Hydroxides are ionic compounds containing the hydroxide ion ($OH^-$), and while they don't occur naturally in most raw foods, specific metal hydroxides are frequently used as food-grade additives. The use of hydroxides in food processing is regulated and has a long history, improving the texture, flavor, and shelf-stability of many products. The key is understanding which types are used and for what purpose.
Calcium Hydroxide (E526): The Traditional Additive
One of the most common food-grade hydroxides is calcium hydroxide, also known as pickling lime or slaked lime. Its applications are extensive and sometimes trace back centuries, particularly in traditional cooking methods.
Nixtamalization of Corn
The most prominent example of calcium hydroxide's use is in the nixtamalization process for corn, which is essential for making products like tortillas, tamales, and masa. Soaking corn kernels in a calcium hydroxide solution helps to:
- Soften the kernels for grinding.
- Remove the hull.
- Significantly increase the bioavailability of niacin (vitamin B3), preventing deficiencies like pellagra.
- Improve the flavor and aroma of the corn products.
Pickling and Firming
Calcium hydroxide is also used as a firming agent in pickling to give vegetables like cucumbers and bell peppers an extra crisp texture. In this process, the calcium ions react with pectin in the cell walls, strengthening them and preventing the vegetables from becoming soft during processing. However, home canners must be careful to rinse the produce thoroughly to avoid neutralizing the acidic brine necessary for preserving the pickles and preventing botulism.
Sugar Processing
During sugar refining, calcium hydroxide is added to sugarcane or sugar beet juice to remove impurities in a process called carbonatation.
Additional Uses
Calcium hydroxide is used as an acidity regulator and fortifying agent in other foods, such as processed fruit, milk products, and infant formulas.
Sodium Hydroxide (E524): The Caustic Additive
Sodium hydroxide, or caustic soda (lye), is a stronger base than calcium hydroxide but is still approved as a direct food additive under strict regulations. Its primary function is as a pH control agent and processing aid.
Peeling Fruits and Vegetables
Sodium hydroxide is used in industrial settings to quickly and efficiently peel fruits and vegetables like potatoes, tomatoes, and peaches. This chemical peeling method saves time and reduces waste compared to manual or mechanical peeling.
Dutch-Processed Cocoa
Dutch-process cocoa is treated with an alkaline solution, often including sodium hydroxide, to reduce its acidity. This darkens the cocoa powder and mellows its flavor, creating a less bitter and richer taste.
Pretzels and Bagels
Traditional Bavarian-style pretzels and bagels are dipped in a sodium hydroxide solution before baking. This gives them their characteristic shiny, brown, and crispy crust. The high alkalinity is what creates this unique texture.
Curing Olives
Sodium hydroxide is used to cure olives and remove their natural bitterness from compounds like oleuropein. This process makes them palatable and ready for consumption.
Magnesium Hydroxide (E528): A Nutritional Fortifier
Magnesium hydroxide is used as a food-grade additive for its ability to regulate acidity and also as a source of the essential mineral magnesium.
Acidity Regulation and Fortification
It is used in foods like citrus juices and fortified cereals to adjust pH levels while also boosting their magnesium content.
Anti-Caking Agent
Magnesium hydroxide can also be used as an anti-caking agent in powdered foods, such as dry mixes and milk powder, to prevent clumping.
Comparison of Common Food-Grade Hydroxides
| Feature | Calcium Hydroxide (Ca(OH)2) | Sodium Hydroxide (NaOH) | Magnesium Hydroxide (Mg(OH)2) |
|---|---|---|---|
| Common Name | Pickling Lime, Slaked Lime | Caustic Soda, Lye | Milk of Magnesia |
| E-Number | E526 | E524 | E528 |
| Primary Use | Firming agent, pH regulator, nixtamalization aid | Chemical peeling, pH control, browning agent | pH regulator, anti-caking agent, fortifier |
| Example Foods | Tortillas, pickles, canned peas, sugar | Dutch-process cocoa, pretzels, olives | Fortified cereals, juices, powdered mixes |
| Safety in Food | Generally recognized as safe (GRAS), with care required for home canning. | Safe at regulated food-grade concentrations; corrosive in pure form. | Generally recognized as safe (GRAS); also used in antacids. |
Natural Alkaline Compounds vs. Added Hydroxides
It's important to distinguish between processed foods that contain added hydroxides and natural foods that create an alkaline effect in the body. Raw fruits and vegetables, despite containing organic acids like citric and malic acid, have a high mineral content (like potassium and magnesium) that contributes to an alkaline load upon digestion.
Alkaline-Rich Foods
- Fruits: Watermelon, dates, raisins, grapes.
- Vegetables: Green leafy vegetables, celery.
- Legumes: Most legumes are considered highly alkaline.
These foods do not contain added hydroxides but are beneficial for maintaining the body's acid-base balance.
Conclusion
While the word 'hydroxide' might sound intimidating due to its association with strong chemical compounds, food-grade hydroxides like calcium, sodium, and magnesium hydroxide are safely used in regulated quantities to produce many common foods. They serve vital roles as acidity regulators, firming agents, and processing aids, contributing to the texture, taste, and safety of a wide range of products from corn tortillas and pretzels to canned vegetables and fortified cereals. Consumers can rest assured that the use of these additives in commercially processed foods is overseen by regulatory bodies to ensure they are safe for consumption when manufactured correctly.
