CHEM 306-02

This week, we had a special guest, Professor Vanja, visiting our class to gives us a lecture on microbiology in cheese. Just until last year, I avoided fresh cheese because I couldn’t stand the strong smell. From Prof. Vanja, I learned that the microbes’ activities and their aging are actually responsible for creating such a strong odor in cheese. We briefly went over the cheese-making process. First, lactic acid bacteria converts lactose sugar to lactic acid. This causes proteolysis of casein, which is protein found in milk, by chymosin in rennet. This process eventually forms curd, which can be manipulated artificially or by the microbes. We also learned about different types of cheese, and why Swiss cheese has holes. Those holes are made by microbes’ production of CO2 gas. It was fascinating to learn how much activity goes on within a food. Cheese is indeed one of the greatest ecosystems.

Using what we learned, we made mozzarella cheese. It was really nice to see how easily and simply we could make cheese from milk, proving Prof. Vanja’’s favorite saying, “Cheese is milk’s leap toward immortality.” We added citric acid to milk and heated it for about 10 minutes and used cheese cloth to obtain the curd. Thanks to my partner Elle’s kneading skills, our mozzarella cheese turned out very nice and compact like the ones we buy from stores! I think I might have to visit Wellesley’s Waasik’s cheese shop to explore the various kinds of cheese that I’ve missed out on in the past years.

This week we also learned why Jell-O does not set when certain fresh fruits are added. Often on boxes of Jell-O there is a warning to not add fresh pineapple, kiwi, or papaya. We set up a few experiments to investigate why this is the case. Annie, Jocelyn and I made orange Jell-O with fresh versus canned pineapple, and Sarah and Amy made orange Jell-O with fresh versus canned (applesauce) apples. Each group set up 4 petri dishes: Jell-O with fresh fruit, Jell-O with canned fruit, Jell-O with water (control), and Jell-O with a reduced amount of water (second control). The Jell-O made with the fresh fruit did not set at all as expected! We learned that some fruits contain protein-ingesting enzymes that break down the gelatin chains into short fragments, thus preventing the gel from setting! Cooking the fruit beforehand breaks down these enzymes so that they cannot destroy the gelatin proteins. I had known that you were not supposed to put some types of fruit in Jell-O, but I never knew why.

From left to right, Jell-O with water, Jell-O with cooked pineapple, Jell-O with fresh pineapple (which became kind of frothy)

In week 4, we learned about the process of agarose gel electrophoresis and how the technique can be used to separate the color components of common food dyes. Although gel electrophoresis is typically used to separate DNA or proteins, it essentially uses electricity to pull selective fragments of molecules across a gel and can be used to separate the components of any molecules by size.

We first went upstairs to the biochemistry lab to prepare the agarose gel. Agarose is one of the components of agar (the other one being agaropectin) and is extracted from seaweed. It is a polysaccaride polymer and comes as a white powder. When dissolved in hot water and cooled, it forms a gel that we can apply and run the samples through. After running a gel in which the all the colors bled into each other, we soon learned that we only had to apply very small amounts of the dyes to the wells of the gel.

A constant charge must be applied in order to get the fragments to move across the gel. We connected our gel to two electrodes, a negative anode and a positive cathode. We tested blue, yellow, red, green, orange, and purple food dyes. We found that all of these dyes were made up of blue, pink, orange, and yellow components. The yellow color components were made of the smallest fragments and travelled the farthest, while the blue color components were made of the largest fragments and traveled the least. Here is a photo of the gel after it was run:

After reading the online sources and McGee’s chapter on Milk and Dairy products, I can’t stop thinking about how much is going on in the block of cheddar cheese in my refrigerator. There’s so much biology and chemistry to explain this magical food!

Two facts that stood out to me:

1. The golden color that we tend to attribute to “wholesome”dairy products? It’s actually contingent upon the amount of carotene that cows convert to vitamin A– cows that don’t convert that much carotene produce more golden-colored milk. This depends on the breed of the animal. Guernsey and Jersey cows produce golden milk, while sheep, goats, and water buffalo produce very white milk. (Which becomes white butter and white cheese, etc.)

2. We’ve learned in past chemistry courses that H+ is an acid, but now we can put that in the context of curdling milk. When the pH of milk is lowered by adding an acid, two things happen:

• First, the negative charge of the capping-casein is neutralized by the addition of H+. This means that the micelles in milk stop repelling each other and begin to loosely form clumps.
• Next, as the pH continues to drop, the casein proteins actually lose their negative charge completely and bond together to form what we recognize as curdling: the proteins form a continuous network.

That’s why, for example, adding lemon juice to a butter-based batter causes the batter to curdle– the proteins in the melted butter lose negative charges and coagulate.

