Characteristics of cereal starch granules surface using nitrogen adsorption Leslaw Juszczak a, * , Teresa Fortuna a , Krystyna Wodnicka b a Department of Analysis and Evaluation of Food Quality, University of Agriculture, 29-Listopada 46 Avenue, 31-425 Krak ow, Poland b Department of General Ceramics, Academy of Mining and Metallurgy, Mickiewicza 30 Avenue, 30-059 Krak ow, Poland Received 12 January 2001; accepted 25 September 2001 Abstract Surfaces of several types of cereal starch granules are investigated using low-temperature nitrogen adsorption. The specific surface, the volume of mesopores and the mean pore diameter are determined using the BET method. Furthermore, pore size distribution, cumulative surface area, volume and mean pore diameter in the range 1.7–300 nm are determined using the BJH method.Surfacecharacteristicsandporecharacteristicsforvariouscerealstarchgranulesarefoundtobedifferent. Ó 2002Elsevier Science Ltd. All rights reserved. Keywords: Starch; Nitrogen adsorption; Pore and surface characteristics 1. Introduction Solid bodies have complex surface structure con- taining pores of various shapes, their size ranging from less than 1 nm to several micrometers. Within such structuresonecanfindclosedandopenendpores–that is those connected to the external surface of the mole- cule. The presence of closed pores in a solid body im- pacts on its density, mechanical strength and heat transfer processes, yet is of no importance for adsorp- tionorliquidflowprocesses.Openporescanbedivided into those open at one or both ends. Because of their shapes,porescanbedividedintocylindrical,conicaland bottle-shaped ones. Major parameters describing the solid surface (Low- ell & Shields, 1991) are: specific surface area, total pore volume, mean pore radius (diameter) and pore volume distribution in relation to pore radius (diameter). Pore size limits are not precisely defined and are mostly arbitrary, depending on actual methods of pore structure analysis, on pore shapes and type of surface processes (Laso n, 1988; Paderewski, 1999). One of the most widely applied classifications is the one proposed by IUPAC (Meyer, Lorenz, R€ ohl-Kuhn, & Klobes, 1994; Sing et al., 1985) which distinguishes: micropores (sometimes also sub-micropores) which are filled with adsorbed substance during adsorption, meso- pores (transition pores) on the surface of which mono- molecular and polymolecular adsorption takes place and where capillary condensation is also possible, and macropores where the adsorbed substance is trans- ported from the granule surface to pores of smaller diameter. The distribution of pore volume in the function of pore radius shows how the given group of pores con- tributes to the total porosity of the system. Porosity is definedastheratioofporevolumetogranulevolume.It is usually obtained by measurements of true and ap- parent true density (Paderewski, 1999). The specific surface can be used as a measure of surfaceactivityofvariousstarchgranules.Development of the specific surface depends on size, shape and po- rosity of granules. In relation to processes taking place at phase boundaries: solid–gas, solid–liquid, the specific surface is understood as the surface accessible to gas or liquid molecules and encompasses the external surface of a solid body as well as its internal surface produced by its porosity. It is defined as the actual surface of the adsorbent per unit mass and is usually expressed in m 2 =g. The specific surface area and the mean pore ra- dius are inversely proportional. A large specific surface indicates the presence of small pores while small values Journal of Food Engineering 54 (2002) 103–110 www.elsevier.com/locate/jfoodeng * Corresponding author. Fax: +48-12-411-77-53. E-mail address: rrjuszcz@cyf-kr.edu.pl (L. Juszczak). 0260-8774/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0260-8774(01)00190-X