Do you have any curiosity or doubts about the “calorific value” on your favorite food label? How do they know that seven biscuits are equivalent to 130 calories or a cup of tea will consume 2 calories?
In fact, there are many ways to determine the calorie value of food. The most common method is to measure the calories of each component (such as protein, fat, carbohydrate, ethanol, organic acid, etc.) in the food and then to add the value of each component. The total value is the food calories.
It is very easy to understand the principle but how do you know the actual heat contained in each component? Before answering this question, we first define “calorie”. In a word: 1 calorie is the amount of heat required to raise the temperature of 1kg (1L) water by 1℃ (for example from 14.5℃ to 15.5℃).
To get the best results we can use a calorimeter to determine the actual heat contained in the food sample. Using a pressurised oxygen vessel calibrated with a substance whose calorific value we know, we can calculate the heat rise generated by the sample.
After the food sample is burned, the calorimeter system calculates the heat contained in the food sample and hence the calorific value. All the elements that make up the food are burned and oxidized. Hydrogen produces water, carbon produces carbon dioxide, nitrogen and oxygen produces nitric acid, minerals are oxidized, etc.
Some food in the calorimeter burn faster. To control the burning speed and process, sometimes it is necessary for the sample to be special treated or to use some combustion additives, such as tablet processing, burning bags, burning capsules and combustion crucible, etc.
Since the human body does not burn food like oxygen vessel, the measurement results are relatively higher. Some food components, such as fiber which the body cannot digest and absorb when digesting food also consume some energy. A portion of the calories in the food will be converted into fat stored in the body. In addition, we also consume a lot of heat when we are working. Therefore, the processes of digestion and absorption of food in the human body are very complicated.
To determine the accurate calorie value of the food burned in the calorimeter, some necessary correction is required. For example, scientific researchers measure calorific values of some animal food and animal waste.
In this way, the effective absorption of food calorific value can be determined.