Carbohydrate degradation/losses

Proteins are constantly being lost via the intestine and, to a lesser extent, via the kidneys. To balance these inevitable losses, at least 30 g of protein have to be taken up with food every day. Although this minimum value is barely reached in some countries, in the industrial nations the protein content of food is usually much higher than necessary. As it is not possible to store amino acids, up to 100 g of excess amino acids per day are used for biosynthesis or degraded in the liver in this situation. The nitrogen from this excess is converted into urea (see p. 182) and excreted in the urine in this form. The carbon skeletons are used to synthesize carbohydrates or lipids (see p. 180), or are used to form ATP. 

In general, it is very difficult reliably to extract and quantitate multiple vitamins from complex food systems, due to their diverse physical and chemical properties. Consequently, the extraction of the vitamins from the food matrix is usually the greatest challenge of vitamin analysis. This is especially true for the naturally occurring vitamins, which are often bound to other food constituents, such as carbohydrates or proteins. To prevent vitamin degradation or loss, the extraction conditions should complement the labile nature of the vitamins. Indiscriminate mixing and matching of extraction and quantitation methods is not recommended, since the extraction conditions can affect subsequent separation and quantitation steps. 

Moreover, we found that the viscosity loss was equally great (Table IV) when methanol, acetone, or water were used in place of dimethoxypro-pane, or even when dioxane and HC1 were used alone. (Despite large decrease in viscosity, the loss in weight of the cellulose was always only about 1-2%). If the extraction of lignin by dioxane depended only upon the breakdown of the carbohydrate, we might have expected that equal degrees of degradation would have produced more nearly equal rates of extraction, but they did not. 

---