This is due to neutralisation of the charge on the hydrophobic colloidal particles.
[1] Lyophilic sols like starch and gelatin act as protective colloids.
The gold number is the weight in milligrams of a protective colloid which checks the coagulation of 10ml of a given gold sol on adding 1 ml of 10% sodium chloride.
Thus smaller the gold number, greater is the protective action.
[3] Gold numbers of some materials Gelatin 0.005-0.01 Albumin 0.1 Acacia 0.1-0.2 Sodium oleate 1-5 Tragacanth 2 [4]