Water sorption isotherms of foods and foodstuffs: BET or GAB parameters?

The aim of the present work is to solve the dilemma about the differences b etween the values of the monolayer and the energy parameters obtained by th e regression of water sorption data by foods and foodstuffs using the Bruna uer, Emmett and Teller (BET) two-parameter isotherm or the Guggenheim, Ande rson and de Boer (GAB) three-parameter isotherm. It is shown that the GAB v alues are more general and have more physical meaning, and that the two BET parameters can be calculated in terms of the three GAB-parameters. Further more, the marked dependency of the BET constants on the regression range as well as the typical upswing at higher water activities observed in the so- called BET plots are explained. It is also shown that the rough agreement e arly reported by L. Pauling, J. Am. Chem. Sec. 67 (1945) 555-557 between mo nolayer values and number of polar groups in the aminoacid side chain in se veral proteins is enhanced if the former are evaluated by means of the GAB sorption equation. (C) 2001 Elsevier Science Ltd. All rights reserved.