Stories From the Lab: Gellin’ with Agar
Hey everyone! Welcome back to my culinary science blog. Today I’m here to give you a behind-the-scenes look at what we as culinary science students do in some of our lab classes. Hopefully you read my last blog post about our multi-protein assignment and creating a fine-dining meal on a $20 budget. If you didn’t, go check it out before reading this one. This time around in class, my partner and I made agar and added a sample of Bulgarian yogurt to it to evaluate the amount of bacteria growth under a microscope!
So, agar-agar—more simply known as agar— is a mixture of different carbohydrates and other materials that have been extracted from red seaweed. Agar is hugely popular in Asia, with countries like China and Japan manufacturing agar and using it as a gelling agent for sauces, juices, candies, and stews. Agar has a high fiber content and is often used as a vegan substitute for gelatin.
For this lab experiment, we used MRS Agar Lactobacilli. MRS agar is named after the three scientists who developed it—DeMan, Rogosa, and Sharpe—in 1960. This type of agar is specifically meant for laboratory use and has a medium culture strength that has additional nutrients added to it. It is the initial base for the isolation, enumeration, and cultivation of lactobacilli. Lactobacilli is a type of bacteria that is somewhat helpful to humans, since it can protect us from potential invasions from pathogens. They are long, slender, and rod-shaped, and grow well in areas with reduced oxygen tension and increased CO2. Food-wise, it can help ferment cabbages and sauerkraut and it is the most common probiotic found in yogurt.
Let the Experiment Begin!
To make the agar petri dishes, my partner and I first added the MRS agar to water and boiled it. We then transferred the product to a glass container with a lid, which we placed in a pressure cooker.
After the agar came to pressure in the pressure cooker, we then added it to a thermocirculator to a set temperature of 45 degrees C. Afterwards, we filled up the petri dishes and stored them in our walk-in refrigerator for one week. While the agar looked and flowed like warmed honey, many of my classmates said it smelled like dog food.
My classmates and I got to experiment with the yogurt samples we made by adding a sample to the agar petri dishes. After the week, we evaluated the results under a microscope using a technique called gram staining, which distinguishes between gram negative and gram positive based on the cell wall of the bacteria. My partner and I used Bulgarian yogurt, which is traditionally unstrained and has a surprising tart flavor while still being creamy.
The results under the microscope were incredible! We got to see up close all the bacteria that had grown. Some of my classmates’ agar petri dishes grew a lot of bacteria, while others grew very few. Some even had huge fungi on them! The smell of the yogurt bacteria after it had grown on the agar petri dishes flabbergasted my class. It had an “off,” rancid smell, which surprised my classmates and even gained the attention of my professor since the original yogurt samples we had made were quite pleasant-smelling.
My classmates even had some extra time to evaluate some sausage that another chef had made under the microscope. It was interesting to see how completely different the shapes of the fermented sausage bacteria were from the yogurt.
Microbial Ecology of Food Systems has become one of my favorite classes of the semester so far. Experimenting with different organisms under controlled spoilage and growth can definitely affect the functionalism of ingredients. Bacteria have much more interaction in foods then you might have thought! It’s another great example of how important it is to understand the science of food.
Tune in next time when my classmates and I have the chance to get creative with proteins.
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