I’m looking forward to learning more about the chemistry and microbiology of cheese tomorrow!

This week in our course, Chemistry of Food, we talked about browning and caramelization, which happens through a process called the Maillard Reaction. This reaction takes place in the presence of amino acids and saccharides, which is why often BBQ sauces are sweet. The food item begins to brown just as the water evaporates, so this is why caramelization occurs when we cook onions for a certain amount of time, which was our experiment for this week!

We chopped up 2 onions and divided the onions evenly between Elle/Sarah and Jocelyn/me. We used 1 tsp. of vegetable oil. Additionally, we wanted to test the effect of adding baking soda (NaHCO3) to the pan so Jocelyn and I added ¼ tsp to our pan while Elle/Sarah did not. Previously with the green bean experiment in our first week, we learned that NaHCO3 weakens pectin through an acid base reaction that breaks pectin’s hydrogen bonds. By breaking these bonds, the water contained in the onion is able to boil at a much faster rate, therefore caramelizing the onion at a faster rate.

Over the span of 30 minutes, we took observations of our two pans of onions every 5 minutes— noting the color, texture, taste etc. By the end, we noted that although baking soda did help the browning process, the taste was horribly bitter and the onions, although quite brown, became rather mushy. I think perhaps we used way too much baking soda and that adding baking soda to help speed up the process of browning would work if we could test for the perfect amount.

Cooking the onions in the science center was a pretty fun process that left the scent of onions dispersing through the labs for quite a few hours afterward. A few friends even texted me to tell me they could smell it long after we were done.

On Monday, I had a chance to go to a Science and Cooking Lecture called “gAstronomy” at Harvard University with Jocelyn and Elle. Bill Yosses, the former White House pastry chef and the author of The Perfect Finish and Steve Howell, the project scientist of NASA Kepler & K2 missions, carried out a variety of demonstrations of how principles chemistry and physics can be applied in gastronomy as well as astronomy. The chef and the scientist alternated back and forth between the edible and the inedible because “the laws to explain this world should apply to world above.” They briefly covered several topics, including the significance of sphere in cooking and the exoplanets, pigments and spectroscopy, importance of pressure etc. Steve did a quick experiment that tested the presence of atmospheric pressure with a hard-boiled egg that doesn’t fit into the mouth of a flask. When he threw a match lit with fire into the flask and placed the egg on the mouth of the flask, it fell into the beaker because the pressure inside the flask got lower compared to the atmospheric pressure.

One of the most memorable demonstrations was using hydrogen peroxide, potassium iodide, and soap to make a soaring chain of foam. When potassium iodide reacts with hydrogen peroxide, it speeds up the decomposition of hydrogen peroxide into oxygen gas and water by taking one of the oxygen molecules from H2O2. The orange food dye was used to make the foam formation more visible. Here is the video. Enjoy!

foam!

Week 2: I enter the classroom with bubbling-over enthusiasm for the topic and just a hint of trepidation concerning the fact that I, a through and through art history major, am now enrolled in CHEM 360. As expected, some of the lecture consisted of molecular diagrams that gave me heart palpitations. But Professor Didem thoroughly explained the chain of concepts from carbons to cutting board and it became fascinating to discover the chemical explanations behind culinary concepts I have a practical understanding of as an avid chef.

For our first test, we made pea butter from two different pea sources; frozen peas and canned peas. The former a livid kelly green, the latter a yellowish olive green. Both samples were blended and then centrifuged. The results revealed two distinct layers in the canned pea tubes and three distinct layers in the frozen pea tubes. The bottom of both samples was the higher density pea solids; cell walls and starches. The top layer was a purified pea broth. I quickly learned in the classroom to refrain from calling it pea water. The middle layer of the frozen peas was this vibrant green, glistening substance. It had a concentrated, nutty-sweet flavor. We had made pea butter!

Later we tasted our way through the rainbow of vegetable and fruit pigments. It was insightful to discover the properties of certain pigments in produce and how it relates to the molecular-level structures. The carotenoids in the crispy yellow pepper I munched on are accessory pigments in photosynthesis and pass solar energy to chlorophyll.

Week 3 included more centrifugal fun! We jumped right into de-pitting three varieties of olives (purple, black, and green) and blending each into a smooth paste. The mixtures were sent to the centrifuge for 40 minutes.

