There are several kinds of additives in instant coffee.

Sweeteners


Non-dairy creamers


Colorants

The specific chemical structures of colorants are unknown up to now, but colorants are extensive used in order to make the instant coffee looks like the well-baked coffee beans after the Maillard reaction. Therefore, caramel color and melanin color would be added into instant coffee to make it alluring.


Food flavor

The natural flavor of coffee will run off through the process of dehydration, therefore, food flavor will be added in order to return the aroma of coffee.


Reference

  1. Capek, P., Paulovičová, E., Matulová, M., Mislovičová, D., Navarini, L., & Suggi-Liverani, F. (2014). Coffea arabica instant coffee—chemical view and immunomodulating properties. Carbohydrate polymers103, 418-426.
  2. Flament, I., & Bessière-Thomas, Y. (2002). Coffee flavor chemistry. John Wiley & Sons.
  3. How it’s Made: Instant Coffee http://coffeestrides.blogspot.com/2014/09/how-its-made-instant-coffee.html

Following Wikipedia pages have also been referenced.

  1. Caramel color https://en.wikipedia.org/wiki/Caramel_color
  2. Carbohydrates https://en.wikipedia.org/wiki/Carbohydrate
  3. Maillard Reaction https://en.wikipedia.org/wiki/Maillard_reaction
  4. Non-dairy creamer https://en.wikipedia.org/wiki/Non-dairy_creamer