[1] Wu, T. and Abbott, J.A. (2002) Firmness and force relaxation characteristics of tomatoesstored intact or as slices. Postharvest Biology and Technology, 59, 59-68. doi:10.1016/S0925-5214(01)00133-8
[2] Singh, K.K. and Reddy, B.S. (2006) Postharvest physco-mechanical properties of orangepeel and fruit. Journal of Food Engineering, 73, 112-120. doi:10.1016/j.jfoodeng.2005.01.010
[3] Mohsenin, N.(1986) Physical Properties of Plant and Animal Materials, second ed. Gordon and Breach, New York, USA.
[4] De Ketelaere, B., Howarth, M.S., Crezee, L., Lammertyn, J., Viaene, K., Bulens, I. and DeBaerdemaeker, J. (2006) Postharvest firmness changes as measured by acousticand low-mass impact devices:a comparison of techniques. Postharvest Biologyand Technology, 41, 275-284. doi:10.1016/j.postharvbio.2006.04.008
[5] ASAE(1993) Compression test food materials of convex shape. In: ASAE Standards. ASAE, St. Joseph, Michigan, Ch. S368.2, pp. 451-455.
[6] Delwiche, S.R. (2000) Wheat endosperm compressive strength properties as affectedby moisture. Transaction of the ASAE, 43, 365-373.
[7] Fidelibus, M.W., Teixeira, A.A. and Davies, F.S. (2002) Mechanical properties of orangepeel and fruit treated preharvest with gibberellic acid. Transaction of the ASAE45, 1057-1062.
[8] Abbott, J.A.(1999) Quality measurement of fruits and vegetables. Postharvest Biology and Technology, 15, 207-225. doi:10.1016/S0925-5214(98)00086-6
[9] Peleg, K. (1999) Development of a commercial fruit firmness sorter. Journal ofAgricultural Engineering Research, 72, 231-238.
[10] De Ketelaere, B. and de Baerdemaeker, J. (2001) Tomato firmness estimation usingvibration measurements. Mathematics and Computers in Simulation, 56, 385-394. doi:10.1016/S0378-4754(01)00309-3
[11] Jarén, C. and Garczía-Pardo, E. (2002) Using non-destructive impact testing for sortingfruits. Journal of Food Engineering, 53, 89-95. doi:10.1016/S0260-8774(01)00144-3
[12] Lien, C. C., C. Ay and C. H. Ting. (2009) Non-destructive impact test for assessment of tomato maturity. Journal of Food Engineering, 91, 402-407. doi:10.1016/j.jfoodeng.2008.09.036
[13] Delwiche, M.J., McDonald, T. and Bowers, S.V. (1987) Determination of peach firmnessby analysis of impact forces. Transaction of the ASAE, 30, 249-254.
[14] Brusewitz, G.H., Mccollum, T.G. and Zhang, X.(1991) Impact bruise resistance ofpeaches. Transactions of the ASAE, 34, 962-965.
[15] García-Ramos, F.J., Navate, J.O.-C., Ruiz-Altisent, M., Díez, J., Flores, L., Homer, I. and Chávez, J. (2003) Development and implementation of an on-line impact sensorfor firmness sensing of fruits. Journal of Food Engineering, 58, 53-57. doi:10.1016/S0260-8774(02)00333-3
[16] Shmulevich, I., Galili, N. and Howarth, M.S. (2003) Nondestructive dynamic testing ofapples for firmness evaluation. Postharvest Biology and Technology, 29, 287-299. doi:10.1016/S0925-5214(03)00039-5
[17] Hahn, F.(2004) Mango firmness sorter. Biosystems Engineering, 89, 309-319. doi:10.1016/j.biosystemseng.2004.07.005
[18] Wang, J., Teng, B. and Yu, Y. (2006) The firmness detection by excitation dynamic characteristics for peach. Food Control, 17, 353-358. doi:10.1016/j.foodcont.2004.12.001
[19] Gutierrez, A., Burgos, J.A. and Molto, E.(2007) Pre-commercial sorting line for peaches firmness assessment. Journal of Food Engineering, 81, 721-727. doi:10.1016/j.jfoodeng.2007.01.006
[20] Reyes, M.G., Paull, R.E., Williamson, M.R. and Gautz, L.D. (1996) Ripeness de-terminationof ‘‘solo” papaya (Carica Papaya L.) by impact forces. Applied Engineering in Agriculture, 12, 703-708.
[21] Van linden, V., Scheerlinck, N., Desmet, M. and De Baerdemaeker, J. (2006) Factors thataffect tomato bruise development as a result of mechanical impact. Postharvest Biology and Technology, 42, 260-270.
[22] Arazuri, S., Jarén, C., Arana, J.I. and Pérez de Ciriza, J.J.( 2007) Influence of mechanical harvest on the physical properties of processing tomato (Lycopersicon esculentum Mill). Journal of Food Engineering, 80, 190-198. doi:10.1016/j.jfoodeng.2006.05.008
[23] Atanackovic, T. M., Spasic D. T. (2004) On Viscoelastic Compliant Contact-Impact Models. Journal of Applied Mechanics, 71, 134-138. doi.org/10.1115/1.1629106
[24] Brogliato, B. (1999) Nonsmooth Dynamics. Springer, London.
[25] Butcher, E. A. and Segalman, D. J. (2000) Characterizing Damping and Restitution in Compliant Impact via ModiRed K-V and Higher Order Linear Viscoelastic Models. Journal of Applied Mechanics, 67, 831-834. doi:10.1115/1.1308578
[26] Chen, H. and De Baerdemaeker, J.(1995) Optimization of impact parameter for reliableexcitation of apples during firmness monitoring. Journal of Agricultural Engineering Research, 61, 275-282. doi:10.1006/jaer.1995.1055
[27] Grotte, M., Duprat, F., Loonis, D. and Piétri, E. (2001) Mechanical properties of the skinand the flesh of apples. International Journal of Food Properties, 4, 149-161.
[28] Batu, A.(2004) Determination of acceptable firmness and colour values of tomatoes. Journal of Food Engineering, 61, 471-475. doi:10.1016/S0260-8774(03)00141-9