“Don’t rub the eyes, Gringo!” or Homework #1

All course materials: Christie, Patricia. SP.287 Kitchen Chemistry course, Spring 2009. (Massachusetts Institute of Technology: MIT OpenCourseWare), http://ocw.mit.edu (Accessed 18 May, 2012). License: Creative Commons BY-NC-SA

Guacamole, Salsa, and Quesadillas

Recipes (PDF files on the original website): Guacamole (PDF), Salsa (PDF) (recipe post coming soon)


From the text: pp. 276-277, 310-312, 337, 352-353, 383, 407, 418-421, 481, 548.

Additional readings:


Kitchen Chemistry Homework #1

Guacamole questions:

  1. Is the avocado a fruit or vegetable? What makes it unique in this respect?
    Avocado is a fruit — a single-seeded fleshy berry. There is a wide variety of botanical fruits that cooks treat as vegetables, because generally they require cooking to make them interesting or soft enough to eat. There are of course exceptions to this rule, such as tomatoes and cucumbers, often used raw in salads.Unlike many other fruits, avocados are unique, since they contain little or no sugar or starch, and are comprised of as much as 30% oil.
  1. Why does guacamole turn brown?
    Guacamole turns brown due to oxidation of avocado flesh with the atmosphere and polyphenol oxidase reaction.
  1. Provide a chemical explanation how we can prevent the browning of the avocado.
    We can prevent the oxidation by stopping the avocado flesh coming in contact with the air, such as covering with plastic or immersing it in water. Another option is to cover cut avocados with acidic substances, such as lemon or lime juice. Slowing down the reaction by cooling or freezing the avocado also works.
  1. Why do apples turn brown? Is this the same mechanism as avocado browning?
    Both avocados and apples (and guacamole) turn brown due to enzymatic browning.
  1. How can we prevent the browning of fruits and vegetables?
    Browning can be prevented by adding an acidic ingredient, such as lemon juice, or by airtight wrapping with a plastic film that blocks oxygen effectively. In the case of mashed avocado, this means pressing the wrap directly to the surface. Chilling the food below about 4’C/40’F will also slow the enzymes down somewhat as will immersing the cut pieces in cold water, which also limits oxygen.
  1. Why do onions make us cry?
    Onions owe their distinctive flavors and smell to sulfur. While growing, the plants take up sulfur from the soil, and build a defense mechanism, which serves the original purpose of deterring animals from eating the plants. The plants incorporate the sulfur into four different kinds of chemical ammunition, which float in the cell fluids while their enzyme trigger is held separately in a storage vacuole. When we cut the onion, we break the cells, the enzyme escapes, and breaks the ammunition molecules in half, which produces irritating, pungent sulfurous molecules. These are very unstable and reactive and continue to evolve into other compounds.The sulfur product produced in onions that is responsible for making us cry is the “lacrimator.” This highly volatile chemical is released into the air, and lands in the onion cutter’s eyes and nose, attacking nerve endings directly, then breaks down into hydrogen sulfide, sulfur dioxide, and sulfuric acid, which cause our eyes to water, to wash away the irritant.
  1. How can we ripen the avocados quickly?
    To ripen an avocado, we can place the fruit in a plain brown paper bag and store at room temperature until ready to eat (usually two to five days). Including an apple or banana in the bag accelerates the process because these fruits give off ethylene gas, a ripening reagent.
  1. Once the avocados are ripe, how can we extend its shelf-life?
    Once ripe, avocados can be stored in the fridge uncut for two-three days. If storing cut fruit, sprinkling it with lemon or lime juice or white vinegar and placing in an air-tight container should prevent it from browning too much and can be stored for a few days. If refrigerated guacamole turns brown during storage, discard the top layer.Pureed avocados freeze very well, and can be used in salads, sandwiches and dips. To freeze an avocado, wash, seed, and peel the fruit. Puree the flesh, adding one tablespoon of lemon juice for each two pureed avocados. Pack the purée into an air-tight container, leaving one inch of space. Seal and label the containers. Freeze and use within four to five months.
  1. What is the name of the pigment in avocados which has been attributed to have health benefits?
    Carotenoids, such as lutein, are among the main pigments found in avocado. According to research, avocados are the highest fruit source of lutein, and can help prevent age-related eye diseases such as cataracts.

