In wine it indicates the available nitrogen for yeast and is known as YAN (Yeast Assimilable Nitrogen).

In fruit juice it indicates fruits quality, regarding maturity and ripeness, but it is also an indicator of juice adulteration.

In fact, almost every fruit product has its own index, so a big difference in this value may indicate a dilution with water or a mix with another fruit product.

The official method of analysis is described by International Fruit and Vegetable Juice Association (IFU) and is known as IFUMA30. The principle is the following.

Upon addition of formaldehyde (from which the method takes its name), one H⁺ ion is liberated per molecule of amino acid. This is titrated against sodium hydroxide solution.

When formaldehyde (CHOH) is added, it reacts with amino (–NH₂) group. Then, one H⁺ ion is liberated per molecule of amino acid and is titrated with sodium hydroxide (NaOH).

The same principle is applied for ammonia.

The total volume of NaOH consumed is proportional to amino nitrogen. This procedure involves toxic reagents, in fact formaldehyde is carcinogenic, dangerous for skin, eyes, respiratory tract and environment. Also, sodium hydroxide is irritating and corrosive. Moreover, this protocol is manual, complex and time-consuming.

Molecules in the sample containing PAN react with o-phthaldialdehyde (OPA) and with a reducing agent in a basic medium generating a chromogen which can be measured spectrophotometrically.

And ammonia is determined enzymatically using the glutamate dehydrogenase (GLDH).

This protocol assures a precise and automated quantification of PAN and ammonia, and consequently of Formol Number, and it is a faster, safer and easier solution.