During this wait time my classmates and I became oil sommeliers and analyzed the viscosity, taste, and appearance of six different oils. I quickly discovered that I am an oil snob. Only the extra virgin olive oil was satisfactory. The rich grip of the initial earthiness and peppery after-bite was very distinct. All I needed was a slice of ciabatta…

When we checked on our high-speed revolving olive mixtures I was delighted to discover a layer of olive solids and liquid gold floating above the pellets. Yes, we had made our own olive oil. I hesitate to term our product “extra virgin” because I learned that such distinctions are conditional not on the chronology of the press but the percentage of free fatty acids. Olive oil’s “acidity” is a result of the degree of breakdown of the triacylglycerols, due to a chemical reaction called hydrolysis or lipolysis, in which free fatty acids are formed. Oil extracted carelessly and/or from poor quality fruit is plagued with higher quantities of these broken down triacylglycerols. High quality oil; meticulously made from healthy, freshly picked olives, normally has a pretty low “acidity”, well under 0.5% FFA. Extra virgin olive oils have less than 0.8% FFA.

It is only Week 3 and I am already enjoying this experience that blends one of my dearest passions with the stimulation of intellectual growth. I look forward to more tasteful discovery!

Jocelyn

To list a few things that we’ve done so far in our Food Chemistry course, there are: taste perception experiment with baby foods, retention of flavor in oil and water experiment, making pea butter, and apple browning experiment.

Among these experiments, I enjoyed making pea butter the most. It was my first time using a non-micro scale centrifuge in a lab. To make pea butter, we used canned peas and frozen peas and saw how the two types produce residues that significantly differed in their tastes. The “butter” made from frozen peas, though it looked a little artificial because it was so green, was much sweeter than that made from canned peas. Seeing different layers that were divided according to the density of liquids and solid was interesting and helped me to question and understand the mechanics of centrifuge.

In class, we discussed about the difference between interaction vs. reaction. Though I’ve been taking chemistry courses in the past and dealt with many reactions, I hadn’t stopped to think about the exact difference between the two terms and thought it was just another comparison between chemical and physical changes. I learned that electrostatic interaction occurs when forces like van der Waals force are so close in distance that it creates transient dipoles or hydrogen bonds create unequal polarity, while reactions occur with formations of new covalent bonds and covalent rearrangement of atoms. So, this course is taking me back to the materials that I may have learned it the past to think more carefully about them in terms of the relationships among different mixtures of food, the cooking medium, stored environment, interaction with our sense receptors, etc.

I’ve been enjoying the experiments and class discussions so far. The things that I learned in class, chemistry labs, or textbooks seem more applicable and cool because of this class. I’m excited for the upcoming topics of browning and jellies!

So far, I’ve really enjoyed the learning in our Food Chemistry course. It has really forced me to recall knowledge and rules from all the different chemistry/biology courses I’ve taken and use them explain the experiments we’re doing in class. The small class size (5 students total!) makes it a comfortable and easy-going environment and the course material is introducing me to a world of applied chemistry outside of medicine. Also we get to eat our experiments, which is definitely a plus.

In week 1, we learned a bit about how flavor can be extended beyond our gustatory system to our other four senses. Sensory receptors in our nose, the texture of food, color of food, and our associated memories all play a factor in how we perceive and experience flavor. These are the factors a chef must consider to create a masterpiece.

We also did an experiment explaining how alkalinity can be used to maintain the greenness in vegetables. Slightly acidic cooking environments, can break the ligand between Mg+ and N in chlorophyll and replace the Mg+ with H’s, causing the vegetable to lose its green color and giving it a yellow hue. Adding a bit of baking soda in the water creates a basic cooking environment, therefore the acidic reaction does not occur as abundantly.

The last experiment we did was flavor partitioning in green beans/asparagus. Through this experiment, we learned that green beans contain more oil-soluble/water-insoluble “flavor” molecules, while asparagus contains more water-soluble “flavor” molecules. Solubility rules explain why it is perhaps better to cook green beans in water and asparagus in oil.

Although we did not go into the details of the complex chemistry behind each experiment , it was enlightening and really cool to see how basic solubility rules and acid/base chemistry can be used and has been used to create tasty meals for generations.

In week 2, we did 2 experiments:

The first experiment, mashed and centrifuged 2 types of peas– canned and frozen. We had to sneak our edibles into the labs and use the large rotors to properly centrifuge our mushed peas. We found that, using different densities and gravity, we could separate the frozen peas into 3 layers– juice, paste, and grinds and the canned peas into 2 layers- salty juice and thick paste. It was really interesting to all the different tastes the 2 types of preparation produced

The second experiment, we tested the browning of apples by placing them in water, boiling water, lemon water (acid), and air. It was obvious that the lemon water preserved the whiteness of our red delicious apple even after 30 minutes. Again we can see acid/base chemistry at work here again.

Anyway, I’m having a great time in this course so far and it has been really exciting for me to learn and work with the group of girls in the course. 🙂

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