The Effects Of Added Sugar In Fruit Juice On Ph

The pH measures the basicity or acidity of a solution on a scale that runs from 0 to 14. At room temperature, solutions with a pH of 7 are considered neutral. Most, though not all, fruit juices have an acidic pH owing to the composition of the fruits used to make them. Adding sugar to fruit juice will not change its acidity or pH.

Acidity

Sucrose, glucose and fructose are more acidic than ordinary alcohols, but they are not considered acids or bases because -- like other alcohols -- their acidity is too weak. Chemists often measure the acidity of a compound using a number called the pKa; the lower the pKa, the more acidic the compound. The pKa of glucose is about 12, meaning that in a 10 percent solution of glucose at pH 7, fewer than 1 in 100,000 glucose molecules has donated a hydrogen ion to the surrounding water molecules.

Acidic Solutions

Increasing acidity ensures that an even more negligible fraction of the glucose molecules present lose a hydrogen ion or become deprotonated. In a 10 percent solution of glucose at pH 3, for example, fewer than one in a billion glucose molecules would be deprotonated at any given time. Ultimately the contribution to the pH of the solution is so negligible that it would be difficult to measure it directly. The same is true of other sugars; while they can act as acids and bases, their acidity and basicity is so weak it makes no difference to the pH of fruit juice.

Fruit Juice

Many fruit juices already contain a variety of compounds that have far more significant effects on pH than glucose or sucrose. According to the United Nations Food and Agriculture Organization, compounds like citric acid, tartaric acid, malic acid and ascorbic acid are found in fruits at concentrations ranging from trace values to three percent of fresh weight. Citric acid can donate up to three hydrogen ions to water; the pKa for the first is about 3, making citric acid roughly 9 orders of magnitude more acidic than glucose.

Lactic Acid

Adding sugar doesn't have a significant effect on the pH of your juice. It can, however, encourage tooth decay via an indirect effect that involves pH. Sugars like sucrose are an ideal food for many of the bacteria that live in your mouth. When they ferment these sugars, these bacteria produce lactic acid as a byproduct, and since the bacteria grow in crevices on and around your teeth, the acid they release can eat away at your enamel over time.