Postharvest Biology and Technology 34 (2004) 187–201 Tomato cultivar grouping based on firmness change, shelf life and variance during postharvest storage Bart De Ketelaere a,∗ , Jeroen Lammertyn b , Geert Molenberghs c , Michèle Desmet b , Bart Nicola¨ ı b , Josse De Baerdemaeker a a K.U.Leuven, Laboratory for Agricultural Machinery and Processing, Department of Agro-Engineering and Economics, Kasteelpark Arenberg 30, 3001 Leuven, Belgium b K.U.Leuven, Laboratory of Postharvest Technology, Department of Agro-Engineering and Economics, de Croylaan 42, 3001 Heverlee, Belgium c Center for Statistics, Limburgs Universitair Centrum, Universitaire Campus, 3590 Diepenbeek, Belgium Received 25 July 2003; accepted 22 March 2004 Abstract The firmness of 13 loose tomato cultivars was followed during a 2-week storage experiment using a non-destructive commercial acoustic firmness sensor. The same experiment was later repeated for a second harvest. The firmness change was modelled using a linear mixed model for repeated measurements showing a significant difference in firmness change among cultivars. Harvest had a significant effect on firmness change, with summer tomatoes being less firm at harvest, but showing a less pronounced firmness decline than autumn tomatoes. The linear mixed model parameters were used to group the different tomato cultivars according to their firmness change, their shelf life and their variance within a cultivar. Ordering of initial firmness across harvest remained more or less the same, indicating that the acoustic firmness tester was suitable for determining differences among tomato cultivars. © 2004 Elsevier B.V. All rights reserved. Keywords: Tomato firmness; Repeated measures; Biological variance; Statistical modelling; Cultivar grouping 1. Introduction Quality inspection and classification of biological products are necessary in the modern market, where large quantities are sold within seconds, often with- out access of the buyers to the product. Conventional ∗ Corresponding author. Tel.: +32-16-32-85-93; fax: +32-16-32-85-90. E-mail address: bart.deketelaere@agr.kuleuven.ac.be (B. De Ketelaere). quality sensors are often destructive and/or time con- suming and may be applied only to small samples of large shipments. High quality standards and the necessity of shelf life determination have increased the need for simple and quick evaluation of the in- ternal properties of each product sold (Galili and De Baerdemaeker, 1996). One of the important quality characteristics of horticultural products is their firm- ness. Firmness is a criterion often used to assess fruit quality as it is directly related to fruit development, ripening after maturity and storage potential. It is used 0925-5214/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2004.03.007