Food preservation
All martian colonists will require food, either brought from Earth, or grown in greenhouses on Mars. To ensure a reliable supply of food, food production should exceed the minimum required by a substantial margin. The excess food can be stored for future need through food preservation techniques.
Environment Manipulation
Freezing is the most cost effective preservation method, due to the ambient external temperature. Food could be stored in containers external to the colony. Refrigeration requires the maintenance of food temperature between freezing and 48 degrees Farenheit. This technique is more complecated than freezing, and requires energy input and control to maintain correct temperatures. Dehydration would require a method of removing the moisture from food. Freeze Drying combines freezing with dehydration. The low ambient pressure could be harnessed for this preservation method.
Chemical Preservation
Salt has been used for millenea to preserve meats. It inhibits the growth of microorganisms that could spoil the food or cause sickness.