Continuing my discussion of pH, with acids and bases. Some important background information:
In food, both the acidity and the sugar content are important. Our taste responses comes from a balance of the two. Some foods have a low pH/high acidity but do not taste sour due to their high sweetener content. A good example of this is cola, which has pH ~3.50 but does not taste sour because of the high sweetener (or non-calorific sweetener if you drink diet) content.
An acid solution occurs when the pH is less that 7 and an alkaline solution is when the pH is above 7. You may have heard of something called litmus paper. This is a quick and dirty method to determine pH. Typically litmus paper turns red in acid and blue in alkali. Additionally, acids typically taste sour and bases taste bitter. If it helps, compare the taste of lemon juice with that of sodium bicarbonate. Lemon juice is an acid solution; it actually contains several acids; with pH 2.2. A solution containing just sodium bicarbonate (5% solution) should have a pH 8.6.
There are several different definitions of acids and bases that are still useful and practical. Arrhenius defined an acid as a proton donor and a base as a compound that donates hydroxyl ions (OH–).
The reactions would look like this:
Acid (AH) —->; A– + H+
Base (BOH) —->; OH– + B+
This was alter by Brønsted-Lowry theory of acids and bases, which kept the same definition for acids, but the definition for bases changed to:
Bases are proton acceptors
Any previously defined acid and base will count as a Lewis acid or base, but there are some compounds that are only Lewis acids or bases.
During food processing it is important to maintain the pH and/acidity. Partly because bacteria cannot grow in a high acid environment. If the pH changed during processing, this would change the way the final product would have to be stored. One way pH is maintained in food and in our bodies, is through buffers. The success of buffers is dependent on the fact that certain acids are weak acids and do not fully dissociate to protons and relevant ions. This will be the topic of my next post on basic concepts.
Introductory Chemistry: Acids and Bases
Background on acid-base reaction theories