Energy Metabolism and Food Preservation Principles

Energy Metabolism in the Human Body

In the cells of our body, a series of chemical reactions which release energy occurs. The final result is CO₂ + H₂O. CO₂ is toxic, so it is stored in the blood and expelled through respiration.

Measuring Food Energy

The energy value of the food is proportional to the energy released when food is burnt in the presence of O₂. Energy released is measured in calories. A calorie is the amount of heat required to increase the temperature of a gram of H₂O by 1ºC. Because it is very small, we use kilocalories.

Energy Sources: Sugars and Lipids

Sugars and lipids provide us with energy. We store them so as to have constantly available energy. Sugars are stored in the liver, while lipids (fat) are stored in various parts of the body. Lipids provide more than double the energy of sugars: 1g of sugars provides 4 kcal when burnt, whereas 1g of lipids provides 9 kcal. It is more advantageous to use lipids as an energy reserve in the medium and long term. Both types should be in our diet in correct quantities; an excess of kcal leads to obesity.

Principles of a Balanced Diet

A good diet is complete and balanced, using foods from all the groups in the correct amount. The criteria for a healthy diet include:

• Food should provide just the right amount of energy for carrying out our activities and our development. Both excess and defect are bad.
• Supply sufficient proteins, vitamins, and minerals.
• Proper distribution of foods which provide energy: sugars (55-60%), lipids (60%), and proteins (15%).

Eating Disorders and Health Issues

Disorders include excess (especially of energy-rich food) leading to obesity. The organism transforms the excess into fats, and the excess of fats in tissues causes obesity. However, this problem is also caused by problems in the endocrine system. Lack of food leads to extreme thinness, often of psychological origin, such as anorexia (rejecting food) and bulimia (eating without control and then vomiting).

Food Spoilage and Microorganisms

Fungi: These grow in food, leading to the appearance of mould. When fungus grows, it means the food is useless for consumption. Bacteria: They are everywhere and cause food rotting, a natural transformation and degradation process of proteins through the action of bacteria. This causes bad-smelling substances which warn us that the food is altered. Other bacteria can make wine bitter.

Traditional and Industrial Food Preservation

Traditional Methods

Traditional methods include drying, salting, and smoking. While not useful for all foods, they are a good solution for keeping food in good condition for a long time (e.g., cod dried and salted, ham salted, salmon smoked). These methods prevent the action of microorganisms.

Temperature Control

Refrigeration: Keeping food in a cold environment. At low temperatures, the action of bacteria and fungi is slowed down. Certain foods should be kept in the refrigerator if they are to be kept for many days. Freezing: More effective than refrigeration. Domestic freezer temperatures are around -10ºC. The action of microbes is detained almost completely. Frozen foods can be kept for long periods provided that the cold chain is not interrupted. If a food defrosts, it cannot be frozen again; it must be eaten immediately or thrown away.

Industrial Preservation and Additives

Additives: Substances added to food in small quantities following health standards. Their function is to improve appearance and flavor, or act as preservatives to make food last longer (the most common is salt). Sterilization: Killing microorganisms in food. For example, pasteurization is applied to milk by heating it to 80ºC for 30 seconds, which kills 99.5% of germs.

Understanding Expiration Dates

Use by date: After this date, you must not eat the food. Best if used by: This is the limit before the food can start being bad. It can still be consumed, although some characteristics may have changed, such as smell or taste.