CHEM 306-02

This past week we explored the finicky nature of emulsions. We beat nearly 3 cups of oil into three yolks, with hopes of achieving a tightly packed, semisolid emulsion of uniformly small droplets. Considerable physical force is required in order to prevent the oil droplets from coalescing into a separate layer. This tendency of liquids to form single large masses and minimize their surface area is an expression of the force known as surface tension. An emulsifier has a fat-compatible tail and water-compatible head where they embed their tails in the droplets and leave their electrically-charged heads projecting into the surrounding water, thus repelling each other instead of coalescing. Large protein and starch molecules help stabilize emulsions by blocking the fat droplets from each other. If the mechanical mixing force is not continuously applied or the mediums are not integrated in small enough increments so the emulsion is not overwhelmed and broken (bottom right of image), then a thick mixture will result (upper right of image).

Now we could not waste our egg whites, so in addition to our mayonnaise we also made those delicate, sweet melt-in-your mouth morsels…meringues. Ovalbumin is the major protein in egg white and is sensitive to heat, which causes it to unfold and coagulate. When the raw foam is cooked, the ovalbumin more than doubles the amount of solid protein reinforcement in the bubble walls. Much of the water evaporates and the heat transforms a semiliquid foam into a permanent solid one. My group made meringues using powder sugar while the other group used fine granulated sugar. Even during the beginning egg white beating stage, it was evident that granulated sugar was more successful than the powder sugar. The powder sugar sample took longer to thicken into a foam with stiff peaks. Research on the properties of egg foams reveal that the sharp crystal edges of granulated sugar cut the proteins and accelerate the process of merging liquid and air. These are the results, powder sugar on the left and granulated sugar on the right.

We could have baked the meringues for a while longer. The centers were still semisolid foam and retained a distinct egg taste, whereas the baked edges were of that wonderfully dissolvable crisp, sweet goodness. But when meringues are in the oven, any chef who delights in the joys of chemistry-concocted confections would not be able to resist pulling out the delicacies a moment too soon.

While the powder sugar meringues achieved flattened spherical bases that a macaroonist may have lauded, the undeniably “winning” meringue was the granulated sugar batch.

This was my first experience making meringues and I look forward to employing this simple, low-fat recipe as a regular entertaining dessert. While abroad in London, I discovered the irresistible combination of chopped strawberries, fresh whipped cream, and crushed meringue…a good ol’ “Eton Mess”.

Last week in our class, we had the pleasure of filling the air of the science center again with the aroma of our tasty treats. This lesson we were learning about emulsions and foams using egg yolk and egg whites. Emulsion is the process of mixing two or more liquids in which one of the liquids is present as microscopic droplets distributed among another liquid. Emulsion is the process we used to create our mayonnaise. By adding vegetable VERY VERY slowly to 3 egg yolks and while beating vigorously (Sarah and I got a serious arm work-out) , we were able to create fluffy mayonnaise over the time span of almost 30 minutes. This process was rather interesting because Sarah and I originally added the vegetable oil in our egg yolks to quickly. Consequently, our mixture remained liquefied and the vegetable oil and egg yolk were separated. Only when we tried again (with more vigorous beating and adding the oil more slowly), were we able to suspend the oil droplets more effectively.

We also learned how to create a foam. This is when we trap pockets of air into a liquid or solid using mechanical energy. In our case, the procedure to make meringue involves beating egg whites with a electronic mixture until the mixture has pretty firm peaks. This took about 15 minutes of consistent beating. Sarah and I used granulated sugar while Elle, Annie, and Jocelyn used powdered sugar. The meringue with the granulated sugar definitely came out with firmer peaks and also tasted a little better (at least I thought so! But Professor Didem preferred the ones with powdered sugar). It was really fascinating to see how without actually performing any chemical reactions, we could observe physical changes to the mixture.

This week we explored dairy products with a mouth-watering introduction talk given by Professor Vanja Klepac-Ceraj, a scholar with personal interest in the microbial communities in cheese. After Vanja left the class with dreamy visions of Gruyere and Munster, we set to work making our own mozzarella cheese.

First, we added 1/8 of a teaspoon of vegetable rennet and ¾ of a teaspoon of citric acid to a half gallon of heated milk. Immediately, curd formation occurred. Curd separation from the whey continued during the 25 minutes of rest.

Citric acid works in much the same way as the traditional rennet containing the enzyme chymosin, obtained from the abomasum of a milk-fed calf.
This enzyme effectively attacks only one milk protein at a single point, targeting negatively charged kappa-casein that repels individual casein particles from each other. By clipping these pieces, chymosin allows the casein particles to bond and form a continuous solid gel, the curd. Plain acidity would also cause milk to curdle but also causes the casein micelle proteins to disperse, thus most of the calcium is lost in the whey. On the other hand, rennet allows the micelles to remain intact and causes each to bond to several others, forming a firm and elastic curd.

