Posts

Coconut

If you’re itching for a tropical getaway, enjoying a coconut snack could help conjure up images of cool sand, blue waters, and swaying palm trees. The coconut tree (Cocos nucifera) and its fruits may very well be the symbol of paradise, since coconut is an ingredient in many Southeast Asian and Pacific Island cuisines. If you find yourself eager to whip up some curry, puttu, Ginataang Manok, macaroons, a cold glass of piña colada, or just feel like sticking a straw into a coconut, take some time to digest a little bit of coconut science before cracking open a coconut. Read more

Vinaigrette

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Homemade vinaigrettes are about as easy as they look: mix oil, vinegar, and spices; shake before pouring. For those who want vinaigrettes without the inelegant step of shaking before serving, the solution is simple; add an emulsifier.

Understanding the role of an emulsifier first requires some familiarity with the primary components in vinaigrette, vinegar and oil. Vinegar is composed of acetic acid and water, which are polar compounds. In a polar molecule, one or a group of atoms have a stronger pull on the electrons in the molecule. Due to this uneven share of electrons between the atoms, weak charges form on opposite ends of the molecule [Figure 1a]. The weakly positive and negative charges on the polar molecule are called dipoles. Oil, on the other hand, is a type of lipid, which is a nonpolar compound. Since the atoms within the lipid are largely identical, the electrons are evenly distributed across the lipid molecule [Figure 1b]. Therefore, nonpolar molecules do not have such well-developed dipoles.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

In solutions, compounds follow the chemistry fiat, like dissolves like. Polar molecules only interact with other polar molecules. Likewise, nonpolar molecules prefer to be surrounded by other nonpolar molecules. When a polar solution, like vinegar, is vigorously mixed with a nonpolar solution, like oil, the two initially form an emulsion, a mixture of polar and nonpolar compounds. However, this emulsion is unstable and will very quickly form layers in what’s known as phase separation. The solutions separate into layers according to their respective densities due to an aversion to each other. (In this case, because oil has a lower density than vinegar, it happens to be the layer floating on top.)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

To prevent phase separation, an emulsifier can be added to the vinaigrette to stabilize the emulsion. Emulsifiers are amphipathic compounds, meaning the molecule has both a polar and nonpolar section [Figure 2]. Common food emulsifiers include egg yolk, soy lecithin, garlic, and mustard. Egg yolk contains the emulsifying agent lecithin. The vegan version is isolated from soy and is thus known as soy lecithin. Lecithin is a commonly used emulsifier in many other food products, such as chocolates, mayonnaise, and Hollandaise sauce. Amphipathic compounds found in garlic include diallyl sulfide, allyl methyl disulfide, and diallyl trisulfide [1]. Mustard, the condiment, is made from mustard seeds. Emulsifying agents in the condiment, such as the pectin rhamnogalacturonan, originate from the mucilage of mustard seeds, a thick, glutinous layer that surrounds the seed hull [2,3].

Figure 2. a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

So with a helping hand from emulsifiers, homemade vinaigrettes can still be as simple yet elegant as they seem, and best of all, ready to serve whenever.

Greek Salad Vinaigrette (Recipe from Ina Garten’s Barefoot Contessa)

½ cup olive oil
¼ cup red wine vinegar
2 cloves garlic, minced
½ tsp Dijon mustard
½ tsp ground black pepper
1 tsp salt
1 tsp dried oregano

  1. In a bowl, whisk together the vinegar, garlic, mustard, salt, pepper, and oregano until well mixed.
  2. While still whisking, slowly add the olive oil.
  3. When a stable emulsion forms, serve with salad or store in a covered bowl or bottle.

References cited

  1. Kimbaris, A.C., Siatis, N.G., Pappas, C.S., Tarantilis, P.A., Daferera, D.J., Polissiou, M.G. Quantitative analysis of garlic (Allium sativum) oil unsaturated acyclic components using FT-Raman spectroscopy. Food Chemistry, 2006; 94: 287-295.
  2. Cui, W., Eskin, M.N., Biliaderis, C.G., Marat, K. NMR characterization of a 4-O-beta-D-glucuronic acid-containing rhamnogalacturonan from yellow mustard (Sinapis alba L.) mucilage. Carbohydrate Research, 1996; 292(1): 173-183.
  3. Leroux, J., Langendorff, V., Schick, G., Vaishnav, V., Mazoyer, J. Emulsion stabilizing properties of pectin. Food Hydrocolloids, 2003; 17: 455-462.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Emulsions & Food Engineering

RutgersCourse

Rutgers Professors Rick Ludescher and Mukund Karwe explain the basic chemical principles of emulsions and introduce food engineering techniques like extrusion and high-pressure processing. If you’ll be on the East Coast this fall, be sure to check out Rutgers’ crash courses in food science and food safety. Read more

