Dimensional Effects on the Prediction of Texturerelated Mechanical Properties of Foods by Indentation

Indentation is a convenient method for evaluating food texture. However, results obtained are empirical and areinfluenced by various testing conditions as well as product dimensions. The present work is aimed at studying the variabilityin the values of fundamental mechanical properties (the Youngs modulus and failure stress) obtained by indentation ofspecimens of different dimensions. To establish a valid comparison, the value of Youngs modulus and failure stress were alsodetermined by compression. A model food system was created by using 1% agar gel fashioned into specimens of three differentdimensions. Flat cylindrical indenters of seven different radii were used for indenting the specimens. To make use of theequation for frictionless elastic indentation, Poissons ratio was also determined independently under compression.Mechanical properties for different experimental conditions were compared. Differences were seen depending on the ratioof depth of the specimen and indenter radius. Under halfspace conditions (for specimen dimensions and indenter radius),values obtained by indentation for Youngs modulus were larger but compared reasonably well with the value obtained bycompression. Values for indentation failure stress were substantially higher than compressive ones, presumably due to elasticconstraint of the yielding region. It was concluded that experimental conditions can be chosen so that Youngs modulus andfailure stress derived from indentation tests can be used reliably to evaluate food texture.