Thermal Degradation of Green Asparagus Texture

A cutting cell was developed to evaluate the texture of green asparagus by measuring its resistance to being cut with a wire. The cell was used in conjunction with a universal texturometer and improved on the single-point method of the Wilder fibrometer. Experimental conditions were determined for using the cell to measure the cutting resistance of asparagus subjected to different extents of heat treatment. Better discrimination between samples was obtained than with a Kramer cell. The fresh asparagus spears. were heated at temperatures between 70 and 100°C for different lengths of time and the kinetics of the degradation of texture was studied. A biphasic (two-component) behavior was observed with each component displaying first-order kinetics, The kinetic parameters calculated by measuring the texture with the wire cell (cutting at a position 5 em from the tip of the asparagus) were E = 9.56 and E = 20.43 kcal/mol (activation energy for components A and B), and k = 1.047 and k = 0.057 min^-1 (rate constants for A and B of asparagus heated at 85°C). When the texture was determined by measuring the shear force with a Kramer cell, the parameters estimated were E = 23.41 and E = 18.32 kcal/mol, and k = 0.25 and k = 0.025 min^-1 Both the wire cell cutting method and the Kramer shear-press method are suitable for evaluating the degree of thermal softening of green asparagus heated to temperatures between 70 and 100°C.