Answer to Question 1
Browning occurred due to the Maillard reaction.
Answer to Question 2
When working with meat the main precaution is preventing the introduction of bacteria into the ground meat. Equipment should be sanitized. Always keep meat refrigerated (36 to 40F) while curing. Those working with meat need to wear food service gloves. Finally, the product needs to be thoroughly cooked and to the correct temperature and then stored properly afterward.