Carbohydrates and food : physical-chemistry aspects

Carbohydrates, a vast biochemical family, are a category of nutrients that make up an important part of our diet. They are the main source of carbohydrates in the majority of human diets. Some are of natural origin, such as sucrose, commonly known as sugar, and produced by sacchariferous plants. While the main low-cost industrial sources are sugar cane (Saccharum robustum, officinarum...) and beet (Beta vulgaris altissima L), sugars are also extracted from fruit (grapes, apples, melons...), from the sap of a particular variety of maple (Acer saccharum), and from leaves (Stevia Rebaudiana). Initially, only sucrose was used as a basic foodstuff. Then it was the turn of native starch, a reserve carbohydrate extracted mainly from corn, to enter the consumer goods market. Then, over time, as science and technology progressed, mankind, armed with new knowledge of carbohydrate chemistry, developed the extraction and purification of other carbohydrates, such as lactose, fructose and glucose, and developed derivatives such as modified starches, polyols and so on.

Often misleadingly referred to as sugars, and the source of numerous derivatives, carbohydrates constitute a remarkable and complex biochemical family that is difficult to define precisely. Indeed, while most publications agree on the degree of polymerization as a criterion for classifying carbohydrates, the bibliography on carbohydrates offers several non-consensual classifications (WHO/FAO in 1998, Dobbing in 1989 and Lehninger in 1981).

The main sources and routes for obtaining carbohydrates and their derivatives are discussed briefly and synthetically in this article, using illustrations to highlight the diversity of the technologies used and the products obtained. Only two examples are developed, namely fructose and lactose.

Next, a biochemical study provides an overview of the many substances that make up the large family of carbohydrates and their derivatives.

The properties of carbohydrates are then examined. Firstly, the main physical properties are reviewed, with particular emphasis on one very important aspect: crystallization, an operation at the heart of sugar extraction and purification technology. Secondly, the main biochemical properties are discussed, with particular emphasis on non-enzymatic browning reactions, which are sometimes avoided because of their harmful effects on the desired product quality, and sometimes induced to modify the color and flavor of certain foodstuffs... Finally, sensory and cognitive properties are addressed.