Carbohydrate Metabolism in Cheddar Cheese. I. n-Acetylneuraminic Acid, 2-Deoxy-d-Ribose, and Phosphorylated Sugars

The persistence of free galactose in Cheddar cheese has frequently been noted, especially as related to the disappearance of lactose and glucose. However, it is known that galactose occurs in a trlsaccharide attached to casein and that ~acetylneuraminic acid is the terminal group in this sugar. Application of the very sensitive thiobarbituric acid color test revealed that there was no change in the concentration of this substance during cheese ripening. A .second sugar, tentatively identified as 2-deoxy-D-ribose, was found in some cheese samples but not in others. Tracing the origin of this sugar, it was found that it is a normal constituent of milk, although its presence has not previously been noted. Further studies of different lots of cheese suggested that during ripening there may at times be inadequate synthesis of pentoses. Consequently, several lots of cheese were analyzed to determine their content of phosphorylated metabolites and the concentrations were high in the samples from which naturally occurring deoxyribose had disappeared. The amounts of these phosphorylated metabolites demonstrated that the disappearance of free galactose is not justification for stating that the cheese is free of fermentable materials.