Chemical properties of food are those properties that cannot be measured without altering the chemical composition of the food material. For example, measuring the water content of food require that the water is removed, which ultimately changes its chemical makeup. Important chemical properties of food are briefly described below.  

Moisture Content

Moisture content is an important test done in the food industry since it may affect spoilage rates, texture, palatability and product cost. For example, high moisture content is likely to increase spoilage rates due to higher chemical and microbial activity. Lack of water can cause such textures as, hardness, crumbliness, and gumminess where they are not desired, or may provide improved palate-enhancing textures such as tenderness, softness and smoothness. Foods with higher moisture content are more costly to transport, hence they may increase product cost. 

Moisture content is generally determined using a convection oven or a rapid moisture analyzer. They essentially follow the same principle. That is, the food is heated and moisture is removed, creating a weight difference between the initial and final sample. Use the following equations when working with moisture and moisture-related problems.  

pH

The term pH stands for potential hydrogen. It represents the relative basicity or acidity of a substance to other substances based on the amount of hydrogen present in the solution. Its value ranges from 1 to 14. This is a logarithmic scale which means that each graduation is 10 times larger than the previous. Hence the difference between a pH of 5 and 7 is not two, but 100. A pH of 7 is neutral (neither acidic nor basic) e.g. water. Below 7 is acidic and above 7 is alkaline. Some foods such as mayonnaise, ketchups and other sauces must be prepared at a pH of 3.4 or less in order to prevent the growth of dangerous bacteria that will make you sick. Hence, managing pH is critical to food safety. In addition, controlling pH can also adjust the taste of the food. That is because certain foods taste better when they are acidified. In the case of jam and jelly production, apart from providing a sour taste, pH is also essential in creating its gel-like structure. 

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The pH Scale

Acidity

Acidity is the percentage of acids present in the food. While pH provide you with information on the relative amounts of acids present, taking the acidity of a food material will tell you exactly how much acid is present. Acidity is caused by the presence of acidic compounds in food. These acids play a significant role in providing the degree of sourness of the food, which can modify flavor and aroma. Examples of common acids in food include:

  1. Citric acid in citrus fruits  
  2. Ascorbic acid (vitamin C) in broccoli and green peppers
  3. Lactic acid in yogurt
  4. Malic acid in apples
  5. Acetic acid in vinegar
  6. Tartaric acid in grapes
  7. Phosphoric acid in carbonated sodas

Flavor Compounds

Flavor compounds or odorants, are the volatile chemical components that enable you to get more enjoyment while eating. As you chew your food, flavors escape and enter your nasal cavity where they are detected by olfactory nerves which transfer the data to the brain for interpretation. Many flavor compounds are formed during the maturation and ripening stage of fruit development which is why fruits taste better when they are ripe. Although major aromatic compounds in a food can play a significant role in the final flavor, the overall flavor experience is typically due to many flavors combined. Therefore isolating flavors and adding them to food may not give you the same sensory experience as when it is in the natural form. Examples of flavor compounds include:

  1. Menthol in peppermint
  2. Cinnamaldehyde in cinnamon
  3. Citral in lemon grass
  4. Vanillin in vanilla
  5. Limonene in citrus 

Keep in mind that not all flavors are liked. Some can be very awful and off-putting for example:

  1. Methanethiol: Smells like rotting cabbage smell
  2. Hydrogen sulfide: Smells like rotten eggs
  3. Putrescine: Smells like rotten meat

Pigments

Pigments are the compounds in food that gives them their color. For example, vegetables are green due to the presence of chlorophyll. Apart from green, food comes in all the colors of the rainbow. Each of these colors is due to a pigment or the combination of pigments in the food. Common pigments include

  1. Anthocyanins: Gives red cabbage and black beans their red and dark color respectively 
  2. Carotenoids: Gives carrots, mangoes and cantaloupes their yellow color  
  3. Betanins: Gives beetroot its red color 
  4. Curcumins: Gives tumeric its yellow color
  5. Carmine: Gives a red color to processed foods 
  6. Myoglobin: Gives meat its red color 

Changes in the color of food is due to changes in the structure of the pigment during processing. For example, anthocyanins are sensitive to pH, ranging from red in acid to blue in basic environments. Myoglobin is sensitive to oxygen. In high oxygen it is pink (oxymyoglobin), in low (1%) oxygen (metmyoglobin) it is brown and is purple when oxygen is absent (deoxymyoglobin).

Enzymes

Enzymes are proteins that speed up the rate of chemical reactions. Humans, animals, plants and all life forms need them to support life. Without enzymes we could not eat, breath, move or digest food. In food they are responsible for countless biochemical reactions including growth, maturity and decay. As enzymatic activity increases, foods tend to decay and spoil faster. Therefore food processing activities such as cooking, freezing, and acidification (adding acid) are essential in controlling their activity. Enzymes are used in certain food processing operations, for example, beer and cheese making. Yes, I know that yeast and bacteria are normally given the credit for these respective processes, however it is really the enzymes in the yeast and the bacteria that does the work. In some food processing operations, the pure enzymes is used. For example,

  1. Amylase: Used to convert starch to glucose in bread to give it a softer texture and improved moisture retention 
  2. Glucose isomerase: Used to convert glucose to fructose in the production of corn syrup
  3. Pectinase: Added to juice pulp to soften it and aid in juice extraction
  4. Papain (from the latex of the green papaya), and bromelain (from pineapple root): Used to tenderize meat 

Enzymatic activity is mainly driven by the following factors: 

  1. Enzyme concentration: How much enzyme if present
  2. Substrate concentration: How much material (substrate) the enzyme has available to breakdown
  3. Temperature: If the temperature is too low, enzymes will slow down their activity, and they may be denatured and deactivated if the temperature gets too high 
  4. pH: A pH that is too high or too low will denature enzymes and stop activity
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Courtney Simons
Courtney Simons
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Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.