ABSTRACT
This chapter describes the order in carbohydrate catabolism pathways, starting from lactose and finishing with d, l-lactate. Inside the cell, galactose is metabolised by the Leloir pathway, rendering glucose-6P, while galactose-6P generated by the phosphotransferase systems enters the tagatose-6P pathway, yielding glyceraldehyde-3P that is incorporated to the glycolysis. In these procedures, glucose from lactose can be phosphorylated by hexokinase in the presence of ATP and then enzymatically oxidised through a coupled reaction with glucose-6P dehydrogenase. Lactose determination through the differential pH procedure also uses enzyme reactions. In the case of glucose determinations, a coupled enzymatic reaction is used where hexokinase phosphorylates glucose to glucose-6P, which on turn reacts with glucose6P dehydrogenase and NAD to form NADH that can be quantified as described above, as its formation is stoichiometric to the amount of glucose in the sample. Medium-infrared, near-infrared and Raman spectroscopy constitute powerful systems for quality control in food and specially in dairy products.
