In The Buff…What are pH buffers and how do they work in food?
Rebekah Fine – Quality Assurance Specialist
A pH buffer is a solution that essentially can maintain the pH of a substance at a constant level. This is essential in food and beverages to maintain the appearance, function and taste of the product. The acidity of food is a measure of the concentration of hydrogen ions within the food product. To understand what pH buffers different foods and drinks need, it is important to understand how they work at a basic level. Let’s say as below, we have a neutral solution with pH 7 with some universal indicator. There is no buffer in this solution (coloured green for neutral) If we added H+ ions which indicate an acid – the solution would turn acidic (indicated by red). Conversely if we added OH- ions which indicate a base – the solution would turn basic (indicated by purple)
Left to Right: Acid H+, Neutral pH7 and Base OH-
Now, what happens when we add H+ ions (acids) or OH- ions (bases) to the neutral solution that has a pH buffer in it like below ? The solution stays the same pH. The pH doesn’t shift to basic or acidic like it did above. The solution containing the buffer is able to resist the action of the H+ or OH- ions to a certain degree. If an enormous amount of acid or base was added, it would not be able to resist but when a small amount is used it can maintain the pH steady.
|The Solution stayed at pH7|
The Solution stayed at pH7
Why does this happen? To understand the concept we must first understand what makes a solution basic Vs. acidic. The more H+ ions in a solution, the more acidic the solution will be. Equally the more OH– ions, the more basic the solution will be. Measuring the free H+ ions and OH– ions determines the pH of the solution. The pH buffer is made up of a weak acid and its conjugate base. A weak acid is known as HA. HA dissociates to H+ and A-. The H+ makes it an acid and the other part, A- is just what makes up the rest of the weak acid. However, since this is a weak acid, the equilibrium shifts to the left side meaning it does not create a lot of A- and H+ ions (ie. It does not make the solution very acidic).
HA ⇌ A− + H+
So now we know there’s a weak acid in the pH buffer, what happens when a base is added to our solution? Bases are known as OH-. When the base reacts with the weak acid in the buffer (HA) it creates water and A- which is a neutral solution. Meaning even though we added a base its still neutral due to the buffers action!
HA + OH– ⇌ A− + H2O
|Here, a base was added (OH) but our weak acid in the pH buffer (HA) combines with it to create water, which is neutral|
What about when we add an acid to the solution? Well we said previously that the buffer is made up of a weak acid and its conjugate Base. We saw above how the weak acid neutralized a base added to the solution. Now we will see how the conjugate base in the pH buffer can neutralize an acid added to the solution below. When we add an acid (H+) we need to neutralize it, we can do this by neutralizing with A–. By adding the conjugate base to the buffer ie. A salt for example NaA, it dissociates to form many A– ions.
NaA → Na+ + A-
These A– ions created from the conjugate base (NaA salt) in the pH buffer neutralizes the H+ acid ions added to the solution and they create a HA, which is a weak acid used in the buffer initially. Since this is a weak acid it wont alter the pH ie. The solution therefore stays neutral here.
H+ + A- → HA
|Here an acid was added (H+) but our conjugate base (NaA) created A- Ions to form HA with the Acid ie: The Solution stays neutral again!|
pH buffers are essential in some foods and drinks for maintaining a constant acidity in the product. Since the buffer is made up of a weak acid and its conjugate base (conjugate salt), additives such as metal salts are usually added to a food that already contains a weak acid. For example sodium citrate (salt/base) can be added to a food containing citric acid (its corresponding weak acid) which would create a buffer solution in the product. Sodium, calcium and potassium citrate are among common salt forms of food grade buffers that could be added to a product. Monopotassium phosphate is also commonly used as a pH buffer in milk and custard products as well as cooked meats. In neutral pH products the pH during the heating process is absolutely critical to prevent protein precipitation so Di potassium phosphate stops the pH slipping below the magic pH window to prevent any protein precipitation during a UHT heating step. We commonly use Tri sodium citrate to lift the pH in fruit pectin jellies to allow the best gel strength within the correct pH window of 3.6 to 3.8 whilst still maintaining a nice acidic fruity flavour. Without the citrate the pH is too low and the resulting gel is very brittle but at pH 3.6 to 3.8 it gives a lovely soft creamy gel.
When picking a buffer for a food or beverage it is important to consider the final desired pH range of the product as certain pH buffers will only work around a specific pH range. pH stability overall is a very important factor to consider for the microbiological, physical and chemical stability for any food or beverage and whilst it may not be an easy challenge to tackle, perhaps a buffer can aid your process In creating the perfect result.
Below is a selection of buffers we have on offer, or for more advice on the use of buffers and to discuss our range of ingredients, speak to one our technically qualified Sales Team
Monosodium Citrate (Sodium Dihydrogen Citrate) Nutrition Grade (~10% Na)
Trisodium Citrate Dihydrate Nutrition Grade (~34% Na)
Disodium Citrate (Disodium Hydrogen Citrate) Nutrition Grade (~19% Na)
Tricalcium Citrate Tetrahydrate Nutrition Grade (~21% Ca)
Tripotassium Citrate Monohydrate (Potassium Citrate Tribasic) Nutrition Grade 20 Mesh (~36% K)
Dipotassium Phosphate Anhydrous (Potassium Hydrogen Orthophosphate) Nutrition Grade (~44% K)
Tripotassium Phosphate Anhydrous Nutrition Grade (~55% K)