LOW-FREQUENCY ULTRASONICS FOR TEXTURE MEASUREMENTS IN CARROTS (DAUCUS-CAROTA L.) IN RELATION TO WATER-LOSS AND STORAGE

The use of low frequency ultrasonics for evaluation of carrot texture was studied. Carrots were pretreated for 24 h in distilled water and e ither dried at 25 degrees C for periods from 0 to 320 min or stored at 100 or 97% relative air humidity for 19 weeks. Uniaxial compression, microscopy, and analyses of density and dry matter provided results fo r evaluating relationships between texture and ultrasonic parameters. The loss of water from turgid carrot tissue did not cause significant change in compressive Young's modulus (E-CY) and fracture work (J). Th e results indicate that the preliminary loss of water caused a decreas e in compressive E-CY and J. At a water loss > 5%, the results indicat e an increase in compressive E-CY and J. The loss of water in the dryi ng experiment had only a small effect on the velocity (nu) and attenua tion (alpha) of ultrasound. The results indicate at the beginning of t he drying period an increase in nu and decrease in alpha. This was fol lowed by a decrease in nu and increase in alpha. E-CY decreased, while strain (epsilon) at failure increased during the storage period, espe cially after storage at low humidity. Studies with scanning electron m icroscopy and light microscopy comparing fresh and stored tissue indic ated that low humidity induced shrinkage of the cell content, changes in wall structure and development of intercellular air spaces. The nu of ultrasound decreased during storage at low humidity contemporary wi th changes in the mechanical and microstructural properties. (C) 1998 Elsevier Science B.V. All rights reserved.