What component of total nutrient admixture should be added last before storing in a refrigerator?

The component that should be added last to a total nutrient admixture (TNA) before storage in a refrigerator is typically the lipid emulsion. This is because lipids can destabilize the mixture and lead to phase separation if added too early. By adding the lipid emulsion last, the stability of the admixture is maintained, ensuring proper nutrient delivery and reducing the risk of complications when the TNA is administered.