Acacia seyal and acacia senegal are two types of trees from which gums for emulsion are extracted. Both grow in a narrow belt of latitude, known as the gum belt, which stretches across northern Africa to the bottom edge of Chad, including Sudan, Eritrea, Kenya, Mali, Mauritania, Niger, Nigeria and Senegal.
Most of the top-grade gum used in the beverage industry today comes from Sudan and Chad. Other countries, such as Uganda and Eritrea, are periodically developing acacia crops.
Of the two, acacia senegal yields the stronger and more-expensive emulsifier. There are far fewer senegal trees, and the tree must be tapped, or scarred, and the resulting sap harvested later. Seyal trees, on the other hand, are self exudating, that is they bleed sap all by themselves; the sap collects and falls on the ground as a nodule.
Nomad people collect sap while they're doing things such as herding goats, or going to their fields. From a formulating standpoint, it is important to understand the sourcing of gum acacia. It's difficult to tell whether it is truly senegal or seyal by looking at powders or looking at labels on bags. The amber-to-brown pieces of resin look similar, and the two molecules are very similar, with only slightly different molecular weights. One can take indirect measurements, such as making an emulsion and seeing how stable it is. This can be a pass/fail gauge. Optical rotation (OR) is typically used as the discerning test to grade one or two. In this process a polarimeter is used to observe the rotation of linearly polarized light as it travels through the sap. A strongly negative OR is an indication of grade-one material.
Unscrupulous collectors try to blend grade one with grade two to increase yield, and because it is difficult to do tests on the ground in Africa, setting up secure channels of procurement is essential.