Salsa Questions:

  1. What makes peppers taste hot?
    From Margen, S. et. al (1992).The wellness encyclopedia of food and nutrition: How to buy, store, and prepare every variety of fresh food. Distributed by Random House. ISBN 0-929661-03-6.
    All hot peppers contain capsaicinoids, natural substances that produce a burning sensation in the mouth, causing the eyes to water and the nose to run, and even induce perspiration. Capsaicinoids have no flavor or odor, but act directly on the pain receptors in the mouth and throat. The primary capsaicinoid, capsaicin, is so hot that a single drop diluted in 100,000 drops of water will produce a blistering of the tongue.Capsaicinoids are found primarily in the pepper’s placenta–the white “ribs” that run down the middle and along the sides of a pepper. Since the seeds are in such close contact with the ribs, they are also often hot. In the rest of the vegetable, capsaicinoids are unevenly distributed throughout the flesh, so it is likely that one part of the same pepper may be hotter or milder than another. You can reduce the amount of heat in a chili pepper by removing the ribs and seeds, but you must wear gloves while doing so.Capsaicinoid content is measured in parts per million. These parts per million are converted into Scoville heat units, the industry standard for measuring a pepper’s punch. One part per million is equivalent to 15 Scoville units. Bell peppers have a value of zero Scoville units, whereas habaneros — the hottest peppers–register a blistering 200,000 to 300,000. Pure capsaicin has a Scoville heat unit score of 16 million.
  1. What is the molecular mechanism for how we perceive capsicum?
    The molecular Mechanism that we perceive capsaicin is that the chemical binds to vanilloid receptors on the peripheral terminals of the nociceptive neurons this then causes cation influx and action potential firing and this causes the burning sensation.
  1. What is the molecular basis for building up resistance to the hotness of the peppers?
    The molecular basis of a tolerance for capsaicin is that a small amount of the substance excites the nervous system to produce endorphins which counteract the pain.
  1. What is cilantro? What other name does cilantro go by?
    Cilantro, or coriander, is said to be the world’s most widely consumed fresh herb. Some people don’t like coriander herb due to its “soapy” aroma. The main component of the aroma is a fatty aldehyde, decenal, which also provides the “waxy” notes in orange peel. Decenal is very reactive, so coriander leaf quickly loses its aroma when heated. It’s therefore used most often as a garnish or in uncooked preparations.
  1. What are some of the medicinal uses for capsicum?
    • When applied to the skin capsicum can help reduce muscle pain by increasing local blood flow.
    • The extract, capsaicin, comes from capsicum. This is the ingredient used in many arthritis creams and ointments to relieve joint pain.
    • Capsicum not only acts as a clot buster in heart attack cases, but it also acts to aid in the coagulation, or clotting of blood, when someone is bleeding freely.
  1. How do you make tortillas?
    Tortillas are just one of the samples of the flatbreads, which are the original breads, and are still a major source of nourishment in many countries throughout the world. The essential characteristic of flatbreads is that they cook very quickly, in as little as two minutes, on a simple hot surface, like a pan, or an oven floor/wall. The heat is often very high, and this means that tiny air-pockets in the dough are puffed up by rapidly vaporizing steam, essentially leavening the dough without the necessity of fermentation. This puffing, and the breads’ thinness, make them tender; and since neither requires a strong gluten, flatbreads can be made from all kinds of grains.
  1. What are quesadillas? And why didn’t Patti give us a recipe for them?
    From Wikipedia: Quesadilla is a flour or corn tortilla filled with a savoury mixture containing cheese and other ingredients, then folded in half to form a half-moon shape. This dish originated in Mexico, and the name is derived from the Spanish word queso (cheese).Have no idea why Patti didn’t give a recipe, but I guess mostly because there isn’t really one 🙂 It’s basically your grilled-cheese sandwich, but using tortilla instead of bread.
  1. Of the peppers tested in Garcer-Claver et al, which pepper had the largest amount of Capsaicin?
    According to Pepper Guide, Habanero has the largest amount of Capsaicin.

Hot Sauce questions:

  1. What was the flavor profile of your hot Sauce? (What were the main ingredients that you used?)
    The flavor profile of my hot sauce was green chili peppers, cilantro, lemon and tomatoes.
  1. How did you make it? Did it turn out the way that you wanted it to? Why or why not?
    I diced all the ingredients finely, mixed it, and refrigerated for a few hours. It turned out nice, just the way I wanted, but next time will remove less placenta from the chilis, so it’s more hot.