Homemade Butter

ButterBigger

Despite the misconception among certain pop culture icons that butter is a carb, butter, like other fats and oils, is a lipid. Broadly defined, lipids are any molecules that have hydrophobic, or water repelling, characteristics.  In contrast to simple molecules like water (H20) or sugar (C6H12O6), butter does not have one molecular formula; rather, it is a mixture of triglycerides. Here is what a triglyceride looks like [1]:

triglyceride

Triglycerides are molecules made of three fatty acids bound to glycerol, a sugar alcohol. Fatty acids are long hydrophobic chains of hydrogen and carbons that repel water. Triglycerides do not have to be the same three fatty acids, but can be mixed and matched. For example in butter, oleic acid (32%), myristic acid (20%), palmitic acid (15%) and searic acid (15%) make up the greatest percentage of the fatty acids [2].

buttercontent

In addition to all these lipids, surprisingly, butter contains water. While oil and water don’t normally mix, in butter, tiny microscopic water droplets are dispersed within the fat.  This is commonly known as a water-in-oil emulsion. An emulsion is any mixture of two liquids that don’t usually mix. The opposite of a water-in-oil emulsion would be an oil-in-water emulsion in which oil droplets are entrapped within water.

To understand the secret of how butter can be made of two immiscible liquids, we need to delve back into the molecular structure.  Butter is made from the cream, which has a higher fat content (15-25%) than milk (5 – 10%) [3].  In milk and cream, which are oil-in-water emulsions, the fatty triglycerides stay suspended in liquid because they are encapsulated in tiny fatty spheres or globules. Each globule is surrounded by a nanoscopically thin layer of phospolipids and stabilizing proteins. Phospholipds have hydrophobic lipid tails that love to repel water; they also have hydrophilic, or water loving, heads that contain a phosphate group (thus the name, phospho-lipid). Here is a picture of a phospholipid [1]:

phospholipid

The phospholipids organize themselves in a thin layer so that the water repelling hydrophobic portions are aligned with the fatty acid chains while the water loving hydrophilic heads interact with the milk liquid.  This allows the fats to remain dissolved in the milk and float around like little water balloons.

Milk Fat globule. (A) Diagram of the phosopholipid layer surrounding a fat globule [3]. (B) Cryo-electron microscopy image of a fat globule [4]. The scale bars are 0.1 μm.

Now, that we have talked about the structure of butter, how to get from cream to butter?  (Remember: milk and cream are oil-in-water emulsions and butter is a water-in-oil emulsion.) The oil-in-water emulsion of the cream is reversed into a water-in-oil emulsion in butter. During the churning or mixing process of butter making, the fatty globules in the cream break open to release the entrapped fat molecules. The hydrophobic fat molecules clump together and mix to form larger fat globules that coalesce into larger solid fat droplets. This processes pushes out the liquid portion and the solid portion becomes the butter.  Since these types of fat molecules typically melt at temperatures of 30 to 41°C (86 to 106°F), this means that at cool temperatures below approximately 39°F (4°C), the remaining liquid gets trapped within the solid fat matrix and is unable to separate out of the butter [5].

milktobutter

Below is a recipe for making your own homemade butter. You don’t need fancy equipment or churners like your ancestors used; a well-sealed glass jar works wonders.  The shear forces generated by rigorous shaking are sufficient to convert your cream into butter.

Ingredients

Heavy whipping cream (6 cups makes about 1lb of butter)
Salt, to taste
Jar with lid, any size

Procedure

1. Fill the jar about ¾ of the way to the top with the heavy whipping cream and close the lid.

2. Shake the jar for about 4-5 minutes until the cream begins to thicken. Shake longer if you wish for a thicker consistency.

The shaking motion breaks down the fat globules. The membranes surrounding each fat globule break, releasing the hydrophobic triglycerides. The triglycerides clump together and push away the hydrophilic liquid, the buttermilk.

3. Drain off the buttermilk and place butter in a small bowl. Knead the butter under cold running water to remove any remaining buttermilk.

4. Salt to taste. Form butter into a ball or log. Serve immediately or refrigerate.

Recipe Adapted From:

Online Resources

  1. General Chemistry Online: What is the chemical structure of butter?
  2. “Overview of the Buttermaking Process” from University of Guelph

References Cited

  1. K562. Overweight & obesity. http://www.indiana.edu/~k562/ob.html
  2. Fatty acids in butter. Percentage composition from Practical Physiological Chemistry, P. B. Hawk, O. Bergeim, Blakiston:Philadelphia, 1943.
  3. Gallier, S. et al. 2012. Structural changes of bovine milk fat globules during in vitro digestion. J Dairy Sci. 95(7): 3579- 3592.
  4. Robenek, H. et al 2006. Butyrophilin controls milk fat globule secretion. PNAS. 103 (27): 10385-10390.
  5. Butter: Some Technology and Chemistry. http://drinc.ucdavis.edu/dfoods1_new.htm

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

Read more by Vince Reyes