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Monday June 26 2017

A Scientist in the Kitchen

Guest blog post by Tanishq Suryavanshi

As a student in both science and culinary school, I find myself having frequent déjà vu as I attend one class after another. Like a lab, the kitchen is a dynamic system where basic principles are applied to achieve desired outcomes.

These principles come from a list of rules that nearly every chef has– and follows religiously. While most chefs develop these rules from experience, only a few are familiar with their scientific origins. My primary focus will be explaining why we follow certain guidelines when cooking vegetables.

People often laugh at the apparent simplicity of vegetable cookery. In actuality, this activity involves complex fields such as protein denaturing, organic chemistry, and cellular structure. These complicated theories gave rise to simple rules of thumb that are used to maximize qualities such as texture, nutrients, and colour.

 

Rule 1: Avoid cooking vegetables in alkaline or basic solutions.

Vegetable texture is controlled by two factors: intracellular water content and cell wall structure. High water content and well-cemented vegetable structures lead to beautifully rigid, crisp taste. During cooking, cell membrane proteins denature and cells lose selective permeability to water, thus losing water [1]. Thus, it is important to minimize other sources of structure loss during cooking.

When vegetables are placed in basic solution, their loss of rigidity is increased. The cell wall is generally “cemented” by substances such as hemicelluloses and pectins. However, when pH rises to alkaline levels, the dissolution of hemicellulose is favoured more. This creates a hollowed out cell wall structure, which, in turn, results in weakened vegetable strength and often yields unflavoured, mushy vegetables [2].

To counter natural water loss, some cooks try to boil vegetables in acidic solution, as this often decreases hemicellulose solubility [2]. On the contrary, the next rule of thumb exemplifies why this may not always be the best idea.

Rule 2: Avoid acids when cooking green vegetables.

Colour is determined by molecules called pigments. Green colour is generally caused by the very well-known pigment, chlorophyll. There are two types of chlorophyll, a and b, which both consist of a magnesium (Mg2+) ion embedded within a porphyrin ring.

When chlorophyll is placed in acidic solution, embedded Mg2+ ions are displaced from the rings by hydronium ions present in solution. This changes chlorophyll’s molecular structure and causes the pigment to emit different wavelengths of light, turning chlorophyll-a greyish-green and chlorophyll-b yellow [1]. These changes result in vegetables that are a drab olive green colour, which makes them seem much less fresh and appealing. Thus, in order to avoid problems with colour, most texts recommend using slightly acidic to neutral water.

The above examples make it evident that a proper scientific background is a huge asset in the kitchen. In an industry where many establishments serve similar meals, qualities such as texture and aesthetic appeal are what separate one establishment from another. As you can see, the true value of a scientist in the kitchen truly is immense.

Sources:

Image from http://www.kalevfitness.com/archives/which-vegetables-should-be-cooked-for-optimal-health

[1] McGee, H. (2007). On food and cooking: the science and lore of the kitchen. Simon and Schuster.

[2] Cheng, H., Zhan, H., Fu, S., & Lucia, L. A. (2011). Alkali Extraction of Hemicellulose from Depithed Corn Stover and Effects on Soda-Aq Pulping. BioRes. 6(1), 196-206.

[3] Gisslen, W. (2010). Professional Cooking, College Version. John Wiley & Sons.

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