A fracture mechanics analysis of the texture of fried potato crust

Texture is critical to french fry quality. Because french fries possess a composite structure, textural optimization during processing must focus on adjusting the texture of both the interior and the crust. The aim of this work was to investigate the effect of fry time on the mechanical properties of the fried potato crust. Slabs of processed potatoes were fried for varying lengths of time, frozen, and thawed. Fracture stress, fracture strain, elastic modulus, and fracture toughness values were obtained from excised crust specimens using a tensile test. Generally, elastic modulus increased as fry time increased while fracture strain and fracture toughness decreased. Fracture stress and elastic modulus were in the range of 100 kN m(-2) and 2 MN m(-2), respectively, while fracture strain was low for a food material (2-7% strain). Two techniques were used to measure fracture toughness: a brittle fracture technique and Andrews' generalized fracture mechanics approach. Fracture toughness measured by the former technique was of the order of 10 J m(-2). As length of fry time increased the crust material changed from a ductile or pliant material to a more brittle material, in line with reported sensory studies on the development of crispness during frying. (C) 2003 Elsevier Ltd. All rights reserved.