose this is due to the development of metal sulfides from metals and minerals in the mud. Now two types of microorganisms flourish, namely species of the genus Clostridium and so called sulfate-reducing bacteria, e.g. Desulfovibrio. The main reactions of the symbiosis between these microorganisms are shown bellow.

Clostridium

(C6H10O5)n	→	C2H6O	+	–COOH
cellulose (toilet paper)		ethanol		organic acids

Sulfate-reducing bacteria

C2H6O

+

CaSO4

→

H2S

+

CH4

+

CaO

+

CO2

+

H2

ethanol

gypsum

hydrogen sulfide

methane

calcium oxide

carbon dioxide

hydrogen

References

• http://www.personal.psu.edu/faculty/j/e/jel5/biofilms/winogradsky.html
• http://www.biology.ed.ac.uk/archive/jdeacon/microbes/winograd.htm
• http://www.mbio.ncsu.edu/MB452/Winogradsky_columns/wc.html
• http://ecosystems.mbl.edu/SES/MicrobialMethods/MicrobialBiogeochemistry2010.pdf
• Samia Azabou, Tahar Mechichi, Sami Sayadi.Sulfatereduction from phosphogypsum using a mixed culture of sulfate-reducing bacteria. Laboratoire des Bio-procédés, Centre de Biotechnologie de Sfax BP “K”, 3038 Sfax, Tunisia

Starting a Winogradsky column

Winogradsky column
day 1

The concept of composting, to recycle the organic waste for growing new plants, is great. But traditional composting requires that you have a garden or at least some special containers outdoors or in the basement. Is there any other way to draw plant nutrients out of organic waste? Perhaps the method of bokashi would be a good alternative for people living in apartments? This form of composting is based on a mixture of microorganisms called EM (effective microorganism). You can buy dried formulas of EM, but why not make your own? The mixture contains three types of species, of which you can find two in the grocery store: baker yeast (Saccharomyces cerevisiae) and a particular kind of yogurt bacteria (Lactobacillus casei). The challange is to isolate the third organism, Rhodopseudomonas palustris. This bacteria is very common in mud. In order to isolate it I make a Winogradsky column.

Materials and method

In a vessel I blend:

• 30 ml pond mud
• 10 ml shredded toilet paper — as carbon source
• 10 ml gypsum — as sulfur source
• 1 ml chalk — as source of calcium carbonate in case the mud has low calcium amount

View sample origin in a larger map

After stirring all the ingredients together I put the blend on the bottom of a glass bottle. Then I put additional 50 ml mud on top of the previously mentioned blend. At last I fill almost all of the remaining space in the bottle with water from the pond. I cover the bottle with a lid and plastic foil fastened with a rubber band. The column will now stand on a windowsill for a month or two. My goal is to get layers of different species of bacteria in the bottle. Each weekend I'll post a photo showing how the experiment proceeds. After growing the bacteria I plan to isolate Rhodopseudomonas palustris from the column and grow it on a separate medium.

References

• B. Lidesten. Bakterier som använder ljus. Nationellt resurscentrum för biologi och bioteknik. (in Swedish)
• Wikipedia's article about Winogradsky column
• Winogradsky column: perpetual life in a tube — Edinburgh University
• G. Ç. DÖNMEZ, A. ÖZTÜRK, L. ÇAKMAKÇI. Properties of the Rhodopseudomonas palustris Strains Isolated From an Alkaline Lake in Turkey. Tr. J. of Biology. 23 (1999).