By straining the mixture through a cheesecloth and heating the solid in the microwave, we further separated the curds from the whey. After much kneading, wringing, and heating to extract excess liquid, we achieved the pliable and slightly stringy consistency that we desired. Fresh mozzarella is a relatively simple process!

Week Four had an exciting agenda of food dye chromatography and adventurous jello-making. I chose to work with apples as our experimental ingredient. We therefore made a jello with applesauce replacing 1/4 cup of water, freshly pureed apples replacing 1/4 cup of water, a control with water and no apple substitute, and an experimental sample with no additional water. I also got creative and created a sample with the normal water content and apple solids chopped into a rough mirepoix.

During the time when we allowed our samples to cool in the refrigerator, our class went into Professor Didem’s lab to conduct a gel electrophoresis experiment. We mixed various colors using the food dye colors available at the generic market. Our first gel broke because our curiosity prompted us to touch it, but I was not at all disappointed about remaking the gel because it gave me the opportunity to work with an analytical scale in measuring out the agarose solids. We ran currents through both gels but the second one was significantly more precise in the resulting bands.

Later, we returned to our jello, which after cooling had formed a loose but continuous network of gelatin molecules immobilizing the water. It had become a very moist solid, or a gel. Upon immediate observation, the fresh apple had turned a deeper brown than the canned apple. This was likely due to preservatives added to the apple sauce to prevent browning. The texture of the apple infused jello’s were slightly gritty, with a more paste-like consistency. I personally loved the texture the apple gave to the jello, it had more substance rather than an immaculately homogenous simple jello. I am eager to experiment with other fruits such as pear or persimmon. My great takeaway: when I am a mother I will certainly be making jello for the kiddos with fruit substitutes; enriched texture and nutrition!

This week we studied the properties of foams and emulsions using egg whites and egg yokes. Foams and emulsions are different types of dispersions in liquids. Foams, like meringue, consist of air bubbles dispersed in liquid egg whites. Emulsions, like mayonnaise, consist of fat globules of oil dispersed in liquid egg yokes. We saw experimentally how foams and emulsions are thermodynamically unstable. Because they consist of two essentially immiscible phases, they will separate back into two distinct phases over time. We saw how air bubbles could pop and deflate our meringues and how adding too much oil at once could prevent the formation of our mayonnaise.

Meringue: Egg yokes contain many different types of proteins. The proteins were denatured using acid (in our recipe, in the form of vinegar) so that they would unfold and be able to incorporate air. We made two versions of our recipe, one with powdered confectioners sugar and one with regular sugar. The batch made with powdered confectioners sugar was deflated and had a chewy-er texture than the batch made with regular sugar. Powdered confectioners sugar has added cornstarch, which absorbs moisture. Perhaps the less dissolved regular sugar in the second batch was able to better stabilize the egg foam.

Mayonnaise: Egg yokes contain lecithin, a fatty acid with both a polar hydrophilic end and a non-polar hydrophobic end. The egg yoke and oil mixture had to be mixed constantly and the oil poured extremely slowly in order to emulsify only 3 egg yokes with nearly 2 ½ cups of oil. Because the mayonnaise contains so much oil, the fat droplets are constantly pressed up against each other and can easily coalesce, ruining the emulsion.

This week, we focused on eggs and emulsion. So, the discussion returned to the topic of proteins. A couple of weeks ago when we examined enzymatic browning, we focused on protein structure, function, and enzymatic activity. This week, in addition to these topics, we talked more about the chemical properties of proteins. Proteins have the abilities to coagulate, emulsify, turn into foams, and high water solubility. This versatility makes eggs an important ingredient in cooking and baking. In eggs, almost all of proteins are in the egg white while the lipids are in the yolk and an interesting fact I learned is that in egg yolk, there is lecithin, which is a good emulsifier (Emulsification is mixing of two or more liquids that are normally insoluble in each other by having one liquid disposed in the other).

Using this knowledge, we made French style meringue and mayonnaise! We made one version of meringues using regular sugar, and another with superfine sugar. The proteins in meringue had to be denatured so that the the peptide bonds could uncoil into long strands. The cream of tartar that is usually included in the procedures for making meringue could be substituted with a drop of vinegar because the purpose was simply to acidify the proteins in the eggs. If heating makes proteins denature without breaking the primary structure, lowering pH has the same effect by making the proteins much less charged and disrupting the salt bridges and hydrogen bonds. The uncoiled amino acids join together and are able to coalesce. After the egg whites foam from constant beating, the bubbles created by the foam allow sugar to dissolve into proteins, making the meringue swell up.

