Water content, one of the most important properties of food

Water is present in practically every foodstuff. The water content has sign ificant importance for a number of reasons. The determination of water cont ent is therefore the most frequent general analysis performed on foodstuffs . A survey of the most widely used methods is given. They are classified in to direct and indirect methods. Direct methods aim at the determination of the water as such. The physical techniques among them are based on a separa tion of the water. Heating techniques which measure a mass loss under certa in conditions are principally problematic as they cannot distinguish betwee n water and other volatile matter. Chemical direct methods are based on a c hemical reaction of the water molecules. The most important technique is th e Karl Fischer titration. Indirect methods can either measure a property of the sample that depends on the water content, or they observe the response of the water molecules to a physical influence. The latter group comprises the use of low-resolution nuclear magnetic resonance, near infrared spectr oscopy and microwave techniques. These extremely rapid methods need a very product specific calibration against a reference method, because water mole cules in different bonding situations may behave differently. (C) 2001 Else vier Science Ltd. All rights reserved.