I liked the taste of the meringues made with regular sugar since the one made with superfine sugar gave a little bit of artificial taste, but both were just fine for some sugary dessert. For mayonnaise, it was surprisingly easy to make it but it did require a lot of arm exercise to whisk it continuously to prevent adding air into the mixture.

Eggs seem like a fun, yet complex food topic, which is why Annie and I are working with eggs on our second project. We’re excited to find out more about the various transformations of eggs and their high nutritional values!

Top: superfine sugar meringues, Bottom: regular sugar meringues

Into the oven!

Meringues are ready!

Superfine sugar meringues

Regular sugar meringues

Beautiful.

Sarah and I are doing our project with Juniper in the Wellesley ville! We recently went in for a second time to discuss our plans on our dish (or ingredient), which is mint oil. Chef Tim’s problem is that he cannot keep his blend of olive oil and mint leaves a vivid green color over time. He says that the method he uses now is to blanch the mint leaves to prevent them from browning. However, his problem could be his storage and usage of the olive oil. He will be e-mailing us the exact recipe and method so we can try to replicate the process as best as possible. Hopefully we will be starting our experimental work soon so that we can see what happens to the prepared mint oil over a bit of time since that is his main concern.

Hopefully we can come up with a good solution as we’ve been working with olive oil and maintaining the  color of leafy greens for the first few weeks!

Last week, we made cheese and butter in our class! I never knew how easy (and tasty) making your own cheese could be. We first heated up half a gallon of milk and then added some citric acid and rennin to the milk making it curdle. After letting the curdling process proceed for about 30 minutes, we then strained the curdles using cheesecloth separating the casein from whey proteins. Microwaving and straining the curdled casein multiple times, our cheese began to solidify. Some of us added salt while others did not and we made our very first mozzarella cheese! It was really delicious and I can’t wait to try this at home.

We learned that citric acid makes milk curdle because the pH affects the polarity of the casein, making each of the protein molecules attract each other. Rennin can speed up this process.

We also made butter in class, which made me realize that the light and fluffy whipped cream that I’ve enjoyed so much is in fact just an intermediate to butter, which is a little gross. However, it’s really interesting how increasing the amount of time we were beating the buttermilk influenced the physical state of the buttermilk. It would be really cool to go through the chemistry behind what is going on there

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This week Annie and I started our research for the “chef’s problem” project, working with Susu Alyward of Susu’s Bakery in the ville. Our assignment is to transform one of their top selling bakery items into a gluten free item. We plan on investigating the chemistry of gluten, the properties of wheat flour substitutes, and how these substitutes might react chemically with the other ingredients in the recipe. I think this will be an interesting topic because while “gluten” and “gluten-free” are very popular and trending food lingo, I am not sure if we all know what they really mean. I learned that gluten found in wheat flour is only formed when it is mixed with water. It forms an extensive interconnected network of coiled proteins, gliadin and glutenin molecules, that produce the “chew” we associate with breads and other pasteries. The challenge in transforming a pastry to be gluten free lies in replicating this mouthfeel and texture with flours that do not contain any of these long chained proteins. From the culinary sources I have found, it seems that most gluten free recipes call for a blend of gluten free flours (in various ratios), the use of either xantham gum or guar gum, and further alterations in baking time, temperature, and the amounts of other ingredients like baking soda. This coming week we will start our baking trials, determining how all of these factors play a role in altering the texture and taste of our transformed gluten free pastry.

Last week, we learned about the molecular components of milk and the chemistry behind cheese making. Milk is made of three simple components: proteins (casein proteins and whey proteins), milk fat, and lactose (a complex sugar combination of glucose and galactose). Cheese is made by curdling milk using an acid, heat and an enzyme called rennet to alter the molecular structure of the casein proteins. In our experiment, each group heated half a gallon of milk in a pot on a hot plate. We added 1/8 of a teaspoon of vegetable rennet and ¾ of a teaspoon of citric acid and could right away see the formation of curds. After letting the milk rest covered for 25 minutes the curds had separated even more from the whey. Why does this happen? Micelles of casein proteins consist of many individual protein molecules with negative charged ends held together by particles of calcium phosphate. Normally these negative charged ends help keep the micelles far apart from one another. The rennet enzyme we add essentially “clips” the ends of these protein molecules, causing the micelles begin to clump together. We further separated the curds from the whey by straining the mixture through cheesecloth and heating the remaining curds in the microwave. I was surprised at how much more whey there was compared to our finished mozzarella cheese product.